Effect of boron on grain-boundaries in Ni3Al†

Positive temperature dependence of the yield stress in TiAl L10 type superlattice intermetallic compound single crystals at 293–1273 K

Many ordered intermetallic alloys have attractive high-temperature properties; however, low ductility and brittle fracture limit their use for structural applications. The embrittlement in these alloys is mainly caused by an insufficient number of slip systems (bulk brittleness) and poor grain-boundary cohesion. Recent studies have shown that the ductility and fabricability of ordered intermetallics can be substantially improved by alloying processes and control of microstructural features through rapid solidification and thermomechanical treatments. These results demonstrate that the brittleness problem associated with ordered intermetallics can be overcome by using physical metallurgical principles. Application of these principles will be illustrated by results on Ni(3)Al and Ni(3)V-Co(3)V-Fe(3)V. The potential for developing these alloys as a new class of high-temperature structural materials is discussed.

https://science.sciencemag.org/content/sci/226/4675/636.full.pdf

Ductile ordered intermetallic alloys

The dislocation structure resulting from the compression of single crystals of Ni3(Al,Ti) at room temperature has been studied using transmission electron microscopy imaging methods. Deformed samples of e = 1% and e = 9% true strain were sliced parallel to (111) and (010) planes. Weak-beam imaging methods reveal the (010) planes to be the dissociation planes of the screw superlattice dislocations. Transition of superlattice dislocations from (111) onto (010) planes by the Kear-Wilsdorf mechanism was identified. Remarkable dislocation movement on (010) planes was found. The flow stress is interpreted as a dislocation interaction on octahedral and cube planes. Measurements of the antiphase-boundary energies on (111) and (010) planes yielded values of γ111 = γ010 =250±30mJm−2

Weak-beam study of superlattice dislocations moving on cube planes in Ni3(Al, Ti) deformed at room temperature

The three elastic stiffness constants of various Ni-based intermetallic Ni3X (X = Mn, Fe, Al, Ga, Ge and Si) with L12 structure have been determined at room temperature by the rectangular parallelepiped resonance method The elastic anisotrophy factor, A, of the compounds is generally large, ranging from 25 to 33 except for Ni3Ge (A = 171) The large anisotropy is believed to be responsible at least partly for the positive temperature dependence of the flow stress observed for these compounds The elastic constants exhibit some correlation with the lattice constants The minor element, X, can be regarded as exerting “chemical pressure” which causes the expansion of the Ni lattice, thus resulting in the decrease of the elastic constant

K. Aoki

Papers

Flow stress and work hardening in Ni3 (Al · Ti) single crystals

Cleavage fracture of the intermetallic compound Ni3Ge single crystals