The effect of Pt contents on the surface morphologies of Pt-modified aluminide coating

Pt-modified aluminide coatings were prepared with varying thicknesses of deposited Pt on the CM247LC substrate by heat treatment and a single step, high-activity pack aluminizing process. Following the heat treatment, the thickness of the interdiffused areas varied according to the thickness of the deposited Pt. In addition, deposited Pt thickness influenced roughening of the surface. Because the surface roughness is affected by two factors: internal stress release and unequal mass flow between Pt and Ni. After pack aluminizing, the Pt-modified aluminide coating, with deposited Pt thicknesses ranging from 4 to 12 µm, consisted of two-phase, one-phase, and interdiffusion regions. The two-phase layer grew thicker as the thickness of the deposited Pt increased. Roughening of the surface also increased as the thickness of the deposited Pt increased from 2 to 8 µm. However, surface roughening of Pt-modified aluminide coating fabricated with 12 µm thick deposited Pt was lower than specimens deposited with 4 and 8 µm Pt thicknesses as a result of increased nucleation and growth of the PtAl 2 phase in the two-phase layer.