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
Diffusion bonding of refractory Nb–Si-based alloy was performed with Ni/Al and Ti/Al nanolayers under the condition of 1473 K/30 MPa/60 min.The NbSS/Nb5Si3 in situ composite with the nominal composition of Nb–22 Ti...Diffusion bonding of refractory Nb–Si-based alloy was performed with Ni/Al and Ti/Al nanolayers under the condition of 1473 K/30 MPa/60 min.The NbSS/Nb5Si3 in situ composite with the nominal composition of Nb–22 Ti–16 Si–3 Cr–3 Al–2 Hf was used as the parent material.The joint microstructures were examined by using a scanning electron microscope equipped with an X-ray energy dispersive spectrometer.Shear test was conducted for the bonded joints at room temperature.Within the joint bonded with Ni/Al multilayer,element diffusion occurred between the base metal and the nanolayer,with the reaction products of AlNb2+Ni3 Al,NiAl and AlNi2 Ti phases.The average shear strength was 182 MPa.While using Ti/Al multilayer,the interface mainly consisted of TiAl,(Ti,Nb)Al and(Ti,Nb)2 Al phases,and the corresponding joints exhibited an increased strength of 228 MPa.In this case,the fracture mainly took place in the TiAl phase and presented a typical brittle characteristic.展开更多
New filler alloy composition of Ti66-Ni22-Nb12(at.%)was designed for NbSS/Nb5 Si3 composite joining and the brazing experiment was conducted at 1200℃and 1260℃,respectively.Compared with the previously reported Ti-Ni...New filler alloy composition of Ti66-Ni22-Nb12(at.%)was designed for NbSS/Nb5 Si3 composite joining and the brazing experiment was conducted at 1200℃and 1260℃,respectively.Compared with the previously reported Ti-Ni-Nb system filler alloys,the concentration of Ni was significantly decreased from 40 at.%to 22 at.%.The filler alloy was fabricated into brazing foils by rapid solidification technique,with about 60μm thickness.The brazing seam mainly consisted of Nb solid solution,(Nb,Ti)5 Si3 and residual NiTi2 phases.Due to the high content of stabilization element Ti in the filler alloy,hexagonalγ-Nb5 Si3 phase was detected in the brazing seam.When increasing brazing temperature or prolonging brazing time,the amount of residual NiTi2 phase within the joint was gradually decreased.The joints brazed at 1260℃for 60 min exhibited three-point bend strength of 317 MPa.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 Beijing Municipal Science & Technology Commission (No. Z171100002217048)the National Natural Science Foundation of China (No. 51705489)
文摘Diffusion bonding of refractory Nb–Si-based alloy was performed with Ni/Al and Ti/Al nanolayers under the condition of 1473 K/30 MPa/60 min.The NbSS/Nb5Si3 in situ composite with the nominal composition of Nb–22 Ti–16 Si–3 Cr–3 Al–2 Hf was used as the parent material.The joint microstructures were examined by using a scanning electron microscope equipped with an X-ray energy dispersive spectrometer.Shear test was conducted for the bonded joints at room temperature.Within the joint bonded with Ni/Al multilayer,element diffusion occurred between the base metal and the nanolayer,with the reaction products of AlNb2+Ni3 Al,NiAl and AlNi2 Ti phases.The average shear strength was 182 MPa.While using Ti/Al multilayer,the interface mainly consisted of TiAl,(Ti,Nb)Al and(Ti,Nb)2 Al phases,and the corresponding joints exhibited an increased strength of 228 MPa.In this case,the fracture mainly took place in the TiAl phase and presented a typical brittle characteristic.
基金financially supported by the National Natural Science Foundation of China(Nos.51605456,51705489 and51804286)the Beijing Municipal Science&Technology Commission(No.Z171100002217048)。
文摘New filler alloy composition of Ti66-Ni22-Nb12(at.%)was designed for NbSS/Nb5 Si3 composite joining and the brazing experiment was conducted at 1200℃and 1260℃,respectively.Compared with the previously reported Ti-Ni-Nb system filler alloys,the concentration of Ni was significantly decreased from 40 at.%to 22 at.%.The filler alloy was fabricated into brazing foils by rapid solidification technique,with about 60μm thickness.The brazing seam mainly consisted of Nb solid solution,(Nb,Ti)5 Si3 and residual NiTi2 phases.Due to the high content of stabilization element Ti in the filler alloy,hexagonalγ-Nb5 Si3 phase was detected in the brazing seam.When increasing brazing temperature or prolonging brazing time,the amount of residual NiTi2 phase within the joint was gradually decreased.The joints brazed at 1260℃for 60 min exhibited three-point bend strength of 317 MPa.
