Amorphous Alloy Coatings for Hard Chromium Replacement

Hard chromium coatings (0.25 to10 mil thick) are used extensively for imparting wear and erosion resistance to components in both industrial and military applications. The most common means of depositing hard chromium has been through the use of chromic acid baths containing hexavalent chromium (Cr+6). However, as a result of its toxicity, exposure levels of Cr+6 have been limited. An alternative technology to hard chromium electroplating, in addition to yielding significantly reduced environmental and health risks, must achieve the hardness and low coefficient of friction provided by hard chromium and must be amenable to industrial applications. Proposed here is an innovative and cost-effective manufacturing process capable of producing environmentally benign amorphous alloy composite surface coatings as a replacement for hard chromium technology. A materials technology optimization and evaluation program is proposed, based upon previous proprietary developments by the applicants in the area of cost-effective production of electrodeposited metals, alloys and composites with refined microstructures. The proposed program seeks to develop a metal matrix composite coating, consisting of an amorphous cobalt-based metal alloy matrix incorporating hard ceramic second phase particles to provide a high strength, highly wear/erosion resistant coating, that can meet all requirements currently provided by hard chrome coatings. Phase I activities will demonstrate the performance enhancement of the amorphous alloy and composite coatings compared to hard chrome through a series of coupon tests evaluating morphology, wear, hardness, corrosion and thermal properties. The successful execution of this Phase I initiative will identify the process conditions required to product amorphous cobalt-based metal alloys and composites and generate baseline material property and performance data. Based on this data, the most promising coatings will be identified for further development, scale-up process optimization and evaluation in Phase II. The successful completion of the proposed effort is expected to result in a replacement technology for current hard chrome coatings that provides enhanced material performance and eliminated the need for the toxic and hazardous Cr+6 electroplating baths. The electrodeposited amorphous alloy composite coating would allow for the retention of numerous benefits associated with hard chrome coating technology (i.e., non-line-of-sight application, excellent adhesion, dimensional consistency and superior surface finish) and allow for the use of existing hard chrome plating infrastructure. This will significantly reduce the time and cost to practical implementation. Moreover, the proposed technology is expected to provide significant performance and life-cycle cost benefits over current hard chrome plating technology.