热处理对新型Ti-6Al-2Mo-2V-3Nb-2Fe-1Zr合金力学性能的影响

Effect of Heat Treatment on Mechanical Properties of a Novel Ti-6Al-2Mo-2V-3Nb-2Fe-1Zr Alloy

研究了固溶、固溶+单级时效和固溶+双级时效三种热处理制度对Ti-6Al-2Mo-2V-3Nb-2Fe-1Zr合金的微观组织和力学性能的影响。结果表明,这种合金热处理前的组织为双态组织,由初生α_(p)相、次生α_(s)相和β相组成,其中初生α_(p)相的体积分数为22%,次生α_(s)相的体积分数为21%;在双相区固溶后,合金原来的热轧态α_(p)和α_(s)相部分转变为β相,其组织由亚稳β相、等轴状初生α_(p)相和粗大片状的次生α_(s)相组成;单级时效后,β相中析出了大量均匀分布的纳米细针状次生α_(s)相;双级时效后α相的体积分数显著提高,随着时效时间的增加初生α相和次生α相的晶粒尺寸逐渐增大。准静态拉伸实验结果表明,与热轧态试样相比双相区固溶态试样的延伸率显著提高,但是屈服强度明显降低;单级时效后试样的强度显著提高,强度-塑性平衡更佳;与热轧态试样相比,双级时效后试样的延伸率有所降低,随着时效时间的增加合金的强度降低而延伸率提高。用加工硬化率曲线解释了不同热处理的钛合金应变硬化率的变化趋势,并基于实验结果拟合了修正的Hall-Petch模型,与实验结果吻合较好。

Herein,the effect of heat treatments(solution,solution+single aging and solution+double aging)on the microstructure and mechanical properties of a novel Ti-based alloy Ti-6Al-2Mo-2V-3Nb-2Fe-1Zr was investigated through microstructure characterization and tensile testing.The microstructure observations indicate that the alloy prior to heat treatment possesses a bimodal microstructure consisted of primary α_(p)phase,secondary α_(s) phase,and β phase,and the volume fraction of the primaryα_(p)phase and secondary α_(s) phase is 22%and 21%,respectively.After solution treated in the dual phase zone,a portion of the original α_(p)and α_(s) phases was replaced by β phase and the alloy microstructure is comprised of metastable β phase,equiaxed primary α_(p)phase,and coarse lamellar secondary α_(s) phase.After single aging,a large number of evenly distributed needle-like nano secondary α_(s) phases are precipitated within the β phase;After double aging,the volume fraction of α_(p)hase increases significantly,while the grain size of primary α_(p)phase and secondary α_(s) phase increases with the increasing aging time.Quasi-static tensile test results reveal that alloys subjected to solution treatment in the dual phase zone exhibit significant enhancements in elongation compared to the as hot-rolled ones,but yielding at lower stress levels.Single aging results in significant increase of strength,thereby presenting an improved strength-ductility balance of the alloy.In comparison with the hot rolling process,the double aging process is unfavored to the ductility,moreover,with the increasing aging time,the strength decreases and elongation increases gradually.Finally,the variation in the work hardening rate of the alloy subjected to different heat treatments may be explained by work hardening rate-strain curves.Based on the experimental data,the modified Hall-Petch constitutive model is fitted,whilst the results predicted by this constitutive model have high coincidence with the experimental data.