Abstract This paper examines the bonding mechanisms of high-speed flame spraying (HVOF) sprayed coatings on the basis of the experiments with the substrate at different surface roughness. In order to determine the dominant adhesion mechanisms of HVOF layers, the layers are applied to substrates of different roughness with completely melted powder particles as well as with powder particles with solid and liquid phases. The spray materials are NiCrBSi and WC-Co. The results of adhesion tests showed that the adhesion of the NiCrBSi layer on the roughened substrate was approx. 40 MPa, while there was no adhesion on the polished substrate. In contrast, the adhesive strength of the WC-Co layer on the polished substrate was already between 20 and 40 MPa. The adhesive strength of the WC-Co layers on the substrate with a roughness greater than 5.8 micrometer already exceeded that of the binder materials. Paper includes a German-language abstract.

Abstract NiCrBSi and Ni-50Cr coatings are deposited using High Velocity Oxygen-Fuel (HVOF) spray process under different spray parameters with two powders of different sizes to clarify the influence of melting state of spray particles on the adhesive strength of the coating. The adhesive strength of coating is estimated according to ASTM C633-79. The melting state of spray droplet is examined from the coating microstructure. It is found that the melting state of spray particles has significant effect on the adhesive strength of HVOF sprayed Ni-based coatings. The significant melting of spray particle does not contribute to the increase in the adhesion of HVOF metallic coatings. On the other hand, the deposition of partially melted large particle contributes to the substantial improvement of adhesive strength of HVOF coating. The subsequent coating presents a dense microstructure and yields an adhesive strength of over 76 MPa, which is doubled compared to the coating deposited with completely molten particles.

Abstract The effects of powder types and HVOF spray systems used to produce Cr 3 C 2 -NiCr coating on the relationships between spray parameters and wear performance were investigated based on the effect of fuel gas conditions on abrasive wear and erosion wear. The relationships between spray parameters and wear properties were obtained by orthogonal regression experimental design method. Four types of powders and two HVOF spray systems were used. It is found that with the increase in fuel gas flow or pressure the abrasive wear and erosion of Cr 3 C 2 -NiCr coatings change following a concave curve. The Cr 3 C 2 -NiCr coating with the best wear performance will be deposited under intermediate fuel gas condition. It is experimentally confirmed that by different types of powders and HVOF systems applicable to HVOF spraying of Cr 3 C 2 -NiCr coating, although the optimized fuel gas conditions to deposit coating with the best wear performance will be influenced by types of starting powders.