The effects of preheating temperature and W powder size on the Self propagating High temperature Synthesis(SHS) of Ti W C system were studied. Preheated mixtures and the decrease of W powder size can accelerate the fo...The effects of preheating temperature and W powder size on the Self propagating High temperature Synthesis(SHS) of Ti W C system were studied. Preheated mixtures and the decrease of W powder size can accelerate the formation of (W,Ti)C powders. The uniphase (W,Ti)C (WC∶TiC=5∶5) powders with 0.32% free carbon were synthesized from Ti, W, C powders by SHS. The powder size of the product was 3~5 μm.展开更多
High quality nano-sized zirconium carbide (ZrC) powders were successfully fabricated via a developed chemical active dilution self-propagating high-temperature synthesis (SHS) method assisted by ball milling pretr...High quality nano-sized zirconium carbide (ZrC) powders were successfully fabricated via a developed chemical active dilution self-propagating high-temperature synthesis (SHS) method assisted by ball milling pretreatment process using traditional cheap zirconium dioxide powder (ZrO2), magnesium powder (Mg) and sucrose (C12H22Oll) as raw materials. FSEM, TEM, HRTEM, SAED, XRD, FTIR and Raman, ICP- AES, laser particle size analyzer, oxygen and nitrogen analyzer, carbon/sulfur determinator and TG-DSC were employed for the characterization of the morphology, structure, chemical composition and thermal stability of the as-synthesized ZrC samples. The as-synthesized samples demonstrated high purity, low oxygen content and evenly distributed ZrC nano-powders with an average particle size of 50nm. In addition, the effects of endothermic rate and the possible chemical reaction mechanism were also discussed.展开更多
TiC-TiB2-Cu composites were produced by self-propagating high-temperature synthesis combined with pseudo hot isostatic pressing using Ti, B4C and Cu powders. The microstructure and mechanical properties of the composi...TiC-TiB2-Cu composites were produced by self-propagating high-temperature synthesis combined with pseudo hot isostatic pressing using Ti, B4C and Cu powders. The microstructure and mechanical properties of the composites were investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the final products were only TiC, TiB2 and Cu phases. The clubbed TiB2 grains and spheroidal or irregular TiC grains were found in the microstructure of synthesized products. The reaction temperature and grain size of TiB2 and TiC particles decreased with increasing Cu content. The introduction of Cu into the composites resulted in a drastic increase in the relative density and flexual strength, and the maximum values were obtained with the addition of 20 wt pct, while the fracture toughness was the best when Cu content was 40 wt pct.展开更多
Using KClO3 as an inner oxidant, MnZn-ferrite powder was synthesized by a self-propagating high-temperature synthesis (SHS) process in normal air atmosphere. The effects of the inner oxidant on combustion temperature,...Using KClO3 as an inner oxidant, MnZn-ferrite powder was synthesized by a self-propagating high-temperature synthesis (SHS) process in normal air atmosphere. The effects of the inner oxidant on combustion temperature, combustion velocity, microstructure and the phase of the product were investigated by XRD and SEM,respectively. The results show that a highly ferritized powder can be obtained as well as the highest combustion temperature and the highest combustion velocity when the inner oxidant content m equals 54(k-16).展开更多
Influence of Fe addition on products of self-propagating high-temperature synthesis (SHS) reaction in 3Ti-Si-2C system was investigated in the present study. Without Fe addition, Ti5Si3 and TiC are the dominant phases...Influence of Fe addition on products of self-propagating high-temperature synthesis (SHS) reaction in 3Ti-Si-2C system was investigated in the present study. Without Fe addition, Ti5Si3 and TiC are the dominant phases along with a small amount of Ti3SiC2 phase and unreacted C left in the final products. As Fe content ranges from 10% to 30%, the products consist of TiC, Ti5Si3, Fe2Ti and unreacted C, but no trace of Ti3SiC2 phase is detected. Furthermore, the amounts of both Fe2Ti and C phases increase with Fe content increasing. Addition of Fe has a great effect on the reaction route and significantly restrains the formation of Ti3SiC2 during the combustion synthesis process, and therefore, the SHS is not an effective fabrication technique to synthesize the ternary Ti3SiC2 ceramic in either 3Ti-Si-2C or Fe-3Ti-Si-2C system. Besides, without Fe addition, Ti5Si3 presents as the coarse irregular appearance with an obviously sintered morphology. In contrast, the shape of Ti5Si3 exhibits more and more spherical (cobblestone-like) and the surface becomes increasingly smooth, because the amount of liquids formed during the SHS reaction increases with the increase of Fe content. On the other hand, with Fe content increasing from 0 to 30 wt.%, the particulate size of TiC decreases from more than 5 μm to 1 μm or less, mainly due to the fact that the combustion temperature decreases with the increase of Fe content in the preforms.展开更多
MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagatin...MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagating high temperature synthesis (SHS). Pure MoSi2 was obtained and a compound of MoSi2 and WSi2was synthesized in the form of predominant solid solution (Mo,W)Si2. By adding aluminum of 5.5 at.% to Mo-Si, the crystal structure of MoSi2 changed into a mixture of tetragonal Cllb MoSi2and hexagonal C40 Mo(Si,Al)2. The (Mo,W)Si2-Mo(Si,Al)2-W(Si,Al)2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-Si. However, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. SHS is an effective technology for synthesis of MoSi2 and MoSi2 matrix composites.展开更多
The mechanism of self-propagating high-temperature synthesis (SHS) of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scannin...The mechanism of self-propagating high-temperature synthesis (SHS) of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope (SEM) with energy dispersive X-ray (EDX) spectrometry, and the combustion temperature was measured. The results showed that the combustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solution. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.展开更多
ZrB2 ceramics were prepared by self-propagating high-temperature synthesis(SHS) and were sintered by hot pressing(HP).The effects of the granularities and doses of raw materials in Zr-B2O3-Mgon SHS process and pro...ZrB2 ceramics were prepared by self-propagating high-temperature synthesis(SHS) and were sintered by hot pressing(HP).The effects of the granularities and doses of raw materials in Zr-B2O3-Mgon SHS process and product were investigated.XRD and combustion temperature curves prove that the ideal SHS reactants of Zr-B2O3-Mg are 50μm Zr powder,75μm B2O3 powder and 400μm Mg powder with 45% excessive.The particle sizes of SHS product,acid-leached product,sintered product are 2-5μm,0.5-2μm,2-10μm respectively.Chemical analysis indicates that the acid-leached product consists of ZrB2(94.59%),ZrO2(3.87%),and H3BO3(1.54%),The sintered product has a relative density of 95.4%.展开更多
Self-propagating high-temperature synthesis(SHS) method was used to synthesize ZrB2/Al2O3 composite powders from B2O3-ZrO2-Al system. X-ray diffractometry(XRD) and scanning electron microscopy(SEM) analyses show...Self-propagating high-temperature synthesis(SHS) method was used to synthesize ZrB2/Al2O3 composite powders from B2O3-ZrO2-Al system. X-ray diffractometry(XRD) and scanning electron microscopy(SEM) analyses show the presence of ZrB2 and Al2O3 as the primary phases in the composite powders, while the presence of a very small amount of ZrO2 is thought to be unreacted zirconium oxide. Transmission electron microscopy(TEM) and high resolution electron microscopy(HREM) observations of microstructure of the composite powders indicate that the interfaces of ZrB2/Al2O3 bond well without any interfacial reaction products. It is proposed that the good interfacial bonding of composite powders results from the ZrB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.展开更多
Self-propagating high-temperature synthesis(SHS)was used to fabricate a Fe(Cr)–Al2O3 nanocomposite.The composite was fabricated by the reactions between the powders of Fe,Fe2O3,Cr2O3,and Al.The effect of blending rat...Self-propagating high-temperature synthesis(SHS)was used to fabricate a Fe(Cr)–Al2O3 nanocomposite.The composite was fabricated by the reactions between the powders of Fe,Fe2O3,Cr2O3,and Al.The effect of blending ratio and mechanical activation of the initial powders and the precursor compressing pressure on the microstructure of the final product was studied by optical microscopy,scanning electron microscopy,transmission electron microscopy,and X-ray diffraction.The significance of the effect of each of the aforementioned parameters on the quality of the composite(assessed by measuring the compressive strength and wear resistance)was determined using a full-factorial design of experiments method.The results showed that the best molar powder ratio that produced the most homogeneous product through a sustainable SHS reaction was Fe:Fe2O3:Cr2O3:Al=10:1:1:4.A lower Fe content caused the Fe(Cr)phase to melt and separate from the rest of the materials.展开更多
In order to investigate the microstructural evolution during self-propagating high-temperature synthesis (SHS) of Ti-Al powder mixture with an atomic ratio of Ti: Al=1:1, a combustion front quenching method (CFQM...In order to investigate the microstructural evolution during self-propagating high-temperature synthesis (SHS) of Ti-Al powder mixture with an atomic ratio of Ti: Al=1:1, a combustion front quenching method (CFQM) was used for extinguishing the propagating combustion wave, and the microstructures on the quenched sample were observed with scanning electron microscope (SEM) and analyzed with energy dispersive spectrometry (EDS). In addition, the combustion temperature of the reaction was measured, and the phase constituent of the synthesized product was inspected by X-ray diffraction (XRD). The results showed that the combustion reaction started from melting of the Al particles, and the melting resulted in dissolving of the Ti particles and forming of Al3Ti grains. As the Al liquid was depleted, the combustion reaction proceeded through solid-state diffusion between the solid Al3Ti and the solid Ti. This led to the forming of TiAl and Ti3Al diffusing layers. In addition, the combustion reaction is incomplete besides TiAl, there are a large amount of Ti3Al and TiAl3 and a small amount of Ti in the final product. This incompleteness chiefly results from the using of coarser Ti powder.展开更多
In this paper, Ti–Cr–Al–C materials were investigated by self-propagating high-temperature synthesis(SHS) according to the experimental study and numerical simulation results. The highest adiabatic combustion tem...In this paper, Ti–Cr–Al–C materials were investigated by self-propagating high-temperature synthesis(SHS) according to the experimental study and numerical simulation results. The highest adiabatic combustion temperature Tadof 2,467.45 K indicates that the2Ti–0Cr–Al–C is the highest exothermic reaction system in the Ti–Cr–Al–C system. The adiabatic combustion temperature decreases with the increase of the Cr content. And a higher exothermal reaction would result in higher porosity which is induced by the high temperature and pressure of C reducing atmosphere and Al vapor. Combustion characterization of the products shows that the geometrical alternating layers result in the high exothermal reaction and flame-front propagating velocity. The higher the Tadis, the thinner the layer is. To demonstrate the process of the microscopic characterization and show the detailed combustion process closed to the experimental observations, the flame-front propagating velocity and temperature distribution were simulated numerically.展开更多
The aim of this study was to develop a high-efficiency joining method of Cf/Al composites and TiA l alloys under the heat effect of laser-ignited self-propagating high-temperature synthesis(SHS). The SHS reaction of...The aim of this study was to develop a high-efficiency joining method of Cf/Al composites and TiA l alloys under the heat effect of laser-ignited self-propagating high-temperature synthesis(SHS). The SHS reaction of Ni–Al–Zr interlayer was induced by laser beam and acted as local high-temperature heat source during the joining. Sound joint was obtained and verified the feasibility of this joining method. Effect of filler metals on the joint microstructure and shear strength was evaluated. When the joining pressure was 2 MPa with additive filler metals, joint shear strength reached the maximum of 41.01 MPa.展开更多
Ti, Al, graphite and diamond powders were used as raw materials to prepare Ti_2AlC matrixbonded diamond composite using self-propagating high-temperature synthesis(SHS) method. The effect of diamond size and content o...Ti, Al, graphite and diamond powders were used as raw materials to prepare Ti_2AlC matrixbonded diamond composite using self-propagating high-temperature synthesis(SHS) method. The effect of diamond size and content on the fabrication of Ti_2AlC-bonded diamond material was investigated. Results showed that Ti_2AlC matrix-bonded diamond composites could be obtained by SHS. The phase composition and microstructure of the Ti_2AlC-bonded diamond material were influenced by the diamond content and size. When the diamond(93 μm) additive amounts were 10% and 20%, the product phases included Ti_2AlC, TiC and Al_3Ti. However, excess Ti and Al persisted in the sample that contained 30% diamond. Diamond bonded well with the matrix in the sample that contained 10% diamond. Moreover, addition of coarse diamond particles with sizes of 93 and 125 μm produced a mainly Ti_2AlC matrix. However, diamond adequately reacted with Ti to form TiC when finer diamond particles(5 and 10 μm) were used.展开更多
Fully dense aluminum nitride(AIN) ceramics were synthesized by self-propagating high-temperature synthesis(SHS) method using AIN powder as raw material with Y2O3additive. The sintering behavior was studied at differen...Fully dense aluminum nitride(AIN) ceramics were synthesized by self-propagating high-temperature synthesis(SHS) method using AIN powder as raw material with Y2O3additive. The sintering behavior was studied at different sintering temperatures and additive contents. The change of phase compositions, secondary phase distributions and grain morphologies during sintering process were investigated. It is shown that fully dense ceramics using AIN powder prepared by SHS method can be obtained when the sintering temperature is above 1830 ℃. Both Y2O3content and sintering temperature have an important influence on the formation of Y-Al-O phase and grain shape. When Y2O3content is identified, the grain morphology converts from polyhedron into sphere-like shape with the rise of sintering temperature. At a certain sintering temperature,the grain size decreases with the increase in Y2O3content. The influencing mechanisms of different YAl-O secondary phases and sintering temperatures on the grain size and morphology were also discussed based on the experimental results.展开更多
The success in synthesizing high purity SnO2 nanobelts via self-propagating high tem- perature synthesis was achieved. According to the experimental results, a relationship between the residual heat of the reaction sy...The success in synthesizing high purity SnO2 nanobelts via self-propagating high tem- perature synthesis was achieved. According to the experimental results, a relationship between the residual heat of the reaction system at 2848 K and SnO2 nanobelts yield was identified. The most appropriate formula for this self-propagating high tempera- ture synthesis method is turned out to be composed of Sn powder and thermite with weight ratio of 1:1.展开更多
In this research, Zr-doped Gd_2Ti_2O_7 pyrochlores, with the composition of Gd_2(Ti_(1-x)Zr_x)_2O_7, were firstly synthesized by self-propagating high-temperature synthesis plus quick pressing(SHS/QP) using CuO as the...In this research, Zr-doped Gd_2Ti_2O_7 pyrochlores, with the composition of Gd_2(Ti_(1-x)Zr_x)_2O_7, were firstly synthesized by self-propagating high-temperature synthesis plus quick pressing(SHS/QP) using CuO as the oxidant and Ti as the reductant. To improve the radiation resistance of titanate–pyrochlore, up to 35 at% Zr was incorporated to substitute the Ti site of Gd_2Ti_2O_7 pyrochlore(Gd_2(Ti_(0.75)Zr_(0.35))_2O_7). XRD and SEM microstructural characterizations showed the formation of a composite ceramic with the major pyrochlore phase and the minor Cu phase. The generated temperature of samples decreased from 1702to 1011 ℃ with increasing Zr content. The effects of sintering temperature and pressure time on phase composition and microstructure were systematically studied. Besides, the influence of thermal transmission on the whole combustion process was also explored. The pyrochlore-based waste form possessed high bulk density of 6.25 g/cm^3 and Vickers hardness of 10.81 GPa. The MCC-1 leaching test showed the normalized elemental leaching rates(42d) of Cu, Gd, and Zr are 1.27×10^(-2), 1.33×10^(-3), and 8.44×10^(-7)g·m^(-2)·d^(-1), respectively.展开更多
The effects of heat treatment on the microstructure and compressive properties of porous Ni-rich NiTi shape memory alloy (SMA) fabricated by self-propagating high-temperature synthesis (SHS) were investigated. The sol...The effects of heat treatment on the microstructure and compressive properties of porous Ni-rich NiTi shape memory alloy (SMA) fabricated by self-propagating high-temperature synthesis (SHS) were investigated. The solution treatment at 1050℃ has little effects on stable Ti2Ni second phase, however, it decreases the amount of Ni4Ti3 phase derived from the SHS process and results in the improvement of the ductility of porous NiTi SMA. The subsequent aging treatment after solution treatment could lead to the precipitation of the discrete Ni4Ti3 phase in NiTi matrix grains, which increases the brittleness of porous NiTi SMA. Porous NiTi SMA presents a composite fracture behavior consisting of a ductile fracture of NiTi matrix and a cleavage fracture of second phase particles. Many cracks existing on the interfaces indicate that the bonding of the matrix with second phase particles is weak.展开更多
The NiAl–TiC–TiB2 composites were processed by self-propagating high-temperature synthesis(SHS) method using raw powders of Ni, Al, Ti, B4 C, TiC, and TiB2, and their microstructure and micro-hardness were investi...The NiAl–TiC–TiB2 composites were processed by self-propagating high-temperature synthesis(SHS) method using raw powders of Ni, Al, Ti, B4 C, TiC, and TiB2, and their microstructure and micro-hardness were investigated. The TiC–TiB2 in NiAl matrix, with contents from 10 to 30 wt%, emerged with the use of two methods: in situ formed and externally added. The results show that all final products are composed of three phases of NiAl, TiC, and TiB2. The microstructures of NiAl–TiC–TiB2 composites with in situ-formed TiC and TiB2 are fine, and all the three phases are distributed uniformly. The grains of NiAl matrix in the composites have been greatly refined, and the micro-hardness of NiAl increases from 381 HV100 to 779 HV100. However, the microstructures of NiAl–TiC–TiB2 composites with externally added TiC and TiB2 are coarse and inhomogeneous, with severe agglomeration of TiC and TiB2 particles. The samples containing externally added 30 wt% TiC–TiB2attain the micro-hardness of 485 HV100. The microstructure evolution and fracture mode of the two kinds of NiAl–TiC–TiB2 composites are different.展开更多
文摘The effects of preheating temperature and W powder size on the Self propagating High temperature Synthesis(SHS) of Ti W C system were studied. Preheated mixtures and the decrease of W powder size can accelerate the formation of (W,Ti)C powders. The uniphase (W,Ti)C (WC∶TiC=5∶5) powders with 0.32% free carbon were synthesized from Ti, W, C powders by SHS. The powder size of the product was 3~5 μm.
基金Funded by the Program for New Century Excellent Talents in University(No.NCET-12-0655)the Guangxi Natural Science Foundation(No.2014GXNSFFA118004)the Self-determined and Innovative Research Funds of WUT(Nos.136643002 and No.2013IV058)
文摘High quality nano-sized zirconium carbide (ZrC) powders were successfully fabricated via a developed chemical active dilution self-propagating high-temperature synthesis (SHS) method assisted by ball milling pretreatment process using traditional cheap zirconium dioxide powder (ZrO2), magnesium powder (Mg) and sucrose (C12H22Oll) as raw materials. FSEM, TEM, HRTEM, SAED, XRD, FTIR and Raman, ICP- AES, laser particle size analyzer, oxygen and nitrogen analyzer, carbon/sulfur determinator and TG-DSC were employed for the characterization of the morphology, structure, chemical composition and thermal stability of the as-synthesized ZrC samples. The as-synthesized samples demonstrated high purity, low oxygen content and evenly distributed ZrC nano-powders with an average particle size of 50nm. In addition, the effects of endothermic rate and the possible chemical reaction mechanism were also discussed.
基金The work was supported by the Foundation of Aerospace Innovation Fund and the National Natural Science Foundation of China(No.90505015)the Foundation of National Key Laboratory for Remanufacturing.
文摘TiC-TiB2-Cu composites were produced by self-propagating high-temperature synthesis combined with pseudo hot isostatic pressing using Ti, B4C and Cu powders. The microstructure and mechanical properties of the composites were investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the final products were only TiC, TiB2 and Cu phases. The clubbed TiB2 grains and spheroidal or irregular TiC grains were found in the microstructure of synthesized products. The reaction temperature and grain size of TiB2 and TiC particles decreased with increasing Cu content. The introduction of Cu into the composites resulted in a drastic increase in the relative density and flexual strength, and the maximum values were obtained with the addition of 20 wt pct, while the fracture toughness was the best when Cu content was 40 wt pct.
文摘Using KClO3 as an inner oxidant, MnZn-ferrite powder was synthesized by a self-propagating high-temperature synthesis (SHS) process in normal air atmosphere. The effects of the inner oxidant on combustion temperature, combustion velocity, microstructure and the phase of the product were investigated by XRD and SEM,respectively. The results show that a highly ferritized powder can be obtained as well as the highest combustion temperature and the highest combustion velocity when the inner oxidant content m equals 54(k-16).
基金Support by the NNSFC (50671044 and 50531030)the NCET (06-0308)+1 种基金the Science and Technology Development Planning of Jilin Province (20070110)the Project 985-Automotive Engineering of Jilin University
文摘Influence of Fe addition on products of self-propagating high-temperature synthesis (SHS) reaction in 3Ti-Si-2C system was investigated in the present study. Without Fe addition, Ti5Si3 and TiC are the dominant phases along with a small amount of Ti3SiC2 phase and unreacted C left in the final products. As Fe content ranges from 10% to 30%, the products consist of TiC, Ti5Si3, Fe2Ti and unreacted C, but no trace of Ti3SiC2 phase is detected. Furthermore, the amounts of both Fe2Ti and C phases increase with Fe content increasing. Addition of Fe has a great effect on the reaction route and significantly restrains the formation of Ti3SiC2 during the combustion synthesis process, and therefore, the SHS is not an effective fabrication technique to synthesize the ternary Ti3SiC2 ceramic in either 3Ti-Si-2C or Fe-3Ti-Si-2C system. Besides, without Fe addition, Ti5Si3 presents as the coarse irregular appearance with an obviously sintered morphology. In contrast, the shape of Ti5Si3 exhibits more and more spherical (cobblestone-like) and the surface becomes increasingly smooth, because the amount of liquids formed during the SHS reaction increases with the increase of Fe content. On the other hand, with Fe content increasing from 0 to 30 wt.%, the particulate size of TiC decreases from more than 5 μm to 1 μm or less, mainly due to the fact that the combustion temperature decreases with the increase of Fe content in the preforms.
基金This project was financially supported by the National Natural Science Foundation of China (No. 50025412)
文摘MoSi2 is presently regarded as the most important material for electrical heating and as one with huge potential for high temperature structural uses. MoSi2 and MoSi2 matrix composites were prepared by self-propagating high temperature synthesis (SHS). Pure MoSi2 was obtained and a compound of MoSi2 and WSi2was synthesized in the form of predominant solid solution (Mo,W)Si2. By adding aluminum of 5.5 at.% to Mo-Si, the crystal structure of MoSi2 changed into a mixture of tetragonal Cllb MoSi2and hexagonal C40 Mo(Si,Al)2. The (Mo,W)Si2-Mo(Si,Al)2-W(Si,Al)2 composite materials were synthesized by adding aluminum of 5.5 at.% to Mo-W-Si. However, if the amount of the added aluminum was not larger than 2.5 at.%, it did not have any significant effect. SHS is an effective technology for synthesis of MoSi2 and MoSi2 matrix composites.
基金This work was financially supported by the Natural Science Foundation of Shaanxi Province, China (No.2004E107)
文摘The mechanism of self-propagating high-temperature synthesis (SHS) of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope (SEM) with energy dispersive X-ray (EDX) spectrometry, and the combustion temperature was measured. The results showed that the combustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solution. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.
文摘ZrB2 ceramics were prepared by self-propagating high-temperature synthesis(SHS) and were sintered by hot pressing(HP).The effects of the granularities and doses of raw materials in Zr-B2O3-Mgon SHS process and product were investigated.XRD and combustion temperature curves prove that the ideal SHS reactants of Zr-B2O3-Mg are 50μm Zr powder,75μm B2O3 powder and 400μm Mg powder with 45% excessive.The particle sizes of SHS product,acid-leached product,sintered product are 2-5μm,0.5-2μm,2-10μm respectively.Chemical analysis indicates that the acid-leached product consists of ZrB2(94.59%),ZrO2(3.87%),and H3BO3(1.54%),The sintered product has a relative density of 95.4%.
基金Project(KNH2021005) supported by Industrialization Programof Economic Committee of Shanghai
文摘Self-propagating high-temperature synthesis(SHS) method was used to synthesize ZrB2/Al2O3 composite powders from B2O3-ZrO2-Al system. X-ray diffractometry(XRD) and scanning electron microscopy(SEM) analyses show the presence of ZrB2 and Al2O3 as the primary phases in the composite powders, while the presence of a very small amount of ZrO2 is thought to be unreacted zirconium oxide. Transmission electron microscopy(TEM) and high resolution electron microscopy(HREM) observations of microstructure of the composite powders indicate that the interfaces of ZrB2/Al2O3 bond well without any interfacial reaction products. It is proposed that the good interfacial bonding of composite powders results from the ZrB2 particles crystallizing and growing on the Al2O3 particles surface with surface defects acting as nucleation centers.
文摘Self-propagating high-temperature synthesis(SHS)was used to fabricate a Fe(Cr)–Al2O3 nanocomposite.The composite was fabricated by the reactions between the powders of Fe,Fe2O3,Cr2O3,and Al.The effect of blending ratio and mechanical activation of the initial powders and the precursor compressing pressure on the microstructure of the final product was studied by optical microscopy,scanning electron microscopy,transmission electron microscopy,and X-ray diffraction.The significance of the effect of each of the aforementioned parameters on the quality of the composite(assessed by measuring the compressive strength and wear resistance)was determined using a full-factorial design of experiments method.The results showed that the best molar powder ratio that produced the most homogeneous product through a sustainable SHS reaction was Fe:Fe2O3:Cr2O3:Al=10:1:1:4.A lower Fe content caused the Fe(Cr)phase to melt and separate from the rest of the materials.
文摘In order to investigate the microstructural evolution during self-propagating high-temperature synthesis (SHS) of Ti-Al powder mixture with an atomic ratio of Ti: Al=1:1, a combustion front quenching method (CFQM) was used for extinguishing the propagating combustion wave, and the microstructures on the quenched sample were observed with scanning electron microscope (SEM) and analyzed with energy dispersive spectrometry (EDS). In addition, the combustion temperature of the reaction was measured, and the phase constituent of the synthesized product was inspected by X-ray diffraction (XRD). The results showed that the combustion reaction started from melting of the Al particles, and the melting resulted in dissolving of the Ti particles and forming of Al3Ti grains. As the Al liquid was depleted, the combustion reaction proceeded through solid-state diffusion between the solid Al3Ti and the solid Ti. This led to the forming of TiAl and Ti3Al diffusing layers. In addition, the combustion reaction is incomplete besides TiAl, there are a large amount of Ti3Al and TiAl3 and a small amount of Ti in the final product. This incompleteness chiefly results from the using of coarser Ti powder.
基金financially supported by the National Natural Science Foundation of China (Nos. 11302068 and 51172057)China Postdoctoral Science Foundation (No. 2013M541261)
文摘In this paper, Ti–Cr–Al–C materials were investigated by self-propagating high-temperature synthesis(SHS) according to the experimental study and numerical simulation results. The highest adiabatic combustion temperature Tadof 2,467.45 K indicates that the2Ti–0Cr–Al–C is the highest exothermic reaction system in the Ti–Cr–Al–C system. The adiabatic combustion temperature decreases with the increase of the Cr content. And a higher exothermal reaction would result in higher porosity which is induced by the high temperature and pressure of C reducing atmosphere and Al vapor. Combustion characterization of the products shows that the geometrical alternating layers result in the high exothermal reaction and flame-front propagating velocity. The higher the Tadis, the thinner the layer is. To demonstrate the process of the microscopic characterization and show the detailed combustion process closed to the experimental observations, the flame-front propagating velocity and temperature distribution were simulated numerically.
基金financially supported by the National Natural Science Foundation of China(Grant No.51075101)
文摘The aim of this study was to develop a high-efficiency joining method of Cf/Al composites and TiA l alloys under the heat effect of laser-ignited self-propagating high-temperature synthesis(SHS). The SHS reaction of Ni–Al–Zr interlayer was induced by laser beam and acted as local high-temperature heat source during the joining. Sound joint was obtained and verified the feasibility of this joining method. Effect of filler metals on the joint microstructure and shear strength was evaluated. When the joining pressure was 2 MPa with additive filler metals, joint shear strength reached the maximum of 41.01 MPa.
基金Funded by National Natural Science Foundation of China(Nos.51602356 and 11472316)the University Innovation Team Project in Henan Province(Nos.15IRTSTHN004,16A430049,17A430034,and 18A430035)Henan Innovative Excellent Scientific and Technological Team(No.CXTD2013048)
文摘Ti, Al, graphite and diamond powders were used as raw materials to prepare Ti_2AlC matrixbonded diamond composite using self-propagating high-temperature synthesis(SHS) method. The effect of diamond size and content on the fabrication of Ti_2AlC-bonded diamond material was investigated. Results showed that Ti_2AlC matrix-bonded diamond composites could be obtained by SHS. The phase composition and microstructure of the Ti_2AlC-bonded diamond material were influenced by the diamond content and size. When the diamond(93 μm) additive amounts were 10% and 20%, the product phases included Ti_2AlC, TiC and Al_3Ti. However, excess Ti and Al persisted in the sample that contained 30% diamond. Diamond bonded well with the matrix in the sample that contained 10% diamond. Moreover, addition of coarse diamond particles with sizes of 93 and 125 μm produced a mainly Ti_2AlC matrix. However, diamond adequately reacted with Ti to form TiC when finer diamond particles(5 and 10 μm) were used.
基金financially supported by the International Cooperation Project of Zhejiang Province (No. 2012C24007)
文摘Fully dense aluminum nitride(AIN) ceramics were synthesized by self-propagating high-temperature synthesis(SHS) method using AIN powder as raw material with Y2O3additive. The sintering behavior was studied at different sintering temperatures and additive contents. The change of phase compositions, secondary phase distributions and grain morphologies during sintering process were investigated. It is shown that fully dense ceramics using AIN powder prepared by SHS method can be obtained when the sintering temperature is above 1830 ℃. Both Y2O3content and sintering temperature have an important influence on the formation of Y-Al-O phase and grain shape. When Y2O3content is identified, the grain morphology converts from polyhedron into sphere-like shape with the rise of sintering temperature. At a certain sintering temperature,the grain size decreases with the increase in Y2O3content. The influencing mechanisms of different YAl-O secondary phases and sintering temperatures on the grain size and morphology were also discussed based on the experimental results.
基金supported by the Natural Science Foundation of Hubei Province (No.2009CDB300)the Fundamental Research Funds for the Central Universities of China (No.5082001)
文摘The success in synthesizing high purity SnO2 nanobelts via self-propagating high tem- perature synthesis was achieved. According to the experimental results, a relationship between the residual heat of the reaction system at 2848 K and SnO2 nanobelts yield was identified. The most appropriate formula for this self-propagating high tempera- ture synthesis method is turned out to be composed of Sn powder and thermite with weight ratio of 1:1.
基金supported by the National Natural Science Foundation of China(Nos.51672228 and 51202203)the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials(No.11zxfk26)+1 种基金the Young Outstanding Scientist Fund of Southwest University of Science and Technology(No.13zx9108)the Postgraduate Innovation Fund Project by Southwest University of Science and Technology(No.16ycx010)
文摘In this research, Zr-doped Gd_2Ti_2O_7 pyrochlores, with the composition of Gd_2(Ti_(1-x)Zr_x)_2O_7, were firstly synthesized by self-propagating high-temperature synthesis plus quick pressing(SHS/QP) using CuO as the oxidant and Ti as the reductant. To improve the radiation resistance of titanate–pyrochlore, up to 35 at% Zr was incorporated to substitute the Ti site of Gd_2Ti_2O_7 pyrochlore(Gd_2(Ti_(0.75)Zr_(0.35))_2O_7). XRD and SEM microstructural characterizations showed the formation of a composite ceramic with the major pyrochlore phase and the minor Cu phase. The generated temperature of samples decreased from 1702to 1011 ℃ with increasing Zr content. The effects of sintering temperature and pressure time on phase composition and microstructure were systematically studied. Besides, the influence of thermal transmission on the whole combustion process was also explored. The pyrochlore-based waste form possessed high bulk density of 6.25 g/cm^3 and Vickers hardness of 10.81 GPa. The MCC-1 leaching test showed the normalized elemental leaching rates(42d) of Cu, Gd, and Zr are 1.27×10^(-2), 1.33×10^(-3), and 8.44×10^(-7)g·m^(-2)·d^(-1), respectively.
基金Project(CityU 1/04C) supported by Hong Kong Grants Council Central Allocation Group Research Project Project(50501007) supported by the National Natural Science Foundation of China+2 种基金 Project(BK2003062) supported by the Natural Science Foundation of Jiangsu Province, China Project(4012001007) supported by the Teaching and Research Award Program for Outstanding Young Teachers of Southeast University Project(9212001352) the Pre-research Project for National Natural Science Foundation in Southeast University
文摘The effects of heat treatment on the microstructure and compressive properties of porous Ni-rich NiTi shape memory alloy (SMA) fabricated by self-propagating high-temperature synthesis (SHS) were investigated. The solution treatment at 1050℃ has little effects on stable Ti2Ni second phase, however, it decreases the amount of Ni4Ti3 phase derived from the SHS process and results in the improvement of the ductility of porous NiTi SMA. The subsequent aging treatment after solution treatment could lead to the precipitation of the discrete Ni4Ti3 phase in NiTi matrix grains, which increases the brittleness of porous NiTi SMA. Porous NiTi SMA presents a composite fracture behavior consisting of a ductile fracture of NiTi matrix and a cleavage fracture of second phase particles. Many cracks existing on the interfaces indicate that the bonding of the matrix with second phase particles is weak.
基金financially supported by the National Natural Science Foundation of China(Nos.51072104 and 51272141)Tai Shan Scholars Project of Shandong Province,China(No.ts20110828)
文摘The NiAl–TiC–TiB2 composites were processed by self-propagating high-temperature synthesis(SHS) method using raw powders of Ni, Al, Ti, B4 C, TiC, and TiB2, and their microstructure and micro-hardness were investigated. The TiC–TiB2 in NiAl matrix, with contents from 10 to 30 wt%, emerged with the use of two methods: in situ formed and externally added. The results show that all final products are composed of three phases of NiAl, TiC, and TiB2. The microstructures of NiAl–TiC–TiB2 composites with in situ-formed TiC and TiB2 are fine, and all the three phases are distributed uniformly. The grains of NiAl matrix in the composites have been greatly refined, and the micro-hardness of NiAl increases from 381 HV100 to 779 HV100. However, the microstructures of NiAl–TiC–TiB2 composites with externally added TiC and TiB2 are coarse and inhomogeneous, with severe agglomeration of TiC and TiB2 particles. The samples containing externally added 30 wt% TiC–TiB2attain the micro-hardness of 485 HV100. The microstructure evolution and fracture mode of the two kinds of NiAl–TiC–TiB2 composites are different.