Effect of Heat Treatment on the Microstructure and Mechanical Properties of Mn-Containing β-Type γ-TiAl Alloy

Abstract:

Manganese, serving as a cost-effective and potent stabilizer of the β-phase, plays a pivotal role in the development of economically viable and easily deformable β-type γ-TiAl alloys. In this investigation, we focused on a low-cost and easily deformable Ti-44Al-3Mn-0.4Mo-0.4W-0.1B-0.1C alloy (at%), which was rolled into 12 mm-diameter bars by vacuum induction melting and conventional hot rolling techniques. The effects of high-temperature treatments at 1270, 1220, and 1170 °C on the microstructure and mechanical properties of the alloy bars were studied by EPMA, TEM, and EBSD. The results show that the microstructure of the alloy contains γ, α₂, and β_o phases after heat treatment. Decreasing the temperature of high-temperature treatment under identical aging conditions significantly reduces the α₂/γ lamellar content within the alloy. Moreover, both the size of the lamellar colonies and the spacing between lamellae exhibit pronounced reductions as the treatment temperature decreases. The tensile performance tests demonstrate that as the temperature of high-temperature treatment decreases, the tensile strength at room temperature and 800 °C of the alloys with different microstructures declines. At room temperature, the elongation of the heat-treated alloys shows a trend of first increasing and then decreasing, and the values are all within the range of 0.5%–1.0%. However, at 800 °C, significant variations in elongation are observed in the alloys. Specifically, an increase in equiaxed γ phase content correlates with enhanced alloy elongation. Compared to samples treated at 1270 °C, those treated at 1220 °C exhibit a 280% increase in elongation, while those treated at 1170 °C show a 480% increase. This enhancement is attributed to the improved deformability of the equiaxed γ phase at elevated temperatures. Additionally, greater activation of dislocations within the β_o phase occurs, while the γ/γ and α₂/γ interfaces impede the movement of twins and dislocations. This study provides a comprehensive discussion on the evolution behavior and patterns of different heat-treated alloys, emphasizing their correlation with mechanical properties.