Hot oscillating pressing sintered AlCoCrFeNi/nanodiamond high-entropy alloy composites

Abstract

Abstract In this work, AlCoCrFeNi/nanodiamond high-entropy alloy composites (HEA/diamond) were prepared for the first time by hot oscillating pressing (HOP) using nanodiamond as the reinforcing phase, and the evolution of microstructure and properties at different sintering temperatures were investigated. The microstructures of the HOPed HEA/diamond high-entropy alloy composites all consisted of the FCC phase, BCC phase and nanocarbide phase uniformly distributed in the interstices of the particles. With the increase in sintering temperature, the original powder particle boundaries in the composites gradually disappeared, the density progressively increased, and the microstructure defects decreased. At 1100°C, the dense density of the material reached its maximum, 99.7%. Moreover, the FCC phase volume fraction and carbide content further increased without significant microstructure coarsening. The hardness and corrosion resistance of the HOPed samples were better than the hot pressing (HP) samples at the same sintering temperature. Especially at lower sintering temperatures (1000°C and below), the microstructure uniformity of the composite material was significantly improved because the original particle boundaries and pores became smaller, and a small number of nanocarbides were uniformly distributed in the powder interstices. The performance of HEA/diamond was greatly enhanced by the carbide pinned reinforcement. The hardness reached a maximum of 566.48 HV1, and the corrosion current density and corrosion rate reached a minimum of 2.916 µm/cm2 and 0.013 mm/year, respectively, which was better than other alloys reported. However, at high temperatures (at 1100°C), the performance decreased due to a large amount of graphitization of diamond to generate carbides, which weakened the interfacial bonding. The results showed that high-density, high-performance HEA/diamond composites could be obtained by HOP at appropriate sintering temperatures.