Method to produce gamma titanium aluminide articles having improved properties

摘要

Methods are presented to produce duplex (DP) microstructures, nearly lamellar (NL) microstructures, and fully TMT lamellar (TMTL) microstructures in gamma titanium aluminide alloy articles. The key step for obtaining a specific type of microstructure is the post-hot work annealing treatment at a temperature in a specific range for the desired microstructure. The annealing temperatures range from T_e+100° C. to T&agr;−25° C. for duplex (DP) microstructures, from T&agr;−25° C. to T&agr;−5° C. for nearly lamellar (NL) microstructures, and from T&agr; to T&agr;+60° C. for fully TMT lamellar (TMTL) microstructures, where T_e is the titanium-aluminum eutectoid temperature of the alloy and T&agr; is the alpha transus temperature of the alloy. The times required for producing specific microstructures range from 2 min to 15 hours depending on microstructural type, alloy composition, annealing temperature selected, material section size, and desired grain-size. The heating rate to the post-hot work annealing treatment is critical and must be fast enough to avoid compositional segregation (in the two-phase field) and uneven grain growth. Cooling schemes and rates after the annealing treatments are determined according to the microstructural features of interest, and their stability.