A comparison of impression, indentation and impression-relaxation creep of lead-free Sn-9Zn and Sn-8Zn-3Bi solders at room temperature

Creep behavior of Sn-9% Zn and Sn-8% Zn-3% Bi solder alloys was studied by impression, indentation, and impression-relaxation tests at room temperature (T > 0.6 T _m) in order to evaluate the correspondence of the creep results obtained by different testing techniques, and to evaluate the effect of Bi on the creep response of the eutectic Sn - 9Zn alloy. Stress exponent values were determined through these methods and in all cases the calculated exponents were in good agreement. The average stress exponents of 8.6 and 9.9, found respectively for the binary and ternary alloys, are close to those determined by room temperature conventional creep testing of the same materials reported in the literature. These exponents imply that dislocation creep is the possible mechanism during room temperature creep deformation of these alloys. The introduction of 3% Bi into the binary alloy enhanced the creep resistance due to both solid solutioning effect and sparse precipitation of Bi in the Sn matrix.