Improvement in the working life of a micro journal bearings with an electroless Ni–P coating

Abstract

The improvement of working life is the main purpose of this paper to evaluate the mechanical properties of the electroless Ni–P coatings of radial micro journal bearings. The study was carried out using different plating parameter combinations, namely, pH values of the plating solution (6, 7, and 8), deposition time (10, 20, and 30 min), and bath temperature (60, 80, and 95 °C). The structure, surface morphology, hardness, and wear resistance of the electroless Ni–P coatings were measured and analyzed. The optimum combination of plating parameters for minimum wear is a pH value of 8, deposition time of 30 min, and bath temperature of 95 °C. When the Ni–P film is annealed at 400 °C, the hardness, wear and surface roughness can get the best values of 960 HV, 0.1 mg, and 0.177 μm, respectively, and this is because the Ni–P coating has changed from an amorphous phase to a crystalline composite phase (Ni + Ni₃P) structure. However, as the annealing temperature continues to increase; the hardness, wear, and surface roughness begin to deteriorate. The coherent relationship of the crystalline composite phase is broken, the grains of the Ni–P coating will grow, and the tensile stress of the Ni–P coating will increase.