The lack of oxidation resistance of titanium alloys when exposed to high temperatures greatly limits its application. This paper uses the inter-diffusion and mutual reaction of the interface during the 800°C cyclic oxidation process to design a special double-layer nitride coating, which can last for 200 hours in the air at 800°C, and no significant changes will occur after 40 cycles. Cracking or delamination will not form obvious oxide film. The coating system has the potential for large-scale industrial production.
Due to the low density, high specific strength and excellent corrosion resistance of titanium and titanium alloys, they are widely used in aero-engine gas turbines (such as fan blades, compressors, etc.), automotive industry and medical implants. It is well known that increasing the inlet temperature of a gas turbine can increase engine efficiency, thereby improving fossil fuel efficiency. However, titanium alloys have insufficient oxidation resistance when exposed to high temperatures, which greatly limits their applications. In many applications, especially in the design of aeroengines, people hope to use titanium or its alloys at higher temperatures, but the threat of oxidation or fire remains a long-standing challenge.
A latest joint study from the University of Manchester and Manchester Metropolitan University in the United Kingdom designed a special double-layer nitride coating by using the inter-diffusion and mutual reaction of the interface during the cyclic oxidation process at 800°C to adjust the coating and The thermal mismatch strain between the substrates provides a new design approach for alloy coatings with excellent performance.
In this work, the researchers used magnetron sputtering technology to prepare a Mo transition layer (300 Nm) on the surface of Ti and Ti6Al4V alloys. Using the inter-diffusion and mutual reaction of the interface during the cyclic oxidation at 800°C, a layered nitride coating system composed of SiAlN top layer, TiN0.26 and Ti5Si3 mixed phase intermediate layer and Ti-Mo solid solution is formed, which makes it more Strong diffusion bonding and excellent oxidation resistance. Through research, it is found that the new TiN0.26 intermediate layer exhibits adaptive integration through mechanical twinning, thereby adjusting the thermal mismatch strain between the coating and the substrate. The coating will not crack, peel and oxidize after being circulated and oxidized in the air at 800°C for hundreds of hours (>40 times).
In general, the double-layered titanium nitride coating of this study, due to mutual diffusion and mutual reaction, the layered nitride coating system exhibits enhanced adhesion after thermal exposure, and it can be adapted to a wide range of applications. Thermal cycle (up to 200 hours in the air at 800°C, 40 cycles), there will be no obvious cracking or spalling, and no obvious oxide film will be formed. This SiAlN coating containing Mo intermediate layer can also be used in other titanium alloys, even γ-TiAl intermetallic compound alloys. In addition, due to the scalability and relatively low cost of magnetron sputtering technology, the coating system has the potential for large-scale industrial production, and it also has potential application prospects in coatings in the field of medical implants.
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