The effects of SiC particles(SiCp)on high temperature oxidation behavior of titanium matrix composites(TMCs)under different powder metallurgy processes were investigated.In situ Ti C+Ti_(5)Si_(3)reinforced titanium ma...The effects of SiC particles(SiCp)on high temperature oxidation behavior of titanium matrix composites(TMCs)under different powder metallurgy processes were investigated.In situ Ti C+Ti_(5)Si_(3)reinforced titanium matrix composites were prepared by discharge plasma sintering(SPS)and argon protective sintering(APS).The results show that the two processes have a negligible effect on the composition and hardness of the samples,but the hardness of the two samples is significantly improved by adding SiCp.The apparent porosity of SPS process is obviously smaller than that of APS process,whereas,the apparent porosity increases slightly with the addition of SiCp.The oxide layer thickness and mass gain of the samples obtained by SPS process are smaller than those obtained by APS process.The oxide thickness and mass gain of both processes are further reduced by adding SiCp.The SPS composites showed the best high temperature oxidation resistance.Therefore,TMCs with Si Cp by SPS can effectively improve the high-temperature oxidation behavior of the materials.展开更多
Dense Nb/Nb5Si3 composites were fabricated via spark plasma sintering technology using Nb, Si, and Al elemental powders as raw materials. The microstructttres of the synthesised composites were analyzed through scanni...Dense Nb/Nb5Si3 composites were fabricated via spark plasma sintering technology using Nb, Si, and Al elemental powders as raw materials. The microstructttres of the synthesised composites were analyzed through scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. The results show that the composites consisted of residual Nb particle phase and Nb5Si3 phase. The microstructure of the Nb/ Nb5Si3 in situ composites was evidently affected by Al addition, which prompted the formation of the Al3Nb10Si3 phase. In addition, the Rockwell hardness of the composites decreased with the increase in AI additions. The Rockwell hardness of Nb-20Si is 60HRC, which decreased to approximately 52.7 HRC when the Al content increased to 15 at%. The oxidation resistance of the Nb/NbsSi3 in situ composites significantly improved with the increase in Al addition.展开更多
For hypereutectic Nb-Si based alloys,primary Nb_(5)Si_(3)phases typically grow in a faceted mode during equilibrium or near-equilibrium solidification,which damages the ductility and toughness.To address this issue,he...For hypereutectic Nb-Si based alloys,primary Nb_(5)Si_(3)phases typically grow in a faceted mode during equilibrium or near-equilibrium solidification,which damages the ductility and toughness.To address this issue,here we artificially manipulate the growth morphology of Nb_(5)Si_(3)using electron beam surface melting(EBSM)and subsequent annealing treatments.Results show that such a non-equilibrium solidification pathway enables the transition from faceted growth to non-faceted dendritic growth of Nb_(5)Si_(3),along with evident microstructure refinement,generation of metastableβ-Nb_(5)Si_(3)phases and elimination of chemical segregation.The transformation fromβ-Nb_(5)Si_(3)toα-Nb_(5)Si_(3)and Nb solid solution(Nbss)particles is triggered by the annealing treatment at 1450°C for 5 h.Also,we find the annealing-mediated formation of inherited Nb_(5)Si_(3)dendrites that maintain the dendritic morphology of the original as-solidifiedβ-Nb_(5)Si_(3)dendrites.This work thus provides a feasible routine to obtain thermally stable and refinedα-Nb_(5)Si_(3)dendrites in hypereutectic Nb-Si based alloys.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
By using Nb and Si elemental powders as raw materials, dense Nb/NbsSi3 composites were successfully fabricated by a spark plasma sintering （SPS） technology. The microstructure of the fabricated composites was analyz...By using Nb and Si elemental powders as raw materials, dense Nb/NbsSi3 composites were successfully fabricated by a spark plasma sintering （SPS） technology. The microstructure of the fabricated composites was analyzed by OM, SEM, XRD and EPMA; the microstructure evolution of the composites was also investigated by a quenching test. The experimental results show that the prepared composites consist of Nb and Nb5Si3 phases; Nb particle uniformly distributes in the in-situ synthesized Nb5Si3 matrix. During the SPS process, an interfacial reaction occurs between Nb and Si particles to synthesize Nb5Si3 until reactant silicon has been completely depleted.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
The high melting point and strong chemical bonding of NbB_(2)pose a great challenge to the preparation of high-density nanostructured NbB_(2)composite coating.Herein,we report a novel,simple,and efficient method to fa...The high melting point and strong chemical bonding of NbB_(2)pose a great challenge to the preparation of high-density nanostructured NbB_(2)composite coating.Herein,we report a novel,simple,and efficient method to fabricate in-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating by plasma spraying Nb_(2)O_(5)–B_(4)C–Al composite powder,aiming at realizing the higher densification and ultra-fine microstructure of NbB_(2)composite coating.The microstructure and properties of in-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating were studied comparatively with ex-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating(plasma spraying NbB_(2)–NbC–Al_(2)O_(3)composite powder).The reaction mechanism of Nb_(2)O_(5)–B_(4)C–Al composite powder in plasma jet was analyzed in detail.The results showed that the in-situ nanostructured NbB_(2)–NbC–Al_(2)O_(3)composite coating presented a lower porosity and superior performance including higher microhardness,toughness and wear resistance compared to the plasma sprayed ex-situ NbB_(2)–NbC–Al_(2)O_(3)coating and other boride composite coatings.Densification of the in-situ NbB_(2)–NbC–Al_(2)O_(3)coating was attributed to the low melting point of Nb_(2)O_(5)–B_(4)C–Al composite powder and the exothermic effect of in-situ reaction.The superior performance was ascribed to the density improvement and the strengthening and toughening effect of the nanosized phases.The in-situ reaction path could be expressed as:Nb_(2)O_(5)+Al®Nb+Al_(2)O_(3),and Nb+B_(4)C®NbB_(2)+NbC.展开更多
基金Funded by the Key Projects of Equipment Pre-research Foundation of the Ministry of Equipment Development of the Central Military Commission of China(No.6140922010201)the Key R&D Plan of Zhenjiang in 2018(No.GY2018021)。
文摘The effects of SiC particles(SiCp)on high temperature oxidation behavior of titanium matrix composites(TMCs)under different powder metallurgy processes were investigated.In situ Ti C+Ti_(5)Si_(3)reinforced titanium matrix composites were prepared by discharge plasma sintering(SPS)and argon protective sintering(APS).The results show that the two processes have a negligible effect on the composition and hardness of the samples,but the hardness of the two samples is significantly improved by adding SiCp.The apparent porosity of SPS process is obviously smaller than that of APS process,whereas,the apparent porosity increases slightly with the addition of SiCp.The oxide layer thickness and mass gain of the samples obtained by SPS process are smaller than those obtained by APS process.The oxide thickness and mass gain of both processes are further reduced by adding SiCp.The SPS composites showed the best high temperature oxidation resistance.Therefore,TMCs with Si Cp by SPS can effectively improve the high-temperature oxidation behavior of the materials.
基金Funded by National Natural Science Foundation of China(No.51271091)Science Project of Jiangxi Ministry of Education of China(No.GJJ12420)
文摘Dense Nb/Nb5Si3 composites were fabricated via spark plasma sintering technology using Nb, Si, and Al elemental powders as raw materials. The microstructttres of the synthesised composites were analyzed through scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. The results show that the composites consisted of residual Nb particle phase and Nb5Si3 phase. The microstructure of the Nb/ Nb5Si3 in situ composites was evidently affected by Al addition, which prompted the formation of the Al3Nb10Si3 phase. In addition, the Rockwell hardness of the composites decreased with the increase in AI additions. The Rockwell hardness of Nb-20Si is 60HRC, which decreased to approximately 52.7 HRC when the Al content increased to 15 at%. The oxidation resistance of the Nb/NbsSi3 in situ composites significantly improved with the increase in Al addition.
基金National Natural Science Foundation of China(Grant No.51571004).
文摘For hypereutectic Nb-Si based alloys,primary Nb_(5)Si_(3)phases typically grow in a faceted mode during equilibrium or near-equilibrium solidification,which damages the ductility and toughness.To address this issue,here we artificially manipulate the growth morphology of Nb_(5)Si_(3)using electron beam surface melting(EBSM)and subsequent annealing treatments.Results show that such a non-equilibrium solidification pathway enables the transition from faceted growth to non-faceted dendritic growth of Nb_(5)Si_(3),along with evident microstructure refinement,generation of metastableβ-Nb_(5)Si_(3)phases and elimination of chemical segregation.The transformation fromβ-Nb_(5)Si_(3)toα-Nb_(5)Si_(3)and Nb solid solution(Nbss)particles is triggered by the annealing treatment at 1450°C for 5 h.Also,we find the annealing-mediated formation of inherited Nb_(5)Si_(3)dendrites that maintain the dendritic morphology of the original as-solidifiedβ-Nb_(5)Si_(3)dendrites.This work thus provides a feasible routine to obtain thermally stable and refinedα-Nb_(5)Si_(3)dendrites in hypereutectic Nb-Si based alloys.
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.
基金the National Natural Science Foundation of China (No.50276023,50574042)
文摘By using Nb and Si elemental powders as raw materials, dense Nb/NbsSi3 composites were successfully fabricated by a spark plasma sintering （SPS） technology. The microstructure of the fabricated composites was analyzed by OM, SEM, XRD and EPMA; the microstructure evolution of the composites was also investigated by a quenching test. The experimental results show that the prepared composites consist of Nb and Nb5Si3 phases; Nb particle uniformly distributes in the in-situ synthesized Nb5Si3 matrix. During the SPS process, an interfacial reaction occurs between Nb and Si particles to synthesize Nb5Si3 until reactant silicon has been completely depleted.
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The authors gratefully acknowledge the financial supports of the National Natural Science Foundation of China(No.52072110)the Natural Science Foundation of Hebei Province(No.E2018202034).
文摘The high melting point and strong chemical bonding of NbB_(2)pose a great challenge to the preparation of high-density nanostructured NbB_(2)composite coating.Herein,we report a novel,simple,and efficient method to fabricate in-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating by plasma spraying Nb_(2)O_(5)–B_(4)C–Al composite powder,aiming at realizing the higher densification and ultra-fine microstructure of NbB_(2)composite coating.The microstructure and properties of in-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating were studied comparatively with ex-situ NbB_(2)–NbC–Al_(2)O_(3)composite coating(plasma spraying NbB_(2)–NbC–Al_(2)O_(3)composite powder).The reaction mechanism of Nb_(2)O_(5)–B_(4)C–Al composite powder in plasma jet was analyzed in detail.The results showed that the in-situ nanostructured NbB_(2)–NbC–Al_(2)O_(3)composite coating presented a lower porosity and superior performance including higher microhardness,toughness and wear resistance compared to the plasma sprayed ex-situ NbB_(2)–NbC–Al_(2)O_(3)coating and other boride composite coatings.Densification of the in-situ NbB_(2)–NbC–Al_(2)O_(3)coating was attributed to the low melting point of Nb_(2)O_(5)–B_(4)C–Al composite powder and the exothermic effect of in-situ reaction.The superior performance was ascribed to the density improvement and the strengthening and toughening effect of the nanosized phases.The in-situ reaction path could be expressed as:Nb_(2)O_(5)+Al®Nb+Al_(2)O_(3),and Nb+B_(4)C®NbB_(2)+NbC.
