Incorporation and Characterization of Graphene Derivatives in Thermal Sprayed Coatings

Licentiatavhandling, 2025

This thesis explores the incorporation and characterization of graphene derivates in thermal spray coatings to enhance wear performance. Graphene nanoplatelets (GNP) and graphene oxide (GO) were integrated into alumina (Al3O2) and WC-Co-Cr matrices respectively, aiming to improve tribological performance and understand the mechanisms to their function as solid lubricants to improve the wear resistance. The study is based on three key scientific questions: the retention and functionality of GNP during wear testing, the effectiveness of molecular-level mixing in tailoring GO coatings on metal powders, and the viability of GO-coated powders made by molecular-level mixing in wear-resistant coatings produced by thermal spraying.

Synchrotron-based techniques, such as Scanning Transmission X-ray Microscopy (STXM) and X-ray Absorption Near Edge Structure (XANES) were employed and revealed that GNPs retained their structure after thermal spraying process. The experiment setup allowed the rotation of the sample relative to the X-ray beam, enabling the detection of GNPs aligned parallel to the sliding direction. After wear testing, amorphization of both the alumina matrix and GNPs was observed, indicated by an increased carbon content within the amorphized alumina regions.

A molecular-level mixing process was developed to coat GO onto metal powders, demonstrating the ability to control coating characteristics through variations in APTES and GO concentrations. This controllability was reflected in both the coverage and thickness of the GO coating on the metal powders, highlighting the process’s capability to tailor the coating properties to meet specific application requirements.

The GO coating process was successfully applied to WC-Co-Cr porous powders, achieving GO deposition on both external surfaces and within the internal pores. These GO-coated WC-Co-Cr powders were then processed via thermal spraying, resulting in coatings with enhanced performance, including reduced porosity, lower coefficients of friction, and increased hardness. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the retention of GO in both the sprayed coatings and wear tracks, even under different surface preparation conditions.