(TiB_(2)+TiB)/Ti-22Al-25Nb复合材料的热变形行为与组织演变

Hot deformation behavior and microstructure evolution of(TiB_2+TiB)/Ti-22Al-25Nb composites

以放电等离子烧结(TiB_(2)+TiB)增强Ti_(2)AlNb基复合材料为初始材料,在Gleeble-3800热模拟实验机上开展了(TiB_(2)+TiB)/Ti-22Al-25Nb复合材料的热压缩变形实验,研究了变形温度1060~1150℃、应变速率0.05~5 s^(-1)范围内复合材料的热变形行为。通过对流变应力-应变数据分析,构建了复合材料在B2单相区内的本构方程,分析了不同Zener-Hollomon(Z)参数下复合材料的组织演变规律。结果表明:(Ti B_(2)+TiB)/Ti-22Al-25Nb复合材料的峰值应力随变形温度的升高和应变速率的降低而降低,压缩曲线存在不连续屈服现象。Z值对复合材料的组织演变和变形机制均有重要影响。当ln Z值处于较高水平(35.88)时,复合材料出现局部塑性流动变形失稳区,动态再结晶程度较低,再结晶晶粒平均尺寸为3.82μm,增强颗粒粒径平均尺寸为6.93μm。当ln Z值处于较低水平(29.11~31.28)时,复合材料心部区域均发生完全动态再结晶。随着Z值降低,当ln Z为29.11时,动态再结晶晶粒长大,其平均尺寸增至9.16μm,并且由于B元素扩散的加快,促进了烧结残余TiB_(2)颗粒向Ti B晶须(Ti Bw)转变,原位反应更加充分,增强颗粒平均尺寸减小至2.77μm,TiBw的团簇现象明显减弱。

Taking the(TiB_2+TiB)reinforced Ti_2AlNb-based composites prepared by the spark plasma sintering as the initial material,the hot compression experiments were carried out on the Gleeble-3800 thermal simulation machine,and the hot deformation behavior of(TiB_2+TiB)/Ti-22Al-25Nb composites in the temperature range of1060-1150℃and strain rate range of 0.05-5 s~(-1)were studied.Based on the analysis of the flow stress-strain data,the constitutive equation of the composites in the B2 single-phase region was established,and the microstructure evolution of the composites under different Zener-Hollomon(Z)parameters were analyzed.The results show that the peak stress of(TiB_2+TiB)/Ti-22Al-25Nb composites decreases with the increase of deformation temperature and decrease of strain rate,and the compression curves exhibit discontinuous yielding phenomenon.The Z value plays an important role in both the microstructure evolution and deformation mechanism of the composites.When the ln Z value is at a high level,reaching 35.88,the local plastic flow deformation instability zone appeares and the dynamic recrystallization degree is low.The average dynamic recrystallized grain size is 3.82μm and the average size of the reinforced particles is 6.93μm.When the ln Z value is at the lower level of 29.11-31.28,the complete dynamic recrystallization occurs in the core region of the composites.With the decrease of Z value,the average dynamic recrystallized grain size increases to 9.16μm when the ln Z value is 29.11.In addition,the in-situ reaction is more complete due to the accelerated diffusion of B element,resulting in the transformation of residual sintered TiB_(2)particles to TiBw.The average size of reinforced particles decreases to 2.77μm.The cluster phenomenon of TiBw is significantly weakened.