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Item Development of binary and ternary chromium, aluminum, carbon thin film coatings for hot corrosion prevention(Montana State University - Bozeman, College of Engineering, 2015) Aw, Lik Ming; Chairperson, Graduate Committee: Roberta AmendolaIncreasing the operating temperature of high temperature energy conversion systems is often very desirable in order to maximize their corresponding efficiencies. Materials selected for high temperature applications must therefore incorporate associated considerations such as creep strength, high temperature corrosion resistance, and thermal fatigue. Hot corrosion is a form of accelerated high temperature oxidation associated with the deposition of salt such as sodium sulfate (Na 2SO 4) on metals or their protective oxide surfaces. Severe corrosion develops when Na 2SO 4 reacts with metals to form eutectic (low-melting point) compositions on the surface of the metal at 700 °C (Type II Hot Corrosion) or when the surface has been wetted by molten Na 2SO 4 at 900 °C (Type I Hot Corrosion). This phenomenon reduces the useful life of materials such as nickel alloys used in high temperature gas turbines for aircraft and marine applications. In this study, a variety of binary and ternary thin film coatings using chromium, aluminum, and carbon as base elements were deposited onto Ni-201 alloy and investigated as a function of exposure to hot corrosion environments. The coatings were deposited using a magnetron sputtering system and were approximately 1.5 microns in thickness. Prototypical Na 2SO 4 was applied to the samples before exposing them for up to 250 hours in an air/SO 2 gas mixture at 700 °C and 900 °C, which simulates Type II and Type I Hot Corrosion, respectively. It was determined that all coatings reduced the specific mass gains (corrosion rates) of the samples when compared to that of an uncoated sample, indicating that they provided protection against hot corrosion. For Type II Hot Corrosion, binary Cr - Al and ternary Cr - Al - C thin film coatings held up after 250 hours of exposure; whereas the other two coatings had completely disintegrated. For Type I Hot Corrosion, all thin film coatings utilized in the study had completely dissolved after 50 hours of exposure. It was suggested that the two most effective coating materials, Cr -Al and Cr - Al - C coatings should be used for future testing and that their thicknesses should be increased to help provide better protection against Type I Hot Corrosion.Item A fundamental study of hot corrosion and interdiffusion of chromium, aluminum, and silicon coatings on a nickel-201 substrate(Montana State University - Bozeman, College of Engineering, 2014) Gill, Zachery Edward; Co-chairpersons, Graduate Committee: Paul E. Gannon and Roberta AmendolaModern turbine engine systems require increased efficiency and durability. To achieve these goals, high-temperature materials with high-strength, low-cost and non-strategic compositions are needed. In advanced turbine applications, combustor liners, blades and vanes are exposed to corrosive combustion byproducts, such as alkali salts, at temperatures up to ~1700°C with high gas velocities, entrained particulates, and other foreign objects at pressures of up to 3 MPa (30 atm). These extreme conditions can drive a dangerous phenomenon known as "hot corrosion", an accelerated form of oxidation that occurs when metals and metal alloys are heated in the temperature range 700-900°C in the presence of alkali salts. An increased understanding of the fundamental behaviors of common high temperature alloys and their degradation mechanisms is therefore critical for the production of reliable components. In this study a model substrate, Nickel 201, was coated on one side with Cr, Al, or Si thin films (~1 micron) via magnetron sputtering physical vapor deposition (PVD). Uncoated and PVD coated samples were then exposed to laboratory air at 700°C and 900°C and to an environment similar in composition to atmospheres found in post combustion turbine systems, comprised of air/SO 2 gas mixture, at 700°C. The exposures were conducted over time intervals observing coating-substrate interactions and surface oxide development. Identical samples were subjected to the same exposures with addition of a deposit of sodium sulfate (Na 2SO 4), a model alkali salt. Sample mass gains were recorded and resulting oxide compositions assessed as a function of exposure time using microscopy techniques on sample surfaces and cross sections. The development of intermetallic species was determined by X-ray diffraction. At 700°C, coated and uncoated samples displayed different oxidation behaviors. Under laboratory air, no hot-corrosion occurred. While at 700°C in air/SO 2 exposures, evidence for hot corrosion on deposited samples was observed. When sodium sulfate was introduced at 900°C, coated and uncoated samples displayed rapid corrosion consistent with hot corrosion. The oxidation processes and coating/substrate inter-diffusion phenomena are presented and discussed in the context of establishing basic approaches to improve the fundamental understanding of hot corrosion, and the protection mechanisms of high temperature materials.