Evolution of Microstructure and Texture during Recrystallization of the Cold-Swaged Ti-Nb-Ta-Zr-O Alloy

Abstract

The deformed microstructure and evolution of microstructure and texture during recrystallization of the cold-swaged multifunctional Ti-23Nb-0.7Ta-2Zr-1.2O (TNTZO, at. pct) alloy were investigated by optical microscope, electron backscatter diffraction, and transmission electron microscope. This alloy has been reported, by Saito et al., to possess a specific dislocation-free plastic deformation mechanism. In this study, the results show a curly grain or swirled structure and a pronounced fibrous 110 h i texture along the swaging axis in the cold-swaged TNTZO alloy. The normal to the swirled grain surface is near 001 h i in the cross section of the rod. This characteristic microstructure can be considered to arise from the plane strain deformation of the grains under applied stress, which is similar to that in ordinary bcc metals after heavily drawing or swaging. It is also shown that recovery involves the redistribution and partial annihilation of dislocations within the deformation bands, and recrystallization proceeds by a typical new grain nucleation-growth mechanism during annealing of the TNTZO alloy. The fibrous 110 h i deformation texture is gradually replaced by random orientations with increasing annealing time. Thus, it could be concluded that the TNTZO alloy deforms by the traditional dislocation glide on 111h i 110 f g, {112}, or {123} slip systems, rather than the dislocation-free mechanism.

Effect of strain rate on the mechanical properties of a gum metal with various microstructures

“…1) of Extruded-GM by EBSD. It has been proposed that swaging can induce <110> fibrous texture in bcc metals [35]. Since swaging is similar to extruding in terms of stress condition, the fibrous texture is consistent with the present result.…”

“…9 (a) is the XRD results from the Extruded-GM, which show strong texture with only β (110) peak identified. This is consistent with extrusion texture of bcc metals and alloys [35]. Fig.…”

Evolution of deformation mechanisms of Ti–22.4Nb–0.73Ta–2Zr–1.34O alloy during straining

“…A dislocation-free plastic deformation mechanism was proposed to explain the origin of the unique properties, based on experimental results and theoretical analysis [1][2][3][4][5][6][7]. However, this suggestion has been challenged by recent studies, in which conventional deformation mechanisms such as dislocation glide, deformation twinning and stress-induced phase transformations were found to be operative in Gum Metal [8][9][10][11][12][13]. For example, stress-induced a 00 martensite (SIM a 00 ) [11,12], stress-induced x phase [11][12][13], 1/2h1 1 1i dislocations [8][9][10] and {1 1 2}h1 1 1ib twins [12,13] were all observed in a deformed typical Gum Metal, Ti-23Nb-0.7Ta-2.0Zr-1.2O (at.%) alloy.…”

“…However, this suggestion has been challenged by recent studies, in which conventional deformation mechanisms such as dislocation glide, deformation twinning and stress-induced phase transformations were found to be operative in Gum Metal [8][9][10][11][12][13]. For example, stress-induced a 00 martensite (SIM a 00 ) [11,12], stress-induced x phase [11][12][13], 1/2h1 1 1i dislocations [8][9][10] and {1 1 2}h1 1 1ib twins [12,13] were all observed in a deformed typical Gum Metal, Ti-23Nb-0.7Ta-2.0Zr-1.2O (at.%) alloy. These deformation mechanisms and {3 3 2}h1 1 3ib twinning were also found in room-temperature compressed Ti-22.4Nb-0.73Ta-2Zr-1.34O (at.%) alloy, which has a slightly lower b stability than that of Gum Metal [14,15].…”

Room temperature creep behavior of Ti–Nb–Ta–Zr–O alloy

“…Instead, the unstable β lattice readily forms giant faults by ideal shear, thus accommodates the plastic strain. In contrast to these observations, a number of studies underline the presence of dislocations and martensitic phases in gum metal [2][3][4][5][6][7][8]. Some studies even claim a fully 1/2 〈111〉 dislocation-gliding controlled plasticity mechanism [5,6].…”