After almost three decades of intensive fundamental research and development activities, intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in automotive and aircraft engine industry. The advantages of this class of innovative high-temperature materials are their low density and their good strength and creep properties up to 750 °C as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments. The background of these heat treatments is at least twofold, i.e., concurrent increase of ductility at room temperature and creep strength at elevated temperature. This review gives a general survey of engineering γ-TiAl based alloys, but concentrates on β-solidifying γ-TiAl based alloys which show excellent hot-workability and balanced mechanical properties when subjected to adapted heat treatments. The content of this paper comprises alloy design strategies, progress in processing, evolution of microstructure, mechanical properties as well as application-oriented aspects, but also shows how sophisticated ex situ and in situ methods can be employed to establish phase diagrams and to investigate the evolution of the micro- and nanostructure during hot-working and subsequent heat treatments.

Design, Processing, Microstructure, Properties, and Applications of Advanced Intermetallic TiAl Alloys†

Titanium-based materials are widely used in various areas due to their unique combination of outstanding characteristics. Properties such as stiffness, strength and wear resistance of conventional titanium alloys can be further enhanced through development of titanium-based matrix composites (TMCs). Additive manufacturing (AM) technology provides a promising platform for highly efficient fabrication of complex-shaped titanium parts. Although AM of titanium and titanium alloys are increasingly being investigated, far less attention has been paid to AM of TMCs due to their additional processing complications. This study aims to review the current state-of-the-art in AM of TMCs as well as key aspects and research trends for the design, fabrication, and further development of high-performance TMCs. The review highlights the promising outlook for AM of TMCs. However, it also draws attention to critical aspects that require further investigation such as optimization of the processing parameters and additional understanding of melting/consolidating of matrix and reinforcement for AM of defect-free TMC components.

Recent developments and opportunities in additive manufacturing of titanium-based matrix composites: A review

For the last several years, gamma titanium aluminide (γ-TiAl)-based alloys, called “gammalloys,” in specific alloy-microstructure forms began to be implemented in civil aero-engines as cast or wrought low-pressure turbine (LPT) blades and in select ground vehicle engines as cast turbocharger rotors and wrought exhaust valves. Their operation temperatures are approximately up to 750°C for LPT blades and around 1000°C for turbocharger rotors.
 This article critically assesses current engineering gammalloys and their limitations and introduces eight strengthening pathways that can be adopted immediately for the development of advanced, higher temperature gammalloys. Intelligent integration of the pathways into the emerging application-specific research and development processes is emphasized as the key to the advancement of the gammalloy technology to the next higher engineering performance levels.

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Advances in Gammalloy Materials-Processes-Application Technology: Successes, Dilemmas, and Future

Development of TiAl alloys with excellent mechanical properties and oxidation resistance

Enhanced nanohardness and new insights into texture evolution and phase transformation of TiAl/TiB 2 in-situ metal matrix composites prepared via selective laser melting

H.Z. Niu

Papers

Microstructure evolution and mechanical properties of a novel beta γ-TiAl alloy

Microstructure and fracture toughness of a β phase containing TiAl alloy

High temperature deformation behaviors of Ti-45Al-2Nb-1.5V-1Mo-Y alloy

Microstructure evolution, hot deformation behavior and mechanical properties of Ti-43Al-6Nb-1B alloy

Microstructure characterization and tensile properties of β phase containing TiAl pancake