Fabrication and characterization of the Ni-P-Al-W multicomponent coatings

Nickel-phosphorus-aluminum-tungsten (Ni-P-Al-W) multicomponent coating was fabricated by multi-gun sputtering technique with novel composite target design. Through X-ray phase identification, the coatings exhibited an amorphous/nanocrystalline feature in the as-deposited state, while the W and Ni crystallites and NiP precipitates were found for the heat treated Ni-P-Al-W coatings. The transforming of coating surface from smooth to wavy contour represented the phase evolution phenomenon by the crystallization and precipitation in the Ni-P-Al-W coating. The introduction of the alloying components of Al and W into Ni-P to form the multicomponent coatings gave rise to the increase in thermal stability and surface hardness of the Ni-P-based coatings. A peak hardness of 15.5 GPa was evaluated for the Ni-P-Al-W coating under 500 °C annealing. The nanocrystallites of Ni and W and the precipitation of NiP compounds were the strengthening mechanisms for the Ni-P-Al-W coatings. In addition, the incorporated Al in the coating dissolved in Ni and W crystallites to enhance the surface hardness through solid solution effect.