Thermal embrittlement and microstructure change in electrodeposited Ni

Abstract

Thermal embrittlement due to sulfur (S) segregation to the grain boundaries (GBs) in electrodeposited Ni and Ni alloys have been previously reported. In this study, microstructural changes in electrodeposited Ni with 220 ppm S transitioning from ductile to brittle fracture were observed by electron backscatter diffraction (EBSD) to determine the types of microstructure that result in thermal embrittlement. Tensile tests of the electrodeposited Ni after annealing showed decreasing tensile elongation to zero with increasing annealing temperature or time. Auger analysis of the fracture surface indicated that thermal embrittlement was due to GB segregation of S. This behavior diverges from the average grain size and fraction of kernel average misorientation detected by EBSD analysis but can be explained by considering average size of the recrystallized grains with (111) orientation. Furthermore, the S concentration at the GBs estimated using the size of recrystallized grains agreed with the values obtained from the Auger analysis. Thus, the S-rich GBs that lead embrittlement, were formed primarily by recrystallization.