Abstract
As part of a research effort to conserve strategic and critical metals, the U.S. Department of the Interior, Bureau of Mines, has developed a modified aqueous electrodeposition method for preparing fe-ni-cr alloy coatings and electroforms. This method involves mechanically suspending cr powder (averaging 2 um diam) in a ferrous- nickelous sulfate electroplating bath and occluding the cr particles in the electrodeposited fe-ni alloy matrix. Subsequent heat treatment of the resulting composite coating forms the ternary alloy. The occlusion process is affected by the quantity of cr powder suspended as well as by the microstructure and composition of the electrodeposited matrix. The largest quantity of chromium is occluded when the electrodeposited matrix exhibits a dual-phase y(ni,fe)-a(fe,ni) microstructure. Coatings with up to 20 wt pct cr have been deposited from an electrolyte containing 20 vol pct suspended cr powder. Heat treatment at 1,100 deg c for 8 h effectively homogenizes the composite coating. Alloys containing 55fe-29ni-16cr produced by this method corroded at a rate of only 0.7 Mm/yr during 240 h of exposure to boiling 65 pct hno3. Applicability of this method to the preparation of electroforms has also been demonstrated.
