Academic literature on the topic 'CRC32'

Virus komputer merupakan program komputer yang dapat menggandakan atau menyalin dirinya sendiri dan menyebar dengan cara menyisipkan salinan dirinya ke dalam program atau dokumen lain. Virus komputer sifatnya dapat merusak misalnya dengan merusak data pada dokumen, membuat pengguna komputer merasa terganggu dengan keberadaannya dalam sebuah sistem komputer, maupun tidak menimbulkan efek merusak sama sekali. Antivirus adalah sebuah jenis perangkat lunak yang digunakan untuk mendeteksi dan menghapus virus komputer dari sistem komputer.Metode CRC32 sebagai metode pada proses scanning salah satunya adalah metode CRC32. Sesuai dengan fungsi utama dari fungsi hashing, CRC32 berfungsi untuk mengambil penanda dari sebuah file yang nantinya akan dipakai sebagai acuan untuk memeriksa apakah suatu file adalah file virus atau bukan. Kecil sekali kemungkinan bahwa dua buah file mempunyai nilai CRC32 yang sama. Hal ini disebabkan perbedaan 1 bit saja pada file akan mengubah nilai CRC32 file tersebut.Perhitungan indeks akan dikonversi kedalam bentuk decimal agar diketahui jelas nilai indeksnya dan dilakukan perhitungan terhadap file yang akan dikoreksi dengan menggunakann bahasa pemrograman visual basic studio 2010

Seiring file yang diunduh dari Internet, maka dibutuhkan pengunduh yang dapat melakukan deteksi error dan cek integritas data secara otomatis setelah proses unduh selesai. Selain file unduh, pengecekan integritas juga dilakukan setelah proses transfer file pada jaringan lokal. Hal ini diperlukan untuk memastikan keutuhan dan integritas file yang diunduh maupun ditransfer. Pengecekan keutuhan dan integritas dilakukan dengan mengecek CRC32 dan SHA256 dari file yang diunduh maupun ditransfer. Hasil pengujian menunjukkan file yang tidak diubah dan file yang diubah menghasilkan nilai CRC32 dan SHA256 yang berbeda, sehingga pengecekan CRC32 dan SHA256 dapat digunakan untuk memastikan keutuhan dan integritas file.

Objective: To give comparative assessment of the basic ways of generating a checksum (CRC code) based on direct, table and matrix algorithms. Methods: Algorithms were compared by means of mathematical methods. In order to achieve the result Java Development Kit software version 1.8 and NetBeans IDE8.2 development environment were used. Results: The methods of generating checksums by means of algorithms were described in detail. For each method under consideration, the time characteristics of their work were given. The comparison of the analyzed methods was conducted. Practical importance: Based on the results of the experiment, it was concluded which method was optimal for the generation of checksums.

Dokumen-dokumen digital dihasilkan dengan menggunakan aplikasi-aplikasi pengolah kata seperti Microsoft Word atau Notepad menjadi sebuah file dengan ekstensi yang berbeda sesuai dengan aplikasi pengolah kata yang digunakan. Seperti halnya dokumen yang bersifat manual, dokumen-dokumen digital ini tidak terlepas dari bahaya kerusakan. Salah satu kerusakan yang sering terjadi pada dokumen digital adalah perubahan yang terjadi didalam dokumen tersebut akibat dari serangan virus atau pemadaman komputer dengan paksa. CRC32 (Cyclic Redundancy Check 32 Bit) merupakan suatu metode yang menggunakan fungsi hash dalam membaca sebuah struktur dalam sebuah file dalam transmisi atau penyimpanan sebuah data. CRC32 dapat digunakan untuk mendeteksi error (kerusakan) pada sebuah data yang mungkin terjadi pada saat transmisi data atau pengiriman data. Perangkat lunak yang dirancang mampu mendeteksi apakah suatu file mengalami perubahan atau kerusakan berdasarkan nilai checksum dan nilai CRC dari file tersebut. Perangkat lunak ini memiliki kelemahan dalam hal proses pendeteksian kerusakan file, dimana perangkat lunak tidak dapat mendeteksi lebih dari satu file sekaligus dalam satu proses pendeteksian. Kata kunci: CRC32, File, Word

The continuous increase in network traffic has sharply increased the demand for high-performance packet processing systems. For a high-performance packet processing system based on multi-core processors, the packet scheduling algorithm is critical because of the significant role it plays in load distribution, which is related to system throughput, attracting intensive research attention. However, it is not an easy task since the canonical flow-level packet scheduling algorithm is vulnerable to traffic locality, while the packet-level packet scheduling algorithm fails to maintain cache affinity. In this paper, we propose an adaptive throughput-first packet scheduling algorithm for DPDK-based packet processing systems. Combined with the feature of DPDK burst-oriented packet receiving and transmitting, we propose using Subflow as the scheduling unit and the adjustment unit making the proposed algorithm not only maintain the advantages of flow-level packet scheduling algorithms when the adjustment does not happen but also avoid packet loss as much as possible when the target core may be overloaded Experimental results show that the proposed method outperforms Round-Robin, HRW (High Random Weight), and CRC32 on system throughput and packet loss rate.

In search for plant-derived cytotoxicity compound against human cancer cells (A549, SK-OV-3, SK-MEL-2, XF498, HCT15), it was found that the chloroform extracts obtained from the whole plant of Carpesium rosulatum MlQ. (Compositae) exhibited significant cytotoxic activity. Four sesquiterpene lactone, CRC1 (2α, 5-epoxy-5,10-dihydroxy-6-angeloyl-oxy-9β-isobutyloxy-germacran-8α,12-olide), CRC2 (2α,5-epoxy-5,10-dihydroxy-6α,9β-diangeloyloxy-germacran-8α,12-olide), CRC3 (2α,5-epoxy-5,10-dihydroxy-6α-angeloyloxy-9β-(3-methyl-butanoyloxy)-gemacran-8α,12-olide), CRC4 (2β,5-epoxy-5,10-dihydroxy-6α,9β-diangeloyloxy-germacran-8α,12-olide) were isolated from the whole parts of C. rosulatum. 2α,5-epoxy-5,10-dihydroxy-6α,9β-diangeloyloxy-germacran-8α,12-olide (CRC2) showed the most potent cytotoxicity with IC50 value of 6.01 μM against SK-MEL-2.

WC–20 mol% SiC ceramics with added Cr3C2 were sintered at 1600°C with a resistance-heated hot-pressing machine. Dense WC–SiC ceramics containing 0.1–0.9 mol% Cr3C2 were obtained. Above 1.2 mol% Cr3C2, the relative density decreased with increasing Cr3C2 content. A small amount of a Nowotny-phase type (Mo5Si3C-type) product was formed by the addition of Cr3C2, and no Cr3C2-based solid solution was found. The WC–20 mol% SiC–Cr3C2 ceramics had very fine equiaxed granular WC grains because of inhibited grain growth of WC. The Young’s modulus of the WC–20 mol% SiC–Cr3C2 ceramics decreased with increasing Cr3C2 content because Cr3C2 has a much lower Young’s modulus than WC. Cr3C2 addition below 0.9 mol% increased the Vickers hardness from 20.9 to 23.0 GPa, but a larger added amount reduced the Vickers hardness. The hardness of the WC–20 mol% SiC–Cr3C2 ceramics and the WC grain size obeyed a Hall–Petch-like relationship, suggesting that the hardness was strongly controlled by the WC grain size. A higher fracture toughness, 6.4 MPa m1/2, was obtained for the ceramics containing a small amount of Cr3C2 than for the binder-free WC. The addition of 0.1–0.3 mol% Cr3C2 improved the fracture toughness without reducing the hardness.

Co-Ni-Cr3C2 nano-composite coatings at various concentrations of Cr3C2 particles were produced by Jet-eletrodeposition. Surface morphology and crystallographic structure of the coatings were investigated by means of SEM and XRD. Mechanical properties of the coatings were determined using Vickers microhardness and friction wear tester. It was found that adding nano-Cr3C2 concentration in electroplating bath weakens the abnormal co-deposition to a certain extent and decreases the deposition amount of co. The increase of the content of nano-Cr3C2 in the bath, the content of nano-Cr3C2 in the coating increases, when the content of nanoparticles is 80g/l, the content of nano-chromium carbide in the coating reaches the maximum value of 25.13 wt.%. With the addition of nano-Cr3C2 particles, the surface of nanocomposite coating is uneven and presents cauliflower head morphology. When the content of nano-Cr3C2 particles is 40g/l, the growth of the coating is the most uniform and compact. The phase structure of Co–Ni/nano-Cr3C2 coatings is not changed by the codeposition of nano-Cr3C2 particles, but it obviously influences the growth and orientation of crystal planes in composite coatings, especially at high nano-Cr3C2 particles content. Maximum microhardness was observed to be 595 Hv for Co-Ni-40g/L Cr3C2 coating and its wear resistance is the best at the same time.

Purpose The purpose of this paper is to investigate the tribological performance of Cr3C2–NiCr–Mo–BaF2 composite sliding against a Si3N4 ball at high temperatures. Design/methodology/approach A Cr3C2–NiCr composite and a Cr3C2–NiCr–Mo–BaF2 composite were prepared using spark plasma sintering. Tribological properties of the composites were investigated using a ball-on-disk type tribotester. The relationships among the microstructure, wear mechanism and tribological performance were determined by analyzing the wear track morphologies and the glaze layer’s phase composition. Findings The wear rate of the Cr3C2–NiCr–Mo–BaF2 composite was approximately one order of magnitude lower than that of the Cr3C2–NiCr composite from 700°C to 900°C when sliding against a Si3N4 ball. The favorable tribological performance of the Cr3C2–NiCr–Mo–BaF2 composite at high temperatures results from the synergistic lubrication of MoOx, BaF2 and BaMoO4. Originality/value This paper reports a new Cr3C2–NiCr matrix self-lubricating composite with better tribological properties than Cr3C2–NiCr composite at temperatures up to 900°C through Mo and BaF2 addition.

The master's thesis deals with encoding payment data invoices into QR codes in accordance with the by square standard. The SAP system along with a process of encoding data into QR codes and by square PAY standard is introduced in my thesis. In compliance with the standard function module is designed for the SAP system which is in the ABAB language, using Smartforms form allowing the QR codes to generate the invoice. The module is then subjected to testing. The results are evaluated in conclusion of the master's thesis and a description of potential further development is assessed as a final step.

O presente estudo está dividido em duas partes. A primeira parte está relacionada à preparação de pós de Cr3C2-25(Ni20Cr) nanoestruturados através do processo de moagem de alta energia, bem como à caracterização dos pós moídos e no estado como recebido. A análise dos dados obtidos nesta etapa do trabalho foi feita utilizando-se uma abordagem essencialmente teórica. A segunda parte deste estudo refere-se à produção e caracterização de revestimentos preparados com os pós de Cr3C2-25(Ni20Cr) nanoestruturados e como recebido. O comportamento destes revestimentos sob erosão-oxidação em alta temperatura foi comparado com base em uma abordagem de caráter mais tecnológico. O tamanho médio de cristalito do pó de Cr3C2-25(Ni20Cr) decresceu rapidamente de 145 nm para 50 nm nos estágios iniciais de moagem e, posteriormente, com o aumento do tempo de moagem, decresceu mais lentamente até atingir um estado estacionário para um tamanho de cristalito em torno de 10 nm. Este estado estacionário corresponde ao início do processo de recuperação dinâmica. A máxima deformação da rede cristalina (δ = 1,17%) foi observada para pós moídos por 16 horas, caracterizando um tamanho crítico de cristalito da ordem de 28 nm. Por outro lado, o parâmetro de rede atingiu um mínimo para pós moídos por 16 horas. Após atingir o tamanho crítico de cristalito, a densidade de discordâncias praticamente não mais varia (estado estacionário) e toda deformação plástica posteriormente introduzida no material é acomodada através de eventos que ocorrem nos contornos de grão, particularmente por meio do processo designado deslizamento de contorno de grão (grain boundary sliding). A energia de deformação armazenada na rede cristalina dos pós de Cr3C2-25(Ni20Cr) moídos com diferentes tempos de moagem foi determinada por meio de medidas da variação de entalpia. Estes resultados indicaram que a máxima variação de entalpia (ΔH = 722 mcal) também ocorreu para pós moídos por 16 horas. Analogamente, a máxima variação do calor específico (ΔCp = 0,278 cal/gK) ocorreu para pós moídos por 16 horas. As seguintes propriedades mecânicas dos revestimentos de Cr3C2-25(Ni20Cr), preparados utilizando-se o processo HVOF de aspersão térmica, foram determinadas: microdureza Vickers, módulo de Young e tenacidade à fratura. As propriedades dos revestimentos preparados com os pós nanoestruturados e como recebido foram comparadas. A dureza e o módulo de Young dos revestimentos preparados com os pós nanoestruturados foram aproximadamente 26% maiores que aqueles preparados com os pós como recebido. A tenacidade à fratura dos revestimentos nanoestruturados foi aproximadamente 36% maior do que o verificado para os revestimentos produzidos com pós no estado como recebido. A resistência à erosão-oxidação do revestimento produzido com o pó nanoestruturado foi em torno de 52% maior do que a do revestimento preparado com o pó no estado como recebido, a 800ºC. Ambos os revestimentos mostraram um aumento da taxa de erosão-oxidação para temperaturas acima de 450ºC.
This study is divided in two parts. The first part is about the preparation of nanostructured Cr3C2-25(Ni20Cr) powders by high energy milling followed by characterization of the milled and the as received powder. Analyses of some of the data obtained were done using a theoretical approach. The second part of this study is about the preparation and characterization of coatings prepared with the nanostructured as well as the as received Cr3C2-25(Ni20Cr) powders. The high temperature erosion-oxidation (E-O) behavior of the coatings prepared with the two types of powders has been compared based on a technological approach. The average crystallite size of the Cr3C2-25(Ni20Cr) powder decreased rapidly from 145 nm to 50 nm in the initial stages of milling and thereafter decreased slowly to a steady state value of around 10 nm with further increase in milling time. This steady state corresponds to the beginning of a dynamic recovery process. The maximum lattice strain (δ = 1,17%) was observed in powders milled for 16 hours, and this powders critical crystallite size was 28 nm. In contrast, the lattice parameter attained a minimum for powders milled for 16 hours. Upon reaching the critical crystallite size, the dislocation density attained a steady state regime and all plastic deformation introduced in the material there after was in the form of events occurring at the grain boundaries, due mainly to grain boundary sliding. The deformation energy stored in the crystal lattice of the Cr3C2-25(Ni20Cr) powders milled for different times was determined from enthalpy variation measurements. These results indicated that the maximum enthalpy variation (ΔH = 722 mcal) also occurred for powders milled for 16 hours. In a similar manner, the maximum specific heat variation (ΔCp = 0,278 cal/gK) occurred for powders milled for 16 hours. The following mechanical properties of Cr3C2-25(Ni20Cr) coatings prepared using the HVOF thermal spray process were determined: Vickers micro-hardness, the Young Modulus and the fracture toughness. The properties of the coatings prepared with the nanostructured and the as received powders were compared. The hardness and Young Modulus of the coatings prepared with nanostructured powders were approximately 26% higher than that of the coatings prepared with as received powders. The fracture toughness of the nanostructured coating was 36% higher. The erosion-oxidation resistance of the coating produced with the nanostructured powder was around 52% higher than that of the coating prepared with the as received powders at 800 ºC. The E-O wastage of both types of coatings increased with temperature beyond 450 ºC.

This thesis investigates the mechanisms of erosion-corrosion of Cr3C2-NiCr thermal spray coatings under high temperature, high erodent velocity, turbine conditions. Erosion-corrosion is a generalised wear phenomenon where the combined effect of each degradation mechanism generates more extensive mass loss than the sum of each mechanism acting independently. Previous research has highlighted several theoretical mechanisms under this generalized process, ranging from the erosion induced breakdown of oxide scales in corrosive environments, through to the development of oxide layers in highly erosive environments. Prior to this current work experimental simulation of these mechanisms has focused on bulk alloy materials with well characterised oxidation responses, under conditions of low temperature, low erodent impact velocity and high erodent flux, conditions which are readily generated within laboratory scale rigs and which tend towards the low impact energy conditions encountered within fluidised bed combustors. Few works have addressed erosion-corrosion under simulated turbine conditions of high temperature, high erodent impact velocity and low erodent flux. While comparative trials have been run under such conditions on a purely mass loss basis, little has been presented regarding the microstructural analysis of such degradation, particularly for materials that rely on the industrially relevant, slow growing oxide scales Cr2O3 and Al2O3. Thermally sprayed Cr3C2-NiCr coatings are routinely applied to combat wear at high temperature due to the high wear resistance imparted by the hard carbide particles and the high temperature oxidation resistant nature of the Cr2O3 oxide formed over both phases. However, most published work characterising the erosion-corrosion response of these coatings has been conducted on a comparative basis by contrasting coatings of various composition ratios, deposited by various techniques, with the response of well characterised bulk materials. Little has been presented on the microstructural mechanism of erosioncorrosion of Cr3C2-NiCr coatings, a point highlighted by the limited understanding of the oxidation mechanism of the Cr3C2 phase, the oxidation mechanisms of the combined composite Cr3C2-NiCr and the influence of the coating splat structure on the oxidation response. While the erosion response of thermal spray coatings and bulk cermets is more widely understood, most works have been conducted under milder conditions than used in the current work. In addition previous works have been conducted primarily on assprayed coatings with few works taking into account the effect of heat treatment induced changes in the coating composition and microstructure that occur with extended in-service exposure at elevated temperature. In addressing the short comings in the current state of knowledge, the aim of this work was to characterise the mechanism of erosion-corrosion of high velocity sprayed Cr3C2-NiCr thermal spray coatings under turbine conditions, incorporating the effect of variation in the composition and carbide distribution with inflight degradation, variations in starting powder morphology, heat treatment, erosion conditions and exposure temperature. 75 Cr3C2-25(Ni20Cr) coatings were deposited by Aerospray HVAF, GMA Microjet HVOF, Stellite Jet Kote HVOF and TAFA JP-5000 HVOF spraying under optimised conditions using agglomerated/sintered and blended powders. The prealloyed powder based coatings, characterised in terms of microhardness, porosity content and phase degradation, were found to exceed the average values of coating quality presented in the literature. The blended powder based coating of this work was comparable with the coating attributes presented in the literature for plasma and HVOF coatings based on this powder morphology. Based on these results the coatings were considered representative of those sprayed industrially and therefore the responses of the samples in this work to oxidation and erosion were considered indicative of the response of industrially applied coatings of this composition in service. Heat treatment trials were conducted on the Aerospray HVAF and Microjet HVOF coatings at 900ºC in air and argon for up to 60 days to simulate the compositional and microstructural development of these coatings under elevated temperature conditions in service. In the prealloyed powder based coatings, rapid carbide precipitation occurred within the first two days in both coatings to reach the steady state composition of 75-80vol%. Minimal in-flight carbide dissolution in the HVAF coating led to preferential carbide precipitation on the retained carbide grains. In the Microjet HVOF coatings, which suffered extensive inflight carbide dissolution, carbide precipitation occurred as fine precipitates in the carbide-free zones, forming large sponge-like agglomerates. With extended exposure Ostwald ripening led to coarsening of the individual carbide grain size and widespread agglomeration of the carbide grains into an extensive three dimensional network after 30 days exposure, with minimal development out to 60 days. Compositionally, heat treatment led to a dramatic reduction in the supersaturated matrix phase Cr content, with the steady state Cr composition of the Microjet HVOF coating exceeding that of the Aerospray HVAF coating based on XRD analysis. Cr3C2 was the only carbide detected with heat treatment. Heat treatment of the blended powder based coating led to sintering of the single phase splats. Diffusion of the carbide elements into the matrix phase splats occurred, allowing fingers and nodules of the carbide to develop into this phase as well as increasing the matrix phase Cr concentration. Oxidation of Cr3C2 by hot stage XRD analysis at 600ºC, combined with TGA analysis at 600-850ºC, supported the mechanism of stepwise decarburisation prior to Cr2O3 formation, presented as one possible mechanism in the literature. Oxidation of the Cr3C2-NiCr coatings over the range 700-850ºC was dependent on the starting powder morphology and the extent of dissolved carbide in the matrix phase. Oxidation of the as-sprayed prealloyed powder based coatings was dictated by the matrix phase, the high Cr concentration resulting from carbide dissolution leading to rapid growth of the Cr2O3 phase over the oxidising carbide grains. Growth stresses induced by such overgrowth lead to the formation of interfacial voids over the carbide grains at high temperature. Heat treatment reduced the matrix phase Cr concentration, resulting in the coating phases oxidising independently with a reduced magnitude of lateral matrix based scale growth over the carbide phase. In the blended powder based coating, bulbous Ni oxides dominated the scale topography. With extended exposure a continuous Cr2O3 scale formed below the faster growing Ni oxides, which enabled lateral growth of the scale over the carbide based Cr2O3 scales. Following heat treatment the matrix phase Cr concentration increased, minimising the development of Ni oxides on this phase. Erosion studies were carried out in a custom built high temperature erosion apparatus. Ambient temperature trials were conducted using Al2O3 erodent at velocities of 150m/s. The as-sprayed prealloyed powder based coatings exhibited a brittle impact response, which was accentuated in the Microjet HVOF coating by the increased extent of in-flight carbide dissolution and the splat structure which made this sample more susceptible to brittle erosion mechanisms. Heat treatment of these coatings led to sintering of the splats and a more ductile impact response due to the increased ductility of the matrix phase. The as-sprayed blended powder based coatings exhibited a range of impact responses from brittle erosion of the carbide through to ductile erosion of the matrix based splats. Mass loss was accentuated by the poor intersplat adhesive strength. Heat treatment led to sintering of the splats, resulting in a more microstructural based erosion response. The two prealloyed powder based coatings generated similar erosion rates under the aggressive conditions, distinctly more erosion resistant than the blended powder based coatings. Heat treatment improved the erosion resistance of all the coatings, however, the duration of heat treatment had a negligible effect on the magnitude of erosive mass loss. Erosion at 800ºC, with an impact velocity of 235m/s, lead to significantly deeper erodent penetration into the coating than noted at ambient temperature. The significant increase in the matrix phase ductility at elevated temperature minimized the impact of carbide dissolution on the matrix impact response in the prealloyed powder based coatings. The primary effect of carbide dissolution was to reduce the carbide concentration, allowing deformation of the matrix to dictate the coating response. Carbide development with heat treatment significantly reduced the ability of the matrix to deform in this manner. The increased matrix phase ductility in the blended powder based coating reduced the concentration of impact energy on the splat boundaries, leading to a more microstructural based erosion response. Heat treatment had a negligible effect on the coating response, given the reduced significance of the splat boundary adhesion. Erosion at 700ºC generated similar erosion responses in the prealloyed powder based coatings to those noted at 800ºC, the lower matrix phase ductility reflected in the more brittle response evident as brittle cracking and fracture. The effect of carbide development with heat treatment was not as dramatic as at 800ºC due to the reduced matrix phase ductility at this temperature. Erosion of the blended powder based coating at 700ºC generated the same spectrum of erosion response as noted at 800ºC in both the as-sprayed and heat treated states, with the variation in matrix phase ductility with temperature overshadowed by the heterogeneous coating impact response resulting from the heterogeneous phase distribution. The steady state erosion rate at 700ºC was comparable across all of the coatings in both the as-sprayed and heat treated conditions. At 800ºC, heat treatment had a negative impact on the prealloyed powder based coatings, but no definitive effect on the blended powder based coatings. The Microjet HVOF coatings were more erosion resistant than the Aerospray HVAF coatings under these conditions. These results pointed to a reduction in the significance of the coating splat structure on the magnitude of erosion, in favour of a more microstructural based response at high temperature. In both the ambient and elevated temperature trials the coating microhardness values proved to be a poor indicator in predicting the magnitude or relative ranking of the erosion response of the different coatings under these aggressive erosion conditions. Erosion-corrosion under turbine conditions of high temperature, high erodent velocity and low erodent flux, was simulated by oxidizing samples at 900ºC and subjecting them to one second of erosion every 48 hours over a period of 60 days. The degradation testing was assessed in accelerated testing in additional trials by polishing the oxide scale formed at 900ºC from the sample surface every 48 hours over the same time period. Under these conditions the coatings formed thick oxide scales that penetrated into the coating. Preferential internal oxidation of the Cr3C2 phase occurred in the coating, consuming the grains in the near surface zone through the formation of Cr2O3 to a depth dependent upon the test temperature. Oxygen ingress occurred along the carbide-matrix interface and was accentuated in the regions of impact damage surrounding the erodent indentations. Internal oxidation of the carbide phase sealed off the pockets of matrix phase which were eventually consumed by oxidation once they were no longer able to maintain a protective Cr2O3 oxide. The extent of internal attack was consistent in the 20, 40 and 60 day samples, suggesting that the internal oxidation front proceeded at a constant rate in front of the erosion front into the coating. The prealloyed powder based coatings were more resistant to such internal degradation relative to the blended powder based coatings, with an internally oxidised zone of 6ìm relative to the 10ìm thick internally oxidized band in the blended powder based coating. While each erodent impact event may be classified as oxidation affected erosion, the low erodent flux effectively led to a long-term response more accurately described as erosion affected oxidation.

The Seamless Stressometer® roll (Seamless STR) is used to measure the flatness of aluminum and steel strip when there is an extreme demand on the surface finish. To protect the roll and strip, the roll is coated with two layers deposited by high velocity oxygen fueled spraying (HVOF), Cr-Ni(Si,B) closest to the roll and WC-Co on top. This solution has several disadvantages; high cost and complicated logistics, corrosion sensitivity and high residual stresses creates the need for two coatings which in turn complicates the process. Cobalt is, in addition, sensitive to low pH coolants and environmentally unfriendly. These problems have given rise to the idea of switching both the method and material of the coating. In the first part of this work, high velocity air fueled spraying (HVAF) was evaluated as an alternative deposition method. Three materials, Cr3C2-NiCr, WC-Co and WC-CrC-Ni were deposited on steel coupons with varying chamber pressure, powder feed rate and distance from the nozzle, in order to evaluate if HVAF can be a valid technique for use in this application and to optimize the spraying recipe. The objectives were to get a sufficiently high thickness per sweep, to be able to make the depositions in a manageable number of sweeps, and to get low porosity, since the coatings need to be dense to be hard and possible to polish smooth. The tests showed that all three materials can be sprayed with the high settings on the parameters to obtain coatings that exceeded the set limits of the objectives. In the second part of this work, the recipe obtained from the first part was used to deposit samples for further analysis. The coatings were compared regarding cost, hardness, friction, wear and pick-up properties to evaluate if a switch in material from WC-Co was possible. The coatings showed both similarities and differences. The friction was very similar for the three materials. Cr3C2-NiCr was substantially cheaper than the other two, had lower hardness and higher porosity, but still probably acceptable values, and was satisfactory regarding wear and pick-up. WC-Co and WC-CrC-Ni were very similar to each other regarding cost, hardness and porosity but WC-Co was the best regarding wear and pick-up, where WC-CrC-Ni was the worst. The only clear advantage of WC-CrC-Ni over WC-Co is the lack of cobalt. Taking everything into consideration, including the fact that the wear and pick-up tests in this work was quite exaggerated, Cr3C2-NiCr is an interesting option for this application due to its low cost and acceptable test results, WC-Co had the best results but is expensive and contains cobalt and WC-CrC-Ni had as good results as WC-Co except for the wear and pick-up tests and does not contain cobalt.

I pappersmaskiner används kräppblad för att kräppa av pappret från en stor roterande cylinder, en så kallad yankee-cylinder. Dessa blad utstår stora nötningar och beläggs därför med antingen en kromoxidbeläggning eller en hårdmetallsbeläggning för att öka bladets nötningsbeständighet. Bladen beläggs med termisk sprutning, kromoxiden via plasmasprutning och hårdmetallen via "High-Velocity-Oxy-Fuel"-sprutning (HVOF). I detta arbete har slitagetester utförts på belagda kräppblad genom att använda en "slider-on-flat-surface" (SOFS) tribometer för att ta reda på vilken av dessa beläggningar som är bäst lämpad för att användas på kräppblad. Vid användning av SOFS belastas kräppbladen med en normalkraft och glider mot en platta till önskad total glidsträcka är uppnådd. För att kunna genomföra slitagetesterna i SOFSen behövdes en fixtur konstrueras och tillverkas och kräppblad behövde kapas till önskad geometri. Det skapades tre koncept för fixturen och med en beslutsmatris gjordes valet vilken av dem som skulle tillverkas. Den tillverkade fixturen håller kräppbladen stabila i både sidled och i glidriktningen och håller kräppbladen i en vinkel likt i verkligheten. Slitagetesterna utfördes vid tre olika glidsträckor med konstant normallast. Efter slitagetesterna analyserades bladen i stereomikroskop och svepelektronmikroskop för att identifiera nötningsmekanismer. De dominerande nötningsmekanismerna var abrasiv och adhesiv nötning. På grund av porositet i beläggningarna ökades antalet sprickor och mer och mer fragment lossnade vid ökande glidsträcka under slitagetesterna. Det visade sig efter mätningar av bortnött bredd på bladet att det hårdmetallbelagda kräppbladet hade bäst nötningsbeständighet. Detta på grund av dess hårda tungstenkarbider som minskade den abrasiva nötningen och spricktillväxten i beläggningen och dess högre duktilitet jämfört med kromoxiden.
Creping blades are used in paper machines for creping tissue paper from a rotating cylinder called a yankee cylinder. These blades experience severe wear and are therefore coated by either chromium oxide or a hard metal coating to make the blades more wear resistant. The coatings are sprayed on to the blade by thermal spraying processes, the chromium oxide coating with plasma spraying and the hard metal coating with "High-Velocity-Oxy-Fuel" (HVOF) spraying. In this thesis wear testing of the coated creping blade using a "slider-on-flat-surface" (SOFS) tribometer has been done to find out which of these coatings that is best suited for coating on the creping blade. When using the SOFS, the creping blade is subjected to a chosen normal force and is scraped against a counterface for a set total distance. In order to execute the wear tests in SOFS, construction and manufacturing of a holder for the creping blades was needed and the creping blades had to be cut to correct geometry. Three concepts were created for the holder and the decicion about which one to manufacture was made with a decision matrix. The new holder holds the creping blades stable in side movements and in the sliding direction. It also keeps the blade at a set angle to the counterface as in the real application. The wear tests consisted of three sliding distances with constant normal load. The blades were analyzed in a stereo microscope and in a scanning electron microscope to identify the wear mechanisms when the wear tests were completed. The major wear mechanisms were abrasive and adhesive wear. Because of porosity in the coatings, the number of cracks increased and fragments from the blades came loose when increasing the sliding distance during the wear tests. It showed that by measuring the eroded width on the blades that the hard metal coated blade had the best wear resistance because of the hard tungsten carbides that lowered the abrasive wear and the crack growth in the coating and because of its higher ductility in comparison to chromium oxide.

Dans les procédés de projection thermique du type HVOF (High Velocity Oxygen Fuel), les propriétés du revêtement sont sensibles aux caractéristiques des particules en vol qui dépendent elles-mêmes des paramètres opératoires. En raison de la complexité des réactions chimiques et des processus thermodynamiques qui interviennent dans la formation du dépôt, l’obtention d’un modèle multi-physique complet et l'accès à une description quantitative du procédé HVOF représentent encore actuellement un défi scientifique majeur. L'étude réalisée a eu pour but de développer une méthodologie robuste reposant sur la méthodologie des réseaux de neurones artificiels (ANN), en vue de répondre à ce besoin dans le cas des revêtements NiCr-Cr3C2 élaborés par HVOF en mettant en oeuvre des paramètres opératoires variables.En premier lieu, 40 séries d’expériences de projection HVOF ont été conduites et les propriétés du revêtement obtenus ont été déterminées et analysées afin de créer les modèles ANN visés. La relation entre les paramètres opératoires, les caractéristiques des particules en vol et les propriétés du revêtement a été étudiée dans une approche initiale "intuitive", réalisée sur la base de considérations physico-chimiques classiques, ce qui a fourni une compréhension préliminaire du processus HVOF et des revêtements. Toutefois, bien que l’effet des paramètres du procédé sur ces derniers puisse être décrit qualitativement, il est impossible d’établir descorrélations quantitatives..Aussi deux modèles ANN ont été développés et mis en œuvre pour prédire les performances du revêtement (en termes de micro-dureté, porosité et taux d’usure) et traduire l’influence des paramètres opératoires (distance de projection, débit d’oxygène et débit de carburant) en faisant intervenir les variables intermédiaires (température et vitesse de particules en vol). Une procédure détaillée de création de ces deux modèles ANN est présentée, qui intègre les phénomènes physiques régissant le processus HVOF. Une série d’expériences supplémentaires a également été menées pour valider la fiabilité et estimer la précision de ces modèles ANN. Les résultats montrent que les modèles implicites ainsi développés ont des qualités prédictives satisfaisantes. La clarification des relations entre les conditions de projection, les comportements des particules en vol et les performances du revêtement est un élément clef pour assurer un contrôle optimal des revêtements déposés par HVOF. De plus, une analyse de la « valeur d’impact moyenne » (MIV) a été réalisée pour évaluer quantitativement l’influence relative de chaque entrée sur les données de sortie en vue d’affiner la prédiction.Enfin, les modèles ANN mis en forme ont été programmées et intégrés dans le système de contrôle de projection HVOF tel qu'il est mis en œuvre au laboratoire, pour parvenir un système de contrôle intelligent. À l’aide de ce système, la température et la vitesse des particules en vol peuvent être calculées à partir des paramètres opératoires et les propriétés de revêtement spécifiques peuvent être estimées. Un modèle ANN inversé a également été développé, qui prédit les paramètres opératoires optimaux à appliquer en fonction du niveau de micro-dureté visé pour le revêtement.Ce travail contribue donc à la mise au point d’un système de contrôle intelligent applicable aux procédés de projection HVOF et la démarche suivie peut en outre être étendue à d’autres techniques de projection thermique.Ainsi, sur la base d'un nombre substantiel de données, ce travail a non seulement produit une analyse de la relation entre les paramètres opératoires du procédé, le comportement des particules en vol et les propriétés du revêtement, mais a également fourni une méthode de prédiction applicable aux revêtements déposés par HVOF, au travers d'un modèle ANN optimisé. Enfin, un logiciel prototype concrétisant un tel système de contrôle intelligent adapté au procédé de projection HVOF a également été élaboré
In the high velocity oxygen fuel (HVOF) spray process, the coating properties are sensitive to the characteristics of in-flight particles, which are mainly determined by the process parameters. Due to the complex chemical and thermodynamic reactions during the deposition procedure, obtaining a comprehensive multi-physical model or analytical analysis of the HVOF process is still a challenging issue. This study proposes to develop a robust methodology via artificial neural networks (ANN) to solve this problem for the HVOF sprayed NiCr-Cr3C2 coatings under different operating parameters.First, 40 sets of HVOF spray experiments were conducted and the coating properties were tested for analysis and to build up the data set for ANN models. The relationship among the process parameters, behaviors of in-flight particles, and coating properties were investigated from an initial view, which provided a preliminary understanding of the HVOF process and sprayed coatings. Even though the effect of process parameters on the behaviors of in-flight particles and thus on the coating’ properties can be roughly summarized, it is impossible to build up direct connections among them.Second, two ANN models were developed and implemented to predict coating’s performances (in terms of microhardness, porosity and wear rate) and to analyze the influence of operating parameters (stand-off distance, oxygen flow rate, and fuel flow rate) while considering the intermediate variables (temperature and velocity of in-flight particles). A detailed procedure for creating these two ANN models is presented, which encodes the implicitly physical phenomena governing the HVOF process. A set of additional experiments was also conducted to validate the reliability and accuracy of the ANN models. The results show that the developed implicit models can satisfy the prediction requirements. Clarifying the interrelationships between the spraying conditions, behaviors of in-flight particles, and the final coating performances will provide better control of the HVOF sprayed coatings. Additionally, mean impact value (MIV) analysis was conducted to quantitatively explore the relative significance of each input on outputs for improving the effectiveness of the predictions.Lastly, the well-trained ANN models were programmed and integrated into the homemade HVOF spray control system to realize an intelligent control system. With this system, the temperature and velocity of in-flight particles can be calculated by entering process parameters, and thereafter obtaining specific coating properties. A reverse ANN model was also integrated, which calculates process parameters based on the microhardness of the coating to guide the selection of the best parameters. This integration provides a preliminary idea for the construction of an intelligent control system for HVOF spray process and can be promoted to other thermal spray technologies.Overall, based on a large data set, this work not only intuitively analyzed the relationship among process parameters, behaviors of in-flight particles, and coating’s properties, but also provided a prediction method for the HVOF spray process and HVOF sprayed coatings via the optimized and well-trained ANN model. In addition, a prototype to realize an intelligent control system for HVOF spray process has also been suggested

Agglomerated and sintered 25Ni(Cr)-75Cr3C2 powder was deposited onto 304 stainless steel substrates by HVOF thermal spraying. Post spraying thermal treatments were carried out on as-sprayed samples at different temperatures (700°C and 800°C) in air (oxidising). Samples were heat treated from 1hour up to 16 days and furnace cooled. The powder, coatings and substrate were characterised by a variety of techniques including optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness testing and thermogravimetric analysis (TGA). The results of agglomerated and sintered powder coating microstructural characterisation show that the as-sprayed coating comprised the carbide phase Cr3C2, a small amount of amorphous phase and a metallic phase which was Ni-rich. The spray process also led to the formation a small amount of Cr2O3 in the coatings. In the heat treated coatings, the carbides Cr7C3 and Cr23C6 were found at the coating substrate interface, the amorphous structure phase was eliminated. With heat treatment, matrix phase supersaturation was reduced, while widespread carbide nucleation and growth generated an expansive carbide skeletal network especially near the coating/substrate interface. An initial softening of the coatings occurred but subsequently the hardness increased again after 2 days was a function of carbide development. The oxidation kinetics of the 25Ni(Cr)-75Cr3C2 powder and coatings during elevated temperature oxidation in air at 650°C to 1000°C have also been studied. The oxidation behaviour was found to be governed by a parabolic rate law up to 800°C. The activation energy of the coating oxidation reaction, Q, was found to be 164 kJ/mol. The mechanism of high temperature oxidation of 25Ni (Cr)-75Cr3C2 coating on top surface has been discussed. Inter-diffusion between the coating and the 304 stainless steel substrate has been investigated. A distribution of the precipitate phase Cr23C6 within the 304 steel was found from etched substrate samples. The decrease of the microhardness measured with distance away from the interface also revealed that diffusion occurred between coating and substrate during the annealing period. Carbon diffusion distances at different annealing conditions in this work have been measured according to the appearance of the Cr23C6 precipitates and variation in microhardness away from the interface. A simple mathematical model has been used to calculate the theoretical carbon diffusion distance in substrate.

There have been enormous advances in technologies for thermal spray over the past few decades. One such application is the replacement of electroplated hard chrome for aerospace and automotive industries. Hard chrome electroplating has been a valuable surface treatment for parts in corrosion and wear applications due to its high hardness, ability to passivate, as well as its low coefficient of friction. In the past two decades, there have been concerns due to limitations in hard chrome's performance as well as environmental effects due to hexavalent chromium produced during processing. High velocity oxy-fuel (HVOF) spray processing has been developed to produce exceptional coating quality due to the very dense microstructures formed with limited porosity.

Cr₃C₂-NiCr has been shown to be a viable replacement to electroplated hard chrome when deposited by HVOF spray techniques. In order to produce optimized coatings with this technology, a process mapping methodology was implemented to understand the relationship between process variables. The variations of oxygen to fuel ratios as well as total volume flows of gases were examined to interrelate process variables with the particle state, stress evolution during deposition, and properties of the coatings. The performance of the coatings in aqueous corrosion and sliding wear environments were correlated back to the properties of the coatings. It has been demonstrated that monitoring the in-flight particles and evolution of stress can be directly correlated to the properties of the coating and in-directly to the coating performance.

Cr₃C₂-NiCr property and performance was also compared to hard chrome and WC-CoCr coatings. It was shown that the optimized coatings of Cr₃C₂-NiCr outperformed hard chrome in both aqueous corrosion as well as sliding wear environments. Cr₃C₂-NiCr was outperformed by WC-CoCr in sliding wear applications due to its lower hardness, but outperformed WC-CoCr in aqueous corrosion due to the denser microstructures that were produced.

Este trabalho investigou o fenômeno da degradação de revestimentos obtidos por aspersão térmica pelas técnicas de HVOF e plasma spray, de um sistema metal cerâmico à base de NiCr (NiCr-Cr3C2), submetido à erosão, desde a temperatura ambiente até 800°C, relacionando a resistência à erosão à sua microestrutura. Os revestimentos erodidos tiveram o sistema NiCr-Cr3C2 com percentual das fases variável. No caso dos revestimentos obtidos por HVOF investigou-se o comportamento em revestimentos com 0, 35, 70 e 75% de fase Cr3C2 na matriz metálica, NiCr. Já no caso dos revestimentos obtidos por plasma spray avaliou-se o comportamento em revestimentos com 0, 35, 70 e 100% de fase Cr3C2 na matriz metálica, NiCr. Para os ensaios de erosão foi construído um equipamento capaz de variar as condições experimentais como velocidade, fluxo, ângulo de incidência do erodente, além da temperatura de ensaio. Os revestimentos foram obtidos a partir dos melhores parâmetros de deposição avaliados em pré-testes, visando-se controlar a porosidade das amostras, conforme a limitação de cada técnica empregada. A superfície das amostras foi levemente lixada antes de serem erodidas para a retirada de lamelas não bem aderidas, visando-se obter um padrão semelhante de rugosidade em cada grupo. As amostras foram submetidas a um fluxo controladonde partículas erodentes de alumina eletrofundida, em ângulos de incidência de 30, 45, 60 e 90º, a uma velocidade mantida em torno de 50 m/s. As temperaturas estudadas foram de 25, 200, 400, 600 e 800ºC. O material foi caracterizado quanto a sua microestrutura (microscopia ótica e eletrônica de varredura, porosidade, rugosidade, fases presentes e sua morfologia), também quanto a propriedades mecânicas como (micro- e nano-) dureza e módulo de elasticidade. O desgaste foi medido pela perda de volume do corpo erodido. Os resultados indicaram que a relação entre a porosidade, temperatura e quantidade de fase Cr3C2 foi determinante no desgaste erosivo dos revestimentos. O aumento de temperatura proporcionou um acréscimo na incrustação de partículas erodentes, na oxidação e na plasticidade dos revestimentos, esta última sendo verificada pelo decréscimo da dureza do material. Além disso, o fenômeno erosão-oxidação fez-se presente acima de 400°C O acréscimo de fase Cr3C2 a matriz metálica proporcionou uma diminuição da incrustação de partículas erodentes, tendo em vista a diminuição da plasticidade dos revestimentos, além do aumento da oxidação e porosidade dos revestimentos. A porosidade, de fato, influenciou decisivamente na resistência à erosão, dividindo claramente os revestimentos em dois grupos, no intervalo de porosidades superior (revestimentos obtidos por plasma spray) e inferior (revestimentos obtidos por HVOF) a 4%. Nos revestimentos de maior porosidade mesmo o acréscimo de uma fase mais dura não proporcionou um aumento da resistência à erosão, pois a porosidade implicou em uma menor área de contato entre as lamelas, facilitando seu arrancamento do revestimento sob ataque erosivo. Já para os revestimentos de menor porosidade o incremento de Cr3C2 proporcionou um aumento da resistência ao desgaste para todo o intervalo de temperatura investigado, devido ao aumento da dureza. Quanto aos mecanismos que proporcionaram o desgaste nos revestimentos observou-se uma preponderância de desgaste dúctil (corte – 30º e platelet – 90º) para os revestimentos metálicos NiCr0,5% e NiCr9%. Com o acréscimo de fase Cr3C2 há uma diminuição da característica dúctil de desgaste, mais acentuada nos revestimentos obtidos por plasma spray. E a partir do acréscimo de 70% de Cr3C2 observou-se alguns mecanismos de desgaste frágeis, como a formação de trincas, e pits. O acréscimo de temperatura proporcionou o aumento da plasticidade dos revestimentos, a diminuição de formação de platelets e no caso do desgaste eminentemente frágil (para o revestimento CrC28%) o arredondamento das bordas desgastadas.
In this work, the degradation behavior of thermal-sprayed NiCr-Cr3C2-based metal-ceramic coatings under erosion at temperatures ranging from room temperature to 800°C was investigated in order to establish correlations between the erosion resistance and the microstructure. In order to obtain coatings with different microstructures, the coatings were produced employing two different techniques - HVOF and plasma spray -; and different amounts of the Cr3C2 ceramic phase in the metallic NiCr matrix: 0, 35, 70, 75% (only by HVOF) and 100% (only by plasma spray). For the erosion tests, an equipment capable of using different conditions of speed, flux and angle of incidence of the erodent at different temperatures was developed. The samples were subjected to a controlled flux of fused alumina erodent particles, with angles of incidence of 30, 45, 60 e 90º, at a speed of about 50m/s. Temperatures of 25, 200, 400, 600 e 800ºC were employed in the tests. The material was characterized regarding its microstructure (optical microscopy, scanning electron microscopy, porosity, rugosity, phase composition and phase morphology) and its mechanical properties (micro- and nano-hardness and Young modulus). The wear was evaluated by measuring the volume loss of the eroded bodies. The results indicated that porosity, temperature and amount of Cr3C2 had a critical role in the erosive wear of the coatings. Higher temperatures increased the incrustation of erodent particles, the oxidation (which was observed above 400°C and was also influenced by porosity), and the plasticity of the coatings. Increasing the Cr3C2 content in the metallic matrix has lowered the incrustation by making the coatings less plastic, and has also increased the oxidation and porosity. In fact, the porosity had a crucial role in the erosion resistance, in such way that it is possible to divide the obtained coatings in two groups: those with porosity level above 4% (obtained by plasma spray) and those with porosity below that level (obtained by HVOF). In the high porosity group, even increasing the level of hard phase was not enough to make the coatings more resistant, because the porosity has lowered the contact area between the lamellas, easing its pull-out by erosive attack. For the low-porosity coatings, on the other hand, increasing the Cr3C2 content made the coatings more wear-resistant in the whole temperature range under investigation. As for the wear mechanisms involved, a preponderance of ductile wear (cutting – 30º and platelet – 90º) was observed for the NiCr0,5% and NiCr9% coatings. With increasing Cr3C2 content, a decrease in the ductile wear characteristic was observed, more prominently in the plasma sprayed coatings. From the 70% Cr3C2 content on, fragile wear mechanisms were observed, as cracks and pits formation. Increasing temperature made the coatings more plastic, reducing the platelet formation and, for the eminently fragile mechanism observed for the CrC28% coating, making the edges of the worn areas less sharp.

Abstract Thermal sprayed chromium carbide (Cr3C2)-25% NiCr (Ni-20%Cr) coatings are extensively used in wear resistant applications especially under conditions wherein operating temperatures are likely to be higher than 500°C . The performance of the Cr3C2-NiCr coatings under such conditions depend on a variety of coating properties like the porosity, microstructure, extent of decarburization of Cr3C2 phase and hardness. One of the parameters which affects the above mentioned coating properties is the characteristics of the powder utilized for thermal spraying. In the present study, Cr3C2-25% NiCr powders obtained from four different sources has been utilized to form Cr3C2-NiCr coatings on steel substrates utilizing the detonation spray coating (DSC) system. The Cr3C2-NiCr powders utilized vary from each other in terms of manufacturing route employed (sintered and crushed, pre-alloyed, blended, etc.), particle size distribution, particle shape and even phases present. The influence of each of these powder characteristics on the coating microstructure, porosity, hardness, extent of carbide dissolution and ultimately on coating performance (i.e. sliding and abrasive wear resistance) has been evaluated.

Abstract Properties of an erosion resistant Cr3C2 - NiCr coating have been studied as a function of both plasma spraying process variables and heat treatment. The as-sprayed Cr3C2 - NiCr coating revealed low hardness value of 380-470 Hv, which provided the coating with a poor erosion resistance. This is directly attributed to the decomposition of Cr3C2 constituent into Cr7C3 and graphite phases during the spraying. It was not the effective way to control the process variables such as arc current and stand-off distance for preventing the decomposition of Cr3C2 constituent. A proper heat treatment on the as-sprayed coating increases the hardness of the coating in a great extent up to 900Hv so that the erosion resistance of the coating is clearly improved. This was confirmed to be attributed to the recovery of Cr3C2 at the expense of graphite phase and the formation of Cr2O3 by the heat treatment. In addition, the formation of Cr2O3 phase plays an important role of increasing the erosion resistance of the coating by healing the microcracks of the as-sprayed coating. These are the microstructural features responsible for the high erosion resistance of the coating after a proper heat treatment.

The high temperature oxidation behavior of detonation-gun sprayed Cr3C2-NiCr coatings with and without 0.4 wt. % CeO2 additive on Ni-based superalloy inconel-718 is comparatively discussed in the present study. Oxidation studies were carried out at 900°C for 100 cycles in air under cyclic heating and cooling conditions on bare and coated superalloys. The thermo-gravimetric technique was used to establish kinetics of oxidation. X-ray diffraction, SEM/EDAX and X-ray mapping techniques were used to analyze the oxidation products of bare and coated samples. The results indicate that Cr3C2-NiCr-CeO2 coated specimen showed better oxidation resistance. The overall weight gain and parabolic rate constant of Cr3C2-NiCr-CeO2 coated specimen was found to be lowest in the present study signifying that the addition of CeO2 in Cr3C2-NiCr powder has contributed to the development of adherent and dense oxide scale on the coating at elevated temperature.

Abstract The effects of powder types and HVOF spray systems used to produce Cr3C2-NiCr coating on the relationships between spray parameters and wear performance were investigated based on the effect of fuel gas conditions on abrasive wear and erosion wear. The relationships between spray parameters and wear properties were obtained by orthogonal regression experimental design method. Four types of powders and two HVOF spray systems were used. It is found that with the increase in fuel gas flow or pressure the abrasive wear and erosion of Cr3C2-NiCr coatings change following a concave curve. The Cr3C2-NiCr coating with the best wear performance will be deposited under intermediate fuel gas condition. It is experimentally confirmed that by different types of powders and HVOF systems applicable to HVOF spraying of Cr3C2-NiCr coating, although the optimized fuel gas conditions to deposit coating with the best wear performance will be influenced by types of starting powders.

Abstract In this paper the oxidation behaviour of WC, Cr3C2, and TiC and their composites with binder metals is compared on the basis of literature data and some oxidation experiments. It was found that the oxidation mechanisms in air, which are more or less equal to service conditions of coatings, seem to be totally different from those in the spray process in the case of WC, but similar in the case of TiC and Cr3C2. Oxide layer scale adhesion strengths and, possibly, the high volatility of WO3 seem to be responsible for this difference. It can also be assumed, that the problem of oxidation of TiC-based materials and Cr3C2-NiCr is that of local oxidation on the surface of the spray powder particles during the spray process. Cr3C2-NiCr and TiC-based materials are characterized by a high oxidation resistance in air. Plain WC-Co oxidizes readily in the temperature range 400-600°C, but alloying with Cr, as for instance in WC-CoCr and WC-(W,Cr)2-Ni spray powders increases the oxidation resistance.