The Effects of Chemistry and Microstructure on Deformation Mechanisms in Titanium-Aluminides

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9622497 Fraser This is a study of the role of a number of intrinsic and extrinsic factors, including chemical and microstructural effects, on the deformation mechanisms operative in titanium aluminide-based systems. The objectives of this research are fourfold: (1) one aim is to determine the anisotropy of the bonding charge densities in titanium aluminide (TiAl) and assess its influence on deformation processes. Accurate values of the Debye-Waller factors are determined on standard samples of known compositions using four-circle x- ray diffraction. Subsequently, low-order structure factors for TiAl are deduced from which the anisotropy of bonding charge densities are assessed. The possible influence of the resulting charge densities on deformation mechanisms are then assessed. (2) the effects of both substitutional and interstitial solute additions on dislocation mobilities are determined. Here, experiments are performed on single phase samples of TiAl to develop an understanding of the interaction between oxygen impurities and dislocations in TiAl. (3) an assessment of the role of Ti3Al on the deformation behavior and micro-mechanisms of fracture in TiAl-based systems is made. The deformation behavior of Ti3Al in lamellar, equiaxed and duplex versions of the microstructures is determined by post-mortem transmission electron microscopy (TEM) studies, with particular emphasis being placed on slip transmission through Ti3Al, and the accumulation of strain at interfaces between TiAl and Ti3Al. (4) the ability to engineer interface properties in TiAl- based systems by solute addition, in an analogous manner to that in Ni-base superalloys, is investigated. %%% The research examines deformation mechanisms in titanium aluminide alloys, whose practical applications are limited by a lack of understanding of a number of important factors related to their mechanical behavior. The effort also contributes to the scientific base for elevated temperature interme tallic compounds. ***