Structure and Properties of a High-Entropy Ti-Zr-Hf-Ni-Co-Cu Alloy Obtained by Mechanical Alloying and Spark Plasma Sintering

In this paper, the synthesis of a high-entropy Ti-Zr-Hf-Ni-Co-Cu alloy (HEA) by powder metallurgy (PM) methods was investigated. This alloy is prospective from high-temperature shape memory effect point of view. The composition of (TiZrHf)(50)Ni25Co10Cu15 was chosen for the study as it promised to show high functional properties. In order to synthesize the alloy, spark plasma sintering (SPS) of its spherical powder was used. The spherical powders were previously obtained by mechanical alloying of elemental powders and subsequent plasma spheroidization (PS). It was shown that the structure of the bulk samples consisted of B2-TiNi-type austenite, low-melting eutectic CuZr and C15 Laves phase. The eutectic, which precipitates during the SPS process, prevents deforming spherical particles and leads to low mechanical properties since the material does not work as a monolith one. The compressive ultimate stress was 425 +/- 15 MPa. However, the hardness of more than 600 HV that is higher than for any binary intermetallic compounds consisted of the HEA elements promises good prospects of PM methods for production of such alloys. For this purpose, a problem of high oxygen content that also results in the liability to brittle fracture should be solved.