Unveiling the dependence of laser energy on ignition critical conditions in TC11 titanium alloy under high temperature airflow

The high combustion susceptibility of titanium alloys under high pressure and temperature airflow has emerged as a critical factor restricting its application in aeroengines. Herein, the effects of airflow pressure and flow rate on ignition critical conditions of TC11 alloy were systematically investigated by using a laser ignition system. Results showed that the combustion occurs within 2–4 s through heating, ignition, and stable combustion stages under laser. Crucially, ignition of TC11 alloy exhibited a strong dependence of laser-power. Below 238 W, the specimen resisted ignition even at temperatures over 1518.7 ± 20.4 K. In contrast, reaching the power threshold led to ignition at 1345.6 ± 23.3 K. Notably, with the increasing ambient pressure, both the critical laser power and ignition temperature further reduced, which followed well with the Frank-Kamenetskii (F-K) theory. According to the modified F-K model, the apparent activation energy (E_a=86.46 kJ/mol) for the ignition of TC11 was merely one-third of the thermal-oxidation activation energy (E_o=231.98 kJ/mol). Furthermore, the post-ignition microstructural evolution showed replacement of the protective oxide layer by dendritic multiphases mainly composed of TiO, α-Ti, β-Ti and TiO₂. Such dependence of laser energy on ignition can be explained by the reaction transition shifted from a diffusion-oxidation mechanism to a multi-path reaction process involving peritectic reactions (L+α-Ti→TiO), leading to localized thermal runaway and ignition, induced by the thermal-shock disruption of passivation under high-energy laser stimulation.