R&D on Composition and Processing of Titanium Aluminide Alloys for Turbine Engines

摘要

Material based on the intermetallic phase TiAl (gamma) exhibits several attractive features that make it a candidate for gas turbine engine applications. Low density, good oxidation resistance and high temperature strength are such characteristics and could result in substitution for the nickel alloy currently used for turbine engine components that operate at intermediate temperatures. The Ti-48Al-1V alloys has been identified as the primary composition of interest in the gamma system and an extensive amount of mechanical property data have been generated in a related program. The aim of this effort was to characterize fatigue crack growth behavior and damage tolerance. The apparent fracture toughness of the gamma TiAl alloy did not vary appreciably with test temperature to 705 deg C (1300 deg F) and was marginal over the design relevant range of temperature. The room temperature apparent fracture toughness, was however, too high for cold proof testing to be a viable flow detection strategy. The rate of cyclic crack growth increased with increasing test temperature and P-ratio. da/dN data seem to be correlated best by the crack tip opening displacement. Thermomechanical fatigue crack growth data are not markedly different from isothermal test results for the three design relevant cycles studied.