The Combustion Behaviors and Flame-Retardant Mechanisms of Cu Coating as Protection for Titanium Alloys

This study investigates the influence of highly thermally conductive coatings on the combustion thresholds of a TC4 titanium alloy, aiming to address the flame-retardant protection requirements for titanium alloys. The findings reveal that, in terms of combustion thermodynamics, as the thickness of the copper coating increases from 100 μm to 300 μm, the critical ignition power rises by 125-170 W compared to the substrate (235 W). Additionally, the critical oxygen pressure increases by 0.21-0.51 MPa relative to the substrate (0.03 MPa), and the ignition temperature is elevated by 119-184 K above that of the substrate (848.80 K). This phenomenon is primarily due to the high thermal diffusivity of copper. Increased coating thickness further enhances heat dissipation, significantly suppressing the local heat accumulation rate and thereby improving the coating's combustion resistance. In terms of combustion kinetics, under fixed experimental conditions, the copper coating extends the ignition delay time by 0.670 s and reduces the combustion propagation rate by approximately 21% compared to the substrate (26.772 mm/s). The post-combustion microstructural analysis indicates that during the reaction process, the copper coating forms a TiCu₂Al-type intermetallic compound (Ti_0.5Al_0.5)Cu. This structure exerts an "anchoring" effect on the substrate material, decreases the Ti/O reaction efficiency, and consequently achieves effective flame retardancy. These findings inform the subsequent design and optimization of copper-based abradable coatings with enhanced combustion resistance.