Effects of Hf additions on high-temperature mechanical properties of a directionally solidified NiAl/Cr(Mo) eutectic alloy

In order to improve the high-temperature mechanical properties of NiAl/Cr(Mo) alloys, the effects of Hf additions on microstructure and mechanical properties were systemically examined. Two directionally solidified alloys with composition of Ni-32Al-28Cr-(6-x)Mo-xHf (x = 0.2 and 0.5 at.%. respectively), named as 0.2Hf and 0.5Hf hereafter, were prepared. The Hf additions disturbed the cellular structure. The 0.2Hf alloy consisted of dendritic structure, while the 0.51-If alloy had an intercellular structure. In the 0.51-If alloy, the Ni2AlHf and Ni16Hf6Si7 precipitates were also confirmed. The high-temperature strength and brittle-to-ductile transition temperature (BDTT) increased with increasing of Hf additions, due to the different strengthening mechanism. In contrast, the ductility and creep resistance decreased with increasing off-If because of the disturbance of cellular structure. (C) 2007 Elsevier B.V. All rights reserved.