Improvement of Room Temperature Ductility of Stoichiometric Ni₃Al by Unidirectional Solidification

Abstract

One of the authors has reported that unidirectional solidification by a floating zone method (FZ-UDS) is effective in improving the room temperature ductility of polycrystalline Ni₃Al without ductility enhancing elements (Acta Metall. Mater., 38 (1990), 2667). More details on the microstructure and mechanical properties of the stoichiometric Ni₃Al grown by FZ-UDS were investigated in this paper. The solidification structure was dependent on the growth rate. The alloys showed a columnar grained and single phase structure with weak ‹100›, ‹110›, or ‹210› texture when the growth rate was above 13 mm/hr, and showed a large tensile elongation of more than 60% at room temperature. Crystallographic slip and transgranular fracture were observed on the fracture surface. Intergranular fracture was completely suppressed. When the growth rate was below than 13 mm/hr, the alloys precipitated martensitic second phases in the columnar grained Ni₃Al matrix and showed a smaller tensile elongation than that of the alloys grown at the growth rate of 24 mm/hr. These results indicate that the FZ-UDS is a promising method to improve the room temperature ductility of polycrystalline Ni₃Al.