CREEP-BEHAVIOR AND DISLOCATION-STRUCTURES IN AL-AL2O3 ALLOYS

Creep tests at high temperatures have been carried out in an Al-Al//2O//3 binary alloy and an Al-Al//2O//3-Si ternary alloy with different grain sizes. Dislocation structures after the steady-state creep have been observed in the temperature range from about 473 K to 873 K. The creep behavior and the contribution of grain boundary sliding in a low stress range at temperatures above 773 K have been examined in detail in the Al-Al//2O//3 alloy. Dislocations were generally distributed rather uniformly, being pinned to dispersed particles when crept at temperatures below 673 K, though incomplete subboundaries were occasionally observed in a high stress range. On the other hand, when crept at temperatures above 773 K, sharp subboundaries, which appeared to be formed associated with the grain boundary sliding, were often observed with the uniform distribution of dislocations. At temperatures above 773 K, the Al-Al//2O//3 alloy was deformed at relatively large creep rates.