Study On High Temperature Oxidation-resistant Coating On TZM Alloy

TZM alloy is being considered as the prime candidate among various molybdenum-based alloys for application in the areas of aerospace, power generation, nuclear reactors, military industries and chemical industries because of its high melting point and strength, low linear expansion coefficient, as well as excellent corrosion resistance and high temperature mechanical properties. However, TZM alloy has a propensity to undergo rapid oxidation at high temperature in air, which restricts its practical applications. Therefore, oxidation-resistant aluminide coatings on TZM alloy are prepared by pack cementation technique and hot-dipping method.In this paper, the process of preparing aluminide coating on TZM alloy by using pack cementation technique and hot-dipping method had been studied, respectively. The microstructure, composition and composing phases of the alloyed layer were tested and analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD). The mechanical properties and oxidation behaviors were tested and evaluated, respectively. The results show that an average diffusion coating thickness of 130μm is achieved on each side of the TZM alloy surface after 12h holding at 1050℃. The coating is double-layered. The aluminide coating is found to be granular in nature, uniform and adherent. The phase constituent of the coating is Al5Mo, Al3Mo and Al4Mo. The hardness of aluminide coating is above 8000MPa. It is also found to be adequately resistant to oxidation after 800℃, 80h cyclic oxidation experiment. The results of hot-dipping aluminide coating on TZM alloy show that the coating contains outer pure aluminum layer and inner alloy layer, and the alloy layer is consisted of Al4Mo and Al5Mo intermetallic compound phase. Adding 0.3wt% amount of rare earth element Ce is helpful to improve coating microstructure. The thickness of alloy layer increases with the hot-dipping temperature and time. The coating is also found to be adequately resistant to oxidation after 800℃, 100h cyclic oxidation experiment.