Effect of post treatments on microstructure and mechanical properties of zirconium oxide coatings produced by plasma spraying method

ABSTRACT MSc. Thesis EFFECT OF POST TREATMENTS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF ZIRCONIUM OXIDE COATINGS PRODUCED BY PLASMA SPRAYING METHOD Görkem DEĞİRMENCİ Kastamonu University Graduate School of Natural and Applied Sciences Department of Materials Science and Engineering Supervisor: Assoc. Prof. Dr. Serkan ISLAK Abstract: In the coatings produced by the atmospheric plasma spray (APS) method, high porosity and poor bonding between the coating layer and the substrate occur. The porosity from the pavement not only reduces the mechanical properties of the coating but also lowers the corrosion resistance. This is caused by the movement of the corrosion medium in the micro channels formed at the coating/substrate interface. In this study, the effects of heat treatment on the microstructure and mechanical properties of ZrO2 - 8% Y2O3 coatings produced on AISI 316L by APS method were investigated. Ceramic coatings were heat-treated at 900 °C, 1000 °C and 1100 °C. Microstructure and phase composition of coatings were investigated by scanning electron microscopy (SEM), X-ray diffractogram (XRD), energy dispersive spectroscopy (EDS). The wear characteristics of the coatings were tested with the ball on disk method in the wear tester with reference to ASTM G133 test standards. According to SEM studies, the maximum pore formation is seen in the non-heat-treated sample, and the pore quantity is decreased as the heat treatment temperature increases. However, it is an inevitable result that the heat treatment negatively affects the interfacial bonding. It was determined from the XRD analysis that t-ZrO2 and c-ZrO2 phases were formed in the coating microstructure. According to the hardness results, the hardness of the untreated coating was 912HV0.2, while the highest hardness was 1045 HV0.2 at 1100°C. According to the wear results, the coefficient of friction and wear rates decreased with increasing heat treatment temperature. It has been determined that the heat loss of the exposed surfaces is the most lost by the SEM photographs and the losses are decreased with the increase of the heat treatment temperature. Key Words: plasma spray, ZrO2, post treatment, surface coating 2019, 52 pages Science Code: 91