Ti2AlNb基合金(B2+O)相区多向锻造微观组织研究

Microstructure of Ti2AlNb-based Alloy processed by Multi-directional Forging in (B2+O) Phase Region

摘要:

通过多向锻造工艺制备Ti2AlNb基合金(B2+O)相区内800℃不同变形道次的试样,水冷冷却后切取中心部位样品,利用电子背散射衍射和X射线衍射技术,分析多向锻造道次对Ti2AlNb钛合金组织演变的影响。结果表明,Ti2AlNb基合金经(B2+O)相区多向锻造变形后获得显著细化的等轴组织,但随着变形道次增加,晶粒尺寸快速降低后趋于平稳,同时变形促进小角度晶界向大角度晶界发生转化；变形后合金相组成主要为B2+O,以及部分残留ɑ₂相,相比初始组织ɑ₂相减少、O相增多；变形后微观应变和位错密度大幅增加,在动态回复作用下,随着锻造道次增加,微观应变增幅逐渐减小,位错密度略有减小。

Abstract:

Multi-directional forging (MDF) process with different cycles was conducted on the Ti2AlNb-based alloy under the temperature of 800℃ in the (B2+O) phase region followed by water cooling. The microstructure was characterized by electron backscatter diffraction(EBSD) and X-ray diffraction (XRD), the effect of MDF process cycles on microstructure evolution of Ti2AlNb-based alloy was analyzed. The experimental results show that the microstructure is significantly refined to submicrometer, the misorientation of grain boundaries has the transforamtion from low angle to high angle and the equiaxed ultrafine grains with high angle boundaries are obtained after MDF processing. The grain size decrease raplidly after one cycle of MDF and the value keeps nearly constant with the increasing number of MDF cycles. After deformation, the major phases of the alloy are B2+O, as well as some residual ɑ₂ phase. The content of ɑ₂ phase decreases while the O phase increases compared to the initial sample. In addition, the microstrain and dislocation density increase significantly after deformation. Because of dynamic recovery, the microstrain saturates to a stability level with the number of cycles increasing, while the dislocation density experiences a slight decrease.