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_Th) 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_Th 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.

生物医学 Co-29Cr-6Mo 合金是适用于激光粉末床融合 (LPBF) 增材制造的合金之一，并且作为植入材料经常用于临界和循环载荷的情况。因此，LPBF 处理的合金的疲劳裂纹扩展 (FCG) 行为和抵抗力是牙科和整形外科应用的重要考虑因素。在这项研究中，进行了 FCG 测试以评估与裂纹生长方向 (CD) 相关的构建方向 (BD) 相关晶粒/细胞结构，CD⊥BD 或 CD//BD，如何影响 FCG 行为。已经发现阈值应力强度因子（ΔK _Th) 值显着更高，并且巴黎方程中的 c 和 m 值对于 CD//BD 样本分别略低于 CD⊥BD 样本的值。失效分析表明，众所周知的缺陷，未融合，对 ΔK _Th和 FCG 率的影响都很弱。已经确定裂纹主要以穿晶和跨细胞方式传播，这与观察到的裂纹路径更加曲折并且在 CD//BD 样品中确定的裂纹扩展阻力比在 CD⊥BD 样品中更高。这将进一步讨论将裂纹段的大小差异与粗糙度引起的裂纹闭合机制联系起来，裂纹段的大小与 BD 相关，因此与晶粒/单元长度有关。