VARIOUS ASPECTS OF THE AIR OXIDATION BEHAVIOR OF A TI6AL4V ALLOY AT TEMPERATURES IN THE RANGE 600-700-DEGREES-C

A study on the air oxidation behaviour of a commercially pure Ti6Al4V alloy between 600 and 700-degrees-C is reported, based on determinatio n of the kinetic curves, microhardness profiles in the metal beneath t he scale, and examination of morphology and composition of the scales. The oxidation kinetics shows a gradual transformation dependent on bo th time and temperature from a diffusive to a nearly linear rate law. It has been observed that such transformation may be associated with t he acceleration of oxide scale growth. This phenomenon is accompanied by a parallel change of the oxide morphology, which is essentially man ifested with the onset of a duplex-type scale starting from 650-degree s-C. Aluminium is found to pile up near the external surface of the ox ide scales, although the presence of a continuous film of alumina may be excluded under any circumstances. Finally, the effect of aluminium and vanadium is beneficial in reducing appreciably the amount of oxyge n dissolved in the surface metal layer, compared with unalloyed titani um.