TC4棒材挤压织构的各向异性及绝热剪切敏感性研究

Anisotropy of Extrusion Texture and Adiabatic Shear Sensitivity of TC4 Alloy Bar

摘要:

钛合金加工过程产生的微观组织取向及织构会对其动态性能,尤其是绝热剪切特性产生影响。本研究采用分离式霍普金森压杆(SHPB),对a+b型TC4棒材挤压方向(ED)及横向(TD)高应变率下的压缩各向异性及绝热剪切特性开展研究,通过数字图像相关法(DIC)及EBSD方法分析局域化演化特性及机制,结果表明：挤压TC4棒材中的a-hcp相具有轴向对称的柱面纤维织构特征,棒材TD方向的屈服强度明显高于ED方向,但其绝热剪切敏感性更强,易发生ASB破坏。EBSD分析认为,轧制织构引起的特定晶体学取向是通过影响位错滑移系的Schmid因子影响屈服,导致变形各向异性,ED 方向的挤压织构使晶粒取向比较一致趋于有利于合金a-hcp相CRSS较低的柱面〈a〉滑移系激活启动,使得其动态屈服强度低于TD方向。同时晶粒间变形更均匀,加之较TD方向低的热效应,使其绝热剪切敏感性明显小于TD方向。研究结果对于理解钛合金微观取向、织构对绝热剪切影响,进而进行织构的控制设计提高结构抗绝热剪切能力具有意义。

Abstract:

The microstructural orientation and texture developed during titanium alloy processing have significant effects on its dynamic mechanical behavior, particularly on adiabatic shear characteristics. In this study, the compression anisotropy and adiabatic shear behavior of the α+β TC4 alloy bar were investigated under high strain rates along the extrusion direction (ED) and transverse direction (TD) using a Split Hopkinson Pressure Bar (SHPB) apparatus. The localized deformation evolution and mechanisms were analyzed through Digital Image Correlation (DIC) and Electron Backscatter Diffraction (EBSD) techniques. The results reveal that the α-hcp phase in the extruded TC4 bar exhibits an axially symmetric cylindrical fiber texture. The yield strength in the TD is significantly higher than that in the ED; however, the TD shows greater adiabatic shear sensitivity and a higher tendency for adiabatic shear band (ASB) formation. EBSD analysis indicates that the specific crystallographic orientations induced by the extrusion texture influence yielding behavior by affecting the Schmid factors of dislocation slip systems, thereby leading to deformation anisotropy. The extrusion texture along the ED aligns most grains favorably for the activation of the basal slip system in the α-hcp phase, which has a lower critical resolved shear stress (CRSS), resulting in a lower dynamic yield strength compared with the TD. Meanwhile, the more homogeneous deformation among grains and the weaker thermal effect along the ED contribute to its lower adiabatic shear sensitivity. These findings provide insights into the influence of microstructural orientation and texture on adiabatic shear behavior in titanium alloys, offering guidance for texture control and design strategies to enhance resistance to adiabatic shear failure.