A study on aluminide and Cr-modified aluminide coatings on TiAl alloys by pack cementation method

The halide-activated pack cementation method was utilized to deposit a suitable coating on TiAl to ensure its oxidation resistance. TiAl alloys were coated by two different pack cementation processes with simple aluminide coating and Cr-modified aluminide coating. The coatings formed on the TiAl alloyed with Nb and Or were thicker and tougher than those formed on the non-alloyed TiAl. The TiAl3 layer formed on the TiAl alloyed with Nb and Cr had much better cyclic oxidation resistance than that formed on the non-alloyed TiAl. This is attributed to a change in the crystal structure of the TiAl3 from the brittle tetragonal DO22 to the ductile cubic LI2 by addition of a small amount of Cr and Nb. The Cr-modified aluminide coating on the TiAl alloyed with Nb and Cr exhibited excellent cyclic oxidation resistance due to formation of the Al67Ti25Cr8 phase as the coating layer. (C) 2000 Published by Elsevier Science S.A. ALI rights reserved.