Analysis of cast TiAl properties for engine materials

A gamma TiAl alloy, Alloy01, was developed for casting aeroengine hot parts in an effort to replace current Ni-base superalloys. To evaluate engineering applicability, many commercial size ingots of Alloy01 were melted, and cast into various component shapes. Property measurements were made on cast-size specimens and in some cases on machined from blade samples. These included tensile strength and ductility, creep and creep rupture strength, low and high cycle fatigue, fracture toughness, crack growth rate, and some physical properties. Some of the important observations were made as follows; the room temperature (RT) strength and ductility are believed to be determined by three major factors, aluminum content, oxygen content, and macro-structural elements. Among those the macrostructure (grain size, grain structures, and shrinkage porosity) was considered most important. The best ductility obtained for as-cast specimens was 0.5%, but a HIP treatment increased the ductility to more than 1%. The alloy exhibited an excellent creep and fatigue strength. A comparison of the property data with those of a superalloy indicated that the TiAl is technically qualified for some of the components without major design changes.