Preparation, microstructure, and mechanical properties of HfN in-situ doped W Re alloys by nitridation-denitridation method

The in-situ synthesis of finely dispersed second phases with high melting points and thermal stability is an effective strategy to address the high cost, inadequate high-temperature performance, and reduced thermal conductivity of tungsten‑rhenium (W Re) alloys. In this study, we employed a novel nitridation-denitridation (NDN) process to synthesize W-10Re-HfN nano powder, in-situ synthesizing nano HfN particles to strengthen and toughen the W Re alloy. Compared to W 10Re, the hardness of W-10Re-2HfN increased significantly from 604 HV to 977 HV, the compressive strength was improved from 1366 MPa to 2181 MPa, and fracture strain increased from 3.6 % to 32 %. Statistical results indicate that HfN particles within the grains or with sizes below ∼36 nm exhibit completely coherent interfaces with the W Re matrix. By combining in-situ synthesis of nitrides with a two-step sintering process, we successfully retained 63 % of HfN particles within the grains and controlled the average particle size of HfN particles at the grain boundaries to be 36 nm, thereby enhancing grain boundary strengthening and coherent interface strengthening. This study innovatively incorporates finely dispersed and highly stable nitrides into W Re alloys through in-situ doping, offering a novel strategy for reinforcing refractory metals.