The value of fatigue predictive NASGRO models hinges on the quality of established parameters to describe the behaviour of the subject material. To establish these parameters for laser powder bed fusion (LPBF) produced Ti-6Al-4V the influence of process inherent microstructure, residual stress, and orientational dependant mesostructure needs to be considered. Examining near-threshold in combination with steady-state fatigue crack growth rates (FCGR's) offers insight into the impact of crack closure in the NASGRO formulation. This study investigates the influence of microstructure, residual stress and orientation of LPBF produced Ti-6Al-4V on establishing parameters for NASGRO models from a foundational perspective. Near-threshold crack growth rate data from Compact Tension (CT) coupons built in three orientations and as-fabricated (AF), stress-relieved (SR) and duplex annealed (DA) state are considered. Optical and scanning electron micrographs are used to consider morphological features. Results show anisotropy in material constraint, used in describing crack closure, between orientations in AF and SR state, lending to unique consideration for each orientation. DA is shown to relieve this effect. Overall, this study establishes and demonstrates the importance of uniquely considering NASGRO parameters for LPBF produced Ti-6Al-4V.

疲劳预测NASGRO模型的价值取决于已建立参数的质量，以描述主题材料的行为。为了建立用于激光粉末床熔合（LPBF）生产的Ti-6Al-4V的这些参数，需要考虑工艺固有的微观结构，残余应力和取向相关的介观结构的影响。结合稳态疲劳裂纹扩展率（FCGR's）检查近阈值，可以洞悉裂纹封闭对NASGRO配方的影响。这项研究从基础的角度研究了LPBF生产的Ti-6Al-4V的微观结构，残余应力和取向对建立NASGRO模型参数的影响。紧密拉伸（CT）试件以三个方向构建并预制（AF）制成的近阈值裂纹增长率数据，考虑了应力消除（SR）和双相退火（DA）状态。光学和扫描电子显微照片用于考虑形态特征。结果显示，在AF和SR状态下的取向之间，用于约束裂纹闭合的材料约束各向异性，这是每个取向的唯一考虑因素。已显示DA可以减轻这种影响。总的来说，这项研究建立并证明了对于LPBF生产的Ti-6Al-4V唯一考虑NASGRO参数的重要性。已显示DA可以减轻这种影响。总的来说，这项研究建立并证明了对于LPBF生产的Ti-6Al-4V唯一考虑NASGRO参数的重要性。已显示DA可以减轻这种影响。总的来说，这项研究建立并证明了对于LPBF生产的Ti-6Al-4V唯一考虑NASGRO参数的重要性。