β斑对TB6钛合金性能及拉伸变形行为的影响

Effect of β fleck on properties and tensile deformation behavior of TB6 titanium alloy

摘要:

通常认为TB6钛合金中的“β斑”会降低构件的力学性能,Fe元素偏析是导致β斑的主要原因。本文利用OM、SEM、EDS、EPMA等微观表征手段,结合对β斑样品拉伸过程的扫描电镜原位观察,分析了β斑区域和正常区域的显微组织、化学成分和硬度差异,研究了β斑对TB6合金拉伸变形行为的影响。结果表明：β斑区域组织中的初生α相含量少于5%,β晶粒粗大达到0.58mm,是正常晶粒尺寸的60倍以上；β斑区域的维氏硬度较正常区域略高；β斑区域中的V和Fe元素含量在宏观上无明显差异,但微区存在波动和不均匀分布,β斑区域的Fe元素含量离散性高于正常区域。V和Fe元素微区成分偏析是导致TB6合金后续加热和变形过程中相变温度差异的主要原因,局部先转变的β晶粒由于缺少晶界α相的钉扎,迅速长大。β斑材料在拉伸变形过程中,裂纹起始于粗大β晶粒的晶界处,晶界和晶内滑移是β斑组织的主要变形方式,β斑TB6合金的断裂模式为沿晶和穿晶混合的断裂模式。

Abstract:

It is generally believed that the "β fleck" in TB6 titanium alloy will reduce the mechanical properties of the component, and the main cause of the β fleck in TB6 alloy is Fe element segregation. In this paper, the differences of microstructure, chemical composition and hardness between β fleck and normal area were analyzed by OM, SEM, EDS and EPMA, and the effect of β fleck on the tensile deformation behavior of TB6 alloy was studied. The results show that the content of primary α phase in β fleck is less than 5%, and the β grain size is coarse up to 0.58mm, which is more than 60 times of normal grain size. The vickers hardness of β fleck was slightly higher than that of normal area. The results of composition analysis showed that there was no significant difference of V and Fe between in β fleck and normal area, but there were fluctuations and uneven distribution of Fe content within the microregions . Fe content dispersion in β fleck was higher than that in normal area. The difference of V and Fe elements in microregions is the main reason for the difference in the phase transition temperature of TB6 alloy during subsequent heating and deformation. The preconverted β grains grow rapidly due to the lack of grain boundary α phase pinning. In the process of in situ SEM tensile, the crack starts at the grain boundary of the coarse β grain, grain boundary and intra-crystal slip is the main deformation mode of β fleck structure. The fracture mode of TB6 alloy contains of β fleck is intergranular and transgranular mixed fracture mode.