The Effects of Annealing on the Mechanical Properties of Electrodeposited Nickel

Publisher Website
Google Scholar
Abstract
Attempts have been made to clarify the existing experimental evidence of the embrittlement of Watts nickel after heat treatment at temperatures in excess of 600°C. Electrodeposits have been prepared from a ‘purified’ solution maintained at pH 4 at current densities of 21·5, 270 and 540 A/m2. It was found with 21·5 A/m2 nickel that the ductility (measured at 20°C) was drastically reduced as the annealing temperature (1 h treatment) increased from 600° to 1000°C, whilst the higher current density materials only registered a small reduction in this property after treatment close to 1000°C. The UTS decreased with increasing annealing temperature in all cases. Metallographic observations revealed that the intergranular embrittlement observed in the low current density nickel was due to the presence of grain boundary discontinuities. These were identified as voids by scanning electron microscopy, and confirmed by specific gravity measurements. Grain boundary voids were also observed in the annealed high current density nickel, but to a far lesser degree. The formation of a gaseous phase within the deposit at temperatures above 600°C is thought to be responsible; hence the voids are in fact gas filled bubbles.