Department of Mechanical Engineering, Auckland University of Technology, Auckland, New Zealand.
Department of Mining & Metallurgical Engineering & Materials Science, University of the Basque Country UPV/EHU, Bilbao, Spain.
J Mech Behav Biomed Mater. 2021 Nov;123:104741. doi: 10.1016/j.jmbbm.2021.104741. Epub 2021 Aug 25.
Biomedical Co-29Cr-6Mo alloy is one of the alloys that are suitable for laser powder bed fusion (LPBF) additive manufacturing and as an implant material is often used in situations of critical and cyclic loading. Thus, fatigue crack growth (FCG) behaviour and resistance of the alloy processed by LPBF are an important consideration for dental and orthopaedic applications. In this study, FCG testing has been conducted to evaluate how build direction (BD) dependent grain/cell structure in relation to crack growth direction (CD), either CD⊥BD or CD//BD, affects FCG behaviour. It has been found that the threshold stress intensity factor (ΔK) value is significantly higher and the values of c and m in Paris equation are slightly lower for CD//BD samples than the values for CD⊥BD samples, respectively. Failure analysis has revealed that the effects of the commonly known defect, lack of fusion, on both ΔK and FCG rate are weak. It has been identified that crack has mainly propagated in a transgranular and transcellular manner, consistent with the observation of the crack path being more torturous and with the higher crack growth resistance determined in CD//BD samples than in CD⊥BD samples. This will be further discussed linking the difference in the size of crack segment, which is BD and thus grain/cell length dependent, to the roughness-induced crack closure mechanism.
医用 Co-29Cr-6Mo 合金是适合激光粉末床熔合（LPBF）增材制造的合金之一，作为一种植入材料，它通常用于承受关键和循环负载的情况。因此，LPBF 加工的合金的疲劳裂纹扩展（FCG）行为和阻力是牙科和矫形应用的一个重要考虑因素。在这项研究中，进行了 FCG 测试，以评估与裂纹扩展方向（CD）相关的构建方向（BD）依赖性晶粒/胞结构，无论是 CD⊥BD 还是 CD//BD，如何影响 FCG 行为。结果发现，对于 CD//BD 样品，门槛应力强度因子（ΔK）值显著更高，Paris 方程中的 c 和 m 值略低于 CD⊥BD 样品的值。失效分析表明，常见缺陷（未熔合）对ΔK 和 FCG 速率的影响较弱。已经确定裂纹主要以穿晶和跨晶方式扩展，这与在 CD//BD 样品中观察到的裂纹路径更曲折以及裂纹扩展阻力更高的情况一致，而在 CD⊥BD 样品中则较低。这将进一步讨论与裂纹段尺寸的差异相关的问题，该差异与 BD 有关，因此与晶粒/胞长度有关，与粗糙度诱导的裂纹闭合机制有关。
