Effect of annealing on tensile properties of electrodeposited nanocrystalline Ni with broad grain size distribution

Abstract

The microstructures and tensile properties of electrodeposited nanocrystalline Ni (nc-Ni) with a broad grain size distribution after annealing at 150, 200 and 300°C for 500 s were investigated. The as deposited broad grain size distribution nc-Ni sample exhibited a moderate strength σ_UTS of ∼1107 MPa but a markedly enhanced ductility ϵ_TEF of ∼10, compared with electrodeposited nc-Ni with a narrow grain size distribution. Annealing below 200°C increased the strength but caused a considerably reduction in tensile elongation. This behaviour is attributed to the grain boundary relaxation and the increased order of grain boundaries after annealing, which can make the grain boundary activities, such as the grain boundary sliding and grain rotations, more difficult. Further annealing at 300°C decreased both the yield strength and tensile elongation significantly due to significant grain growth.