Formation of Diffusion Aluminide Coatings on gamma-TiAl Alloy with In-Pack and Out-Pack Processes

摘要

In this investigation, Ti-48Al-2Nb-2Cr (at.%) alloy was aluminized by two kinds of pack cementation processes, in-pack and out-pack processes. In both methods, pack powder mixture consisting of 10 wt% Al, 5 wt% AlCl3, and balance Al2O3 was used to aluminize gamma-TiAl at 1000 A degrees C for 6 h. The coated samples were characterized by XRD and SEM. The results indicated that a single-layered TiAl3 coating by thickness of approximately 100 mu m was formed by the use of in-pack method, but a two-layered aluminide coating including an outer thin layer of TiAl3 with thickness of approximately 2 mu m and also an inner layer of TiAl2 with thickness of approximately 10 mu m was formed by out-pack process. In both methods, aluminide coatings with uniform structure free from any microcracks were formed on the surface of the substrates. The results showed that the flux of active aluminum atoms on the substrate surface in out-pack method is to be expected to be much slower than in-pack method.