Project Status: Completed
Date Announced: Wed, 11 March 2009
Date Completed: Fri, 28 May 2010
With the high price of corrosion and wear resistant alloys in bulk form, there are major financial incentives to use coated, lower cost substrates. However, despite much research effort and many application development studies, corrosion resistant alloy (CRA) coatings, e.g. Ni alloy 625, prepared by thermal spraying still provide greatly inferior corrosion resistance when compared to parent material of the same composition. Even the most advanced thermal spray processes, such as high velocity oxy-fuel (HVOF) and plasma spraying, produce coatings with interconnecting pathways (due to the presence of micro-scale porosity and oxides); hence substrate attack by corrosive media is usually inevitable. However, the recent development of cold spray technology has made possible the deposition of virtually pore-free and oxide-free metallic coatings. The process involves the acceleration of fine powders to 500-1000m.s-1 in a supersonic inert gas jet. On impact with the target surface, the solid particles experience very rapid deformation, forming a bond with the substrate and each other to produce a very dense and strong coating. To date, published articles have related to demonstration of the concept, equipment development and process modelling using ductile metals e.g. Cu. Published data on corrosion and wear resistance are very limited, and data pertaining to cold spray deposit cohesive strength are limited to a few basic metals e.g. Cu and Ni. Data are needed for more useful engineering materials, e.g. corrosion resistant metals and alloys and metal-bonded carbide, so that cold spray can be validated for applications such as corrosion resistant vessels, hard-facing, spray-forming and additive manufacturing. There is, also, little understanding of the relationship between cold spray particle flight characteristics and coating properties, and no published process economic data. It is the aim of this project, therefore, to address these technology gaps.