Effects of Cu addition on creep characteristics of Sn–9Zn lead-free solders

In the present study, the transient, and steady state creep of Sn–9Sn and Sn– 9Sn-0.7Cu ternary alloy was investigated in the temperature range from 323, to 403 K at different five stresses ranged from 3.62 to 11.22 MPa. The transient creep parameters n and β were found to be markedly affected by the creep test conditions, T and ϭ. The parameter β was found to be increased by increasing transformation temperature, also; n was found to increase by increasing T irrespective of the applied stress. The steady-state creep rate ε´st was found to increase with increasing both T and ϭ for two alloys. The relationship between steady-state creep rate ε´st and the stress is ε´st = Cϭ m where m=(∂lnε´st/∂lnϭ), is the strain rate sensitivity parameter. This exponent is increased with increasing T in both alloys. Addition of small amount of 0.7Cu to the binary alloy increased its creep resistance and ductility and was found to be enhancing the plasticity of the ternary alloys. This behavior was attributed to the formation of the intermetallic compounds (IMCs) Sn5Zn8 and Cu6Sn5 during solidification. These IMCs played the role of pinning action for the moving dislocations and consequently leading to the increase of its creep resistance. Microstructural changes were investigated by Optical microscope (OM), and X-ray diffraction