|Comparative study of microstructural and mechanical properties of two directionally solidified intermetallic nickel-based alloys|
vol. 40 (2002), no. 4, pp. 209 - 221
Microstructure, hardness, room-temperature tensile properties, high-temperature compressive properties, and creep of two directionally solidified and annealed multiphase intermetallic alloys with chemical composition Ni-21.7Al-7.5Cr-6.5Ti and Ni-20.2Al-8.2Cr-2.4Fe [at.%] were studied. The microstructure of both as-grown alloys consisted of γ' (Ni3Al)-phase, γ-phase (Ni-based solid solution), β (NiAl)-phase and α-Cr precipitates. Microstructural changes observed during annealing significantly increased room-temperature yield stress of the alloy with addition of Ti and ductility of the alloy with addition of Fe. The compressive yield stress increased with increasing temperature, reaching peak values at about 700 and 760 °C for the alloy modified by Ti and Fe, respectively. For both alloys the creep stress exponent was determined to vary between 4.0 and 4.5 over the studied temperature range from 700 to 877 °C. The apparent activation energy for creep was calculated to be 380 and 316 kJ.mol -1 for the alloy modified by Ti and Fe, respectively.
multiphase intermetallics, mechanical properties, phase transformations, microscopy
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