热处理对含锰β型γ-TiAl合金组织和力学性能的影响

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

摘要:

以一种低成本、易变形的Ti-44Al-3Mn-0.4Mo-0.4W-0.1B-0.1C合金（at%）为研究对象，利用真空感应熔炼及常规热轧工艺制备了直径为12 mm的棒材，采用EPMA、TEM、EBSD等检测手段，研究了1270、1220、1170 ℃高温处理对合金棒材的组织与力学性能的影响规律。结果表明，热处理后合金的显微组织均由γ、α₂、β_o三相组成。在相同时效制度条件下，随着高温处理温度的降低，合金中α₂/γ片层含量明显减少，且片层晶团尺寸和片层间距显著降低。拉伸性能测试表明，随着高温处理温度的下降，3种组织的室温和800 ℃抗拉强度均降低。室温下，3种热处理后的合金延伸率呈现先增加后降低的趋势，数值均处于0.5%~1.0%范围；800 ℃下，3种热处理后的合金延伸率存在明显差异，随着等轴γ相含量的增加，合金延伸率随之增加。对比1270 ℃高温处理，1220 ℃热处理试样的延伸率提高了280%，1170 ℃热处理后提高了480%。这是由于相较室温拉伸，在高温拉伸时，等轴γ相的变形能力大大增强，β_o相内位错开动较多，并且γ/γ和α₂/γ界面会阻碍孪晶和位错的运动。同时还对不同热处理组织演变行为与规律、组织与力学性能关系进行了深入讨论。

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.