High temperature oxidation of Ti-47%Al-1.7%W-3.7%Zr alloys

Alloys of Ti47Al-1.7W3.7Zr were oxidized between 900 and 1050 °C in air. These alloys displayed much better oxidation resistance than pure Ti-(47,51)Al alloys, but poorer oxidation resistance than Ti-(45-52)Al-2W-(0, 0.5)Si alloys. The oxide scales consisted primarily of an outer TiO2 layer, an intermediate Al2O3 layer and an inner (TiO2+Al2O3) mixed layer. In these oxides, WO3 and ZrO2 coexisted, mainly in the inner (TiO2+Al2O3) mixed layer. Additionally, some of the W and Zr existed as dissolved ions in the (TiO2, Al2O3) oxide scale. Tiny Ti-W-Al-O compounds and the nitrides, Ti2AlN and TiN, formed mainly around the scale/matrix interface. Below the scale, oxygen preferentially diffused along the W-enriched β-Ti islands in the (Ti-enriched, Al-depleted) matrix area. The detailed scale characteristics and oxidation mechanism are described.