IMPROVEMENT OF ROOM-TEMPERATURE DUCTILITY OF STOICHIOMETRIC NI3AL BY UNIDIRECTIONAL SOLIDIFICATION

Stoichiometric polycrystalline Ni3Al was grown unidirectionally by a floating zone method. The solidification structure was strongly dependent on the growth rate. A columnar grained structure with a strong < 111 > texture was obtained with the growth rate over 13 mm/h. The alloy exhibited a large tensile elongation of 17% at room temperature without the addition of boron. The combined mode of transgranular fracture and intergranular fracture was observed on the fracture surfaces, with traces of crystallographic slip. It is considered that the large room temperature ductility in this alloy is attributed to the substantial suppression of intergranular crack initiation and its catastrophic propagation.