Structure and Properties of Arc Sprayed Steel Coatings

Abstract

A review of thermal spraying processes and coating materials is followed by a detailed description of arc spraying. The basic principles involved in the production and deposition of spray droplets are discussed together with gas/metal reactions and the formation of oxides. Published literature relating to the measurement of adhesion and cohesion, bonding mechanisms, the development and measurement of residual stress and mechanical properties of sprayed coatings is reviewed. Three commercially available coatings were investigated, mild steel, a 1% carbon 2% chromium steel and a 13% chromium steel. Process variables were spraying distance, deposition rate, arc voltage and atomising pressure. The coatings were characterised by optical metallography, scanning electron microscopy and micro-analysis, gas and chemical analysis. A collar tyne shear adhesion test, employing a mild steel substrate, was used to assess bonding of coating to substrate. Residual stress was determined from dimensional changes of the collar. Adhesion arose mainly from mechanical interlocking and was generally increased with hot, large particles and ranged from 10-155 MPa. With a cylindrical substrate the shrinkage stress developed during cooling markedly contributed to adhesion, it ranged from OQ - 188 MPa and was material dependent...