The Mechanism of Microstructure and Properties Variation of Sn under Current Stressing

Abstract

This study investigated the mechanism of the microstructure and properties variation of Sn under current stressing The pure Sn strip specimens were subjected to current stressing under current density 5 5~7 5 kA/cm? for 0 5h 2cycles The specimens were rapidly quenched with liquid nitrogen after current stressing to freeze the microstructure for investigation The mechanical and electrical properties of the pure Sn strips were investigated using Vickers micro-hardness tester and 4-point probe respectively The microstructure variation under different current stressing conditions was investigated using electron back scattered diffraction analysis(EBSD) and transmission electron microscope(TEM) The activation energy for the properties and microstructure variations induced by electric current stressing was estimated and the mechanisms behind were further disclosed in this research The HRTEM figures which showed the increasing dislocation density after current stressing indicated that electron wind force contributed to the distortion of lattice structure and the generation of dislocation The result of EBSD showed the variations in grain size and grain orientation The fraction of fine grain is generally raised under all current stressing conditions Grain refinement and grain growth were respectively observed at low current density (5500 A/cm?，6500 A/cm?)and high current density(7500 A/cm?) Grain refinement was attributed to the formation of dislocation as nucleation site along with the current-induced Joule heat which promotes recrystallization behavior In general all the electric current stressing conditions investigated were found to enhance the micro-hardness and lower the sheet resistance of the Sn strips The improvement of micro-hardness could be attributed to the grain boundary strengthening and strain strengthening The drop of sheet resistance could be attributed to the variation in grain orientation

Date of Award	2019
Original language	English
Supervisor	Kwang-Lung Lin (Supervisor)