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Wrought TiAI products manufactured by conventional hot-working procedures, such as forging and extrusion, suffer from structural and chemical inhornogeneities, which are major concerns for the reliability of components. In an attempt to overcome these problems, TiAI alloys were hot worked by torsional deformation. Using this method, a much higher strain and mechanical work can be imparted, which triggers dynamic recrystallization. The metallurgical potential of this technique will be assessed. Particular emphasis is placed on shear localization processes, which often lead to premature failure of the workpiece. [ABSTRACT FROM AUTHOR]

Based on the investigations of the microstructure of ingots depending on the content of aluminum and alloying additives and cooling rate, a new concept of alloying of γ-TiAl + α2-Ti3Al alloys has been developed, which is directed on the production of a chemically uniform cast material with a fine-grained structure. The results obtained open new opportunities in the designing of γ+α2 alloys with an improved processing plasticity. [ABSTRACT FROM AUTHOR]

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The hot-working behavior of γ(TiAl)-based alloys was investigated in order to understand fundamental aspects of the evolution of the microstructure and to establish guidelines for advanced alloy design and processing. The investigations involved a wide range of Al compositions and are based on metallographic investigations of the deformed samples. Particular emphasis was placed on the effects of phase composition and casting texture. It was found that the behavior of dynamic recrystallization was significantly influenced by the Al content of the alloys. Under the same deformation conditions, dynamic recrystallization was fastest for alloys with nearly stoichiometric composition, whereas the recrystallization kinetics decreased for lower or higher Al contents. This result can be attributed to the effect of the Al concentration on the micromechanisms of deformation and diffusion as well as on the initial cast microstructure, which changed from fully lamellar to equiaxed near-γ microstructures by raising the Al content from 45 to 50 at. pct. Further, it was observed that the casting texture, i.e., the orientation of lamellae with respect to the deformation axis, significantly influenced the recrystallization behavior. In this respect, the development of shear bands due to kinking and bending of lamellae is concluded to play an important role in the recrystallization behavior and seems, in general, to be a particular feature of the microstructural evolution of lamellar alloys on hot working. [ABSTRACT FROM AUTHOR]

The evolution of preferred orientations during processing appears to be of significant importance for the use of γ-titanium aluminide alloys, since the desired lamellar microstructures exhibit a strong anisotropy of mechanical properties. In this work, texture development has been investigated after hot extrusion and sheet rolling, which are considered to be technologically relevant wrought processes. As texture evolution certainly is dependent on several factors, involving deformation properties, recrystallization kinetics, and, particularly, the phase constitution at hot-working temperature, different processing conditions and alloy compositions were investigated. By comparing the results, it is indicated that the determined textures can be understood by the deformation modes of the dominating phase at hot-working temperature and the subsequent phase transformations. However, the current understanding of texture evolution is far from being complete, as no model can be presented which quantitatively accounts for the contribution of the different processes mentioned. [ABSTRACT FROM AUTHOR]

Copyright of Klinische Wochenschrift is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Two-phase titanium aluminide alloys are being considered as lightweight materials to replace nickel-based superalloys in some high-temperature aero-engine applications. However, at an intended service temperature of 700 °C the strength and creep resistance of the titanium aluminides are inferior to those shown by superalloys. Therefore, precipitation-hardening treatments using carbon additions were tested for an improvement of the strength. Ageing of a Ti-48.5 at. % Al-0.4 at. % C alloy for 24 h at 750 °C after a solution treatment for 4 h at 1250 °C, followed by quenching, leads to the formation of perovskite-type precipitates, significantly improving the high-temperature strength. The size distribution and volume fraction of the perovskite precipitates were measured using small-angle neutron scattering (SANS). The results after extended ageing periods show that although the precipitate size distribution changes significantly, the effect on the yield strength is relatively small. [ABSTRACT FROM AUTHOR]

Thermal neutrons were used to investigate the texture of intermetallic Ti[sub 47]A1[sub 49](Cr, Nb, Mn, Si, B)[sub 4] and Ti[sub 45]A1[sub 45]Nb[sub 10] alloys. The aim was to learn about the influence of different extrusion temperatures and annealing treatments. A relatively strong ingot texture was weakened by extrusion, independently of the processing temperature (1250-1380 °C). However, subsequent annealing has no remarkable influence on the texture sharpness. Therefore, texture has only a minor influence on the anisotropy of hotworked materials. A comparison of the two TiA1 alloys shows a pseudo-cubic deformation behavior for Ti[sub 45]A1[sub 45]Nb[sub 10], which results in a 'double-fiber' < 101] < 110] texture. This pseudo-cubic behavior indicates a high potential of Ti[sub 45]A1[sub 45]Nb[sub 10] for plain strain deformation with sufficient ductility at ambient temperature. [ABSTRACT FROM AUTHOR]