Correlation of the Particle Behavior, Microstructure and Phase Evolution During the Optimization of HVOF Sprayed WC-12Co Coatings by Means of DoE

Abstract

Abstract Due to their outstanding properties, WC-Co cermet coatings are widely used in the field of wear protection. It has been reported by many researchers, that their macroscopic and tribological behavior is largely determined by the process conditions and the feedstock powder characteristics respectively. Although the manufacturing route for high velocity oxy fuel(HVOF)flame sprayed WC-Co coating is in an advanced state, there is still a lack of knowledge about the complex relationships between the thermo-kinetic in-flight particle behavior, the microstructure formation and the phase evolution during the spray process. However, a fundamental understanding is not only necessary to provide coatings with optimized properties, but also to meet economic aspects with regard to the HVOF process. In this study the dependencies between the HVOF process parameters and characteristics (chamber pressure, thermal energy transferred to the coolant), the thermo-kinetic in-flight particle behavior (temperature, velocity and the spray particle size) with the microstructure formation (carbide content and size, free mean path of the binder phase, porosity), thermal phase reactions and the mechanical properties (hardness, toughness, roughness) were investigated. Statistical design of experiments (DoE) is utilized to enable a systematic analysis of several influencing factors along with their interactions on the coatings properties and to find optimized spray conditions. X-ray diffraction (XRD) applying high-energy synchrotron radiation has been used, not only to provide a phase analysis in deeper regions of the coating structure, but also to achieve more detailed information on phases which are not or hardly detectable by XRD using a conventional X-ray laboratory source. In addition the sliding and abrasive wear properties at optimized coating properties are studied.