SLIDING WEAR BEHAVIOR OF MARBLE DUST PRE-MIXED WITH NiCr COATINGS ON MILD STEEL SUBSTRATES AT ELEVATED TEMPERATURE

Abstract

In this research, microsized marble dust is spray-coated on mild steel substrates through a well-designed high-velocity oxy-fuel (HVOF) spraying route. For this, a standard spray set up Hipojet 2700 is used. Marble dust is an ornamental stone waste generated in huge quantities during the depletion and processing of ornamental stones to make them usable. Commercially available spray-grade NiCr powder is added with a proportion of 10% by weight in the marble dust prior to deposition to increase its flowability and adherence. The coating on the mild steel substrates is deposited with a spray distance of 200mm and a fuel (LPG) feed rate of 55-60g/min. Dry-sliding wear trials under controlled conditions on the deposited coatings are conducted as per ASTM G 99-05 using a tribometer capable of operating at a wide temperature range. A parametric analysis of the test results using MINITAB 18 software shows that the control factors such as sliding velocity, specimen temperature, sliding distance and normal load, in the declining sequence, are significant in affecting the specific wear rate (SWR) of the coatings. Based on this, further experimentations are carried out separately for a wider range of the sliding velocity and specimen temperature keeping all other factors constant to study their individual effects on the wear rate more precisely. The morphologies of the worn surfaces are studied to ascertain the possible mechanisms taking place during the wear process leading to coating mass loss.