The effect of the aluminide coating on the thermal properties and oxidation resistance of Inconel 625 Ni-base superalloy

摘要

An investigation was conducted to synthesize βNiAl coating on the nickel based superalloy Inconel 625 in the low activity chemical vapor deposition process (CVD). The deposition was carried out for 8 hours at 1050℃ using the BPXpro3252 IonBond company equipment. Surface morphology and cross-section microstructure of the diffusion coating were studied and compared using an optical microscope, an X-ray diffractometer and a scanning electron microscope (SEM) equipped with an energy dispersive spectroscope. It was found that 29 μm thick aluminide coating consisted of two layers: an outer one and the inner interdiffusion one. The outer layer consisted of the βNiAl phase. The inner one consisted of the βNiAl phase with chromium, molybdenum and niobium carbides (M_(23)C_6 and MC type) inclusions. Outer layer hardness was about 564 HV0.002 while interdiffusion layer hardness was about 725 HV0.002. Thermal diffusivity of Inconel 625 superalloy with and without coating was measured using a NETZSCH model 427 laser flash diffusivity apparatus. The thermal diffusivity measurements were conducted in the argon atmosphere at the temperature interval 20 - 1200 ℃. Thermal diffusivity of the uncoated Inconel 625 Ni-base superalloy at the room temperature is about 2 mm~2/s, while for the coated superalloy thermal diffusivity is about 2.8 mm~2/s. The increase of the temperature from 20 to 1200 ℃ leads to the increase of the thermal diffusivity of the coated sample from 2.8 to 5.6 mm~2/s. Cyclic oxidation tests for both coated and uncoated superalloys were performed at 1100℃ for 1000 h in the air atmosphere. The aluminized samples exhibited a small mass increase and the a- AI_2O_3 scale was formed during the oxidation test.