Academic literature on the topic 'Heat resistant alloys. Precipitation hardening. Powder metallurgy'

The influence of plastic deformation and heat-treatment on the precipitation of Al3(Sc, Zr) particles and the effect of these precipitates on hardening and softening processes of dilute ternary Al-0.2wt.%Sc-0.1wt.%Zr alloy was investigated. Behaviour of two differently prepared alloys (mold cast and prepared by powder metallurgy – PM) was investigated in as-prepared and in cold rolled state. Both alloys exhibit the same peak age hardening, PM one reaches it already during extrusion at 350°C. Both cold rolled alloys are highly resistant against recovery, which proceeds without rapid hardness decrease at high temperatures. Evolution of hardness agrees well with that of resistivity and with TEM observation.

Alloys from austenitic and ferritic stainless steel found to be satisfactory for a great many applications. However, for applications that require higher levels of strength and hardness from the martensitic grades are frequently specified. Martensitic stainless steels offer significantly higher strengths but have to low ductility. For this reason for application where high levels of strength and a moderate ductility is required, the precipitation strengthened stainless steels are often considered. One of the most popular alloy of this kind of stainless steel is 17-4 PH. The aim of the present paper was to examined the influence the process parameters in conventional powder metallurgy processing on the mechanical properties of the 17-4 PH alloy in both as-sintered and heat treated conditions. In was found that temperature of aged is a very sensitive parameter for obtained high strength and acceptable ductility.

Pre-alloyed micron-sized 6005A Al alloy (AA 6005A) powders, with a Mg/Si atomic ratio of 0.75, obtained by high pressure inert gas atomization were consolidated by uniaxial cold pressing at 200 MPa into cylindrical Al containers and hot extruded at 450, 480 and 500 °C with an extrusion rate of 7:1, followed by artificial T6 precipitation hardening. Ageing conditions were varied between 170 °C and 190 °C and times of 6, 7 and 8 hours. The microstructure of the extruded profiles was analysed using X-Ray diffractometry (XRD), light optical microscopy (LOM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) was used to study the possible phase transformations. After our results, the peak-aging hardness condition was achieved at 180 °C for 6 h. Mechanical properties of the powder metallurgy (P/M) aluminium alloys consolidated by hot extrusion were superior to those of the extruded profiles of wrought alloy using conventional ingot metallurgy (I/M) billets. AA 6005A wrought P/M alloy via T6 heat treatment shown yield stress of 317 MPa and elongation of 21% at the extrusion pre-heating temperature of 500 °C.

AbstractThis paper presents the results of a study on the impact of a precipitation hardening treatment on the mechanical properties of 17-4PH stainless steel open-cell foams produced using a powder-metallurgy-based process patented by the National Research Council Canada (NRC). Pre-alloyed powder was used to manufacture stainless steel (SS) foams with either medium or high porosity by changing the nature of the organic binder used to process the porous materials. Some of these were kept in the as-sintered state, while others were submitted to the H900 precipitation hardening treatment frequently prescribed for 17-4PH stainless steels.Metallurgical and physical characterization was carried out on the resulting materials, along with mechanical testing at the micro (indentation testing) and macro (compressive testing) scales. It was found that the Medium-Porosity Foams (MPF) and High-Porosity Foams (HPF) had very different morphologies, the HPFs having a delicate porous structure featuring thin sintered walls with many openings (a.k.a. windows) between the main cells, while the MPFs exhibited much thicker walls with few windows connecting the larger pores. As expected from these foam morphologies, the mechanical properties of MPFs were much higher than those of the more porous and delicate HPF materials. For both foam types, the average mechanical properties were improved by the H900 treatment. A comparison with compressive properties of 17-4PH foams taken from the literature resulted in reasonable agreement. However, the large scatter observed on the average compressive properties of the NRC foams and the slightly different structure/composition of the literature materials mean that any comparison between these porous alloys must be interpreted with caution.

Mechanical alloying and powder metallurgy procedures were used to manufacture very fine-grained bulk material made from chips of the 2024 aluminum alloy. Studies of solution treatment and precipitation hardening of as-received material were based on differential scanning calorimetry (DSC) tests and TEM/STEM/EDX structural observations. Structural observations complemented by literature data lead to the conclusion that in the case of highly refined structure of commercial 2024 alloys prepared by severe plastic deformation, typical multi-step G-P-B →θ” →θ’ →θ precipitation mechanism accompanied with G-P-B →S” →S’ →S precipitation sequences result in skipping the formation of metastable phases and direct growth of the stable phases. Exothermic effects on DSC characteristics, which are reported for precipitation sequences in commercial materials, were found to be reduced with increased milling time. Moreover, prolonged milling of 2024 chips was found to shift the exothermic peak to lower temperature with respect to the material produced by means of common metallurgy methods. This effect was concluded to result from preferred heterogeneous nucleation of particles at subboundaries and grain boundaries, enhanced by the boundary diffusion in highly refined structures. Transmission electron microscopy and diffraction pattern analysis revealed the development of very fine Al4C3 particles that grow due to the chemical reaction between the Al matrix and graphite flakes introduced as a process control agent during the preliminary milling of chips. Al4C3 nano-particles are formed at high temperatures, i.e. during hot extrusion and the subsequent solution treatment of the samples. Highly refined insoluble particles such as aluminum carbide particles and aluminum oxides were found to retard recrystallization and reduce recovery processes during solution treatment of preliminarily milled materials. Therefore, the as-extruded material composed of a milled part and chip residuals retained its initial bimodal structure in spite of solution heat treatment procedures. This points to a high structural stability of the investigated materials, which is commonly required for new technologies of high-strength Al-based materials production.

The effect of equal-channel angular extrusion (ECAE) on mechanical properties of an AA2017 produced by powder metallurgy is investigated. Special attention is given to the influence of heat treatment, processing temperature and backpressure on the workability for achieving high strength and moderate ductility. This is of special interest, since it is often reported that Al-Cu alloys have low ductility and therefore are prone to cracking during severe plastic deformation. It is shown that ECAE at high temperatures (>220°C) does not necessitate backpressure to ensure homogeneous deformation but leads to a significant sacrifice in strength due to in-situ precipitation. Thus, most of the extrusions are done at considerably low temperatures. Performing room temperature-extrusion is most effective in achieving high strengths but also requires high backpressures. Due to severe strain hardening during processing, the strength increase is combined with a reduction in ductility. Recently it was reported that a post-ECAE aging of pre-ECAE solution treated material is effective in enhancing the ductility of aluminium alloys. This approach was successfully transferred to the current alloy. A high-temperature, short-time aging after only one extrusion, for example, doubles the failure strain to a value of ~13%. Compared to the naturally aged condition with coarse grains that serves as reference (T4), an increase of 15 % in yield stress (YS) was obtained while retaining the ultimate tensile stress (UTS). Another effective approach is the combination of a pre-ECAE solution treatment with subsequent under-aging prior to ECAE. It is shown that performing ECAE at medium temperatures (160-180°C) enables a better workability and additionally gives higher strengths and better ductility compared to the processing in the water quenched condition. A remarkable YS of 530 MPa and an UTS of 580 MPa combined with a moderate failure strain of 11.6 % were achieved.

Abstract Carpenter CTS-XHP alloy is a powder-metallurgy, air-hardening, high-carbon, high-chromium, corrosion-resistant alloy. The Carpenter CTS family of alloys is used for many blade applications. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness. It also includes information on corrosion and wear resistance as well as forming, heat treating, and machining. Filing Code: SS-1057. Producer or source: Carpenter Specialty Alloys.

Abstract Carpenter CTS-204P (Micro Melt 20-4) alloy is a highly wear- and corrosion-resistant, air-hardening martensitic cold-work stainless die steel produced using Carpenter’s Micro-Melt powder metallurgy process. The excellent wear resistance of the alloy is provided by a significant volume fraction of hard vanadium-rich carbides, while the outstanding corrosion resistance of the alloy is obtained as a result of the chromium-rich matrix. This datasheet provides information on composition, physical properties, hardness, and elasticity. It also includes information on corrosion and wear resistance as well as forming, heat treating, and machining. Filing Code: SS-1051. Producer or source: Carpenter Specialty Alloys.