Effect of P content on stress relaxation and clustering behavior in Cu-Ni-P alloys

Stress relaxation behavior and cluster distributions in Cu-P alloy and Cu-Ni-P alloys with different P content have been investigated by means of three-dimensional atom probe (3DAP). The overall improvement in the stress relaxation performance is considered in terms of dislocation pinning by solute atoms and clusters. The Cu-Ni-P alloy with low P content forms a low density of Ni-P clusters during annealing and shows a greater improvement in stress relaxation resistance than the Cu-P alloy. It is shown that the pinning effect of solute P has much less impact on the stress relaxation behavior in Cu alloys than the effect of the clusters. It is demonstrated that the clusters play a key role in the stress relaxation in Cu alloys and that the stress relaxation performance can be related to the volume fraction of the clusters. © 2010 The Japan Institute of Metals