Powder metallurgical processing of CrMnFeCoMo high entropy alloy: Phase evolution, microstructure, thermal stability and mechanical properties

Abstract

The outstanding properties of the high entropy alloys (HEAs) are attributed to various factors like composition, microstructure, phase formation, synthesis route etc. In this regard, the present investigation deals with phase evolution, microstructure, thermal stability and microhardness properties of an equiatomic quinary Cr-Mn-Fe-Co-Mo high entropy alloy synthesized by mechanical alloying followed by pressure-less sintering. The structure and phase evolution with milling time was studied by x-ray diffraction technique. After completion of 40 h of milling, two simple solid solution phases with BCC structure (a = 3.146 ± 0.002 Å and 2.873 ± 0.002 Å) along with a minor amount of undissolved α-Mn were identified. Phase formation, chemical composition, thermal stability etc. were also evaluated using electron microscopy and differential thermal analysis (DTA) methods as well as in-situ high temperature x-ray diffraction technique. In the sintered sample, four phases consisting of two BCC solid solutions, σ (sigma) and μ (mu) type phases are observed to coexist and to be stable up to the melting point. The phase formation was predicted by Thermo-Calc approach and was compared with the experimental observation as well as other calculated results. The sintered samples were tested by instrumented hardness tester for evaluation of mechanical properties and was found to exhibit high hardness (9.3 ± 0.3 GPa) and Young’s modulus (∼245 ± 6 GPa).