Impact of Microstructure on Remelting Parameters and Mechanical Behavior of Thermally Sprayed NiCrBSi Coating

The present study concerns controlling and quantifying the impact of the remelting thermos-cycle curve parameters on the microstructure evolution and mechanical properties of remelted NiCrBSi coatings. This coating was chosen for this study because it shows good results while subjected to heat treatment. Understanding heat transfer during the remelting of porous coatings NiCrBSi remains a significant challenge in the coating technology and industry. Two different thermal spraying technologies are used: oxygen fuel (OF) and high-velocity oxygen fuel (HVOF). The working temperature versus time were monitored using infrared thermal imaging during surface flame melting (SFM). Optical, electron microscopy and characterization are utilized to investigate the impact of porosity and precipitates size on cooling curve parameters. X-ray diffraction is used for the phase analysis of NiCrBSi coatings as-sprayed and after remelting. Two methodological innovations are introduced; the quantification of the remelting cooling rate and the utilization of the thermo-cycles curve to calculate the energy required for the remelting. The results obtained suggest the size of the resulting precipitates highly depends on the cooling rate, rather than on the subcooling; the porosity of the as-spray coating has a significant effect on the size of the precipitates obtained and that the size of the precipitates has a similar effect to the porosity size on the fracture toughness.