The amount of cathodic absorption of hydrogen increases with increase in either the percentage of rhenium or the amount of absorbing sulfur in electroformed nickel-rhenium alloys. According to the results of thermal hydrogen outgassing process, the absorbing hydrogen (AH) of the crack-free alloy deposits exists in a stable hydride state. However, when the amount of AH is greater than the solubility in the stable hydride state, the hydride formation becomes unstable. and cracked deposits are formed. Because the absorbing sulfur enhanced the solubility of AH in the stable hydride state, a crack-free alloy electroform with a greater amount of AH was obtained.