THE STRESS-CORROSION PERFORMANCE OF DIFFUSION-BONDED NICKEL-BASE ALLOYS

Excellent mechanical strength can be achieved in diffusion-bonded nickel-base alloys when approximately 0.01 mm of nickel is plated on the surfaces before bonding. However, rapid stress corrosion cracking (SCC) takes place in the bond line region when such materials are tested in high-purity water at 360-degrees-C. The failures are caused by the low concentration of chromium in the nickel-rich bond line region. Long-time high-temperature anneals to diffuse chromium into the bond line dramatically improve the stress corrosion resistance. Measurements of the local chromium in the bond line and separate tests of Ni-Cr binary alloys show that chromium contents approaching that of the bulk alloy are necessary to eliminate the cracking susceptibility.