热-机械处理对亚稳β钛合金微观组织和力学性能的影响

Effect of Thermo-Mechanical Treatment on Microstructure and Mechanical Property in Metastable β Titanium Alloys

摘要:

采用X射线衍射、透射电镜和力学性能测试等手段，系统研究了热-机械处理对亚稳β Ti-25Nb-2Mo-4Sn合金微观组织和力学性能的影响。结果表明：由于合金中β稳定化元素含量不足，固溶处理后的合金中含有大量的α"马氏体，合金呈现低屈服强度。经过相同的时效处理（400 ℃/2 h），固溶态和冷轧态样品的相组成分别为β+ω和β+α相。冷变形引入的大量位错和晶界可有效抑制时效过程中ω相的形成，并促进α相的析出。冷轧态样品经475 ℃时效15 min后弹性模量为65 GPa，屈服强度和抗拉强度分别为1033和1113 MPa，实现了低模量和高强度的良好匹配。

Abstract:

The influence of thermo-mechanical treatment on microstructure and mechanical property of Ti-25Nb-2Mo-4Sn alloy was systematically investigated by X-ray diffraction, transmission electron microscopy and tensile test. Results show that the high-temperature β phase cannot be fully stabilized and a large amount of α" martensites forms after a solution treatment at 800 °C for 1 h followed by water quenching, which is caused by the low content of β-stabilizers (Nb and Mo) in Ti-25Nb-2Mo-4Sn alloy. In this case, the alloy exhibits low yield stress. It is also found that even under the same aging treatment of 400 °C for 2 h, the aging products for the solution treated specimen and the cold-rolled specimen are β + ω and β+α, respectively. Cold rolling deformation induces a mass of dislocations and grain boundaries could suppress the formation of ω and alternatively promote α phase precipitation. Upon a cold rolling and aging at 475 °C for 15 min, superior mechanical properties are achieved in Ti-25Nb-2Mo-4Sn alloy, with yield strength of 1033 MPa and tensile strength of 1113 MPa, combining with a low elastic modulus of 65 GPa.