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.