Hot Corrosion Behavior and Its First Principle Calculation of TiN/Ti Coating on TC4 Substrate
When helicopters take off and land in the desert areas,the compressor blades of titanium alloys are impacted by sand particles. TiN/Ti coating is used for the protection of compressor blades against erosion due to its excellent performance. During service of the aircraft,chloride ions in humid coastal environment,S in the industrial atmosphere and impurities generated from fuel combustion could cause hot corrosion to the compressor blades and affect the comprehensive performance of the compressor. Currently,there are relatively abundant researches on the erosion resistance of TiN/Ti coating,but the research of hot corrosion behavior of TiN/Ti coating is limited. The study on the coupled behavior of hot corrosion and erosion is an important basis for the overall evolution of TiN/Ti coating. In this work,the TiN/Ti coating was prepared on Ti6Al4V (TC4) titanium alloy substrate by Metal Vapor Vacuum Arc (MEVVA) and Filtered Cathodic Vacuum Arc (FCVA) process,and the hot corrosion experiment of intact TiN/Ti coating and eroded TiN/Ti coating were carried out at 300 ℃/120 h. The corrosion medium was 95％Na2SO4+5％NaCl. The erosion experiment was carried out with irregularly shaped SiO2 particles. The erosion angle was 45°,the erosion speed was 130 m/s,and the sand supply rate was 6.4 g/min. The hot corrosive microstructures of the intact TiN/Ti coating and eroded TiN/Ti coating were analyzed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). After the hot corrosion of TiN/Ti coating,the droplets were oxidized and corroded to be loose,and the morphology of the intact area of the TiN/Ti coating remained almost unchanged. The corrosion rust was produced at the cutting edge of the TiN/Ti coating,and the columnar structure of the TiN/Ti coating of the corrosion rust area was blurred,and granular corrosion products and irregular corrosion pits gradually appeared,eventually leading to bulging and cracking. After erosion,the erosion pits on the surface of the TiN/Ti coating destroyed the integrity of the coating,the erosion intensified the tendency of corrosion,the coating around the erosion pits was more prone to corrosion than that of non-erosion area and the corrosion products were mainly oxides containing Ti element. In addition,the hot corrosion behavior of TiN coating was calculated based on the first principle. Three first principle corrosion calculation models were established,such as intact TiN coating,TiN coating with pores and Ti droplets on the surface. Among them,pores and droplets were the common defects of TiN coating. It was found that during the hot corrosion process,the electron clouds of O in SO42-and Ti in the intact TiN coating and Ti in the droplet were in contact,and there was a tendency of charge transfer and bonding,specifically Ti losing electrons and O gaining electrons. The corrosion mainly occurred between O in SO42-and Ti,which was consistent with the experimental result of hot corrosion. The results of the first principle calculation can reflect the effect of defects such as droplets and holes on the hot corrosion behavior of TiN coating from the microscopic point of view,which can provide a theoretical basis for analyzing the mechanism of hot corrosion of the TiN/Ti coating.
TiN coatinghot corrosion behaviorerosionfirst principlecharge transfer
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维普
