Mechanical Properties of Fe-Modifie Ll₂-Type Al₃Ti

Abstract

The room temperature ductility of an L12-type A13Ti alloy containing 7.5 at.% Fe has been improved substantially by hot isostatic pressing (HIP) after arc casting. This L12-type alloy can be deformed in compression to 11.4 % at room temperature after HIPing, retaining the original shape of compressive specimens, while compressive specimens without HIPing following heat-treatment for homogenization (HHT) fracture into small pieces when deformed to similar strain. At temperatures higher than 400°C, specimens for both HHTed and HIPed conditions show similar behavior, having strains to failure of greater than 12 % plastic strain. Fracture occurs at room temperature by brittle transgranular cleavage with a smooth surface in HHTed specimens, while in HIPed specimens, fracture occurs by both transgranular and intergranular modes. Transgranularly fractured surfaces in the latter case have rough surfaces with fine structure, indicating ductile fracture as compared with that for HHTed specimens. In both HIPed and HHTed specimens, no fracture surfaces are flat and parallel to any crystallographic planes. High resolution electron microscopy has revealed that a pair of superlattice partial dislocations on a (111) plane have a spacing of approximately 11 nm (2–3 times larger than that for Al-23Ti-6Fe-5V) giving an antiphase boundary energy of 95 mJ/m2. Since this energy is relatively low, the present alloy may be ductile because of its ready emission of dislocations at crack tips, according to the Rice-Thomson criterion. Improvement of room-temperature ductility of this alloy is attributed primarily to the reduction of a large population of cavities formed upon arc casting.

Fabrication of novel Al–L12-type Al2.7Fe0.3Ti refiners by spark plasma sintering and their refining performance

“…It is known that alloying with a certain amount of a transition element, such as chromium, manganese, iron, cobalt, nickel, copper zinc, rhodium, palladium, silver, platinum, or gold, causes the transformation from the D0 22type tetragonal structure of Al 3 Ti to a high-symmetry L1 2 cubic structure. [29][30][31][32][33] This transformation increases the symmetry of Al 3 Ti intermetallic compounds. Therefore, if L1 2 -type intermetallic compound particles are used as heterogeneous nucleation sites, the lattice registry with the metal matrix does not change from plane to plane.…”

Formation of L12modified Al2.5Cu0.5Ti phase by heat treatment of spark-plasma-sintered Cu/Al3Ti specimens

“…[12][13][14] It is known that, upon the replacement of some of the Al atoms with Cu, Fe, Ni, Cr, or Zn, the crystal structure changes from the unfavorable low-symmetry tetragonal D0 22 structure to the L1 2 structure. [15][16][17][18][19][20] Moreover, by changing the replacing element, the lattice constant of L1 2 phases is controllable. In our previous studies, the effects of L1 2 modified intermetallic compound particles, such as Al 2.5 -Cu 0.5 Ti 21) and Al 2.7 Fe 0.3 Ti, 22,23) on the grain refining performance of an Al cast were studied.…”