Influence of Overtemperature Treatment on Microstructure and Properties of Precision-Cast Ti2AlNb Alloy

Abstract:

Microstructure evolution of precision-cast Ti₂AlNb alloys after overtemperature treatments at 750 and 850 °C was investigated by optical microscope and scanning electron microscope, and Image J metallurgy analysis software was used for quantitative analysis. The variation of mechanical properties before and after overtemperature treatment was tested. Results show that the Ti₂AlNb alloy consists of B2 phase and lamellar O phase before and after overtemperature treatment. After overtemperature treatment, partial B2 phase is transformed into the O phase, and the lamellar structure of O phase suffers discontinuous coarsening and spherolization. The coarsening degree is increased with the increase in temperature and prolongation of treatment time, and O phase content is also gradually increased. The microhardness and tensile properties of Ti₂AlNb alloys at room and high temperatures are decreased with the increase in temperature and prolongation of treatment time, and the high-temperature tensile strength exhibits relatively larger decrement. An obvious linear relationship exists between microhardness and O phase content. Both the microhardness and the O phase content are important parameters to evaluate the overtemperature service damage degree of precision-cast Ti₂AlNb alloy.