Thermal rejection and growth of gas bubbles in electrodeposited nickel

Abstract

In thick sections of a nickel electrodeposit annealed over the temperature range 200° to 1000°C, tiny (<100Å diam) gas bubbles were first observed after anneals at 500°C. Most of the hydrogen in the specimens was evolved before or during the formation of the bubbles. With increasing annealing treatment the gas bubbles coarsened, large grain-boundary bubbles developed, and significant swelling occurred. Bubble growth ceased at about 6 pct swelling during a 1000°C anneal. During annealing, considerable softening occurred in two stages, a rapid stage followed by a slow stage. Rapid softening constituted the largest portion of the total softening and is thought to be associated with redistribution of impurities and lattice defects, during which bubble nuclei are formed. Slow softening coincided with the appearance of visible bubbles, many of which were found to pin grown-in dislocations; coarsening of these bubbles is believed to cause slow softening. Deposits from certain types of plating baths are quite susceptible to swelling, and in these cases the degree of swelling increases strongly with increasing initial hardness of the deposits when some critical hardness is exceeded.