Invited Speaker

Assis. Prof. Shaoyun Zhou

Nagoya University

Title: Fabrication of GaN (gallium nitride) coatings on stainless steel via kinetic spray method

Profile:

Dr. Shaoyun Zhou was born in 1996 in Lanzhou, Gansu Province, China. She earned her Ph.D. in Engineering from Tohoku University, Japan (September 2022), and has served as a Designated Assistant Professor in the Department of Materials Process Engineering at Nagoya University since October 2022. Her research mainly focuses on ceramic cold spray, aerosol deposition, femtosecond-laser processing, joining of dissimilar materials and porous materials. Over the past four years, she has secured and led several competitive projects, including a Japan society for the promotion of science (JSPS) Grant-in-Aid for Early-Career Scientists, the Toyota Scholar Program, research grants from Epson, the Japan Aluminium Association research grants, and Japan science and technology agency’s (JST’s) “Next-Generation Researcher Challenging Research Support Project”. She Received the 2023 Morimura Houmei Foundation Incentive Award from the Japan Fine Ceramics Association. She is also listed as an inventor on one Japanese and three Chinese invention patents.

Abstract:

Ceramic materials are inherently characterized by high melting points and brittleness, which pose manufacturing challenges in diverse applications. Kinetic spray methods, such as Cold Spray (CS) and Aerosol Deposition (AD), have emerged as promising techniques for depositing coatings without significant chemical reactions or phase transformations. However, it has been established that native oxide layers impede metallurgical bonding in kinetic spraying of metallic materials. Due to inherent challenges and the limited research on brittle ceramic particles, a consensus on the impact of oxide layers on ceramic coating bonding remains elusive. In this study, agglomerated GaN powders, featuring primary particle sizes of tens of nanometers and agglomerate diameters of several microns, were used to successfully fabricate nanoporous GaN coatings on stainless steel substrates via Low-Pressure Cold Spray (LPCS). During high-velocity particle impact, native oxide films on both particles and substrates were removed, followed by the generation of a new oxide layer at the particle-substrate interface. X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) were employed to characterize interface oxidation, clarifying chemical stability and oxidation types. Local heteroepitaxy near the interface, associated with newly formed gallium oxide, promoted coating formation. The GaN coatings exhibited boundary amorphization and high dislocation density, attributed to high strain rates during particle impact. Thus, bonding mechanisms between nitride ceramic particles and stainless steel substrates can be attributed to newly formed interfacial oxidation and boundary amorphization. To mitigate environmental interactions, the Aerosol Deposition (AD) technique was also explored as an alternative kinetic spraying method for GaN coatings. Preliminary results indicate that successful GaN deposition through AD significantly depends on optimized process parameters, particularly those achieving high particle velocities. Consequently, dense and crack-free GaN layers were successfully fabricated at room temperature using helium as the process gas. Ongoing studies aim to investigate internal interfaces and clarify underlying bonding mechanisms. In conclusion, this research demonstrates the feasibility and effectiveness of kinetic spray methods for fabricating GaN coatings. The insights gained not only validate this novel approach for GaN deposition but also provide valuable guidance for kinetic spraying of a broader range of ceramic materials.