titaniumaluminide

Titanium aluminide, commonly written as TiAl, is an intermetallic compound formed from titanium and aluminum. The most studied phase is gamma titanium aluminide (gamma-TiAl, TiAl), typically near the equimolar composition. Other Ti-Al intermetallics include Ti3Al (alpha2).

Crystal structure and properties: Gamma-TiAl has an ordered tetragonal crystal structure, which provides high-temperature strength and stiffness but can lead to low ductility at room temperature. The alpha2 phase Ti3Al has a hexagonal structure and different mechanical behavior. These materials are often processed to achieve a refined mixture of gamma and alpha2 grains, which can enhance performance under load at elevated temperatures.

Processing and alloying: TiAl alloys are produced by ingot metallurgy or powder metallurgy, followed by hot working and heat treatment to control phase fractions. Alloying additions such as niobium, chromium, and silicon can improve creep resistance, oxidation resistance, and, to some extent, ductility. To protect against high-temperature oxidation, surface coatings such as aluminide coatings or MCrAlY are commonly applied.

Applications and limitations: TiAl alloys offer relatively high specific strength and good high-temperature performance with low density, making them attractive for aerospace and automotive components such as turbine blades, vanes, and exhaust valves. Limitations include brittleness at room temperature, limited fracture toughness, higher material cost, and processing challenges that can complicate manufacturing.

Research and outlook: Ongoing work seeks to improve ductility and toughness through optimized microstructure and processing, expand applications via improved manufacturability, and reduce costs through alloy development and advanced fabrication methods.