Abstract
Ni-P-W composite deposit on the mild steel substrate was derived by the electroless process. The composition of the eletroless coating was Ni-10.7wt.%P-8.7wt%W analyzed by electron probe microanalysis (EPMA). The coating was annealed at various temperatures from 350°C to 600°C for 4h and the structure at different heat-treated temperature was studied by X-ray diffraction, and transmission electron microscope (TEM). The crystallization behavior was evaluated by the differential scanning calorimeter analysis with continuously heating from room temperature to 550°C at different heating rates. The hardness at all depths of the coating on the substrate could be acquired by the nanoindentation. From the DSC analysis, the onset temperature and crystallization temperature were 397.7°C and 405.5°C, respectively, at the heating rate of 10°C/min. The activation energy of the Ni-P-W coating was 307 kJ/mol analyzed by Kissinger, and Augis and Bennett methods with different heating rates. The Ni-P-W coating showed an amorphous structure in the as-deposited state and exhibited a relatively low hardness of approximately 6.8 GPa. As temperature was raised to 380°C, the hardness was slightly increased to 8.7 GPa due to the partial precipitation of Ni and Ni 3 P in the amorphous matrix. On heating to 500°C for 4 h, the hardness reached the maximum value of 12.3 GPa with a grain size of 33.1 nm and followed by gradual degradation above 500°C.