FeCoCrNiMo high-entropy alloys prepared by powder metallurgy processing for diamond tool applications

High-entropy alloys (HEAs) show good mechanical properties like high strength, hardness and wear resistance, and this makes them attractive for application in diamond tools. However, there are severe obstacles to improving the mechanical properties of normal diamond tools with metal-matrix alloys. Here, we report the formation of FeCoCrNiMo HEAs by powder metallurgy processing, starting from a gas-atomised powder followed by mechanical milling and consolidation by spark plasma sintering. Our results show that FeCoCrNiMo HEAs with pure FCC phase can be obtained by this method. Specimens with higher hardness can be obtained at higher temperatures and low pressures, while specimens with higher bending strength are formed at lower temperatures and pressures. FeCoCrNiMo HEAs have remarkably higher hardness and better wear behaviour than metal-matrices commonly in used diamond tools, which indicates that a new type of diamond tool with superior properties can be realised from HEAs.

Special theme block on high entropy alloys, guest edited by Paula Alvaredo Olmos, Universidad Carlos III de Madrid, Spain, and Sheng Guo, Chalmers University, Gothenburg, Sweden.     

Powder metallurgy approach for control of microstructure and properties in high strength aluminum alloys

High-strength products made from atomized Al-Zn-Mg-Cu-Co alloy powders have good combinations of strength, ductility, resistance to stress-corrosion cracking and fracture toughness. Powder Metallurgy (PJM) methods produce fine metallurgical structures and compositions which cannot be produced by Ingot Metallurgy (IJM) methods. Fine structures result from very rapid solidification and from the effect of fine dispersoids in restricting grain growth. Stress-corrosion cracking (SCC) performance is favored by grain morphology of PJM products. Co₂Al₉ particles in PJM products are 0.02 to 2.0 μm spheroids occurring frequently on grain boundaries where they may serve several functions in slowing SCC attack. Oxide particles are irregular shapes, 0.01 to 0.04 μm in size, occurring in clusters at grain boundaries and in grain bodies. Some of the oxide particles are magnesium oxide and alter the environment in a SCC crack to arrest attack. Porosity is not a significant factor in the structure of PJM products made by a vacuum compacting process. P/M wrought products have superior combinations of high strength and stress-corrosion cracking resistance compared to IJM 7075 and 7050 alloys. While equaling the fracture toughness of 7075 alloy, the PJM products at present have somewhat lower fracture toughness than 7050 alloy, due in part to a larger amount of second-phase particles in the form of Co₂Al₉ and oxide. This paper is based on an invited presentation made at a symposium on “Advances in the Physical Metallurgy of Aluminum Alloys” held at the Spring Meeting of TMS-IMD in Philadelphia, Pennsylvania, on May 29 to June 1, 1973. The symposium was co-sponsored by the Physical Metallurgy Committee and the Non-Ferrous Metals Committee of TMS-IMD.     

Powder metallurgy approach for control of microstructure and properties in high strength aluminum alloys

High-strength products made from atomized Al-Zn-Mg-Cu-Co alloy powders have good combinations of strength, ductility, resistance to stress-corrosion cracking and fracture toughness. Powder Metallurgy (PJM) methods produce fine metallurgical structures and compositions which cannot be produced by Ingot Metallurgy (IJM) methods. Fine structures result from very rapid solidification and from the effect of fine dispersoids in restricting grain growth. Stress-corrosion cracking (SCC) performance is favored by grain morphology of PJM products. Co₂Al₉ particles in PJM products are 0.02 to 2.0 μm spheroids occurring frequently on grain boundaries where they may serve several functions in slowing SCC attack. Oxide particles are irregular shapes, 0.01 to 0.04 μm in size, occurring in clusters at grain boundaries and in grain bodies. Some of the oxide particles are magnesium oxide and alter the environment in a SCC crack to arrest attack. Porosity is not a significant factor in the structure of PJM products made by a vacuum compacting process. P/M wrought products have superior combinations of high strength and stress-corrosion cracking resistance compared to IJM 7075 and 7050 alloys. While equaling the fracture toughness of 7075 alloy, the PJM products at present have somewhat lower fracture toughness than 7050 alloy, due in part to a larger amount of second-phase particles in the form of Co₂Al₉ and oxide.     

粉末冶金法制备CrFeNiCuMoCo高熵合金的组织与性能

利用粉末冶金法制备CrFeNiCuMoCo高熵合金,用带有能谱的扫描电子显微镜(SEM/EDS)、X射线衍射仪、显微/维氏硬度计、电化学工作站、材料试验机等对CrFeNiCuMoCo高熵合金组织结构进行分析并测试其硬度、耐蚀性和压缩性能.结果表明:CrFeNiCuMoCo高熵合金组织形貌简单;物相主要由FCC和BCC两相组成,Mo元素和Cu元素在合金中存在偏析现象;合金的耐蚀性能优异,与304不锈钢相比,自腐蚀电流密度减小1个数量级;组元间原子半径的差异导致较大的晶格畸变,阻碍位错的运动,使得固溶强化效应增强;Mo元素起到细化晶粒作用,使该合金具有较高的硬度和抗压强度,合金硬度为485 HV,抗压强度约为1 385MPa;断裂类型为脆性解理断裂.     

Powder metallurgy industry and managerial economics

The phase composition and structure of two-layer thermal-barrier metal-ceramic coatings applied by electron-beam vapor deposition in one process cycle are investigated. It is shown that the outer ceramic layer has a two-phase (monoclinic-tetragonal) structure and is characterized by an axial growth texture of columnar crystallites with prevailing <001> orientation. High-temperature isothermal annealing in an oxidizing medium increases the amount of the tetragonal constituent in the outer ceramic layer of the thermal-barrier coating. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 7–8 (456), pp. 100–106, 2007.     

难熔高熵合金:制备方法与性能综述

从加工方法、微观结构以及各类性能三方面介绍了难熔高熵合金(Refractory high-entropy alloys,RHEAs),最后对难熔高熵合金的发展和未来进行了展望。以MoNbTaVW为代表的难熔高熵合金在高温下表现出优于传统镍基高温合金的压缩屈服强度,且屈服强度随温度的变化更加缓慢,高温力学性能优异;以MoNbTaVW、MoNbTaTiZr、HfNbTiZr等为代表的难熔高熵合金,与商用高温合金、难熔金属、难熔合金以及工具钢相比,展现出更优的耐磨性能。以W₃₈Ta₃₆Cr₁₅V₁₁合金为代表的难熔高熵合金在辐照后,除了析出小颗粒第二相外,不存在位错环缺陷结构,抗辐照性能优异。提出了难熔高熵合金未来发展的两大方向:建立高通量的实验和计算方法继续探索更多的难熔高熵合金组成和结构模型;探索多场耦合环境下难熔高熵合金的服役行为。      

激光增材制造技术制备高熵合金研究进展

介绍了激光增材制造高熵合金的工艺方法,从成形工艺、合金元素含量（摩尔分数）、热处理工艺和增强相添加等几个方面综述了国内外激光增材制造高熵合金的研究进展,分析了激光熔化沉积和选区激光熔化成形两种主要激光增材制造技术,以及两种技术制备高熵合金的微观结构和力学性能,指出了高熵合金激光增材制造技术的发展趋势及存在的主要问题,并提出了改进措施。     

Processing and microstructure of powder metallurgy Al-Fe-Ni alloys

Prealloyed rapidly solidified Al-Fe-Ni alloy powder with dispersoid volume fractions of 0.19, 0.25, and 0.32 FeNiAl₉ was produced by air atomization. The powder was degassed, canned, and consolidated to full density by vacuum hot pressing and extrusion or by direct extrusion. Microstructures in the alloy powder and consolidated material were characterized by means of optical, scanning (SEM), and transmission electron microscopy (TEM) and constituent phases identified by X-ray diffraction. The coarsening kinetics of the FeNiAl₉ dispersoid were monitored by differential scanning calorimetry (DSC) and by quantitative metallography. Atomized powders exhibited two scales of microstructures: optically featureless regions and regions with a coarse dispersoid morphology. Within the featureless regions, there are three morphologies, namely, a fine uniform precipitate microstructure, a cellular microstructure, and an eutectic microstructure. The only dispersoid observed in the atomized powders and consolidated material was FeNiAl₉. The two scales of microstructure were retained after consolidation, and after hot extrusion, the typical microstructure consisted of a recovered matrix structure with a grain size of 0.2 to 0.3 μm and equiaxed intermetallics of average diameter 0.1 μm. The microstructure was resistant to coarsening up to approximately 370 °C. Coarsening kinetics in this alloy system were consistent with a grain boundary diffusion model (activation energy 146 kJ/mol) and were not appreciably affected by dispersoid volume fraction.     

多主元高熵合金成相研究进展

多主元高熵合金是基于"多元高乱度"的设计思想而提出的新型多元合金,具有高强度、高硬度、耐腐蚀、抗磨损和良好的高温热稳定性等优点。阐述了高熵合金的定义及成相理论,介绍了最近几年来国内外在高熵合金成相理论的研究领域取得的实质性进展。     

基于神经网络模糊控制的粉末冶金烧结炉

为解决粉末冶金管式烧结炉温度控制精度不高、能耗大的难题,提出了一种基于神经网络模糊控制的PID参数自适应控制系统。运行结果表明,该系统稳定性好,节能显著,控温精度可达±3℃,很好地满足了粉末冶金工艺的要求。     

Cr-Si粉末冶金工艺及其物理-力学性能

粉末冶金制作法主要有热压(HP)、热等静压(HIP)及常压烧结(Sinter)三种.采用热压及热等静压法可以很容易地得到高致密化的高温金属硅化物,但若要进行大尺寸的产品烧结,必须提升生产设备的规格和能力,例如加大热压机力吨位、扩大热压炉腔体等,致使设备投资及生产成本相对昂贵.所以大部分厂商宁可采用常压烧结法,虽然该法的高致密化工艺条件不易控制,却因可以制作大尺寸金属硅化物,加上设备投资及生产成本相对降低,使许多大厂已投入相当大的人力和物力在开发此工艺.该文作者试用不同真空烧结温度,造成Cr-Si合金粉末烧结性质的差异,探讨稳定而可大量生产的可行性;并通过对温度的控制,来改善Cr-Si的物理性质与力学性质.结果表明,提高烧结温度会使Cr-Si合金产生部分液相烧结的现象,从而使孔隙率显著下降;但显微结构也随之有偏析与晶粒粗化的现象.     

Structure and properties of Nb-Al alloys prepared by powder metallurgy

The structure and short-time strength of Nb-Al alloys of two compositions prepared by powder metallurgy are studied. The mechanical alloying of niobium with aluminum in a planetary ball mill in air is shown to result in simultaneous alloying of niobium with oxygen. During subsequent vacuum high-temperature sintering, disperse particles of a complex oxide, whose tentative composition is (AlNb)₂O₃, form in the alloy structure. The short-time strength at 1250°C of the prepared alloys exceeds that of nickel-aluminum superalloys.     

Influence of impurities on the properties of powder metallurgy and cast iron-manganese alloys

Translated from Poroshkovaya Metallurgiya, No. 6(306), pp. 56–61, June, 1988.     

Stress-strain behavior and shape memory effect in powder metallurgy TiNi alloys

The shape memory properties of the TiNi alloy produced by a powder metallurgical method have been evaluated from tensile stress-strain curves. The contamination of the powders during atomization can be suppressed by applying the Plasma Rotating Electrode Process (P-REP), so that the compact made by Hot Isostatic Pressing (HIP) is expected to exhibit the shape memory effect identical to the typical alloy grown from melt. The fracture behavior of the P/M alloy is also studied, and the improvement of fracture strength of the P/M alloy is attempted.