Influence of multi‐step sintering on microstructural evolution and interfacial characteristics of Mo 2 FeB 2 ‐based cermets

Abstract It has been reported that high‐quality Mo 2 FeB 2 ‐based cermets can be fabricated by multi‐step sintering under vacuum. Herein, the influence of multi‐step sintering on microstructure evolution and interfacial characteristics of Mo 2 FeB 2 ‐based cermets has been systematically investigated by a wide range of material characterization techniques, including XRD, SEM, and TEM. During solid‐state sintering, fine Mo 2 FeB 2 particles, WC, and Cr completely dissolved, whereas a majority of coarse Mo 2 FeB 2 particles remained undissolved. During liquid‐phase sintering, large amounts of the dissolved particles precipitated on the remaining coarse Mo 2 FeB 2 particles and formed M 3 B 2 solid solutions (M = Mo, Fe, Cr, and W), resulting in most grains having a black core/gray rim structure. Moreover, a small portion of solid solutions precipitated directly from some W and Cr‐rich areas of the liquid binder phase, thus forming some coreless grains. The rim/binder interface between the core/rim structure grains and Fe‐based binder phase was atomically smooth with an incoherent relationship. In addition, it was found that M 3 B 2 solid solutions had the same crystal structure as Mo 2 FeB 2 , both of which belong to tetragonal structure. Interestingly, a thin layer, formed locally at rim/binder interface, was proved to be a B‐deficient tetragonal M 3 B 2− x compound, where the lattice mismatch between the M 3 B 2 and M 3 B 2− x was 1.9%. The formation of the transition layer can be ascribed to the fact that the last few solid solutions with several atomic‐layer thicknesses could not precipitate on the rims and remain at the grain boundary during cooling, rendering a rim/layer/binder sandwich structure.