Fatigue Crack Propagation in Copper Bicrystals Having the Grain Boundaries of #EPSILON#3 Vicinal Domain

摘要

The criterion for occurrence of intergranular fatigue cracking in copper has been investigated from the view point of both the grain boundary (GB) character and the cyclic deformation property of constituent grains. The copper bicrystals were prepared to have several orientation relationships close to #EPSILON#3(111) coherent twin (#EPSILON#3 vicinal domain) so as to change the GB character rapidly with increasing deviation angles |triangle open#theta#| from the #EPSILON#3 relation. These bicrystals were shaped to single-edge-notched specimens in which a GB plane was perpendicular to the tensile axis. The fatigue crack propagation tests were carried out in air at room temperature. The specimens having deviation angles |triangle open#theta#| less than 3 deg involved no intergranular fatigue cracking. When the |triangle open#theta#| values were ranged from 3 deg to 5 deg , the ratio of the intergranular cracking increased. In the specimens having the |triangle open#theta#| values more than 9 deg , the intragranular cracking became predominate again. The increase in the intergranular cracking with increasing deviation angle at the |triangle open#theta#| values less than 5 deg could be understood in terms of the increasing GB susceptibility to the GB damage due to air environment. On the otter hand, the intragranulasr cracking at the |triangle open#theta#| values more than 9 deg could be attributed to the formation of the persistent slip bands in the constituent grains and subsequent crack propagaion preferentially along them.