Investigation and Optimization of Tribological Behavior of Electroless Ni–B Coating at Elevated Temperatures

Abstract

Friction and wear characteristics of heat-treated (350 °C for 1 h) electroless Ni–B coating at different operating temperatures are investigated systematically in the present work. Load and sliding speed are also considered as the design variables. Mass loss and coefficient of friction are considered as the responses. The design variables are varied at three equally spaced levels. Taguchi’s L27 orthogonal array is used to carry out tribological tests on a pin-on-disk tribotester. Grey relational analysis is used to predict the optimal parametric setting to minimize mass loss and coefficient of friction. The optimal condition predicted by grey relational analysis is 500 °C operating temperature, 10 N load, and 60 rpm speed. Prior to tribological tests, coating characteristics are determined using energy-dispersive X-ray analysis, scanning electron microscope, and X-ray diffraction techniques. A globular surface morphology is exhibited by the as-deposited coatings. On heat treatment, the surface of the coating resembles a cauliflower. Coating microhardness is determined by Vicker’s microindentation technique. Heat treatment leads to a significant improvement in microhardness in comparison with as-deposited coatings due to precipitation of crystalline and hard boride phases of nickel.