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钛合金高温变形过程往往伴随微裂纹的产生与扩展,且其与微观组织形态密切相关,显著影响了钛合金的成形质量和成形极限。为此,利用金相照片建立了基于TA15钛合金真实组织的二维多晶体微观有限元模型,采用微裂纹扩展时间,定量研究了不同组织形态的TA15钛合金等温拉伸过程中的沿晶微裂纹形成与扩展规律。结果表明:微裂纹优先形成于三角或四角晶界处,更容易沿α-β相界扩展;等轴组织随着α相体积分数升高,微裂纹更易产生和扩展;网篮组织与魏氏组织中微裂纹易于沿与加载轴垂直取向的片层α相界面扩展,魏氏组织晶界α相为微裂纹扩展提供了路径;三态组织中微裂纹易于沿片层α相界面扩展,但是等轴α相与片层α相的交织使界面形貌复杂,阻碍微裂纹扩展。相同加载条件下,微裂纹扩展的难易顺序为:三态组织、网篮组织、魏氏组织、等轴组织。
The high temperature deformation process of titanium alloy often accompanied by the generation and expansion of microcracks, and closely related with the microstructure, significantly affected the forming quality and forming limit of titanium alloy. For this reason, a two-dimensional polycrystal microstructure finite element model based on the real structure of TA15 titanium alloy was established by metallographic photographs. The microcrack propagation time was used to quantitatively study the morphologies of TA15 titanium alloy in isothermal stretching process Crack formation and propagation law. The results show that the micro-cracks are preferentially formed at the triangular or tetragonal grain boundaries and more easily spread along the α-β phase boundary. The micro-cracks are more likely to occur and expand with the increase of α-phase volume fraction. The micro-cracks in the microstructure tend to extend along the α-phase interface of the lamella oriented perpendicular to the loading axis. The α-phase in the Westend tissue provides a path for the propagation of micro-cracks. The micro-cracks in the tri-state microstructure tend to expand along the α-phase interface. The interlacing of the equiaxed α phase with the α phase of the lamellae complicates the interface morphology and hinders the propagation of microcracks. Under the same loading conditions, the order of the microcrack expansion is as follows: tristate, basket, Westend, equiaxed.