Effect of rapid solidification and alloying addition on lattice distortion and atomic ordering in L1 0 tial alloys and their ternary alloys
01 Oct 1988-Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science (Springer-Verlag)-Vol. 19, Iss: 10, pp 2445-2455
TL;DR: In this article, the lattice parameters of binary and ternary L10 type titanium alloys were studied by X-ray diffractometer using the foils and their powders.
Abstract: Binary and ternary L10 type titanium alloys were rapidly quenched into thin foils by the hammer-anvil quenching technique. The nominal alloy compositions include Ti1-xAlx and (Ti1-xAlx)100-@#@ yMy, wherex = 0.5 to 0.6; y= 1 to 4; and M is V, Cr, Mn, Fe, Co, Ni, and Ge. Lattice parameters of Ll0 phases in these alloys were studied by X-ray diffractometer using the foils and their powders. Simultaneously, long-range order parameters of these Ll0 phases in the as-quenched foils and the annealed powders were determined from the superlattice intensity measured by X-ray diffractometer. Rapid quenching suppresses long-range ordering (S) during solidification and, thereby, reduces lattice distortion (c/a) in Ll0 titanium alloys. A small amount of alloying element has a large effect on thec/a ratio. The atomic size effect and probably substitutional site preference play an important role in such ac/a reduction. From the density measurement, it is found that antisite defects are a predominant mode in Al-rich off-stoichiometric TiAl compound alloys. Determined long-range order value is significantly low in as-quenched binary TiAl due to rapid quenching, and the highest ordering occurs at as-quenched Ti45Al55 alloy. The relationship betweenc/a andS in Ll0 Ti45Al55 may be written asc/a = 1 + 0.025 ·S.
Citations
More filters
TL;DR: In this paper, the basic phase diagram and crystal structure of both the Ti3Al and TiAl phases are reviewed, followed by a consideration of chemistry-processing-microstructure-deformation/fracture-mechanical property relationships in monolithic material.
Abstract: Attractive elevated-temperature properties and low density make the titanium aluminides very interesting for both engine and airframe applications, particularly in the aerospace industry. The challenge to the materials scientist is to maintain these characteristics while building-in “forgiveness”. The basic phase diagram and crystal structure of both the Ti3Al and TiAl phases are reviewed, followed by a consideration of chemistry-processing-microstructure-deformation/fracture-mechanical property relationships in monolithic material. Conventional and innovative synthesis methods are presented, including use of hydrogen as a temporary alloying element. Composite concepts as a method to enhance not only “forgiveness” but also elevated-temperature behaviour are discussed. Environmental effects are evaluated prior to consideration of present and projected applications of both monolithic and composite material. It is concluded that while the titanium aluminides in monolithic form can be used now in non-demanding applications, much further research and development is required before this material class can be used in critical applications, especially in composite concepts.
388 citations
TL;DR: In this article, all available literature on the constitution of Ti−Al is reviewed and the phase diagram for this system is assessed based on a critical evaluation of these data, and a critical phase diagram is presented.
Abstract: All available literature on the constitution of Ti−Al is reviewed. Based on a critical evaluation of these data the phase diagram for this system is assessed.
362 citations
TL;DR: In this paper, the authors show that the deformation behavior of polysynthetically twinned TiAl with a nearly stoichiometric composition depends strongly on the angle between the twin boundaries and the compression axis.
Abstract: Polysynthetically twinned crystals of TiAl with a nearly stoichiometric composition have been grown and deformed in compression at room temperature. The yield stress and deformation behaviour depend strongly on the angle between the twin boundaries and the compression axis rather than on the crystallographic orientation of the compression axis. The yield stress is high when compression is perpendicular or parallel to the twin boundaries, and is generally very low for specimens where the twin boundaries are at an intermediate angle to the compression axis. The ratio of the highest to the lowest values of yield stress is almost 8:1. This large difference in yield stress has been found to be related to the difference in the deformation mode; for compression perpendicular or parallel to the twin boundaries, shear deformation always occurs across them while, for compression at an intermediate angle, shear deformation is parallel to the boundaries. The former mode of deformation is much harder than the...
264 citations
TL;DR: In this article, the mechanical behavior of binary TiAl alloys containing 46 to 60 at. pct Al has been studied in bulk materials prepared via rapid solidification processing and the results on the deformation and fracture modes as a function of test temperature are also discussed.
Abstract: The mechanical behavior of binary TiAl alloys containing 46 to 60 at. pct Al has been studied in bulk materials preparedvia rapid solidification processing. Bending and tensile tests were carried out at room temperature as a function of Al concentration. A few alloys were also tested from liquid nitrogen temperature to ∼ 1000°C. Deformation substructures were studied by analytical transmission electron microscopy and fracture modes by scanning electron microscopy (SEM). It was found that both microstructure and composition strongly affect the mechanical behavior of TiAl-base alloys. A duplex structure, which contains both primary y grains and transformedγ/α
2 lamellar grains, is more deformable than a single-phase or a fully transformed structure. The highest plasticities are observed in duplex alloys containing 48–50 at. pct Al after heat treatment in the center of theγ + α phase field. The deformation of these duplex alloys is facilitated by 1/2[110] slip and {111} twinning, but very limited superdislocation slip occurs. The twin deformation is suggested to result from a lowered stacking fault energy due to oxygen depletion or an intrinsic change in chemical bonding. Other factors, such as grain size and grain boundary chemistry and structure, are important from a fracture point of view. The results on the deformation and fracture modes as a function of test temperature are also discussed.
199 citations
TL;DR: In this paper, the second-order elastic stiffness coefficients of a Ti{sub 44}Al{sub 56} single crystal (ital L}1{sub 0} structure were measured at room temperature using a resonant ultrasonic spectroscopy (RUS) technique.
Abstract: The six independent second-order elastic stiffness coefficients of a Ti{sub 44}Al{sub 56} single crystal ({ital L}1{sub 0} structure) have been measured at room temperature for the first time using a resonant ultrasonic spectroscopy (RUS) technique. These data were used to calculate the orientation dependence of Young`s modulus and the shear modulus. The Young`s modulus is found to reach a maximum near a [111] direction, close to the normal to the most densely packed planes. The elastic moduli and the Poisson`s ratio for polycrystalline materials, calculated by the averaging scheme proposed by Hill, are in good agreement with experimental data and theoretical calculations.
136 citations
References
More filters
TL;DR: In this article, the preferred orientation of uranium bars in the α range was determined by x-ray diffraction using a Geiger counter, and it was shown that hot rolling with a slight reduction causes the 010 planes to become strongly and the 110 planes weakly oriented perpendicular to the rolling direction.
Abstract: Synopsis The preferred orientation of uranium bars hot-rolled and cold-rolled in the α range has been determined quantitatively by x-ray diffraction using a Geiger counter. It is shown that hot rolling with a slight reduction causes the 010 planes to become strongly and the 110 planes weakly oriented perpendicular to the rolling direction. Further hot rolling causes the 110 planes to become strongly and the 010 planes weakly oriented perpendicular to the rolling direction. Cold rolling with light reduction causes the 010 planes to become strongly and the 130 planes weakly oriented in the planes perpendicular to the rolling direction.
484 citations
TL;DR: In this paper, the juxtaposition of two binary eutectic diagrams should produce a liquidus with a slope of zero at the melting point of the congruently melting compound.
Abstract: The juxtaposition of two binary eutectic diagrams should produce a liquidus with a slope of zero at the melting point of the congruently melting compound.
448 citations
TL;DR: In this paper, the tensile properties of the intermetallic compound TiAl have been determined at several temperatures in the range 25 to 1000°C, and the results indicate that the ductilebrittle transition behavior of TiAl at about 700°C is controlled by the trailinga/6 [112] partial dislocation components of the superdislocations overcoming their pinning barriers.
Abstract: The tensile properties of the intermetallic compound TiAl have been determined at several temperatures in the range 25 to 1000°C. Additional variables studied were the influence of strain rate and the effect of exposure to oxidizing conditions prior to testing. The modes of deformation under the various testing conditions were studied in the electron microscope, the modes of fracture were studied in the scanning electron microscope, and these data were correlated with the mechanical properties. The results indicate that the ductilebrittle transition behavior of TiAl at about 700°C is controlled by the trailinga/6 [112] partial dislocation components of thea [011] superdislocations overcoming their pinning barriers. It was also shown that prior exposure to oxidizing conditions does not markedly influence the mechanical properties of TiAl.
436 citations
TL;DR: In this paper, a floating zone method was used to obtain the fundamental knowledge on the plasticity of TiAl single crystals with five orientations and the yield stresses of all orientations tested show a positive temperature dependence similarly to most Ll2 type superlattice intermetallic compounds.
335 citations
01 Jun 1974-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, the deformation substructure of TiAl (Llo type ordered lattice) was tested in compression, and the factors determining it were investigated, and equi-Schmid factor lines have been constructed in an attempt to evaluate the importance of the sense of the applied stress on the deformability of the alloy.
Abstract: The deformation substructure of TiAl (Llo type ordered lattice) tested in compression, and the factors determining it were investigated. Two types of dislocations take part in the plas-tic deformation, namely a/2 [110] and a/2 [Oil]. The latter type will disorder the Llo super-lattice and therefore would be expected to move in pairs as superdislocations. Some obser-vations are essentially in agreement with the predictions, however the large proportion and morphology of a/2 [O1l] dislocations observed was unexpected. Twins of the [112] (111) type play an important role in the deformation of the alloy, and the early stages of their formation have been recorded. Finally, equi-Schmid factor lines have been constructed in an attempt to evaluate the importance of the sense of the applied stress on the deformation capability of the alloy.
292 citations