Synthesis and properties of Ti-Al coating by high-frequency induction heated combustion

Abstract

Ti-Al coatings with porosities of 1.11%− 2.28% were synthesized in situ via high-frequency induction heated combustion synthesis (HFIHCS) method within several minutes. The adiabatic temperatures at different preheating temperatures were calculated thermodynamically. The microstructure, phase composition, cross-sectional microhardness, oxidation, and corrosion resistance to molten aluminum alloy of the as-received coatings were investigated. The results showed that the Ti-Al reaction could be self-sustained when the preheating temperature reached 605 K. The combustion reaction and pore-forming mechanisms of the as-received Ti-Al coating conformed to liquid-solid reaction and thermal explosion, respectively. The coating microstructure followed a core-shell ring-shaped microstructure model, which was incomplete Ti nuclei, Ti3Al, TiAl and TiAl2 phases from inside to outside. The average microhardness of the substrate, interface and coating were 508.57, 454.54 and 377.18 HV0.2, respectively. The microhardness fluctuation was the largest at the coating-substrate interface. The oxidation kinetics of the as-received coating approximately followed a linear rate law with an oxidation rate constant of 0.3943 mg·cm−2·h−1 and a rate exponent of 1.2372. The oxide layer consisted of an outer layer of TiO2, an inner layer of nitrogen-containing compounds and a mixed layer of TiO2 and Al2O3 between them. The corrosion mechanism of the as-received Ti-Al IMC coatings in molten A380 alloy was mainly controlled by the combination of compounds formed at the liquid-solid interface and diffusion of liquid metal into the as-received Ti-Al coating, rather than by the dissolution mechanism of the as-received Ti-Al coating.