One-step in-situ reaction plasma spraying via Al-TiO₂-B₄C to build a TiB₂-TiC/Al₂O₃ coating with enhanced strength-toughness synergy

To address the difficulty of achieving strength-toughness synergy, complex process, and a single evaluation system in plasma-sprayed TiB₂-TiC/Al₂O₃ coatings, this study proposed a one-step in-situ reaction plasma-spraying method based on the Al-TiO₂-B₄C system. This process couples the exothermic reaction with rapid solidification, achieving the in-situ synthesis and deposition of TiB₂-TiC/Al₂O₃ coatings in one step. Compared with the ex-situ coating (from TiB₂-TiC-Al₂O₃), the in-situ coating (from Al-TiO₂-B₄C) exhibited a structure featuring dense nanograins and tightly bonded interfaces. This unique architecture maintained high hardness while reducing porosity by 83.0%, increasing fracture toughness (K_IC) by 87.5%, enhancing crack propagation resistance (CPR_s) by 331.6%, and improving critical failure load (L_c2) by 66.0%. The strengthening mechanisms stemmed from the multi-level heterogeneous structure formed by in-situ reaction, multiple toughening effects at the micro-nano scale (crack bridging-deflection-branching), and the synergistic enhancement of grain boundaries/interfaces. Furthermore, to address the limitation of a single evaluation system, this study established a comprehensive assessment methodology combining acoustic emission and scratch test criteria with CPR_s and Weibull analysis. Through this “in-situ synthesis-multi-mechanism toughening-multi-signature damage evaluation” collaborative strategy, this study provides a feasible design strategy and evaluation framework to mitigate the problem of imbalance in strength and toughness of composite coatings.