During the induced codeposition of Ni and W, the deposition rate of Ni is faster than that of W. Therefore, as the electroplating proceeds, the relative concentration of Ni ions in the plating bath continuously decreases, leading to a corresponding reduction of the Ni content in the deposited coating, thereby forming a compositionally graded Ni-W alloy. By calculating the ratio of consumed Ni to the initial Ni in the bath, the electrolytic depth of the plating bath is obtained, which affects the compositional variation range within the coating. In this study, multilayer graded alloys were fabricated by sequentially electrolyzing multiple identical plating baths containing 5 g L^-1 nickel sulfate hexahydrate to an electrolytic depth of over 75%. In the single-layer graded Ni-W alloy, the W content gradually increases from 30.58 wt.% to 46.60 wt.%, accompanied by a transition in crystal structure from a crystalline to an amorphous state. Potentiodynamic polarization measurements, high-temperature and high-pressure corrosion tests, and copper-accelerated acetic acid salt spray (CASS) tests were conducted on the uniform alloy, single-layer graded alloy, as well as 4-layer and 8-layer graded alloys. The results indicate that the corrosion resistance of the graded alloys is significantly improved compared to the uniform alloy. Furthermore, multilayer alloys exhibit higher corrosion resistance than the single-layer alloy; however, further increasing the number of layers yields marginal improvement, with the 4-layer and 8-layer graded alloys showing similar performance. Specifically, the corrosion potential of the 4-layer graded Ni-W alloy in a 3.5 wt.% NaCl solution is -430 mV (vs. SCE), with a corrosion current density of 2.625 μA cm^-2. Its annual corrosion rate in the high-temperature and high-pressure corrosion test is 0.1306 μm year^-1, and rust spots only begin to appear after 120 h in the CASS test. After heat treatment at 500 °C, the hardness of the alloy reaches 1138 HV. Compared to the uniform alloy, it exhibits a lower coefficient of friction; after 30 min of rotary wear testing under a normal load of 100 N in a water medium, the mass loss is 0.0159 g, representing only 18.93% of the mass loss observed for the uniform alloy. This research also provides a novel multilayer alloy preparation strategy for other systems, effectively enhancing their corrosion resistance and mechanical properties.

Gradient alloy; multilayer Ni–W alloy ; Corrosion; wear