Compression Behavior of L1 2 Modified Titanium Trialuminides Alloyed with Chromium and Iron
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Compression Behavior of L12 Modified Titanium Trialuminides Alloyed with Chromium and Iron Tohru Takahashi and Tadashi Hasegawa Department of Mechanical Systems Engineering, Faculty of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan ABSTRACT L12 modified titanium trialuminides have been prepared by replacing 9at.% of the aluminum in Al3Ti with chromium and/or iron. The materials were recrystallized into single phase polycrystals after isothermal forging resulting in an average grain diameter of about 40µm. Lattice parameter of the material containing 9 at.% chromium or 9 at.% iron, are 0.3959nm and 0.3939nm, respectively. The lattice parameters varied linearly with composition between these values for additions of both chromium and iron. Uniaxial compression tests were performed at temperatures ranging from 293K to 1300K. The yield strength is not sensitive to chemical composition within the range of compositions tested. Flow stress serrations of a few % were observed at temperatures around 600K, where intermittent drops in flow stress started immediately after yielding and continued to the end. These serrations were observed up to about 800K. At 900K and above the materials became fully deformable. Quasi steady state flow and strain softening were observed at 1200K and 1300K, respectively, due to dynamic recrystallization.
INTRODUCTION Al3Ti is very brittle material at ambient temperature and the origin of this brittleness is attributed to its of D022 ordered crystallographic structure [1-4]. The deformability can be strikingly improved by modification of the crystal structure into the L12 structure by replacing some of the aluminum by a third element, such as chromium, manganese, iron, along with several others [5-11]. However, the deformability is not always improved by such alloying, even if the resulting crystal structure is L12. And the reason for this is unknown. In the present study chromium and/or iron have been used as the third element to produce the L12 ordered structure, and the amount of aluminum replaced by the third element was fixed at 9 at.%. Two ternary alloys, Al66Ti25Cr9 and Al66Ti25Fe9, which will hereafter be referred to as 9Cr and 9Fe materials, respectively, and two quaternary alloys were investigated. The chemical composition of the quaternary alloys is Al66Ti25Cr6Fe3 and Al66Ti25Cr3Fe6, and will be referred to as 6Cr3Fe and 3Cr6Fe, respectively. The microstructures of these materials were characterized, and compression tests were performed in air.
EXPERIMENTAL PROCEDURES The L12 modified titanium trialuminide phase has been reported to form within a relatively narrow composition range around Al66Ti25X9, where the third element, X, is chromium, N3.10.1
manganese, iron and so on [12]. In the present study, the aluminum and titanium contents have been fixed at 66 and 25 at.%, respectively, and chromium and iron have been added as the third and fourth elements. The total amount of chromium plus iron is thus 9 at.%, and the chromium and iron co
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