The Microstructure, Creep, and Hardness Properties of Powder Metallurgy Beta Gamma TiAl-4Nb-3Mn Alloy

摘要

Pre-alloyed beta gamma titanium aluminide powder with a nominal composition of TiAl-4Nb-3Mn is consolidated by hot isostatic pressing. After consolidation, a step cooled heat treatment is performed to homogenize the material and produce a fully lamellar microstructure. Various aging heat treatments are then performed with the goal of forming interfacial beta phase precipitates along lamellar interfaces. The step cooled heat treatment produces a relatively fine microstructure with a lamellar spacing of 0.04 μm and an average lamellar colony size of 60 μm. The aging heat treatments generate beta phase precipitates along lamellar colony boundaries but not along lamellar interfaces, and result in lamellar degredation and grain growth. Constant load tensile creep and room temperature hardness tests are performed on step cooled heat treated and step cooled heat treated and aged specimens. Creep resistance, generally, improves with aging time, even with no interfacial precipitation, and the lamellar degredation that occurs with aging. The microstructures of the as-tested specimens are characterized and related to the creep properties. The hardness values are also compared as a function of selected heat treatment condition and microstructural features.