Composition and microstructure of arc-sprayed 13% Cr steel coatings

A series of 13% Cr steel wear-resistant coatings have been produced by arc spraying using a range of spraying conditions. The resultant coatings have been examined with optical and scanning microscopes. It has been established that the range of particle sizes varies across the spray beam particularly if the gun-substrate distance is short. At the centre of the beam where the particles are larger, it has been shown that the mean particle are S_A is related to the spraying distance d by a relationship of the form.

where n is an exponent. It is suggested that the gun emits large particles which disintegrate in flight. The use of a small aperture in an arc-restricting air cap produced a general reduction in particle size across the spray beam at all gun-substrate distances.X-ray analysis demonstrated that the combined iron and chromium contents of the deposits were reduced when comparison was made with the composition of the original wire. The longer spraying distances (i.e.d > 50 mm) and use of the finer air caps also reduced the metallic content of the coating. Spot analysis on spray particles revealed a central metallic region with a small residual oxygen content and an outer region of varying thickness (depending on spraying conditions) which contains a significant fraction of oxide.