Abstract
The electroless Ni-P-W coatings were deposited on the mild steel in the alkaline solutions. The compositions of Ni-P-W and Ni-P coatings were evaluated by electron probe microanalysis. The effect of thermal cycle at 400 and 450 °C on the crystal of the electroless deposit structure was studied by X-ray diffraction (XRD). The thermal stability of electroless Ni-P and Ni-P-W coatings with the identical phosphorus content was analyzed by differential scanning calorimetry. With similar precipitated Ni 3 P in both heat-treated Ni-P and Ni-P-W films, the tungsten addition into the nickel-phosphorus based coatings effectively increases microhardness and thermal stability. After eight times of thermal cycling test at 400 °C, the XRD analysis shows that Ni-P films have completely crystallized and the hardness is degraded to a lower value. On the contrary, the Ni-P-W films have not completely crystallized and thus a high value of hardness can be retained without appreciable degradation. © 2003 Elsevier B.V. All rights reserved.