Long exposure test in air, conducted on super-lattice coatings at 850°C for 4,000 hours

Abstract

Purpose– The purpose of this study is to investigate the high-temperature behavior of newly developed high-impulse power magnetron sputtering system (HIPIMS) coatings and compare them to the standard TiAlCr system deposited on to a Ti–Al intermetallic alloy. The corrosion test was performed in air for 4,000 hours at 850°C.Design/methodology/approach– In this study, air oxidation test was performed at high temperature. Design and methodology is described in detail in the methodology section in the submitted manuscript. The test was carried out by discontinuous exposure of the three different systems produced by different deposition technique. The exposed samples were investigated using scanning electron microscope coupled with energy dispersive X-ray spectroscopy. The exposed samples were investigated from the surface and cross-sections.Findings– The performed study shows that HIPIMS coatings had a much better oxidation resistance at a high temperature than that offered by the standard physical vapor deposition (PVD) system. HIPIMS costing developed Al–Cr oxide on the surface; however, cracks and detachments were found at the interface between the coating and the substrate. TiAlCr coating spalled off from the material due to the critical thickness reached; moreover, high brittleness and lack of adherence were found. Due to poor oxidation resistance, TiAlCr coating was discarded from the test after 3,000 hours of exposure.Originality/value– The work performed in this study was designed for 4,000 hours oxidation at 850°C. The long-term exposures are not commonly met in the research work due to the cost and time. The work clearly shows differences between new type of coatings and standard PVD system applied on TiAl lightweight alloy.