Combustion Microstructures and Frictional Ignition Resistance of Ti-6Al-4V Titanium Alloy

The effects of the contact pressure Pfric and the oxygen concentration c0 on the ignition resistance of Ti-6Al-4V were studied by friction in oxygen-enriched atmosphere. The relationship of Pfric-c0 was built to quantitatively describe the ignition resistance, the combustion microstructures were investigated by XRD, SEM and EDS. Further, the principle of improving the ignition resistance was proposed. It indicates that the relationship of Pfric-c0 obeys parabolic law. The c0 decreases by 4% when the Pfric increases from 0.1MPa to 0.25MPa, manifesting that the ignition resistance depends on c0 strongly (or equivalent flow pressure Peq). The ignition resistance of Ti-6Al-4V is 42.9% of that of TB12. When Peq varies from 0.1~0.5MPa, the critical ignition temperature Т* is approximate to 568~461K. Violent sparks form during frictional ignition. The low ignition resistance of Ti-6Al-4V probably results from not only the composite oxides of TiO2, Al2O3 and V2O5 generating during ignition which could not prevent the rapid interaction between Ti and O, but also the Al and V elements in the heat-affected zone which could not stop or slow the massive diffusion of O towards the alloy.