Effect of temperature on isothermal low cycle fatigue properties of Sn–Ag eutectic solder

Low cycle fatigue tests on as-cast Sn–Ag eutectic solder (96.5Sn–3.5Ag) were carried out using the non-contact strain-controlled system at 0.1 Hz under various temperatures (20, 85, 120 °C). The relationship between stress range at the first cycle and inverse temperature for various strain ranges followed the Dorn’s equation with the activation energy in the range of 62–72 kJ/mol, which suggests that pipe-diffusion-controlled dislocation climb are the main deformation mechanism. The low cycle fatigue behavior in this temperature range followed the Coffin–Manson equation. The fatigue ductility coefficient was found to be influenced by temperature. Steps at the boundaries of Sn-dendrites were the initiation sites for microcracks for all temperatures studied. The link up of these cracks and the crack propagation inside the specimen occurred both transgranularly through Sn–Ag eutectic phase and/or Sn dendrite, and intergranularly along Sn-dendrite boundaries. Propagation of stage II crack for different temperatures could be characterized by C*-parameter.