Thermally induced bond failure of electroless nickel/IVD aluminum coatingsdeposited on steel

Experiments were conducted to investigate methods to improve the bond of an electroless nickel/ion vapor deposited (IVD) aluminum coating applied to a steel substrate for use at an elevated temperature of 482 degrees C. Sampl es were prepared by coating steel panels with columnar IVD aluminum followe d by the application of electroless nickel from a sodium hypophosphite plat ing solution. Surface treatment of the underlying aluminum was varied by ph ysically compacting the columnar structure of the aluminum by glass-bead pe ening and/or grit blasting. The cooling atmosphere after application of the aluminum was also investigated by using nitrogen to reduce the potential o f aluminum oxidation prior to application of the electroless nickel coating . Results show that at elevated temperatures atomic diffusion takes place c reating voids that eventually lead to failure of the electroless nickel coa ting. Bond failure can be retarded, but not eliminated, by using a nitrogen atmosphere to prevent oxidation of the IVD aluminum and by retention of th e aluminum columnar structure before overcoating with electroless nickel. ( C) 2000 Elsevier Science S.A. All rights reserved.