Ni-25Al-15Cr （atomic percent, %） alloy was directionally solidified （DS） under argon atmosphere in an Al2O3-SiO2 ceramic mold by standard Bridgman method. The microstructure of the as-fabricated alloy was studied ...Ni-25Al-15Cr （atomic percent, %） alloy was directionally solidified （DS） under argon atmosphere in an Al2O3-SiO2 ceramic mold by standard Bridgman method. The microstructure of the as-fabricated alloy was studied using optical microscope, X-ray diffractometer, and scanning electron microscope. The alloy consisting of dendritic β- NiAl phase, interdendritic γ/γ′ phase, and transient layer γ′ phase, has been investigated. This alloy exhibits superplastic deformation behavior at 1 273-1 373 K over an initial strain rate range of 8. 35×10 ^-4 -1. 67×10^-2s^-1. The maximum elongation of 280% with strain rate sensitivity index m= 0. 22 was obtained at the temperature of 1 323 K and an initial strain rate of 8. 35×10^-3s^-1. Transmission electron microscopy （TEM） observations indicate that the superplastic deformation stems from the balance between high resistance （by dislocation sliding） and strain softening （by dynamic recovery and recrystallization）.展开更多
The oxidation behavior of NiAl-30.75Cr-3Mo-0.25Ho alloy from 1300 to 1500 K in air atmosphere was investigated. The results reveal that oxidation resistance of the alloy is improved by the addition of Ho. At 1500 K, t...The oxidation behavior of NiAl-30.75Cr-3Mo-0.25Ho alloy from 1300 to 1500 K in air atmosphere was investigated. The results reveal that oxidation resistance of the alloy is improved by the addition of Ho. At 1500 K, the oxidation kinetic curve obeys the parabolic law （n ≈0.5）, whereas the oxidation kinetic curve of the tested alloy follows the cubic relations （n ≈ 0.3 - 0.4） from 1300 to 1450 K. An activation energy of about 261 kJ·mol^-1 was determined for the tested alloy. It is found that a continuous and compact Al2O3 layer has formed on the surface of NiAl-30.75Cr-3Mo-0.25Ho alloy after oxidation 100 h at various tested temperatures. A rich-Ho solution formed on the boundaries of Cr（Mo） phase. Doped little amount of Ho in NiAl-31Cr-3Mo alloy promotes the transformation from θ-Al2O3 phase to α-A1203 phase, and decreases the size of Al2O3 and the crack forming in the oxidation scale prolongs the spalling time of the film at high temperature. The volatilizing oxides of Cr, Mo and the reactive element effects （REEs） make the mass gain lower than that of pure NiAl.展开更多
文摘Ni-25Al-15Cr （atomic percent, %） alloy was directionally solidified （DS） under argon atmosphere in an Al2O3-SiO2 ceramic mold by standard Bridgman method. The microstructure of the as-fabricated alloy was studied using optical microscope, X-ray diffractometer, and scanning electron microscope. The alloy consisting of dendritic β- NiAl phase, interdendritic γ/γ′ phase, and transient layer γ′ phase, has been investigated. This alloy exhibits superplastic deformation behavior at 1 273-1 373 K over an initial strain rate range of 8. 35×10 ^-4 -1. 67×10^-2s^-1. The maximum elongation of 280% with strain rate sensitivity index m= 0. 22 was obtained at the temperature of 1 323 K and an initial strain rate of 8. 35×10^-3s^-1. Transmission electron microscopy （TEM） observations indicate that the superplastic deformation stems from the balance between high resistance （by dislocation sliding） and strain softening （by dynamic recovery and recrystallization）.
文摘The oxidation behavior of NiAl-30.75Cr-3Mo-0.25Ho alloy from 1300 to 1500 K in air atmosphere was investigated. The results reveal that oxidation resistance of the alloy is improved by the addition of Ho. At 1500 K, the oxidation kinetic curve obeys the parabolic law （n ≈0.5）, whereas the oxidation kinetic curve of the tested alloy follows the cubic relations （n ≈ 0.3 - 0.4） from 1300 to 1450 K. An activation energy of about 261 kJ·mol^-1 was determined for the tested alloy. It is found that a continuous and compact Al2O3 layer has formed on the surface of NiAl-30.75Cr-3Mo-0.25Ho alloy after oxidation 100 h at various tested temperatures. A rich-Ho solution formed on the boundaries of Cr（Mo） phase. Doped little amount of Ho in NiAl-31Cr-3Mo alloy promotes the transformation from θ-Al2O3 phase to α-A1203 phase, and decreases the size of Al2O3 and the crack forming in the oxidation scale prolongs the spalling time of the film at high temperature. The volatilizing oxides of Cr, Mo and the reactive element effects （REEs） make the mass gain lower than that of pure NiAl.
