Effect of copper on the mechanical properties of alloys formed by powder metallurgy

Alloys formed by powder metallurgy are typically porous, which reduces their strength. In this study, we attempt to improve the mechanical properties of an alloy composed of 0.6 wt% C, 1.0 wt% Ni, 0.3 wt% Mo, 0.7 wt% Mn and the balance Fe by addition of 8 wt% Cu. To form the alloys, powders are blended and compacted in a dual-action hydraulic press and then sintered in a furnace at 1150 °C. Alloys with and without Cu are used in specific parts designed for impact testing. Stress analysis is performed using ANSYS, which validates the operation of the parts. The strength of the body geometry according to its design is determined by considering the manufactured material and the loads that it is subjected to during operation. SEM images revealed that the alloy without Cu contains martensite and bainite phases with large, irregular pores. In contrast, the alloy with Cu has a considerably lower pore concentration. During sintering, Cu forms a liquid phase that can fill the spaces between the particles of the alloying powders. The result is an alloy with increased density and toughness; the density of the alloy increases from 7.2 to 7.8 g/cm³ upon addition of Cu, and its toughness increases from 22 to 34 J.     

Effect of temperature-related factors on densification,microstructure and mechanical properties of powder metallurgy TiAl-based alloys

In the present work, the influence of temperature-related factors, including sintering temperature, heating step and temperature-control mode, on the densification, microstructure and mechanical properties of Ti-46.5Al-2.15Cr-1.90Nb-(B, Y, Mo) alloys prepared by SPS has been investigated and discussed in detail. The results obviously indicate that the sintering temperature plays a key role on densification and phase transition, when compared with the heating step and temperature-control mode. Based on the experimental results and theoretical analysis, the densification process and microstructural evolution of TiAl-based alloys during sintering are studied. Moreover, the mechanical properties of the sintered alloys are determined by the combined effects of the densification and microstructure. The obtained results will help to optimize the microstructure and properties for this kind of intermetallic alloys through controlling sintering parameters during powder metallurgy process.     

Effect of carbon on the weldability of Fe-Mn-Al alloys

Based on the composition of 30% Mn, 10% Al, balance Fe, Fe-Mn-Al alloys with different carbon contents and thus different ferrite contents were studied. Tensile tests and U-bend tests on the autogenous GTA welded specimen were utilized to evaluate the weldability. FN measurement, optical metallography, and SEM-EDAX were used to study the microstructural characteristics of the weld metal and the base metal heat affected zone. It was found that the carbon content has a strong influence on the amount of residual ferrite in the Fe-Mn-Al weld metals studied. After heat treatment, the amount of residual ferrite is reduced and annealing twins were found in the weld metal. Tensile strengths in excess of 900 MPa in both the longitudinal and transverse welding directions were obtained. The elongation of the butt-jointwelded specimen is substantially less than that of the base metal, especially for the fully austenitic weld metal. U-bend test results gave an indication of good weldability for the Fe-Mn-Al alloys.     

Effect of surface treatment on the spot weldability of Fe-Mn-Al-Cr alloys

An Fe-26.3Mn 6,8Al-5.5Cr-0.9Mo-1.0C alloy was employed to study spot weldability. A series of Lobe curves was obtained under various welding conditions including electrode force, weld current, weld time and hold time. The acceptable weld currents ranged from 3.5–6kA, which is narrower than those of HSLA and plain carbon steel. The effect of surface treatment on the weldability of this alloy system was investigated. For an untreated specimen with -Al₂O₃ layer on the surface, the Lobe curve exhibits a narrower range than those of surface acid-pickled specimens. In addition, for the surface untreated specimen, the plug size was linearly proportional to the weld time. However, for the surface acid-pickled specimen, the degree of dependence of plug size on the weld time decreased as the electrode force increased. It was also observed that the indentation was proportional to the weld current for this alloy system. The dependence of indentation on the weld time was influenced by both the surface condition and the electrode force.     

Diffusion-based microalloying of aluminium alloys by powder metallurgy and reaction sintering

A diffusion-based technique of microalloying aluminium powder metallurgy products was examined to expand the range of feasible alloying additions. Thermodynamic calculations and diffusion rates for several elements suggested that tin and silver were the most promising; these elements were successfully alloyed into AA 2014 on both a macroscopic and a microscopic scale. The final microstructures were examined using X-ray diffraction, X-ray mapping and energy-dispersive electron probe microanalysis. Silver additions were homogeneous throughout the alloy microstructure, whereas tin was concentrated in intergranular regions only. The results suggested that the technique was viable for a variety of microalloying elements. Also, the extent of alloying was predicted reasonably well using a mathematical mass balance model.     

Strengthening effects in precipitation and dispersion hardened powder metallurgy copper alloys

The hardening of copper and copper alloy matrix using powder metallurgy (PM) techniques and different ways for dispersoids formation, as well as analysis of their single and combined effects on the strength of obtained material at room and elevated temperatures, have been presented and discussed. Gas atomized Cu–3.8 wt.%Ti and Cu–0.6 wt.%Ti–2.5 wt.%TiB₂ (Cu–Ti–TiB₂) powders and mechanically alloyed powder Cu–4 wt.%TiB₂ were used as starting materials. The powders were consolidated by hot isostatic pressing (HIP) and hot pressing (HP). Optical, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX), as well as transmission electron microscope (TEM) were used for microstructure characterization of the compacts. High strengthening of the Cu–Ti compacts was achieved by thermal treatment (aging) as a consequence of the development of modular structure and precipitation of metastable Cu₄Ti_(m). Hardening in the Cu–Ti–TiB₂ compacts is due to simultaneous influence of the following factors: the development of modular structure, precipitation of metastable Cu₄Ti_(m), and the presence of TiB₂ dispersoid nanoparticles. In case of Cu–TiB₂ compacts, high starting values of hardness and hardness on the elevated temperatures result from the presence of finely distributed TiB₂ particles in copper matrix obtained by mechanical alloying. Cu–Ti–TiB₂ composite yields much higher hardness values compared with the binary Cu–Ti alloys, owing to primary TiB₂ dispersions formed during atomization. Separation of metastable Cu₄Ti precipitate and the presence of significantly finer TiB₂ particles in the copper matrix are the reason for higher hardness values at peak temperatures (400–500 °C) in multiple-hardened copper alloy compared to the dispersion-hardened.     

Correlation between microstructure and tensile properties in powder metallurgy AZ91 alloys

The ultrafine-grained (0.3–1.3 μm) AZ91 alloys, which were fabricated by powder extrusion in the range of 200 to 350 °C and subsequent aging at 100 °C for 8 h, exhibit a remarkable yield stress of 360–478 MPa and moderate tensile elongations of 6–8%. A composite structure was developed after extrusion with uniform β (Mg₁₇Al₁₂) particles dispersed in magnesium matrix. The extrusion temperature has an indirect role on yield stress since partial dissolution of β particles induced by high extrusion temperature fails to retard grain growth. Moreover, the strength was further enhanced by the formation of nano-scale precipitates during artificial aging. The high strength could be attributed to a combination effect of grain refinement, particle reinforcement and precipitation hardening.     

Effect of laser surface melted zirconium alloys on microstructure and corrosion resistance

Zirconium alloys were laser surface melted (LSM) using a continuous wave CO₂ laser at energy densities of 4,7 and 10 kJ cm^–2. LSM samples examined using SEM and optical microscopy exhibited resolidified regions with several different microstructures, including ultrafine martensite. Corrosion performance was obtained by steam autoclave tests and immersion tests in 10% FeCl₃ at room temperature. Coarser microstructures performed better than fine microstructures in autoclave tests, while fine microstructures performed better than coarse microstructures in 10% FeCl₃ immersion tests. Accelerated corrosion in the autoclave and immersion tests was observed to occur near the laser beam overlap region. The surface chemistry was examined for alloy segregation using secondary iron mass spectroscopy. Tin and iron alloy elements segregated near the periphery of each melt pool. Segregated regions containing increased iron concentrations associated with each laser pass were responsible for accelerated corrosion.     

The mechanical properties of Fe-Co heterogeneous alloys fabricated by powder metallurgy techniques

Fe-Co heterogeneous alloys fabricated by powder metallurgy techniques were hot rolled, cold rolled and then heat treated. These processes produced a type of fibre-reinforced composite which consisted of fibrous Fe and Fe-Co phases. The tensile strength of the alloys depended on the composition and degree of order of the Fe-Co phase. The rule of mixtures was applicable, provided that the dependence of strength in the Fe-Co phase on Co content was considered.     

Effect of carbon content on workability of powder metallurgy steels

Workability behaviour of steel powder metallurgy performs containing 0%, 0.4% and 0.8% of carbon were completely investigated experimentally. Cold upsetting of abovementioned powder metallurgy sintered steels preforms with two different aspect ratios namely 0.39 and 0.59 was carried out with graphite as lubricant and the formability behaviour of the preforms under triaxial stress state condition was determined. The formability stress parameter was evaluated for all the above said preforms and its variation with respect to axial strain was plotted, studied and discussed relative to their as sintered microstructures. Also the characteristics of various stress ratio parameters with respect to axial strain were analyzed and presented.     

Control of microstructure and component shape in rapidly solidified/powder metallurgy titanium alloys

Extensive use of titanium rapidly solidified/powder metallurgy (RS/PM) components requires not only careful control of the microstructure for optimum mechanical properties but also cost-effective processing. A new direct reduction process for production of titanium alloy powder will be presented. Control of the microstructure in conventional alloys such as Ti-6Al-4V and in non-conventional dispersion strengthened terminal and intermetallic alloys will be discussed. It will be shown that RS/PM processing allows production of a fine grain size and useful dispersions of rare earth and metalloid phases; phases which normally form as gross undesirable particles. The use of hydrogen as a temporary alloying element, thermochemical processing, will be discussed and it will be demonstrated how this treatment can lead to refined microstructures with enhanced mechanical behaviour. Cost-effective processing using near-net shape techniques such as the ceramic mold process, rapid omnidirectional compaction (ROC), and the use of RS/PM preforms for subsequent isothermal forging will be presented. Microstructural control and shape-making used in unison should lead to increased use of titanium components in advanced aerospace systems. work done as a consultant to Metcut-Materials Research Group     

Microstructure and mechanical properties at elevated temperature of Mg-Al-Ni alloys prepared through powder metallurgy

Mg-Al-Ni alloys were prepared by powder metallurgy, and their microstructure and elevated temperature mechanical properties were investigated. Results indicate that, in addition to α-Mg matrix, both coarse Al_3Ni_2 particles and fine Al Ni nano-particles exist in the Mg-Al-Ni alloys. The strength at 150?C is improved with the increase in Ni content. Mg-18.3Al-8Ni alloy possesses a compressive strength of234.7 MPa and a yield strength of 146.5 MPa. Plasticity is also improved with a low concentration of Ni. Mg-11.3Al-2Ni alloy possesses a compression ratio of 17.3%. The phases of Al_3Ni_2 and Al Ni in the alloys block the movements of grain boundaries and dislocations during the deformation at elevated temperature. The existence of Al Ni phase provides a non-basal slip system, leading to the improvement in plasticity. Finally, the formation mechanism of Al-Ni phases in the process is discussed with thermodynamics and kinetics.     

Synthesis and characterization of bulk amorphous/amorphous composite alloys through powder metallurgy route

In the present study, amorphous Ni₆₀Nb₂₀Zr₂₀ and Ti₅₀Cu₂₈Ni₁₅Sn₇ alloy powders were synthesized separately using a mechanical alloying (MA) technique. The dual-amorphous-phased (Ti₅₀Cu₂₈Ni₁₅Sn₇)_100−x (Ni₆₀Nb₂₀Zr₂₀) _x (x = 0, 10, 20, and 30 vol%) powders were prepared by mixing the corresponding amorphous powders. The dual-amorphous-phased powders were then consolidated into bulk amorphous/amorphous composite (BA/AC) alloy discs. The amorphization status of as-prepared powders and bulk BA/AC composite discs was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The microstructure of the BA/AC discs showed that the Ni₆₀Nb₂₀Zr₂₀ phase is distributed homogeneously within the Ti₅₀Cu₂₈Ni₁₅Sn₇ matrix. The (Ti₅₀Cu₂₈Ni₁₅Sn₇)₇₀(Ni₆₀Nb₂₀Zr₂₀)₃₀ BA/AC disc exhibited a relative density of 96.6% and its Vickers microhardness was 726 kg/mm².     

机械合金化和粉末冶金法制备Fe-Mn-Si基形状记忆合金的研究进展

铁基形状记忆合金由于价格低廉、强度高、加工性能好、可焊接等优点引起广泛重视。机械合金化(MA)和粉末冶金(PM)作为制备材料的新工艺,可以用来制备性能优越的形状记忆合金。本文详述了机械合金化和粉末冶金工艺在制备Fe-Mn-Si基形状记忆合金过程中对合金相变、组织与性能的影响,以及此类合金在新领域的应用。最后提出了现阶段在研究MA/PM工艺制备Fe-Mn-Si基SMA中有关工艺参数、相变机制以及回复应力和低温应力松弛所存在的问题。     

Study of the properties of low-cost powder metallurgy titanium alloys by 430 stainless steel addition

Titanium is a lightweight metal with an outstanding combination of properties which make it the material of choice for many different applications. Nonetheless, its employment at industrial level is not widespread due to higher production costs with respect to competitor metals like steel and aluminium. In this work the production of low-cost titanium alloys is attempted by combining the utilisation of a powder metallurgy process and cheap alloying elements (i.e. commercial 430 stainless steel powder optimised for the powder metallurgy industry). Low-cost titanium alloys are fabricated by blending elemental titanium with stainless steel. The behaviour of the powders as well as that of the sintered materials are analysed and compared to that of a master alloy addition Ti6Al4V alloy. The produced low-cost titanium alloys show comparable properties to both wrought and powder metallurgy titanium alloys and, therefore, they are proposed as an alternative to obtain structural component made out of titanium alloys.