STUDIES ON ABRASIVE AND EROSIVE WEAR BEHAVIOR OF THERMAL SPRAYED COATINGS

Abstract

One of the most common causes for the poor performance of a number of engineering components is material degradation due to wear in the form of adhesion, abrasion, erosion and corrosion. The abrasive and erosive wear is encountered in a wide range of applications such as in the mining, cement, steel, coal, thermal power stations and other industries. The coating technology is one of the rapidly growing technologies such as weld surfacing, thermal spraying, PVD etc. for controlling wear. Among the various types of thermal-sprayed processes, flame and high velocity oxy-fuel (HVOF) spraying processes are cost effective and easily adaptable to the industrial processes. In present work, three types of coating materials namely, Ni-base (EWAC1004 EN), Co-base (EWAC 1006 EE) alloys and WC-Co- NiCr (MEC 1031 C) composite powders were used for the development of coatings on steel substrate. To improve mechanical (hardness), metallurgical (microstructural refinement) and tribological characteristics (abrasive and erosive wear behavior) of coatings various strategies namely, grain refinement by compaction and rare earth alloying (cerium oxide (CeO2) and lanthanum oxide and (La203)) and post spray heat-treatment of 1004 Ni-base coatings, dispersion and precipitation hardening by adding tungsten carbide and chromium carbides in 1006 Co-base alloy, were adopted. The metallographic study of all the coatings was carried out using SEM micrographs and Dewinter Material Plus 4.1 micrograph analyzer software for microstructural analysis. Normal hardness (Hv5) and microhardness (Hv0.1) of the coatings was measured using Vickers hardness tester. All the coatings were subjected to XRD analysis to identify various phases present in the coatings. Elemental mapping of the rare earth modified coatings were also carried out to study the distribution of various elements in the coatings. The porosity (%) in the coatings was measured using micrographs taken at a magnification of 50x by point counting method according to ASTM standards (E 2109-01, E 562-05e1). The pin-on-disk abrasive wear tester (in which test sample was moved in spiral path against abrasive paper) was used for abrasive wear study while high temperature solid particle erosion tester was used for erosion study of coatings. Microstructure of 1004 powder coating in as-sprayed and compacted condition mainly showed average grain size of Ni-solid solute cells in the as-sprayed coating was approx. 28 pm while that in the case of compacted coating was approx. 18 pm. The grain refinement in the compacted coating is primarily due to deformation experienced iv