An investigation on the development and wear performance of chromium-MWCNTs transformed HVOF sprayed nano-WC-CoCr coatings

Abstract

This research work presents a detailed study of development and wear performance of high chromium and multiwalled carbon nanotubes (MWCNTs) reinforced nano-WC-CoCr based coatings. The CoCr binder matrix was modified by increasing the Cr element (10 & 16 wt%) and keeping the fixed proportion of MWCNTs (2 wt%). The coating deposition was done by using Praxair JP-5000 HVOF spray gun with optimized process parameters. SEM, EDS, and XRD were performed to study the surface morphologies, elemental compositions and phases present in the feedstock powders and developed coatings. Micro-hardness, percentage porosity, surface roughness and indentation fracture toughness of the deposited coatings were evaluated. The solid particle erosion and reciprocating abrasive wear testing were conducted in order to evaluate the wear resistance of modified coatings. The worn-out surfaces obtained after erosion testing revealed the removal of material by microcutting and ploughing of CoCr binder matrix, pull-out and fracturing of nano-WC grains. The SEM images revealed the formation of wear tracks on the coatings surfaces, which were caused by the micro-cutting and sideways displacement of CoCr and nano-WC grains during the reciprocating abrasive wear testing. The addition of Cr in higher proportion along with MWCNTs significantly enhanced the fracture toughness of nano-WC-CoCr coating. The improvement in fracture toughness may be attributed to increased metallic binder contents along with the bridging and gluing of splats by MWCNTs. The nano-WC-CoCr coating with 10 wt% Cr + 2 wt% MWCNTs exhibited the enhanced wear resistance in all the test conditions as compared to the other coatings.