Ti-30Nb-1Mo-4Sn合金热机械处理过程中的相组成及力学性能演化

Evolution of Phase Constitution and Mechanical Properties of Ti-30Nb-1Mo-4Sn Alloy Subjected to Thermo-mechanical Treatment

采用X射线衍射(XRD)、透射电子显微镜(TEM)观察和力学性能测试,系统研究了具有低弹性模量的亚稳β钛合金Ti-30Nb-1Mo-4Sn(wt%)在热机械处理过程中的相组成与力学性能演化。研究结果表明:固溶态合金具有较低的结构稳定性,拉伸过程中出现应力诱发马氏体相变,导致合金呈现较低的屈服强度;固溶态合金经时效处理后,由于缺乏异质形核点并且时效时间较短,第2相析出很少,其稳定性并没有明显提高,淬火的过程中仍然会发生马氏体相变,因此其屈服强度也不能得到显著提高。合金经冷轧变形后,晶粒显著细化并引入大量形变位错,大量的缺陷为α相析出提供了形核点,因此在时效处理时析出大量细小α强化相之后,合金的屈服强度和断裂强度显著提高。值得注意的是,冷轧态合金选择一个合适的退火温度(350℃),可以使时效处理后的强度达到最大值,进一步提高退火温度,发生再结晶,位错密度下降,导致合金强度剧烈下降。

The evolution of phase constitution and mechanical properties of a low-modulus metastable β-type Ti-30Nb-1Mo-4Sn（wt％） titanium alloy subjected to thermo-mechanical treatment,is systematically investigated using X-ray diffraction apparatus （XRD）,transmission electron microscopy （TEM） and mechanical testing.The results indicate that the solution-treated alloy exhibits low structural stability and undergoes stress-induced martensitic transformation,leading to a quite low yield stress.Even though the solution-treated alloys are subjected to aging treatment,the amount of precipitates is small due to the lack of heterogeneous nucleation sites and relatively short duration,leading to the low stability of the alloy.As a result,martensitic transformation occurs during quenching and the strength of the specimens is not improved significantly.After cold rolling,grain refinement takes place and large amount of dislocations is induced which provides sufficient heterogeneous nucleation sites for the a precipitation,therefore,the yield strength and tensile strength of the cold rolled alloy are significantly improved during aging treatment.It is worth noting that the maximum strength can be obtained in the cold rolled plus annealed alloys with a proper annealing temperature （350 ℃）.Moreover,the strength of the alloy declines sharply with further increased annealed temperature,which can be attributed to the decrease in the density of dislocations due to recrystallization.