Crystallization behaviors and microhardness of sputtered Ni–P, Ni–P–Cr and Ni–P–W deposits on tool steel

The Ni–P-based coatings, including binary Ni–P, ternary Ni–P–Cr and Ni–P–W, were fabricated by the RF magnetron sputtering technique with dual target of electroless Ni–P alloy and a third metal element. To evaluate the influence of the doping element in Ni–P deposit, differential scanning calorimeter (DSC) analysis was employed to characterize the temperature of phase transformation. The phase transition during thermal evolution under heat-treatment was analyzed by X-ray diffractometry (XRD). Crystallization behavior in binary and ternary Ni–P-based coatings was quite distinct due to the addition of Cr and W. Microhardness tests indicated that the sputtered Ni–P–Cr and Ni–P–W coatings exhibited superior hardness and excellent thermal stability than the Ni–P coating. In addition, chromium exhibited compatible thermal characteristics with the tungsten for the ternary Ni–P-based system. The strengthening mechanism in the sputtered Ni–P–Cr and Ni–P–W deposits is also discussed.