Compressive Properties of Porous NiAl Fabricated by Unidirectional Solidification

초록

Intermetallic compound NiAl with B2 crystal structure has been widely researched for few decades. Because of its high melting point, low density, good electrical and thermal conductivity, NiAl has been considered as a promising structural material at elevated temperature. However, NiAl has several drawbacks such as poor low temperature ductility and high temperature creep strength. Recently, several studies have been reported to reduce these drawbacks from directional solidifying. The purpose of this study was to investigate the temperature dependence of compressive properties of lotus NiAl when the cylindrical pore was unidirectionally existed in the NiAl matrix by directional solidifying. Lotus NiAl rods were fabricated by using continuous zone melting technique under a pressurized hydrogen gas. Compressive specimens were cut from the ingot and carried out compression test at 298K, 673K and 873K. Also, nonporous specimens were tested for the comparison with lotus specimens. After compression test at 298K, all specimens showed brittle behavior but lotus specimens showed higher ductility than nonporous specimens. After compression test at 673K, lotus NiAl showed ductile behavior but nonporous NiAl showed still brittle behavior on the contrary. In the case of 873K, all specimens showed ductile behavior. Compressive stress and yield stress of lotus and nonporous NiAl was decreased with increasing temperature. Anisotropic compressive properties between parallel and perpendicular solidification direction to the compressive direction were also shown. Crystallographic orientation of each solidifying direction was confirmed by electron backscattered diffraction (EBSD).