近等温变形量对TC4-DT钛合金组织参数和拉伸性能的影响

Effects of Near-Isothermal Deformation Amounts on Microstructure Parameters and Tensile Properties of TC4-DT Titanium Alloy

利用光学显微镜、扫描电镜、电子探针、金相图像分析软件等研究近等温变形量对TC4-DT钛合金显微组织和拉伸性能的影响规律。研究发现:随热变形程度的增大,晶界α相逐渐被破碎,晶内粗大的片状α相宽度逐渐增大,但是细片状的α相宽度变化不大。粗片状α相是由元素扩散引起的成分偏析形成,60%的变形程度下元素扩散充分,不同形态α相之间合金元素成分差别降低,使得最终组织较为均匀。晶内粗片状α相含量和位向随变形程度升高而变化,低变形程度下(20%)α/β相界不会成为位错滑移的障碍,位错主要集聚于晶界导致沿晶断裂。高变形程度(60%)使原来的两相位向关系被打破,相界成为位错滑移的障碍,强度和塑性都得到提高,室温拉伸断口呈现穿晶断裂。实验结果表明在本实验条件下60%的变形量可以获得较好的强度和塑性匹配。

The influence of near-isothermal deformation amounts on microstructures and tensile properties of TC4-DT titanium alloy was studied by using optical microscope （OM） , SEM, EPMA and metallurgical image-analysis software. Results showed that with the deformation amount increasing, grain boundary awas changed from intact to broken up. Inside primary β grain the size of coarse plate was increased and the width of acicular a did not changed much. The formation of coarse plate a was attributed to the element segregation induced by atom diffusion. At 60% deformation degree, atom diffusion was proceeded sufficiently which reduced the composition difference among different morphology a and resulted in a homogeneous microstructure. The content and orientation of coarse a varied with the increasing of deformation amounts. At low deformation degree （20%） , the phase boundaries of or/13 could not become the obstacle for dislocation gliding and this made the dislocation concentrated in grain boundary a which led to intergranular fracture. While at higher deformation degree （60%） , the orientation between a and β was disturbed, the phase boundaries of a/βbecame the obstacle for dislocation gliding which enhanced both strength and ductility, and tensile fractographs showed transgranular fracture. Conclusion has been obtained that a better combination of strength and plasticity can be reached at 60% deformation degree at this experiment condition.