Nano‐Scale Design of TiAl Alloys Based on β‐Phase Decomposition

Abstract

Phase decomposition and ordering reactions in β/B2‐phase containing TiAl alloys were utilized to establish a novel, previously unreported, type of laminate microstructure. The characteristic constituent of this microstructure are laths with a nanometer‐scale substructure that are comprised of several stable and metastable phases. Microstructural control can be achieved by conventional thermomechanical processing and leads to a structurally and chemically very homogeneous material with excellent mechanical properties. The physical metallurgy of this novel type of alloy has been assessed by transmission electron microscope investigations and mechanical testing.

Ab Initio Study of the Elastic and Mechanical Properties of B19 TiAl

“…Alloying and heat treatments are effective ways to overcome the brittleness and to improve the hot workability. The usage of these techniques can lead to the formations of several lower symmetry ordered phases in the microstructure [1][2][3]. Among lower symmetry phases, the orthorhombic B19 phase is commonly observed in γ-TiAl-based intermetallics.…”

“…The calculated G/B ratios of B19 TiAl from the EDM is 10.03% and 14.18% lower than the theoretical data of γ-TiAl (0.62) and α 2 -Ti 3 Al (0.65) [42], respectively, indicating that B19 TiAl is more ductile than γ-TiAl and α 2 -Ti 3 Al. Experimentally, Appel et al [3,[8][9][10] have measured the mechanical properties of γ-TiAl-based intermetallics with the microstructure containing B19 phase and found that the existence of B19 structure can give the intermetallics relatively high tensile ductility. According to Pettifor's rule [12], a material has more metallic (angular) bonds and thus is more ductile (brittle) if it has a larger positive (negative) Cauchy pressure.…”

“…Ducher et al [5] observed the variants of B19 TiAl phase to form in Fe containing γ matrix in Ti-48Al-2Cr-2Nb alloy. Appel et al [3] made a careful observation of B19 phase in Ti-(40-44)Al-8.5Nb alloys and admitted the B19 phase to be a transitional phase between the cubic β (A2 structure) and/or β o (B2 structure) phase and the orthorhombic O-Ti 2 AlNb phase. Additionally, the occurrence of B19 phase was observed by Schmoelzer et al [6] in Ti-45Al-3Mo-0.1B alloy and by Song et al [7] in Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy, which facilitates the precipitation of γ phase from α 2 phase.…”

In Situ Synchrotron Study of B19 Phase Formation in an Intermetallic γ‐TiAl Alloy

“…Among these are hexagonal ω-related phases [9] and orthorhombic phases. [10,11] Abe et al [10] reported on an orthorhombic phase with B19 structure (Pmma) that forms very fine precipitates upon rapid cooling in a Ti-48 Al alloy. Tanimura et al [12] observed the formation of B19-phase as a metastable transitional phase during the A3→D0 19 +L1 0 precipitation sequence.…”

First-Principles Investigations on Structural and Elastic Properties of Orthorhombic TiAl under Pressure

“…One strategy to improve their ductility and hot workability is to employ a combination of alloying and heat treatments to encourage the formation of more ductile phases. Nevertheless, the strategy can also induce the formations of some lower symmetry ordered phases which are constituents of the microstructure [1][2][3]. As a significant constituent, the orthorhombic B19-TiAl phase is commonly observed in TiAl-based alloys [2][3][4][5][6][7].…”