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Modifications of plating conditions improved the properties and plating characteristics of hot-hard Cr-Fe alloys for use as erosion-resistant electroplate linings for gun tubes. Stress reduction in the plate and better plate coverage of the machinery scratches on steel were the principal improvements. A plate was deposited on an electropolished bore of an erosion- gage weapon insert without a Cr-strike plate; the alloy adhered well to the steel surface after heating for 2.5 hr at 750 deg F. The wear-resistance of Cr- Fe plate was improved by adding SiOsub2 and glycine to the plating bath to modify the deposit from a columnar to a banded structure. The banded, unlike the columnar structure, developed stress cracks, but is expected to provide increased uniformity on gun tube bores.

Experiments were continued on the application of 94% chromium, 6% iron alloy plate to the bore surfaces of cannon. After moving-anode tests were unsuccessful, a satisfactory technique was developed using full-length anodes in the bore of 4-foot-long sections of 40-mm gun tubes. Plates were then produced with good appearance, good plating efficiency, and adequate dimensional control, but the adhesion to the base metal was not good enough for gun-type service. Several erosion-gage weapon inserts were plated and test fired. Each test resulted in failure by separation of the plate from the bore surface. Some improvement in adhesion was achieved by a thin chromium plate between the steel base and the chromium-iron alloy plate. A bonding heat treatment also effected some improvement. However, erosion-gage weapon-firing tests showed that adhesion was still not sufficient to withstand the conditions encountered in gun tube service.