Effect of microstructure morphology on the high temperature tensile properties and deformation in directionally solidified NiAl-Cr(Mo) eutectic alloy

Abstract

High temperature tensile properties and microstructure morphologies of directionally solidified NiAl-Cr(Mo) alloy under different compositions and withdrawal rates were investigated. Tensile strength of 513.8MPa was obtained in the directionally solidified NiAl-36Cr-6Mo hypereutectic alloy at 1000°C, which is the highest value reported in the NiAl-Cr(Mo) alloy until now. In addition, perfect cellular eutectic alloy solidified at fast withdrawal rate possessed higher tensile strength and elongation than planar eutectic alloy solidified at low withdrawal rate when they had the same composition. This is because bonding strength between eutectic cells in the perfect cellular eutectic alloy was high, which resulted in high crack propagation resistance and harmonious deformations in the intracellular and intercellular regions. The results above may change the locked-in view that only regular eutectic microstructure morphology grown with planar solid/liquid interface could be used in the eutectic in-situ composites. Perfect cellular microstructure morphology grown in a far fast rate could be also used, which would result in high efficiency in the industrial production. Refined microstructure, larger volume fraction of strengthening phase and dispersion strengthening of second phase particles were contribute to the improvement of high temperature tensile strength of the directionally solidified NiAl-Cr(Mo) alloy. However, the bonding strength of interface was obviously different in the alloys with different microstructure morphologies, which had significant effect on the tensile strength. When bonding strength of phase interface was low, the other strengthening factors could not be able to play their due roles, thus leading to relatively low tensile strength.