不同组织TA15钛合金等温拉伸微裂纹扩展规律的有限元建模研究

Finite element modeling and study on the propagation rules of microcracks in TA15 titanium alloy with different microstructures during isothermal tension

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。

High-temperature deformation of titanium alloy is always accompanied by microcracks initiation and propagation which is closely related to microstructural morphology and has significant effect on forming quality and forming limit. Therefore, a two-dimensional poly- crystalline finite element model was built based on the real microstructures by using metallographs of TA15 titanium alloy. Meanwhile, mi- crocrack propagation time was adopted to quantitatively study the law of intercrystalline microcraeks initiation and propagation in different microstructures during the isothermal tension of TA15 titanium alloy. The resuhs reveal that microcracks prefer to initiate at the triangle or quadrangle grain boundaries and grow along α-β phase boundary. In the equiaxed microstructures, with the volume fraction of α phase increasing, microeracks tend to initiate and propagate easily. In basketweave and Widmanstatten microstructures, microcracks are more likely to grow along the lamellar α interfaces being perpendicular to the loading axis. Grain boundary α phase in Widmanstatten microstructure provides paths for microcracks propagation. In tri-modal microstructure, microcracks tend to propagate along the interface of lamellar α phase, while the intricate morphology due to the intertexture of the equiaxed and lamellar ct phases leads to difficulty for mierocracks propagation. Finally, the order in difficulty for microcrack propagation under the same conditions is： tri-modal, basketweave, Wid- manstatten and equiaxed microstructures.