Boride-based conversion coatings for iron and titanium alloys

Metallic components are often limited in applications by their poor wear or corrosion resistance. As aconsequence, a variety of methods are available for surface treatment of metallic components, includingvariants of thermal spraying as well as physical vapour deposition (PVD) techniques. As an alternative,pack-boriding, where the components are heat-treated in a powder bed containing one or more boron sources,is a promising method of surface modification, as it is both low-cost and non-line-of-sight (a drawback of thepreviously mentioned thermal spray or PDV techniques). In particular, alloy components based on titanium oriron (i.e. various grades of steels) have significant potential for post-forming boriding treatments, formingeither TiB2/TiB or FeB/Fe2B composite coatings.In the present work, in conjunction with Roll-Royce Canada, aqueous suspension-based coating methods willbe developed and evaluated for depositing the pack-boriding powder components onto the surface of bothtitanium (grades 2 and 5) and steel (1xx and 3xx series) articles. The suspension-based approach offerspotential benefits in obtaining good "pack"-coatings on complex-shaped components, and may also reduce theamount of material used for the heat-treatment step (i.e. boron source, initiator and inert filler). The coatedsamples will then be heat-treated to assess the effects of boriding on mechanical properties, such as hardnessand tensile strength. Comparison will be made with more conventional "dry" pack-boriding approaches. Thedeposited coatings will be assessed using optical and scanning electron microscopy, while phase developmentwill be determined using x-ray diffraction.