Precipitation-hardenable nickel-base alloys possess good strength@ ductility@ and corrosion resistance from cryogenic temperatures to above 1600' F. These properties are obtained through the addition of many alloying agents including chromium@ cobalt@ aluminum@ titanium@ molybdenum@ columbium@ boron@ and zirconium. Mechanical properties may be varied over a wide range through manipulation of the solution treating and aging procedures and alloy content. The principal strengthening phase is gamma prime (a precipitate based upon the NhAI compound)@ but its composition and kinetics will vary with alloy content and it may include titanium@ columbium@ and possibly molybdenum. Many other phases@ most notably the carbides@ are also found. Carbide-phase morphologies exert control over elevated-temperature ductility; however@ the morphologies and compositions of the carbides depend upon the alloy@ temperature of formation@ and prior history. As a result of the great strengths and complexities of the alloys@ welding and postweld heat treating have proved to be expensive problems. The chief difficulties are microfissuring (during welding) and strain-age cracking (during postwelding heat treatment). Porosity@ hot cracking@ and lack of fusion are also encountered unless extra precautions are taken.
BULLETIN 128-1968 history
1968BULLETIN 128-1968 WELDING OF PRECIPITATION-HARDENING NICKEL-BASE ALLOYS