STUDY ON HOT CORROSION RESISTANCE OF A NEW DIRECTIONAL SOLIDIFICATION Ni–BASED SUPERALLOY

The hot corrosion resistance of a new directional solidification (DS) Ni–based super-alloy DZ68 was studied and compared with K438 alloy. The results indicate that the microstructure of DZ68 alloy is more uniform than K438 alloy after heat treatment. There are small size carbides in the microstructure of DZ68 alloy after heat treatment, but there are big size carbides and a lot (γ+γ') eutectic in the microstructure of K438 alloy. The hot corrosion of DZ68 alloy is uniform, and the corrosion products are mainly (Ni, Co)Cr2O4 and Al2O3. More (Ni, Co)Cr2O4 exists in outer corrosion layer and more Al2O3 exists in inner corrosion layer. For the K438 alloy the hot corrosion is not uniform, NiO is the mainly corrosion product in outer corrosion layer and CrS is the main corrosion product in inner corrosion layer. Moreover, the segregation of Ti can induce segregation of other elements in the two alloys, which leads to a severe local corrosion of alloys. Under the same expermental condition, the corrosion resistance of DZ68 alloy is a little better than that of K38 alloy.