Effect of ultrafine microstructure on interdiffusion-driven phase transformations in Ni-Sn sandwich diffusion couples

Abstract

Solid-state diffusion in materials is greatly influenced by microstructural features such as grain boundaries, dislocations, and second phase particles. However, a systematic investigation of structure-kinetics correlation during interdiffusion is largely missing. Herein, a novel sandwich diffusion couple approach was utilized to demonstrate the effects of microstructure on interdiffusion-driven phase formation in the Ni-Sn system. Pure Ni samples were prepared by cold rolling (CR) and spark plasma sintering (SPS) with different microstructures. Two sandwich diffusion couples were prepared– a) NiAM/Sn/NiCR and b) NiCR/Sn/NiSPS, for phase growth analysis at each interface after annealing at 200 °C for 96 h. The intermetallic phase Ni3Sn4 formed at the NiAM/Sn, NiCR/Sn, and NiSPS/Sn interfaces had the thickness of 6, 14, and 41 µm, respectively, consistent with larger parabolic growth constant for the NiSPS/Sn interfaces. The enhanced kinetics at the SPS interface could be attributed to the presence of ultrafine-grained (UFG) (∼320 nm) microstructure dominated by high-angle boundaries.