High Temperature Oxidation Resistance and Degradation Mechanism of Al-Si Coatings on Nickel-Based Superalloy at 1000 ℃
Si-modified NiAl coating has been studied by researchers due to its good performance in high temperature corrosive environment,but the effect of Si content on the high temperature oxidation resistance of the aluminide coatings has been seldom studied.To figure out this issue,three modified NiAl coatings with different Si contents were prepared by varying the Si contents 8wt％,17wt％and 30 wt％in the slurry.Phase structures and microstructures of the simple NiAl coatings and three Si-modified NiAl coatings before and after oxidation were analyzed by XRD,SEM and EPMA,etc.The results show that the δ-Ni2Al3 and β-NiAl are the primary phases of the four aluminide coatings.Si mainly locates in the upper zone of the Si-modified NiAl coatings in the form of silicides as CrSi2,Cr5Si3 and Ni2Si.After oxidation at 1000 ℃ for 500 h,the simple NiAl coating has the maximum mass gain of 1.93 mg/cm2,while the Si-modified NiAl coating with Si content of 8wt％has the smallest mass gain.The dopant of Si into NiAl coatings can promote the formation of protectiveα-Al2O3 film,retard the outward diffusion of refractory metal elements and improve the surface quality of the oxide film,resulting in reduced oxidation rate.However,the addition of Si reduces the Al content on the surface layer of the coating and may make the coating insufficient of β phase to maintain the selective oxidation of Al in the later period of long-time oxidation.Therefore,when the Si content is 8wt％,the Si-modified NiAl coating possesses the best oxidation resistance.
slurry methodAl-Si coatinghigh temperature oxidationstructure
NETL
NSTL
万方数据
