Cold Metal Transfer cladding of wear and corrosion resistant coatings in engine applications

Abstract

Wear and corrosion are severe problems in gas and diesel engine components and to prevent these problems, number of solutions are available. In this thesis one of the possible solutions, cladding of engine components is studied with a state-of-the-art welding process, Cold Metal Transfer. CMT is a rather new and cost-effective method of welding and cladding with a limited heat input and a large variety of available materials. During this thesis, a great number of cladding tests with different cobalt-base alloy filler materials on different metallic base materials were run. These tests aimed to optimize the cladding parameters for a cored Co-alloy filler wire. Another region of interest was to optimize the tribological properties of the coatings in order to reduce friction coefficient and increase the wear resistance of the components. In this thesis, a powder feeder was used to spray particles into the melt pool during cladding. It was discovered that CMT is able to restrain problems traditional overlay welding pro-cesses exhibit: high heat input resulting in unwanted changes of the base material, which also leads to high dilution and large amount of spattering during the process. The to-and-fro movement of the filler wire reduces the heat input and the precise process control with mechanical droplet detachment reduces the amount of spattering greatly. The CMT-process optimization was successful for Co-base filler wire, and optimal param-eters were achieved by cladding tests and analyzation of the results. The optimization resulted in low-diluted (<5 %) Stellite-coating (450-500 HV1) with a proper fusion bond and a narrow Heat Affected Zone (HAZ).