OXIDATION CHARACTERISTICS OF TI-14AL-21NB ALLOY AT HIGH-TEMPERATURES IN PURIFIED OXYGEN

The oxidation characteristics of Ti-14Al-21Nb (mass%) have been studied over a temperature range 1000 similar to 1300 K in a flow of purified oxygen under atmospheric pressure. The mass gain due to oxidation at 1000 K for 100 ks is negligibly small, though a very thin scale is formed. The oxidation at and below 1200 K follows nearly parabolic rate laws. The scale consists mainly of an outer rutile layer and a thin inner layer which is a porous mixture of small grains of rutile, alumina, and niobium oxide. On the other hand, above 1200 K parabolic manner of oxidation is disturbed by the occasional appearance of acceleration periods. This acceleration is attributable to the local fracture of the scale resulting in multilayer scales. A model for the development of scale structure is presented on the basis of the detailed metallographic examinations.