Effect of ageing on the properties of the W-containing IRIS-TiAl alloy

TL;DR

This study investigates how aging at 800°C affects the microstructure and mechanical properties of a tungsten-containing TiAl alloy, revealing limited microstructural changes and moderate effects on strength and creep resistance.

Contribution

It provides detailed insights into the microstructural stability and mechanical behavior of the IRIS-TiAl alloy after aging, highlighting tungsten's role in limiting microstructural evolution.

Findings

Limited microstructural evolution after aging

Moderate decrease in mechanical properties

Microstructural stability due to low tungsten diffusivity

Abstract

The effects of ageing at 800 $^\circ$C on the properties of the IRIS alloy (Ti$_{49.9}$Al$_{48}$W$_2$B$_{0.1}$) are studied. The initial microstructure of this alloy densified by Spark Plasma Sintering (SPS) is mainly composed of lamellar colonies which are surrounded by $\gamma$ grains. The evolutions of the alloy strength and creep resistance resulting from this ageing treatment are measured by the related mechanical tests. The microstructural changes are investigated by scanning and transmission electron microscopies and by X-ray diffraction. The main structural evolutions consist in a shrinkage of the lamellar areas and in a precipitation of $\beta_0$ phase, which is accompanied by a moderate segregation of tungsten and a decrease of the $\alpha_2$ lamellar width. However, these evolutions are relatively limited and the microstructural stability is found to result mainly from the low diffusivity of tungsten. Conversely, a moderate effect of this ageing treatment on mechanical properties, at room and high temperatures, is measured. Such experimental results are interpreted and discussed in terms of the microstructural evolutions and of the deformation mechanisms which are activated at different temperatures under various solicitations.