酸化物分散強化形超合金の高温クリープ疲労微小き裂の発生と成長

抄録

The behavior of initiation and growth of small cracks were investigated in creep fatigue at 1273K (1000°C) using a smooth round-bar specimen of an oxide (Y₂O₃) dispersion-strengthened (ODS) superalloy, Inconel MA 754, produced by means of the mechanical alloying process. The elongated grain structure was attained by extrusion and isothermal annealing. The experimental results are summarized as follows : (1) Multiple traverse cracks (Type A) were initiated on the surface along grain boundaries perpendicular to the stress axis from the early stage to the middle stage of life. However, most of them were arrested immediately after the initiation by the grain boundary along the stress axis. (2) Transgranular cracks (Type B) began to appear from the middle stage of life. Although the grain boundary along the stress axis interfered with the growth of the Type B crack, the crack broke through the barrier and formed a main crack which brought about failure of the specimen. (3) While the elongated grain structure worked to prevent the growth of Type A cracks, it showed little effect on that of Type B cracks.