Sb Additions in Near-Eutectic Sn-Bi Solder Decrease Planar Slip

This study examines the changes in strain rate dependence and the deformation behavior of near-eutectic Sn-Bi alloys as a function of Sb concentration using nanoindentation. Alloying near-eutectic Sn-Bi solder with Sb has been shown to increase the strain to failure under tensile and shear conditions in solder ball geometries, with Sb additions remaining in solid solution up to 0.5 wt.% Sb. In this study, the resulting hardness of the three Sb-containing Sn-Bi alloys (Bi-42Sn eutectic, Bi-42Sn-0.5Sb, Bi-42Sn-1.0Sb) exhibits little solid solution hardening at room temperature, and the alloys all exhibited similar strain rate sensitivity behavior, independent of composition for this microstructure. Using nanoindentation and post-indentation microscopy to analyze the deformation behavior of these alloys, the out-of-plane deformation and slip behavior does change with composition. Solute Sb increases the strain hardening behavior at low strains while decreasing planar slip and out-of-plane deformation. The observed changes in deformation modes in this nanoindentation study with the addition of Sb as a solid solution alloy (less slip planarity, more uniform deformation, and more strain hardening) could play a role in previously observed changes in tensile failure modes without the formation of SbSn intermetallic compounds.