Stellite12钴基合金的疲劳性能及其断裂机理研究

采用三点弯曲疲劳法测得光滑试样和直缺口试样的S-N曲线以研究Stellite12钴基合金的疲劳性能,并通过断口形貌观察进一步探究该钴基合金的断裂过程。结果表明:光滑试样的疲劳极限为545 MPa,约为原始抗弯强度1552 MPa的25.4%;直缺口试样的疲劳极限约为101MPa,约为静态抗弯强度517.6MPa的19.1%。对于疲劳敏感性,光滑试样与直缺口试样的疲劳敏感性分别为397和31。此外发现疲劳裂纹多萌生于近表层聚集的碳化物处,同时表面缺陷也可诱发疲劳裂纹的萌生。疲劳裂纹的扩展主要表现为碳化物的穿晶断裂,钴基体在应力比R=0.1的疲劳加载条件下虽表现出一定的韧性且呈现出较多的撕裂脊,但也呈现出一定的脆性断裂模式,因此疲劳裂纹扩展模式为真疲劳与静态疲劳的混合模式。

Fatigue properties and fracture mechanism of Stellite12 cobalt-based alloy

The three-point bending fatigue method was used to determine the S-N fatigue curves of smooth specimens and straight-notched specimens to study the fatigue properties of Stellite12 cobalt-based alloy, and the fatigue fracture processes of the cobalt-based alloy were investigated by the observation of fracture morphology.The results show that the fatigue limit of the smooth specimen is 545 MPa, which is about 25.4% of the original bending strength of 1552 MPa. The fatigue limit of the straight-notched specimen is about 101 MPa, which is about 19.1% of static bending strength of 517.6 MPa. The fatigue sensitivity of smooth specimens and straight-notched specimens is 397 and 31, respectively. In addition, it is found that the fatigue cracks can initiate in the carbides aggregated regions in the near surface. Surface defects can also induce the initiation of fatigue cracks. The transgranular fracture of the carbides dominates in the crack propagation. The cobalt base metal presents a lot of tearing ridges under the condition of stress ratio R=0.1, but it also shows a certain degree brittle fracture mode, so the fatigue crack propagation mode is a mixed mode of true fatigue and static fatigue.