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Columbium, chromium, cobalt and tantalum have been identified as metals vital to the aerospace industry. This investigation was undertaken to determine the effects of substitutions of other elements to maintain the properties of Alloy 718. The room and elevated temperature tensile properties, and the stress-rupture properties were examined for a series of 13 alloys with substitutions of molybdenum, tungsten, vanadium, titanium and boron for the reduced columbium. The substitution of molybdenum and tungsten and vanadium were unable to recover the properties of the original alloy. The structure and properties indicated that these additions did not alter the volume fraction of Y". Based on literature information, titanium and columbium additions were selected to substitute Y ' precipitation for the decreased Y" precipitation while maintaining the slow coarsening rate needed in Alloy 718. The result was an alloy with 3.89Cb + 1.27Ti, strengthened by both Y" and Y '. The hardening rates of the 3.89Cb + 1.27Ti alloy was comparable to an alloy with 3.2Cb, indicating a similar precipitation sequence. Microstructural analysis as a function of the aging temperature indicated that the Y ' phase precipitated first while Y" precipitation followed but provided the greater contribution to the room temperature hardness and strength. The strength of the standard alloy decreased rapidly at temperature above 540°C, and the benefit of boron diminished at the higher temperatures. The higher titanium contents prevented a dramatic loss in strength at temperatures up to 650°C. The stress-rupture tests indicated that similar stress-rupture strength can be expected for the Alloy 718 and the alloy with 3.89Cb + 1.27Ti. Superalloy 718--Metallurgy and Applications Edited by E.A. Loria The Minerals, Metals & Materials Society, 1989

Structure/Properties Effects of Substitutions for Reduced Columbium in Alloy 718