scope:

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.