Microstructure and mechanical properties of CoCrFeNiTa high entropy alloy prepared by mechanical alloying and spark plasma sintering

The equiatomic CoCrFeNiTa high-entropy alloy (HEA) was prepared by mechanical alloying and spark plasma sintered at different temperatures in this work. The microstructural evolution of alloy powder and microstructure and mechanical properties of the sintered HEA were investigated. The results show that the particle size of HEA powder is decreased gradually with the increase of milling time and then tends to be unchanged basically. The composition of the HEA powder becomes uniform, and metastable face-centered cubic (FCC) phase and Laves phase with Co2Ta type are obtained eventually. The HEA sintered at 1100 °C exhibits a near-full density (99.15%). Supersaturated FCC and Laves phases with a grain size of 1.32 μm and 1.26 μm are formed in the HEA blocks, and many Ta2[Co, Cr, Fe] precipitates with a size of about 23 nm were observed in the FCC matrix. Mechanical properties were measured using Vickers hardness and uniaxial compression testing techniques. The HEA sintered at 1100 °C shows an ultra-high hardness of 9.37 GPa and compressive strength of 2177 MPa respectively. This is mainly ascribed to the combined effect of the grain refinement strengthening, solid solution strengthening, second phase strengthening including Laves phase and nano-sized precipitates. It provides a new way to prepare high strength and high hardness materials.