Abstract
Lattice strain evolution during deformation processing of Ti-Al alloys at high temperature is important in terms of its microstructural evolution and microstructural stability. It is shown here that careful evaluation of lattice parameters is critical for the understanding of thermal expansion, crystallographic order, chemical composition and response to pressure, allowing to identify phase transitions and segregation, in addition to the measurement of the more conventional quantities phase composition and order parameter. The lattice parameters of Ti-45Al-7.5Nb-0.25/0.5C (at. %) alloys were calculated using both Rietveld and single peak fitting methods from data obtained by in-situ synchrotron diffraction experiments at high temperature under atmospheric and high pressure respectively. The lattice strain evolution as a function of temperature in a Ti-45Al-7.5Nb-0.25C (at. %) alloy under high pressure was compared with that of a Ti-45Al-7.5Nb-0.5C (at. %) alloy heated under atmospheric pressure. The contribution of each of the four lattice strain factors is semi-quantitatively assessed in the temperature range investigated.
Highlights
Titanium aluminides are attractive candidate materials for applications in the automotive industry, and more importantly for applications at high temperature in aerospace industries, mainly due to their low density and excellent mechanical properties [1,2,3]
The evolving lattice strains were calculated by equation (1), Lattice strains at standard atmospheric pressure ε = εhkl = (G0 − G)/G0 (1)
Lattice strains of the Ti-45Al-7.5Nb-0.5C alloy at standard atmospheric pressure are shown in Figures 4 and 5 for the co-existing phases, α2/α and γ, respectively
Summary
Titanium aluminides are attractive candidate materials for applications in the automotive industry, and more importantly for applications at high temperature in aerospace industries, mainly due to their low density and excellent mechanical properties [1,2,3]. A new route for the processing of titanium aluminide components under high pressure has been proposed [4], for example, by utilizing a 0.8 GN forging press to manufacture large aerospace products [5] or a new 0.54 GN die-forging press currently being commissioned [6]. Since these forming processes operate at elevated temperature and pressure, it is imperative that the microstructural integrity of the work-pieces be maintained, especially by limiting grain growth during hightemperature processing and minimizing the development of internal stresses during forging operations. The evaluation of lattice parameters is a very sensitive measurement to determine phase transformations of various kinds [14,15,16]
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