Abstract
Ni-P-W alloy deposit on the mild steel substrate was obtained by the electroless process. Various thermal heat-treatment temperatures from 350 to 600°C for 4 h were performed on the coating to evaluate the effect of crystallization behavior and grain size on the mechanical properties. The microstructure at as-deposited and heat-treatment states were investigated by the X-ray diffraction (XRD) and transmission electron microscope (TEM). The hardness at all depths of the coating on the substrate could be acquired by the nanoindentation. 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. The Young modulus of the amorphous Ni-P-W coating showed a relatively low value of 195 GPa. However, for increasing the heat-treatment temperature accompanied with the grain growth, the Young modulus was enhanced to the maximum of 233 GPa and then decreased gradually with temperature. © 2004 Elsevier B.V. All rights reserved.