Abstract
Binary Ni-P and ternary Ni-P-Cr alloy coatings were fabricated by the RF magnetron sputtering technique with dual targets of electroless nickel alloy as well as an additional element metal. The as-deposited Ni-P and Ni-P-Cr coating exhibited amorphous structure. The thermal property of coating was investigated by the annealing test for 4 hours and also by cycling test for 30 minutes in N2 atmosphere at 400 and 450C. The related mechanical properties were evaluated by Knoop microhardness test, and the measured microhardness was employed to evaluate the thermal stability of the binary and ternary alloy. The microhardness was 1250HK and 1380HK for Ni-P alloys at 400C and ternary Ni-P-Cr at 450C, respectively, after 4 hours annealing. For cycling test over 8 times cycles at 400 □C, the microhardness of Ni-P-Cr deposit was 1200 HK, in which full recrystallization of Ni3P precipitation was not yet completed. To evaluate the influence of Cr doping in Ni-P deposit, the differential scanning calorimeter (DSC) analysis was employed to characterize the temperature of phase transformation in the Ni-P-based coatings, including binary Ni-P, ternary Ni-P-Cr and Ni-P-W. Crystallization behavior in binary and ternary Ni-P-based coatings was quite distinct due to the addition of Cr and W. Microhardness test 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 characteristic with the tungsten for the ternary Ni-P-based system. Strengthening mechanism in sputtered Ni-P-Cr and Ni-P-W deposits would also be discussed.