In this work, the Nb-14Si 24Ti-10Cr-2Al-2Hf-0.1Y alloy （at.%） was processed by the liquid-metal-cooled directional solidification （DS） at 1750 ℃ with withdrawal rates of 1.2, 6, 18 mm/min and post heat treatment ...In this work, the Nb-14Si 24Ti-10Cr-2Al-2Hf-0.1Y alloy （at.%） was processed by the liquid-metal-cooled directional solidification （DS） at 1750 ℃ with withdrawal rates of 1.2, 6, 18 mm/min and post heat treatment （HT） at 1450 ℃ for 10 h. The microstructures of the direction- ally solidified and heat treated samples were investigated. The results show that the microstructure of directionally solidified alloy mainly consists of petaloid Nbss ＋ Nb5Si3 eutectics and Ti-rich Nbss ＋ Nb5Si3 ＋ Cr2Nb eutectics. With the increase of withdrawal rate, the primary NbsSi3 is eliminated, Nbss ＋ Nb5Si3 eutectic cells turn round and connected with the microstructure refine- ment and Nbss ＋ Nb5Si3 ＋ CrzNb eutectics turn to a river-like morphology. After heat treatment, Nbss ＋ Nb5Si3 ＋ Cr2Nb eutectics disappeared and petaloid Nbss ＋ Nb5Si3 eutectics turn to a spe- cific fiber-mesh structure gradually, which is promoted by higher withdrawal rates. Furthermore, both the volume fraction of Cr2Nb and the content of Cr in Nbss of Nbss ＋ Nb5Si3 eutectics change regularly with the increase of withdrawal rate and heat treatment at 1450 ℃ for 10 h.展开更多
An Nb-14Si-22Ti-4Cr-2AI-2Hf-0.15Y（at.%） alloy was prepared by directional solidification （DS） with liquid metal cooling, and the withdrawal rates selected were 1.2, 6, and 18 mm-min1, respectively. The Influence o...An Nb-14Si-22Ti-4Cr-2AI-2Hf-0.15Y（at.%） alloy was prepared by directional solidification （DS） with liquid metal cooling, and the withdrawal rates selected were 1.2, 6, and 18 mm-min1, respectively. The Influence of withdrawal rate and heat treatment on the microstructural evolution, fracture toughness and tensile strength at room temperature were investigated. Results show that the directionally solidified microstructure is composed of primary （Nb, X）ss dendrites and （Nb, X）ss/a-（Nb, X）5Si3 eutectic cells aligning with the growth direction. The formation of bulk Nb3Si is suppressed. With an increase in withdrawal rate, the dendrite arm spacing of （Nb, X）ss decreases, and the （Nb, X）ss/a-（Nb, X）5Si3 eutectic cells become finer and distribute homogeneously. Directional solidification can significantly improve the room temperature fracture toughness, especially the alloy with a withdrawal rate of 6 mm.min-1; its average value reaches 14.1 MPa.m^0.5, about 34% higher than that of the alloy without directional solidification. The withdrawal rate has obvious effect on tensile strength, and the tensile strength is improved from 200 MPa to 429 MPa as the withdrawal rate increases from 1.2 mm.min-1 to 1.8 mm-min-1. After heat treatment, the primary （Nb, X）ss branches become coarser; both the room temperature fracture toughness and tensile strength of the alloys solidified at 1.2 and 6 mm.min 1 are somewhat lower than the corresponding values of the alloy without heat treatment, while they are higher than the corresponding values of the alloy without heat treatment when solidified at 18 mm-min4.展开更多
基金supported by National Natural Science Foundation of China (No. 51101005)
文摘In this work, the Nb-14Si 24Ti-10Cr-2Al-2Hf-0.1Y alloy （at.%） was processed by the liquid-metal-cooled directional solidification （DS） at 1750 ℃ with withdrawal rates of 1.2, 6, 18 mm/min and post heat treatment （HT） at 1450 ℃ for 10 h. The microstructures of the direction- ally solidified and heat treated samples were investigated. The results show that the microstructure of directionally solidified alloy mainly consists of petaloid Nbss ＋ Nb5Si3 eutectics and Ti-rich Nbss ＋ Nb5Si3 ＋ Cr2Nb eutectics. With the increase of withdrawal rate, the primary NbsSi3 is eliminated, Nbss ＋ Nb5Si3 eutectic cells turn round and connected with the microstructure refine- ment and Nbss ＋ Nb5Si3 ＋ CrzNb eutectics turn to a river-like morphology. After heat treatment, Nbss ＋ Nb5Si3 ＋ Cr2Nb eutectics disappeared and petaloid Nbss ＋ Nb5Si3 eutectics turn to a spe- cific fiber-mesh structure gradually, which is promoted by higher withdrawal rates. Furthermore, both the volume fraction of Cr2Nb and the content of Cr in Nbss of Nbss ＋ Nb5Si3 eutectics change regularly with the increase of withdrawal rate and heat treatment at 1450 ℃ for 10 h.
基金financially supported by the National Natural Science Foundation of China(No.51101005)
文摘An Nb-14Si-22Ti-4Cr-2AI-2Hf-0.15Y（at.%） alloy was prepared by directional solidification （DS） with liquid metal cooling, and the withdrawal rates selected were 1.2, 6, and 18 mm-min1, respectively. The Influence of withdrawal rate and heat treatment on the microstructural evolution, fracture toughness and tensile strength at room temperature were investigated. Results show that the directionally solidified microstructure is composed of primary （Nb, X）ss dendrites and （Nb, X）ss/a-（Nb, X）5Si3 eutectic cells aligning with the growth direction. The formation of bulk Nb3Si is suppressed. With an increase in withdrawal rate, the dendrite arm spacing of （Nb, X）ss decreases, and the （Nb, X）ss/a-（Nb, X）5Si3 eutectic cells become finer and distribute homogeneously. Directional solidification can significantly improve the room temperature fracture toughness, especially the alloy with a withdrawal rate of 6 mm.min-1; its average value reaches 14.1 MPa.m^0.5, about 34% higher than that of the alloy without directional solidification. The withdrawal rate has obvious effect on tensile strength, and the tensile strength is improved from 200 MPa to 429 MPa as the withdrawal rate increases from 1.2 mm.min-1 to 1.8 mm-min-1. After heat treatment, the primary （Nb, X）ss branches become coarser; both the room temperature fracture toughness and tensile strength of the alloys solidified at 1.2 and 6 mm.min 1 are somewhat lower than the corresponding values of the alloy without heat treatment, while they are higher than the corresponding values of the alloy without heat treatment when solidified at 18 mm-min4.
