Effect of heat-treatment on the microstructure and fatigue properties of lamellar γ-TiAl alloyed with Nb, Mo and/or C

Abstract

In this study, the effect of the heat-treatment was investigated on five different γ-TiAl compositions alloyed with 7 at.% of Nb and varying content of Mo and C. Mechanical properties of as-received and heat-treated alloys were assessed using tensile and symmetrical tension-compression cyclic loading at room temperature and 750 °C. Scanning electron microscopy, electron back-scatter and X-ray powder diffraction, as well as high-resolution scanning transmission electron microscopy, were used to characterize microstructural changes induced by the heat-treatments. Modification of lamellar substructure in terms of a significant decrease of lamellar spacing directly affects the mobility of dislocations. Together with the change in the phase composition of the alloys, it is the key mechanism leading to the improvement of the ultimate tensile stress, fracture plastic strain as well as higher cyclic strength. It also increases the cumulative plastic strain in cyclic loading both at ambient and elevated temperatures.