Application of HVOF WC-Co-Cr coatings on the internal surface of small cylinders: Effect of internal diameter on the wear resistance

J Pulsford,F Venturi,Z Pala,S Kamnis,T Hussain

doi:10.1016/j.wear.2019.202965

Abstract

Due to the restrictions and mediocre performance of current methods of coating complex shaped parts in which line of sight processes currently struggle, the development of new coating methods is essential, with High Velocity Oxy-Fuel (HVOF) thermal spray coatings being a good candidate. In this study, a new compact High Velocity Oxy-Air Fuel (HVOAF) thermal spray torch designed to coat internal surfaces was traversed within cylindrical pipes of internal diameters (IDs) of 70 mm, 90 mm and 110 mm and a WC-10Co-4Cr coating was applied with a commercially available powder feedstock. Powder and coating microstructures were analysed using SEM/EDX and XRD. Fracture toughness and microhardness of the coatings were measured, and dry sliding wear performance was investigated at two loads: 96 and 240 N. It was found that the coating sprayed at 90 mm (medium ID) had a lower specific wear rates at both test loads due to the highest fracture toughness and microhardness; whereas, the coating sprayed at 110 mm (high ID) showed the highest specific wear rates at both low and high conditions due to poor fracture toughness.

Highlights

The development of an alternative method of coating complexshaped parts in which line of sight processes are limited is currently essential, due to the regulatory limitations (REACH legislation, Regulation (EC) No 1907/2006) restricting the use of currently used methods such as electroplated hard chrome (EHC)
The aim of this work is to demonstrate that WC-Co-Cr High velocity oxyfuel (HVOF) thermal sprayed coatings with useful tribological properties can be applied on internal surfaces within cylinders of internal diameters (IDs) as low as 70 mm, as well as showing the potential effect of how changing the internal diameter affects these properties in order to assist future spray parameters optimisation
Spray torch developed by Castolin-Eutectic Monitor Coatings Ltd, (UK) in a setup allowing for the simulation of coating the internal surface of a cylindrical pipe with internal diameter of 70 mm, 90 mm and 110 mm

Summary

Introduction

The development of an alternative method of coating complexshaped parts in which line of sight processes are limited is currently essential, due to the regulatory limitations (REACH legislation, Regulation (EC) No 1907/2006) restricting the use of currently used methods such as electroplated hard chrome (EHC). The line of sight nature of thermal spray processes prevented their use in many applications, such as coating internal surfaces and complex shaped parts, due to the large dimensions and stand-off distance required. In order to mitigate these limitations, a new generation of thermal spray systems have been developed, in the form of spray torches with much smaller dimensions able to fit in narrower spaces andeffectively coat surfaces at much shorter stand-off distances [5]. This potentially enables the use of thermal spraying to coat internal surfaces in which non-line of sight processes like EHC were once required.

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