Material Creep Behavior with Prediction of Tertiary Creep Failure by a Spherical Micro-indentation Method

In this research, material time-dependent behavior of Sn3.5Ag, Sn37Pb and Sn5Sb solder alloys were studied by a depth sensing micro-indentation method at room temperature. Stress exponent values were determined through a constant loading process utilizing a spherical micro indentation method, where the strain rate is extracted from the indentation rate. The measured stress exponent values are in good agreement with conventional creep experiments. Utilizing a multiple loading and partial unloading micro-indentation testing procedure, time-dependent stiffness changes of these materials could be measured. This continuous stiffness responses during a creep test can be correlated to test material’s microstructural changes during creep, therefore making it capable to predict onset of tertiary creep failure. Test results show a correlation between measured continuous stiffness response and creep damage with the capability to predict the onset of tertiary stage.