Identification of Whisker Grain in Sn Coatings by Analyzing Crystallographic Micro-Texture using Electron Back-Scatter Diffraction
by Piyush Jagtap, Aritra Chakraborty, Philip Eisenlohr, and Praveen Kumar
Here, we attempt to understand the age-old question of “where do whiskers in Sn coatings grow?” by performing grain orientation mapping in conjunction with a simple analysis of the stress field in the vicinity of a whisker grain. Electron back-scatter diffraction (EBSD) was used for orientation mapping of Sn grains in a 4 μm thick Sn coating deposited on brass. It was observed that whiskers consistently grew from low-index grains with (100) or near-(100) orientations that were surrounded by grains with similar orientations, which were then partially surrounded by grains with high-index planes, such as (211), (321) and (420). Strong elastic anisotropy and overall a high fraction of high-angle grain boundaries were also consistently observed in the vicinity of whiskers. In addition, full-field three-dimensional crystal elasticity simulations were performed using the EBSD orientation maps to analyze local stress variations in the vicinity of the whisker grain. These simulations indicate the presence of a high compressive hydrostatic stress around the whisker grain, which could then possibly create conducive conditions for whisker growth observed experimentally.