A Theoretical Description of the Ignition Conditions for TC17 Alloy in Oxygen-Enriched Atmospheres

Titanium alloys can be ignited under extreme conditions including high pressure, high temperature, and high-speed friction. A theoretical description of the ignition conditions for titanium alloys is critical for their safe use in aerospace industries. In this study, a chemical-absorption-controlled ignition model for bulk TC17 alloy in oxygen-enriched atmospheres was developed based on Semenov's thermal ignition theory. The adsorption coefficient, reaction order, and activation energy for the ignition of TC17 alloy were obtained by fitting the model with the experimental critical oxygen pressure and critical ignition temperatures. The fitting results showed that the chemical-absorption-controlled ignition model fitted better with the experimental data compared with the diffusion-controlled ignition model, implying that the ignition process was controlled by chemical absorption rather than oxygen diffusion through the oxidation layer. Moreover, the activation energy for the ignition of TC17 alloy bars was obtained to be 50.01 kJ/mol, which was only less than one-fourth of that of non-isothermal oxidation (231.98 kJ/mol), indicating that the ignition requires much lower activation energy than oxidation. The chemical-absorption-controlled ignition model successfully predicted the ignition temperature of TC17 alloy bars with different diameters with the relative error within 4.41%, demonstrating the validity of the model.