Thermal stability of the nickel-base superalloy B-1900 + Hf with tantalum variations

The microstructure of the solutionized and aged nickel-base superalloy B-1900 + Hf was examined after additional aging at 982 °C for 72, 250, and 1000 hours. Alloy compositions that were examined contained the normal 1.34 at. pct (4.3 wt pct). Ta as well as 0.67 at. pct and zero Ta levels. The γ phase agglomerated, became plate-like in morphology, and decreased in volume fraction for all three alloys throughout the aging treatments. Changes which occurred in the γ and γ' phase compositions were nearly complete after 72 hours of aging while changes in the MC carbide composition continued throughout the aging. Blocky M₆C carbides precipitated along the grain boundaries of all three alloys in the first 72 hours of aging. In addition, an acicular form of this Mo/Cr/Ni-rich carbide developed in the intragranular regions of the Ta-containing alloys. Formerly an Undergraduate Student, Department of Metallurgical Engineering, Michigan Technological University.