Ti-6Mo-5V-3Al-2Fe-2Zr合金中次生α相对强度和塑性的影响

Effects of SecondaryαPhase on Strength and Ductility of Ti-6Mo-5V-3Al-2Fe-2Zr Alloy

利用EBSD、扫描电镜和透射电镜观测时效处理后新型近β钛合金Ti-6Mo-5V-3Al-2Fe-2Zr的次生α相尺寸、形貌和分布,对时效态合金进行室温拉伸试验,研究次生α相对合金强度和塑性的影响。结果表明:时效温度由520℃升高至560℃,晶内析出的αi相尺寸变化不大但间距明显减小,时效温度继续升高,αi相宽度和间距明显增大。时效时间由4 h延长至8 h,αi相宽度增大但间距减小,时效时间延长至12 h,αi相无明显变化。建立次生α相与合金强度的关系式,并计算次生α相对合金强度的影响项,二者相吻合,表明αi相间距是影响该合金强度的主要因素。经560℃/8 h时效处理后,αi相间距最窄,抗拉强度最高为1502 MPa。晶内和晶界析出的次生α相联合影响合金塑性。经560℃/8 h时效处理后,形成最小间距的α_(i)相和连续的α_(GB)相,合金塑性最差。经过680℃/8 h时效处理后,形成沿晶界分布且向晶内平行生长的α_(WGB)相,此外α_(GB)相不连续且α_(i)相间距最大,合金塑性大幅度提高。

The size,morphology and distribution of the secondaryαphase in the novel near β titanium alloy Ti-6Mo-5V-3Al-2Fe-2Zr were observed by EBSD,SEM and TEM.Tensile properties of aged alloys were measured at room temperature.Effects of secondary α phase on strength and ductility of alloy were studied.The results show that with the increase of aging temperature from 520℃ to 560℃,the size of the intragranularαi phase changes little but the spacing decreases.With further increase of aging temperature,the width and spacing of theαi phase increase.As the increase of aging time from 4 h to 8 h,the width of theαi phase increases but the spacing changes little.When the aging time is 12 h,there is no significant change in theαi phase.A relationship equation between secondary α phase and alloy strength was established,which shows a good agreement with the calculated values of strength change induced by secondary α phase.It can be indicated that the spacing of theαi phase determines the alloy strength.The spacing of α_(i) phase is the smallest and the ultimate tensile strength is the highest(1502 MPa)after aging at 560℃ for 8 h.The alloy ductility is affected by both intragranular α phase and grain boundariesαphase.The continuous α_(GB) phase and α_(i) phase with the smallest spacing form after aging at 560℃ for 8 h,resulting in poor alloy ductility.The α_(WGB) phase,which is distributed along the grain boundaries and grows parallel into the grains,as well as discontinuousαGB phase andαi phase with the largest spacing,form after aging at 680℃ for 8 h,resulting in significant improvement of alloy ductility.