一方向凝固Al-Li合金を用いた高温高サイクル疲労における第1段階き裂進展挙動の観察

抄録

High-cycle fatigue tests were carried out using directionally-solidified Al-Li alloy at 453K, and the first stage fatigue crack growth behavior was investigated by employing an elaborate replication technique. It was shown that the directionally-solidified alloy predominantly revealed the typical stage I fatigue fracture; that is, the fracture occurred on the crystallographic {111} slip planes and preferentially in <101> directions, which are the most important slip system in f.c.c. materials. It was also found that the rate of the stage I crack growth, whose crack tip was far apart enough from neighbouring grain boundaries, proportionally increased with crack length, and that it rapidly decreased as the crack tip approached to neighbouring grain boundaries. Such a stage I crack growth behavior was compared with Tanaka model, which was proposed based on the phenomenon that the crack tip plastic deformation at small crack tip was blocked by neighbouring grain boundaries. The stage I crack growth behavior not only far apart from but also near grain boundaries obtained in this work could be successfully evaluated by Tanaka model. The above results suggested that the crack tip sliding displacement played an important role in the stage I crack growth.