Compressive Properties of Lotus NiAl at Room Temperature

초록

Intermetallic compound NiAl with ordered BCC structure is an attractive structural material for its using at elevated temperature because of its high melting point, low density and high strength. Brittleness at room temperature and low creep strength at elevated temperature, however, are obstacles for its using. Recently, several studies have been reported about preventing brittle behavior by controlling materials structure. The purpose of this study was to investigate the 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. Also, nonporous NiAl rods were fabricated under a pressurized argon atmosphere with the above method for the comparison with Lotus NiAl. Specimen size was 5x5x7.5mm and its pore axis to the compressive direction was parallel and perpendicular. Specimens were homogenized and carried out compression test in the strain rate of 1.1x10-3/s at room temperature. Strain to the fracture of Lotus NiAl was much higher than nonporous NiAl approximately 4 to 5 times. Also, Lotus NiAl exhibited much higher energy absorption to the fracture per unit volume than that of nonporous specimens. The specimen, of which pore axis to the compressive direction ddj was parallel, presented higher yield strength than that of perpendicular. Initial crack was generated around the pore, and then subsequently propagated and stop at the other pore while the load was increasing. The behavior of the crack was confirmed by scanning electron microscopy. From the result of the present work, it could be a possible method to prevent brittle behavior when cylindrical pore is existed in the matrix of brittle material