Size-dependent deformation and interface-governed failure in TiC–Ni–Mo cermets revealed by in situ microcompression

TiC-based cermets are promising materials known for their exceptional strength and deformability. However, studies on their micro-scale deformation mechanisms remain limited. In this work, we investigate micro-scale deformation in a TiC-Ni-Mo cermet through in situ scanning/transmission electron microscope microcompression tests on pillars (0.4-5µm in diameter) and finite element analysis. As the pillar diameter decreases, both strength and ductility increase, accompanied by a shift in deformation mode from brittle fracture to yielding. A critical diameter of 2 µm marks the brittle-to-ductile transition, with the smallest pillars (0.4 µm) exhibiting a remarkable fracture strength of ~9.5 GPa and ~13% strain, compared to ~4 GPa and ~2.5% strain at 5 µm. TiC/TiC grain boundaries are identified as primary crack nucleation sites, while TiC/Ni interfaces sustain high local stresses without immediate decohesion. The Ni binder accommodates plastic deformation through dense dislocation activity. Simulations reveal stress hot spots and replicate the observed failure sequence. Size reduction decreases the fraction of TiC/TiC boundaries, thereby enhancing both strength and deformability. These findings establish a clear structure-mechanics relationship and offer design guidelines: maximize the load-bearing TiC/Ni interfacial area and minimize weak TiC/TiC boundaries to improve cermet performance.​