き裂開閉口測定に基づくＮｉ基超合金の高温における微小疲労き裂進展の調査

Abstract

Fatigue small crack growth behavior was studied in three kinds of Ni-base superalloys at high temperature and was compared with the physically long crack behavior; a single crystal alloy, CMSX-2, a directionally-solidified alloy, CM247LC-DS and a polycrystalline alloy, CM247LC-CC. The crack opening-closing behavior was also measured by means of a new device originally developed and improved. The experimental results indicated that the small cracks exhibited a higher growth rate than the long cracks at the same stress intensity factor range in all of the materials. However, the rates of small crack growth in the CMSX-2 and CM247LC-DS agreed with those of the long crack, when they were correlated with the effective stress intensity factor. This shows that the crack opening-closing effect is mainly responsible for difference of small and long crack growth rates. In contrast to these two materias, the lack of similitude between small and long crack propagation rates was still found in CM247LC-CC, even if the crack closure effect was taken into account.