热循环对Ti-6Al-4V合金显微组织与疲劳性能的影响

Effect of Thermal Cycling on Microstructure and Fatigue Properties of Ti-6Al-4V Alloy

摘要:

对Ti-6Al-4V轧制板材依次进行了920_oC, 800_oC, 850_oC, 900_oC四次热循环,研究了材料在每次热循环后的显微组织及微观织构的演变,并对热循环前后的拉伸和旋转弯曲疲劳性能进行了比较。结果表明,原材料中存在的长条a相发生再结晶后趋于等轴化,其组织不均匀性在920_oC,800_oC两次热循环后得到根本性改善,再经历850_oC, 900_oC两次热循环后,初生a相进一步等轴化并稍有长大,其体积分数维持稳定。原材料具有较强的横向织构,有多个平行于轧制方向的宏观带存在,导致了轧向的疲劳性能优于横向,中值疲劳极限分别为497MPa/474MPa。热循环后横向织构强度有所减弱,并且出现了一定程度的(0001)基面织构。经历4次热循环后,材料的显微组织发生粗化,拉伸强度降低了约20MPa,轧向/横向的中值疲劳极限下降至441MPa/441MPa。

Abstract:

Consecutive thermal cycling at 920_oC, 800_oC, 850_oC, 900_oC was performed onthe Ti-6Al-4V alloy for investigatingmicrostructure,texture evolution, tensile and rotating bending fatigue properties. After four cycles, the elongated grains in the as-received alloy disappeared due to recrystallization andthe microstructure was homogenized. Equiaxedgrains grew a little larger, from ~12mm to ~16mm, while the volumnfractionremained stable. The as-received Ti-6Al-4V alloy exhibited a transverse texture, and formed microzones parallel to the rolling direction.The rotating bending fatigue limit in the rolling direction was higher than that of the transverse direction, which was 497MPa/474MPa, respectively. The intensity of the transverse texture was weakenedafter each thermal cycle and (0001) basal texture appeared. Both the ultimateStensileSstrength and yield strength decreased for about 20MPa after four thermal cycles due to a grain coarsening. The fatigue limit of transverse/longitudinal directions decreased to441MPa/441MPa, respectively.