冷却速率对BT14钛合金组织及性能的影响

Effect of cooling rate on microstructure and properties of BT14 titanium alloy

对热锻态的BT14钛合金棒材在940℃下以不同的冷却速率进行热处理,采用光学显微镜（OM）、扫描电镜（SEM）、透射电镜（TEM）和力学性能测试等分析了该合金热处理后的显微组织、拉伸性能和冲击性能。结果表明：冷却速率对合金的显微组织和力学性能影响显著;经过940℃热处理后,冷却速率较慢时初生α相明显长大,合金的微观组织由双态组织转变为等轴组织;冷却速率较快时,初生α相呈长条和等轴状混合分布,次生α相来不及析出,以马氏体α′形式析出,在随后的时效过程中转变为尺寸极细小的次生α相;不同冷却速率对合金的室温拉伸强度的影响规律是：固溶时效最高,水淬、空冷次之,炉冷最低;水淬和固溶时效后合金的冲击性能较差,炉冷最高。

Hot-forged BT14 titanium alloy bars were heat-treated at 940 ℃ at different cooling rates, and microstructure, tensile and impact properties of the alloy after heat treatment were analyzed by means of optical microscope, scanning electron microscopy, transmission electron microscopy and mechanical properties test. The results indicate that the cooling rate has a significant effect on the microstructure and mechanical properties of the alloy. After heat treatment at 940 ℃, when the cooling rate is slow, the primary α phase of the alloy grows significantly, and the microstructure changes from double state structure to equiaxed structure. When the cooling rate is fast, the primary α phase is distributed in the form of long strip and equiaxed mixed phase, and the secondary α phase is precipitated in the form of martensite α′ phase before it can be precipitated, and then transforms into a very small size secondary α phase in the subsequent aging process. The room-temperature tensile strength of the alloy is the highest after quenching and solid solution aging treatment, followed by water quenching and air cooling, and the tensile strength is the lowest after furnace cooling. The impact toughness of the alloy after water quenching and solid solution aging is poor, while it is dramatically improved after furnace cooling.