RETARDATION OF INTERGRANULAR FRACTURE AT INTERMEDIATE TEMPERATURES BYA BOUNDARY NODE IN A CU-9 AT-PERCENT AL-ALLOY TRICRYSTAL

The effect of a boundary node on intergranular fracture at intermediat e temperatures is discussed from creep tests employing a Cu-9 at. % Al alloy tricrystal. In situ observation to measure the amount of grain- boundary sliding is made during the creep tests. At temperatures betwe en 773 and 923 K under an applied stress of 35 or 40 MPa, cracks to ca use intergranular fracture appear in bicrystal and tricrystal specimen s after the occurrence of a critical amount of grain-boundary sliding. The boundary node lowers the rate of the grain-boundary sliding and t hereby retards the intergranular fracture. This is different from the effect of the boundary node at higher temperatures, where the boundary node becomes a preferential site for crack formation.