In the current study, effects of remelting process parameters of Ni-based NiCrBSi coatings deposited by flame spraying were investigated. Coatings were remelted by using oxyacetylene torch at 950, 1000, 1050 and 1100 ?C. Temperatures were controlled by four thermocouples which were placed in the substrate. Effect of remelting process were investigated by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction pattern (XRD), micro and nano hardness, porosity measurement and roughness. Results showed that remelting decreased porosity and surface roughness, eliminated splat boundaries and improved metallurgical bonding between the coating and substrate. Coatings microstructure consisted of Ni-rich matrix with Ni-Ni 3 B eutectic and hard carbide and boride precipitations. Microstructure of the as-sprayed sample was similar to NiCrBSi powders with fine grain size (less than 5 mm). In the remelted coatings, microstructure was similar to the as-sprayed sample but with coarser precipitated particles (5-15 mm). Moreover, a white zone with no precipitate and rich of Ni and Fe formed in the coating close to the coating/ substrate interface. The thickness of this zone increased by increasing the remelting temperature. Results of X-ray diffraction patterns showed presence of ?-Ni, Ni 3 B, Ni 31 Si 12 , CrB, and Cr 7 C 3 phases in the as-sprayed and remelted samples. No significant phase transformation occurred due to remelting process. However, all the peak intensities except Ni phase changed as a result of remelting process. Remelting process caused remarkable decrease in porosity level from 12% for the as-sprayed sample to 2% for the remelted sample at 1100 ?C. Pore shape in the as-sprayed sample was irregular, elongated, and more than 50% of them were sharp disk-shaped. While after remelting process, pore shape changed to near spherical and non-flat spheroidal; and more than 80% of them were spherical. Micro hardness of all the remelted samples decreased because of dissolution and growth of precipitates in the microstructure. Micro hardness decreased more by increasing the temperature of the remelting process. The average hardness of the as-sprayed sample was 970 HV, while by remelting process and increasing its temperature the hardness decreased to its minimum value of 830 HV for the as-sprayed sample that remelted at 1100 ?C. Remelted coatings were ranked according to the well-known ratio of hardness (H) to elastic modulus (E); the higher H/E ratio is related to the higher wear resistance. The as-sprayed sample which remelted at 1050 ?C exhibited low porosity (2.4%), moderate micro hardness (860 HV) and highest H/E and ratio.
