Effect of Boron and Tungsten Addition on Superplasticity and Grain Growth in Electrodeposited Nickel Alloys

The effect of W and B addition on the superplastic deformation and grain growth of electrodeposited nanocrystalline Ni alloys with a crystal grain size of approximately 20 nm was investigated with the aim of improving the mechanical properties by maintaining fine grain sizes during superplastic deformation. A maximum elongation of 12% was recorded for electrodeposited Ni -1.8 at% W at a temperature of 350 degrees C and a strain rate of 1.0 x 10(-4)s(-1). The electrodeposited Ni W failed to exhibit superplasticity because the segregated W at the grain boundaries increased the energy required for grain boundary sliding. In contrast, the electrodeposited Ni-0.06 at% B exhibited superplasticity with a recorded elongation of 362% at a temperature of 450 degrees C and a strain rate of 1.0 x 10(-4)s(-1). With the addition of B, the optimal superplastic strain rates of the electrodeposited Ni-B shifted to lower values than that of the electrodeposited Ni. The grain size and hardness of the electrodeposited Ni-B after superplastic deformation were smaller and higher, respectively, than those of the electrodeposited Ni. The addition of B successfully suppressed grain growth and improved the mechanical properties after superplastic deformation.

Automated summary

The addition of W and B has different effects on the superplastic deformation and grain growth of electrodeposited nanocrystalline Ni alloys. The addition of W increases the energy required for grain boundary sliding, thereby inhibiting superplasticity; while the addition of B successfully suppresses grain growth and improves the mechanical properties after superplastic deformation.