The individual effects of niobium and silicon on the oxidation behaviour of Ti3Al based alloys

The oxidation kinetics of the Ti3Al based alloys with Nb (0 to 20 at%) or S i (0 to 15 at%) addition was carefully measured at 800 and 900 degrees C, r espectively. The oxide scale was characterised by high temperature in-situ XRD, SEM, EPMA and conventional XRD. The weight gains of the alloys were gr eatly reduced by Nb or Si addition. The improvement of the oxidation resist ance in the Ti3Al alloys by Nb addition is attributed to the formation of a compact scale. The Formation of a compact scale is favoured not only by do ping effect but also by the TiN layer which barriers the outward Al diffusi on into the scale to form porous intermixed titania/alumina. Si addition pr omotes the formation of a compact TiO2 layer in the oxide scale and the for mation of SiO2, thus the oxidation resistance of the Ti3Al based alloys is improved. The oxidation behaviour of the allays with Si addition is a combi native function of the alpha(2)-Ti3Al matrix and the Ti5Si3 silicide phase. (C) 1999 Elsevier Science Ltd. All rights reserved.