Effects of Y modification on microstructure and growth mechanism of pack aluminizing coatings on Nb substrate

Abstract:

Y modified aluminizing coatings were prepared on pure Nb substrates by aluminizing in the pack mixtures with Y₂O₃ addtion. The effects of Y on the microstructure and growth mechanism of the coatings were studied. The results show that the Y has no obvious effect on the phase constitution of the coating and the grain morphology of NbAl₃ phase. With the increase of Y₂O₃ content in the pack mixtures, the Y content on the coating surface increases. After Y modification, the growth mechanism of the coatings is changed from being controlled by the intergranular diffusion of Al atoms to being controlled by the intragranular diffusion of Al atoms, which reduces the growth rate of the coatings and contributes to the formation of two kinds of silk textures (<010>//ND and<110>//ND) in the columnar crystal area of NbAl₃ phase.

Key words:Nb; Pack cementation; Aluminide coating; Reactive element effect