Wetting and Interactions Between Selected Ceramics and Ni-Base Braze Alloys

Abstract

Wetting tests were performed with two commercial Ni-base braze alloys on a selection of ceramic materials in vacuum between 1000 and 1150°C. The two alloys were Ni-5Si-3B and Ni-7Cr-5Si-3Fe-3B(wt%). The ceramic substrates included Al2O3, Si3N4, TiC/TiN coated Si3N4, SiC, a SiC/SiC CVI composite and a TiC/TiN coated SiC/SiC CVI composite. In one experiment a thin foil of Ti was placed between the braze alloy and the ceramic in an attempt to promote wetting. With Al2O3, Si3N4 and TiC/TiN coated Si3N4 there were no observable reactions between braze and substrate, the wetting was poor (contact angles Θ ≥ 110°) and the braze drops detached themselves after solidifying. With a thin foil of Ti between the braze alloy and the Si3N4 ceramic a restricted reaction was noticed and wetting occurred (Θ≈70°). The braze detached itself but in this case this was due to fracture through a brittle reaction product. The bulk SiC substrate exhibited a strong chemical reaction with the braze. The SiC/SiC composite exhibited “good” wetting but this could be explained by the open porosity of the material and a penetration of the braze alloy. On the two SiC/SiC materials the braze alloy adhered to the ceramic and reaction could be observed. Wetting tests were also performed on the superalloys, Hastelloy X and Incoloy 909; both exhibited satisfactory wetting behaviour.