Demeneghi Gabriel, Gradl Paul, Mayeur Jason R, Hazeli Kavan
NASA Marshall Space Flight Center, Huntsville, USA.
Mechanical and Aerospace Engineering Department, University of Alabama in Huntsville, USA.
Heliyon. 2024 Mar 27;10(7):e28679. doi: 10.1016/j.heliyon.2024.e28679. eCollection 2024 Apr 15.
Size effects, influencing a material's strength, elongation, fatigue limit, and longevity, depend on the operative and dominant deformation and failure mechanisms. This study explores the size effects in additive manufactured (AM) GRCop-42 (Cu-4at%Cr-2at%Nb) thin wall structures fabricated via laser-powder bed fusion (L-PBF) and their impact on fatigue life. The influence of internal defects and surface topography on the fatigue life of specimens in both as-built and hot isostatic pressed (HIP) conditions across different thicknesses is investigated. Where micro-computed tomography (CT) was used to quantify the internal porosity of as-built, pristine HIP'd, and fatigued HIP'd specimens, and laser microscopy was employed to quantify the surface topography of specimens prior to fatigue. Additionally, quasi-static tests were used to establish baseline mechanical properties (i.e. yield strength (YS), ultimate tensile strength (UTS), and elongation) to frame fatigue testing conditions. Results indicate a significant enhancement in fatigue life for HIP'd specimens for both thicknesses, with internal defects depicting a greater impact than surface topography. Furthermore, fractographic analysis suggests that thicker specimens exhibit higher resistance to crack propagation during fatigue testing in the absence of substantial porosity. Thus, the size effects observed on the fatigue life of L-PBF GRCop-42 appears to be dominated by internal defects.
尺寸效应会影响材料的强度、伸长率、疲劳极限和寿命，它取决于起作用的主要变形和失效机制。本研究探讨了通过激光粉末床熔融（L-PBF）制造的增材制造（AM）GRCop-42（Cu-4at%Cr-2at%Nb）薄壁结构中的尺寸效应及其对疲劳寿命的影响。研究了内部缺陷和表面形貌对不同厚度的原样和热等静压（HIP）处理后的试样疲劳寿命的影响。其中，使用微型计算机断层扫描（CT）来量化原样、原始HIP处理后的和疲劳后的HIP处理后的试样的内部孔隙率，并使用激光显微镜来量化疲劳前试样的表面形貌。此外，使用准静态试验来确定基线力学性能（即屈服强度（YS）、极限抗拉强度（UTS）和伸长率），以确定疲劳试验条件。结果表明，两种厚度的HIP处理后的试样的疲劳寿命都有显著提高，内部缺陷比表面形貌的影响更大。此外，断口分析表明，在没有大量孔隙的情况下，较厚的试样在疲劳试验中表现出更高的抗裂纹扩展能力。因此，在L-PBF GRCop-42的疲劳寿命上观察到的尺寸效应似乎主要由内部缺陷主导。
