A Novel Dual-Phase Gradient Material of High-Entropy Alloy Prepared by Spark Plasma Sintering

A novel dual-phase gradient material of a high-entropy alloy (HEA) FeCoCrNiMo0.15 was fabricated by spark plasma sintering (SPS) processing. After SPS, the HEA specimens consisted of a single face-centred cubic (FCC) phase in the centre but dual FCC and body-centred cubic (BCC) structures near the surface. Surprisingly, the sintering pressure was sufficient to influence the proportion of phases, and thus, the properties of HEA samples. The hardness of the specimen sintered under a pressure of 30 MPa increased gradually from 167 HV in the centre to 634 HV near the surface due to the gradual increase in the fraction of the transformed BCC phase. This phase transformation, which could be influenced by pressure indicated a major possibility for designing gradient HEA materials.