Preparation of Mo2FeB2-based cermets with a core/rim structure by multi-step sintering approach

摘要

A novel multi-step sintering approach was adopted to eliminate the boride reticular structure from Mo2FeB2-based cermets. First, Mo2FeB2 hard phase was synthesized by reaction boronizing sintering and pulverized into powders. Subsequently, the pre-sintered powders were mixed with other compositions, and then the mixture was pressed and sintered. During solid-state sintering, most of the coarse Mo2FeB2 hard phase particles remained undissolved. The boride complex solid solutions containing small amounts of Cr and W precipitated around the remaining Mo2FeB2 hard phase particles during liquid phase sintering, resulting in a black core/gray rim structure. The SAED analysis revealed that the black cores and the gray rims of Mo2FeB2 grains possessed the same crystal structure with similar lattice parameters. Notably, the gray rims enriched in W and Cr improved the wettability of the system, leading to the elimination of large pores. Furthermore, the as-prepared Mo2FeB2-based cermet demonstrated superior mechanical properties, i.e., transverse rupture strength of 2219 MPa and fracture toughness of 23.1 MPa m(1/2), which were 15% and 25.5% higher than the traditional Mo2FeB2 -based cermet, respectively.