Effects of Ball Milling Time on CoCrFeNiTi High Entropy Sintered Alloys

In this study, CoCrFeNiTi high entropy alloy (HEA) powder was treated by ball milling (BM) for up to 50 hours and sintered compacts were fabricated by spark plasma sintering (SPS). XRD analysis confirmed that the BM powder formed a single BCC solid solution phase after 25 hours, and a nanocrystalline structure was obtained due to the reduction in crystallite size and increase in dislocation density. Meanwhile, after sintering, the main phase changed to FCC, and secondary phases such as CoTi 2 , CrFe, and TiC were precipitated. Carbon analysis by EMIA and EPMA showed that the carbon content in the powder and sintered compact increased with increasing BM time, which is considered to be the cause of TiC formation. Micro-Vickers hardness tests showed maximum hardness at the initial state, decreased at 5 hours, and then recovered after 15 hours due to the effect of secondary phase precipitation and microstructure. The effects of BM treatment and sintering conditions on phase structure, microstructure, element distribution, and mechanical properties were clarified, suggesting that it is an effective method for controlling the properties of HEA.