TA33合金保载疲劳裂纹萌生的取向依赖性与微织构效应

Orientation Dependence and Microtexture Effects on dwell Fatigue Crack Initiation in TA33 Alloy

摘要:

近α型 TA33合金因具有优异的高温性能以及良好的室温疲劳强度，已成功应用于先进航空发动机整体叶盘。然而，准确理解微观尺度的疲劳裂纹萌生仍是工程领域一大挑战，核心原因在于裂纹萌生过程对微观组织的固有敏感性。因此，针对两种微织构区域（MTR）特征不同的TA33合金，开展了疲劳寿命及保载疲劳敏感性的研究。研究表明，MTR显著增加了保载疲劳敏感性并导致了更大的裂纹萌生面，这与MTR内位错滑移及裂纹传递性密切相关。消除MTR后，no-MTR合金萌生区被限制在2~3个晶粒范围内，裂纹源区面积显著缩小。同时，由于晶粒取向比较分散，多位置形核使合金保载疲劳敏感性降低至2.86。这些萌生特征均与[0001]取向域内的基面滑移密切相关，不仅在低施密特因子（SF）的硬晶粒基面上开裂，在高SF范围内同样存在萌生现象，均表现出显著的“近基面”取向依赖性。

Abstract:

Near-α TA33 alloy has been successfully employed in integrally bladed disks of advanced aeroengines due to its outstanding high-temperature performance and favorable room-temperature fatigue strength. Nevertheless, accurately understanding fatigue crack initiation at the microscale is still a major challenge in engineering, which mainly stems from the inherent sensitivity of the crack initiation process to the microstructure. Therefore, the fatigue life and dwell fatigue sensitivity of TA33 alloys with different microtexture region (MTR) characteristics were systematically investigated. Results show that MTR significantly aggravates dwell-fatigue sensitivity and gives rise to a larger crack initiation area, which is closely associated with dislocation slip and crack transmission within MTR. After removing MTR, the crack initiation zone in the no-MTR alloy is confined to 2~3 grains, and the area of the crack source region is remarkably reduced. Meanwhile, the dispersed grain orientations and multi-site nucleation decrease the dwell-fatigue sensitivity of the alloy to 2.86. These initiation characteristics are closely related to basal slip in the [0001] orientation domain. Crack initiation occurs not only on basal planes of hard grains with low Schmid factor (SF) but also in the high SF range, both exhibiting a pronounced near-basal orientation dependence.