Elevated Temperature Compressive Properties of Lotus NiAl

초록

Intermetallic compound B2 aluminide NiAl is an attractive high temperature structural material because of its high melting temperature, low density, good thermal conductivity and high stiffness. However, inherent low temperature brittleness and inadequate high temperature strength are obstacles which prevent NiAl from being widely applied. Recently, several studies have been reported to reduce both of these drawbacks by directional solidifying. The purpose of this study was to investigate the elevated temperature compressive properties when the cylindrical pore was unidirectionally existed in the NiAl matrix. Lotus NiAl rods were fabricated by using continuous zone melting technique under a pressurized hydrogen atmosphere from raw ingot. Compressive specimens were cut from the ingot and carried out compression test at 673K and 873K. Also, nonporous specimens were tested for the comparison with lotus 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 was also confirmed. Crystallographic orientation with direction was different that (100) plane was dominantly oriented in the parallel specimen, and (110) plane was oriented in the perpendicular specimen confirmed by electron backscattered diffraction (EBSD). Microstructure and fracture surface was observed with optical and scanning electron microscope (OM, SEM).