Fatigue Small Crack Growth in a Single Crystal Ni-Base Superalloy at Elevated Temperature.
Fatigue Small Crack Growth in a Single Crystal Ni-Base Superalloy at Elevated Temperature.
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单晶镍基高温合金在高温下的疲劳小裂纹扩展。
DOI：
10.2472/jsms.41.1261
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
S. Nohmi
中科院分区：
文献类型：
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作者：
M. Okazaki;T. Imai;Takayuki Satoh;S. Nohmi
对单晶镍基高温合金CMSX-2在873 K空气中进行了应变比为零的应变控制低周疲劳试验。CMSX-2合金的疲劳强度高于其他几种多晶镍基高温合金和定向凝固合金CM 247 LC-DS。采用复型技术研究了疲劳小裂纹扩展行为。在宏观上，小裂纹扩展速率随裂纹长度的增加而成比例地增加。然而，在微观水平上，它们受到微观结构的显著影响。通过对裂纹路径、断口形貌和裂尖附近变形的微观观察发现，当裂纹长度足够短时，小裂纹在{100}立方面上的γ相基体中扩展，γ'相的变形可以忽略不计。另一方面，随着裂纹变长，裂纹扩展面转换为{111}滑移面。在此阶段，裂纹以滑移面脱粘机制快速扩展，切割γ'相。当应力强度因子范围达到某一临界值时，裂纹扩展面发生上述转变。在此基础上，对CMSX-2和CM 247 LC-DS在小裂纹扩展速率和疲劳强度方面的差异进行了讨论。
Strain-controlled low-cycle fatigue tests were carried out on a single crystal Ni-base superalloy, CMSX-2, under a strain ratio of zero at 873K in air. The CMSX-2 showed higher fatigue strength, compared with some other kinds of polycrystalline Ni-base superalloys or with a directionally-solidified superalloy, CM247LC-DS. The fatigue small crack growth behavior was also investigated by using a replication technique. The small crack growth rate increased proportionally with increasing crack length on the macroscopic level. On the microscopic level, however, they were significantly affected by the microstructure. From the microscopic observations of the crack path, fracture surface and deformation around the crack tip, it was found that the small cracks propagated in the γ phase matrix on {100} cubic planes, accompanying with negligible deformation of γ' phases, when the crack length was short enough. As the crack became longer, on the other hand, the crack propagation planes were converted onto {111} slip planes. In this stage the crack rapidly grew by the slip plane decohesion mechanism, cutting the γ' phases. The above transition of crack propagation plane occurred when the stress intensity factor range reached a critical value. Based on the foregoing results, the differences in the small crack growth rate and the fatigue strength between CMSX-2 and CM247LC-DS were also discussed.