Influence of growth rate on the microstructure and mechanical behaviour of a NiAl-Mo eutectic alloy

The effect of the growth condition on the microstructure and mechanical behaviour of the NiAl-Mo eutectic alloy was investigated. Samples of the eutectic alloy were prepared using an arc furnace under argon atmosphere and then directionally solidified. The samples directionally solidified showed regular and aligned eutectic microstructure. Compression tests were performed at room temperature and 1173 K. Vickers hardness was determined at several temperatures, from room temperature to 1150 K. Mechanical properties of NiAl were also determined. Results showed that when the growth rate is gradually increased from 8 to 50 mm/h the aligned microstructure presents higher fibre density, which leads to higher strength level at room temperature, while further increase in the growth rate causes the microstructure the loose regularity. NiAl presents a well defined mechanical behaviour transition, while the NiAl-Mo eutectic alloy softens almost linearly. The highest yield strength value of NiAl-Mo was found to be about 1200 and 300 MPa at room temperature and 1173 K, respectively. (C) 2004 Elsevier B.V All rights reserved.