High-entropy alloys (HEA) are multinary alloys obtained by blending at least five metallic elements in compositions close to their isoatomic fractions (5–35 at%). Generally, HEAs are produced by arc melting and casting. However, the cast specimens undergo phase separation and have a non-uniform microstructure. In contrast to ingot metallurgy, powder metallurgy has several advantages such as the possibility of alloying metals with high melting points and large differences in melting points and specific gravity. Therefore, we investigated the preparation of HEAs by mechanical alloying (MA), which produces an alloy powder with a uniform microstructure, followed by consolidation by spark plasma sintering (SPS). In this study, CoCrFeNiTi HEA sintered after MA-SPS was subjected to direct current plasma nitriding with screen (S-DCPN) to evaluate the characteristics of the nitrided layer as a function of nitriding temperature. Ball milling with heptane in an argon atmosphere using pure powders of Co, Cr, Fe, Ni, and Ti as raw materials was performed for 50 h. Subsequently, sintered compacts were prepared by SPS and treated with S-DCPN at 673, 773, and 873 K for 15 h in 75% N 2 –25% H 2 at a gas pressure of 200 Pa. A screen made of austenitic stainless steel SUS316L was installed as an auxiliary cathode to ensure uniform heating and nitrogen supply during the plasma nitridation process. Then, X-ray diffraction test, cross-sectional microstructure observation, surface microstructure observation, cross-sectional hardness test, roughness test, glow discharge optical emission spectrometry, corrosion test, and wear test were performed on the nitrided samples. The corrosion test results demonstrated that corrosion resistance increased with decreasing nitriding temperature. Furthermore, the results of the roughness and wear tests confirmed that abrasive wear occurred on the specimens nitrided at 873 K.

Laser Powder Bed Fusion (L-PBF) processes are becoming more viable in place of traditional castings in a variety of industries. To compete, novel material grades are being considered with additive manufacturing (AM). In maximizing performance and manufacturing efficiency through AM, a novel approach to heat treatment and Hot Isostatic Pressing (HIP) processing needs to be considered. It has been shown that combining key heat treatment processes with (HIP) by utilizing fast cooling rates can benefit static properties as well as improve turn-around time for HIP processing [1,2]. Argon pressures up to 207 MPa with cooling rates above 170°C per minute are now available in production sized HIP systems to design ideal HIP cycles for high pressure heat treatment. Additive manufacturing with high pressure heat treatment is in need of further investigation for establishing new qualification standards. This study investigates designed High-Pressure Heat Treatment cycles to consider mechanical performance on LPBF CoCr. The combined cycles investigate possible alternatives to historically accepted two step HIP then heat treat processing by combining densification with homogenization treatment into one step. Tensile, fatigue, hardness, microstructure and Charpy impact performance are explored to seek optimal properties and with streamlined thermal processing. It was found that all trial conditions exceeded Electron Beam Melted (EBM) AM CoCr expectation, but traditional processing provided a slight advantage in ultimate tensile stress. One of the novel processes explored, “common” was found to provide a slight improvement on yield stress and direct hardness. Published fatigue data is rare for CoCr, however data generated from this study showed a slight advantage to the “common” HPHT process primarily for lower applied stress levels. Microstructures were comparable across all trial processes. It is recommended that each novel processing route be considered as viable alternatives to traditional processing, but that the “common” processing may prove advantageous for both mechanical properties and streamlined manufacturing.