Effect of Mechanical Alloying and Sintering Behavior on the Microstructure and Properties of NbMoTaWRe Refractory High Entropy Alloy

An equiatomic refractory high-entropy alloy (RHEA) NbMoTaWRe is prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The effects of mechanical alloying and sintering behaviors on the microstructure and properties of the RHEA are investigated. After ball-milling for 30 h, the metastable and supersaturated MA powders with the body-centered cubic (BCC) structure are obtained. Then, the MA powders are sintered using the SPS method under the sintering temperature range of 1700–1900 °C, and the C atoms and WC introduced by the MA process reacts with the metastable and supersaturated Ta/Nb phase of the MA powers to form the face-centered cubic (FCC) structure (Nb, Ta)C particles along the BCC matrix boundaries during the SPS process. The NbMoTaWRe alloy sintered at 1800 °C consisted of BCC matrix and FCC-type (Nb, Ta)C particles has high compactness (porosity fraction is 0.32%), fracture strength (2630 MPa), plastic strain (6.82%), and hardness (992 ± 20 HV). These excellent properties of this RHEA are mainly attributed to the combination of multi-effects, including sintering densification, grain refinement strengthening from the refined sizes (3.80 μm) BCC matrix, precipitation strengthening from the (Nb, Ta)C particles, solid solution strengthening from multi-principal elements and interstitial solid solution strengthening from C atoms dissolving into BCC matrix.