Structure and Mechanical Properties of HVOF Sprayed (WC-Co+Co) Composite Coating on Ductile Cast Iron

Abstract

An investigation was conducted to determine the role of Co particles in the WC-Co coating produced with the High Velocity Oxygen-Fuel (HVOF) spraying on microstructure, mechanical and wear properties in a system of type: WC-Co coating/ductlile cast iron. The microstructure of the thermal sprayed WC-Co+Co coating was characterized by scanning electron (SEM) and transmission electron (TEM) microscopes as well as the analysis of chemical and phase composition in microareas (EDS, XRD). For analysis of the quality and adhesion of coatings, the scratch–test was applied. It was found that as a result of the HVOF spray of WC-Co powders with the addition of Co particles, the coatings of low porosity, high hardness, a very good adhesion to the substrate, compact structure with partially molten Co particles and finely fragmented WC particles embedded in a cobalt matrix, coming to the size of nanocrystalline sizes were obtained. Moreover, the results were discussed in reference to examination of bending strength considering cracking and delamination in the system of (WC-Co+Co)/ductile cast iron as well as hardness and wear resistance of the coating. It was found that the addition of Co particles was significantly increase resistance to cracking and wear behaviour in the studied system.

Keywords

• thermal spraying
• HVOF
• WC-Co coating
• wear resistant