Ni-Mo-P coatings on thrust plate of a gear pump to enhance its mechanical,tribological,and corrosion resistance properties

Abstract

Thrust plate in an external gear pump is one of the most important element which aligns the rotating gears and prevents the leakage through lateral clearances between rotating and non-rotating surfaces. It acts as a sacrificing element and fails frequently under fluctuating load pressure condition. The present research aims at enhancing the relative mechanical and tribological properties of the sacrificial thrust plate through electroless Ni-Mo-P coatings. Molybdenum (Mo) concentration in the electroless bath were tested for their effects on surface morphology, hardness, phase formation, wear rate, and wettability. A hard and self-lubricating layer (Al, Ni, Si, and Mo phases) on the coated surface was indicated by the compositional analysis performed using EDS and XRD. Results show that the microhardness of the coated surfaces has increased significantly by 149.5% (maximum hardness ~ 183.45 HV_0.2) for 32 g L⁻¹ Mo concentration. With 32 g L⁻¹ Mo, the maximum coating thickness and water contact angle were 58 µm and 111°, respectively. The base material’s coefficient of friction was 0.5, whereas it was 0.25, 0.10, 0.06, and 0.03 for the samples made with 8, 16, 24, and 32 g L⁻¹ Mo concentration, respectively. Compared to the uncoated sample, the maximum decrement in corrosion rate was found to be about six to seven times in the coated sample (with 32 g L⁻¹ Mo). As a result, the developed coating surfaces provide hardness, lubricity, hydrophobicity, corrosion, and wear resistance simultaneously. The methodology of surface treatment can be used to modify the surface of critical hydraulic components having significant wear like in case of hydraulic cylinders.