Fracture toughness of thermally sprayed MoSi₂ composite with different melting indices

Whether the in-situ multiphase doping, especially the metastable phase, makes the thermally sprayed materials tough or brittle is still unknown. In this sense, plasma sprayed MoSi₂ composite was accordingly fabricated to investigate the effect of in-situ multiphase doping on the fracture toughness by melting index (M.I.) tuning. The fracture toughness of plasma sprayed MoSi₂ composite was improved with M.I. increasing. The maximum fracture toughness can reach to 5.64 MPa m^1/2 at a M.I. of 0.59, which was the highest among currently reported single-phase-derived thermally sprayed MoSi₂ composites. A large number of metastable β generated in plasma sprayed MoSi₂ composite were responsible for such remarkable improvement. The fracture toughness of the plasma sprayed MoSi₂ composite, however, would decline as M.I. value exceeded 0.59. Over-heating derived crystallization, which decreased the positive effect of β caused the fracture toughness deterioration.