Examination of factors influencing the bond strength of high velocity oxy-fuel sprayed coatings

Several types of Ni and Co based composite coatings were deposited by high velocity oxy-fuel (HVOF) spray process using WC–Co, SiC–Co, TiC–Co (or Ni), Al2O3–Ni, W–Ni composite powders and large metallic powders in order to examine the factors influencing the bond strength of HVOF coatings. The bond strength of coatings was measured with the pull-off test method according to ASTM C-633-79 standard. It was found that the conventional state parameters of spray particles including temperature, velocity and momentum were not directly correlated with the bond strength of HVOF coatings. The physical properties of the non-melting phases in a two-phase particle significantly influence the bond strength of HVOF coatings. The effective mass of non-melting phases in a spray particle, which is defined as the product of density and square of volume fraction of solid phase in the two-phase particle, is proposed to give a good correlation with the bond strength of the coatings. It was found that the bond strength of HVOF coatings is correlated well with the parameter proposed.