MoB ₂ ‐Modified TiB ₂ Ceramics Prepared by Reactive Pressureless Sintering

ABSTRACT Titanium diboride (TiB 2 ) is a representative ultra‐high‐temperature ceramic; however, its limited sinterability and intrinsic brittleness restrict structural applications. In this study, TiB 2 ‒MoB 2 ceramic composites were fabricated via reactive pressureless sintering at 1550°C to investigate the effects of MoB 2 content on densification behavior, microstructural evolution, and mechanical property trends. A compositional series from TiB 2 ‐rich to Mo‐rich was characterized using XRD, SEM/EDS, X‐ray computed tomography (CT), and mechanical testing. TiB 2 ‐rich ceramics exhibited dense, near single‐phase microstructures with the highest hardness and flexural strength. Increasing MoB 2 content promoted phase segregation, grain‐boundary‐associated porosity, and heterogeneous fracture paths, leading to reduced hardness and strength but progressively enhanced fracture resistance. Fracture toughness increased to values approaching ∼10 MPa·m 1/2 , attributed to increased crack‐path tortuosity, crack deflection, and intragranular fracture at TiB 2 ‒Mo‒boride interfaces. Notably, the intermediate 50TM composition showed the most balanced performance, achieving a relative density of ∼94.7%, a flexural strength of ∼323 MPa, and a fracture toughness of ∼8.9 MPa·m 1/2 . These results demonstrate that controlled MoB 2 incorporation enables systematic tuning of densification and mechanical properties in TiB 2 ‐based refractory ceramics.