Connecting Creep Constitutive Parameters to Microstructural Deformation in Sn

Abstract

The deformation behavior of solders based on β-Sn is influenced by a high homologous operating temperature and microstructural heterogeneity. In this study, the deformation mechanisms of single-crystal and polycrystalline Sn were investigated using high-temperature nanoindentation combined with post-indentation microscopy. Constant strain-rate and dynamic mechanical analysis tests were conducted between 30℃ and 180℃ (0.6–0.9 Tm) to quantify hardness, pop-in, and creep constitutive parameters. Hardness decreases with increasing temperatures (as expected), while pop-in loads shift to lower values at higher temperatures, indicating thermally assisted activation of plastic deformation. Indentations into polycrystalline Sn regions exhibit higher stress exponents (n ≈ 6.8–7.4) and activation energies at moderate temperatures than indentations in single grains remote from any boundaries, reflecting the influence of grain boundary constraints in accommodating plasticity. At higher temperatures, both microstructures converge toward lower stress exponents and activation energies, suggesting a transition toward deformation mechanisms increasingly governed solely by thermally activated processes. Microstructural characterization reveals slip band formation, dislocation localization, and grain boundary sliding, demonstrating that deformation in polycrystalline Sn at these temperatures results from the combined effects of intragranular dislocation activity and intergranular strain accommodation.