In this paper, a new Co10Fe10Mn35Ni35Zn10 high entropy alloy (HEA) is identified as a strong candidate for the single face-centered cubic (FCC) structure screened using the upgraded TCFE2000 thermodynamic CALPHAD database. The Co10Fe10Mn35Ni35Zn10 HEA is fabricated using the mechanical (MA) procedure and pressure-less sintering method. The Co10Fe10Mn35Ni35Zn10 HEA, which consists of elements with a large difference in melting point and atomic size, is successfully fabricated using powder metallurgy techniques. The MA behavior, microstructure, and mechanical properties of the Co10Fe10Mn35Ni35Zn10 HEA are systematically studied to understand the MA behavior and develop advanced techniques for fabricating HEA products. After MA, a single FCC phase is found. After sintering at 900℃, the microstructure has an FCC single phase with an average grain size of 18 μm. Finally, the Co10Fe10Mn35Ni35Zn10 HEA has a compressive yield strength of 302 MPa.

Fe-base superalloy powders with Y2O3 dispersion were prepared by high energy ball milling, followed by sparkplasma sintering for consolidation. High-purity elemental powders with different Fe powder sizes of 24 and 50mm were usedfor the preparation of Fe-20Cr-4.5Al-0.5Ti-O.5Y2O3 powder mixtures (wt%). The milling process of the powders was carriedout in a horizontal rotary ball mill using a stainless steel vial and balls. The milling times of 1 to 5 h by constant operation(350 rpm, ball-to-powder ratio of 30:1 in weight) or cycle operation (1300 rpm for 4 min and 900 rpm for 1 min, 15:1) wereapplied. Microstructural observation revealed that the crystalline size of Fe decreased with an increase in milling time by cyclicoperation and was about 15nm after 3 h, forming a FeCr alloy phase. The cyclic operation had an advantage over constantmilling in that a smaller-agglomerated structure was obtained. The milled powders were sintered at 1100oC for 30 min invacuum. With an increase in milling time, the sintered specimen showed a more homogeneous microstructure. In addition, ahomogenous distribution of Y-compound particles in the grain boundary was confirmed by EDX analysis.

The synthesis of NiTi alloy powders by hydrogen reduction and dehydrogenation process of NiO and TiH2 powder mixtures is investigated. Mixtures of NiO and TiH2 powders are prepared by simple mixing for 1 h or ball milling for 24 h. Simple-mixed mixture shows that fine NiO particles are homogeneously coated on the surface of TiH2 powders, whereas ball milled one exhibits the morphology with mixing of fine NiO and TiH2 particles. Thermogravimetric analysis in hydrogen atmosphere reveals that the NiO and TiH2 phase are changed to metallic Ni and Ti in the temperature range of 260 to 290oC and 553 to 639oC, respectively. In the simple-mixed powders by heat-up to 700oC, agglomerates with solid particles and solidified liquid phase are observed, and the size of agglomerates is increased at 1000oC. From the XRD analysis, the presence of liquid phase is explained by the formation and melting of NiTi2 intermetallic compound due to an exothermic reaction between Ni and Ti. The simple-mixed powders, heated to 1000oC, lead to the formation of NiTi phase but additional Ni-, Ti-rich and Ti-oxide phases. In contrast, the microstructure of ball-milled powders is characterized by the neck-grown particles, forming Ni3Ti, Ti-oxide and unreacted Ni phase.