The influence of raw powder particle size on the properties and microstructures of Ti (C, N)-based cermets has been studied. The conclusions are as follows: The microstructures of cermets were composed of two kinds of...The influence of raw powder particle size on the properties and microstructures of Ti (C, N)-based cermets has been studied. The conclusions are as follows: The microstructures of cermets were composed of two kinds of grains, the one with black cores surrounded by obvious rim structures, and the other whose cores were white with unconspicuous rim structures and adhesive phase. In the cermet made from fine powders, the amount of grains with white cores was much more than that in cermet made from coarse powders. In addition, their properties were also much better.展开更多
Ultrafine Ti(C,N)-based cermet was sintered by SPS from 1050℃ to 1450℃ and its sintering properties,such as porosity,mechanical properties and phase transformation,were investigated by optical microscopy (OM),scanni...Ultrafine Ti(C,N)-based cermet was sintered by SPS from 1050℃ to 1450℃ and its sintering properties,such as porosity,mechanical properties and phase transformation,were investigated by optical microscopy (OM),scanning electron microscopy (SEM),X-ray diffraction (XRD),and differential scanning calorimeter (DSC).It is found that the spark plasma sintering properties of Ti(C,N)-based cermet differ from those of conventional vacuum sintering.The liquid phase appearance is at least lower by 150℃ than that in vacuum sintering.The porosity decreases sharply below 1 200℃ and reaches minimum at 1 200℃,and afterwards it almost keeps invariable and no longer increases.SPS remarkably accelerates the phase transformation of Ti(C,N)-based cermet and it has a powerful ability to remove oxides in Ti(C,N)-based cermets.Above 1 350℃,denitrification occurred.Fresh graphite phase formed above 1 430℃.Both the porosity and graphite are responsible for the poor TRS.展开更多
Spark plasma sintering(SPS)and conventional vacuum sintering(VS)wereemployed to fabricate ultrafine Ti(C,N)-based cermets.The shrinkage behavior,microstracture,andporosity and mechanical properties of the samples fabr...Spark plasma sintering(SPS)and conventional vacuum sintering(VS)wereemployed to fabricate ultrafine Ti(C,N)-based cermets.The shrinkage behavior,microstracture,andporosity and mechanical properties of the samples fabricated by SPS were compared with those of thesamples sintered by VS using optical microscopy,scanning electron microscopy,universal testingmachine,and rockwell tester.The results are as follows:(1)The shrinkage process occurred mainlyin the range of 1000-1300 deg C during the VS process,and only a 0.2 percent linear shrinkage ratioappeared below 800 deg C;during the SPS process,a 60 percent dimensional change occurred below800 deg C as a result of pressure action.(2)By utilizing the SPS technique,it is difficult forobtaining fully dense Ti(C,N)-based cermets.Due to the much existence of pores and un-combinedcarbon,the mechanical properties of the sintered samples by SPS are inferior to sintered ones byVS.(3)grain size of the samples sintered by SPS is still below 0.5 urn,but not by VS;because oflow sintering temperature,there are no typical core/rim structures formed in the sintered samplesby SPS1;the main microstructures of the sintered samples by SPS2 are a white core/grey shellstructure,whereas by VS show a typical black core/grey shell structure.展开更多
Effect of two-stage sintering parameters such as heating rate, top sintering temperature and holding time, sintering temperature and holding time at the second stage on relative density, transverse rupture strength(TR...Effect of two-stage sintering parameters such as heating rate, top sintering temperature and holding time, sintering temperature and holding time at the second stage on relative density, transverse rupture strength(TRS) and microstructures of powder injection molded Ti(C, N)-based cermets were investigated, by means of Archimedes’s method, three-point bending test and micrographic analysis. The results show that the optimum sintering cycle for powder injection molded Ti(C, N)-based cermets comprises rapid heating (10℃/min) at low temperatures, slow heating (5℃/min) at intermediate temperatures, holding at the highest sintering temperature (1420℃) for a short time (10min), and holding at the second stage (1360℃) for a longer time (6h) to avoid grain coarsening, and that its TRS reaches 624MPa, and there are little pores in their microstructures.展开更多
The microstructure and mechanical properties of Ti(C, N)-based cermets with different content Mo were studied. Different Mo contents were added into Ti(C, N)-based cermets. Effect of sintering temperature on mechanica...The microstructure and mechanical properties of Ti(C, N)-based cermets with different content Mo were studied. Different Mo contents were added into Ti(C, N)-based cermets. Effect of sintering temperature on mechanical properties of the cermets was also investigated. Specimens were fabricated by conventional powder metallurgy techniques and vacuum sintered at different temperatures. The microstructure and the fracture morphology were investigated using scanning electron microscope. Transverse strength and hardness were measured. The results show that the microstructure is uniform and the thickness of rim phase is moderate when the content of Mo is 8%. The mechanical properties are the best when the content of Mo is 8% and the sintering temperature is 1450℃.展开更多
The availability using oxygen-rich powders to prepare ultrafine Ti(C,N)-based cermets was investigated. The deoxidation process, denitrification phenomenon and the effect of deoxidation on microstructure and mechanica...The availability using oxygen-rich powders to prepare ultrafine Ti(C,N)-based cermets was investigated. The deoxidation process, denitrification phenomenon and the effect of deoxidation on microstructure and mechanical properties of sintered samples were discussed, respectively. The results show that oxygen in the samples prepared even with high oxygen contained in starting powders can be almost completely cleaned away through suitable sintering process. The ultrafine oxygen-rich powders have a significant effect on microstructure, which promotes the formation of white core phase. A ultrafine Ti(C,N)-based cermet with mean particle size of 0. 30 μm, uniform microstructure and excellent mechanical properties is successfully prepared. It is also found that there exists severe denitrification phenomenon in the preparation process of ultrafine Ti(C,N)-based cermet.展开更多
The wettability and bonding in Ni/Ti(C, N) systems with multiple carbide additions were studied by sessile drop technique and vacuum brazing technique, respectively. The phase characterizations of substrates and fract...The wettability and bonding in Ni/Ti(C, N) systems with multiple carbide additions were studied by sessile drop technique and vacuum brazing technique, respectively. The phase characterizations of substrates and fracture surfaces were conducted by XRD. The microstructures at metal/ceramic interfaces and fracture surfaces were observed via SEM in back scattered mode and second electron mode, respectively. Furthermore, an X-ray energy-dispersive spectrometer (EDS) attached to SEM was used to study the elements diffusion in interfacial regions. The results reveal that diffusion and dissolution mechanism controlled reactive wetting takes place in the system in high temperature wetting. Results also show that the contact angles decrease with multiple carbide additions, and the effect of multiple carbide additions is stronger than that of single additions. The contact angle reaches the lowest value in the lowest TiC content case. The enhancement of the wettability is due to alloying procedure during high tempe展开更多
The surface modification of multi-walled carbon nanotubes(MWCNTs) was carried out using plasma treatment. The microstructures of the prepared cermets with different additions of MWCNTs were investigated by scanning el...The surface modification of multi-walled carbon nanotubes(MWCNTs) was carried out using plasma treatment. The microstructures of the prepared cermets with different additions of MWCNTs were investigated by scanning electron microscopy(SEM), transmission electron microscopy(TEM), energy dispersive X-ray analysis(EDX), and X-ray diffraction(XRD). Mechanical properties such as transverse rupture strength(TRS), fracture toughness(K_(IC)), and hardness(HRA) were measured. The results showed that some reactive groups were successfully modified on the surface of MWCNTs, resulting in the improvement of dispersibility. Most of the amorphous carbons and impurities were peeled from the MWCNTs. Increasing MWCNT addition decreased the dissolution of tungsten, titanium, and molybdenum in the binder phase. The cermet with 0.5 wt% MWCNT addition showed the highest TRS and fracture toughness. The strengthening mechanisms were attributed to the finer grain size, the homogeneous microstructure, and the higher volume fraction of binder phase in the binder. The toughening mechanisms were characterized by bridging and pulling-out.展开更多
基金the National Natural Science Foundation of China, the Doctoral EducationFoundation of China, the State Key Laboratory of Powde
文摘The influence of raw powder particle size on the properties and microstructures of Ti (C, N)-based cermets has been studied. The conclusions are as follows: The microstructures of cermets were composed of two kinds of grains, the one with black cores surrounded by obvious rim structures, and the other whose cores were white with unconspicuous rim structures and adhesive phase. In the cermet made from fine powders, the amount of grains with white cores was much more than that in cermet made from coarse powders. In addition, their properties were also much better.
基金FundedbytheNationalNaturalScienceFoundationofChi na (No .5 0 0 74 0 17)andStateKeyLaboratoryofAdvancedTechnol ogyforMaterialsSynthesisandProcessingofWuhanUniversityofTechnology
文摘Ultrafine Ti(C,N)-based cermet was sintered by SPS from 1050℃ to 1450℃ and its sintering properties,such as porosity,mechanical properties and phase transformation,were investigated by optical microscopy (OM),scanning electron microscopy (SEM),X-ray diffraction (XRD),and differential scanning calorimeter (DSC).It is found that the spark plasma sintering properties of Ti(C,N)-based cermet differ from those of conventional vacuum sintering.The liquid phase appearance is at least lower by 150℃ than that in vacuum sintering.The porosity decreases sharply below 1 200℃ and reaches minimum at 1 200℃,and afterwards it almost keeps invariable and no longer increases.SPS remarkably accelerates the phase transformation of Ti(C,N)-based cermet and it has a powerful ability to remove oxides in Ti(C,N)-based cermets.Above 1 350℃,denitrification occurred.Fresh graphite phase formed above 1 430℃.Both the porosity and graphite are responsible for the poor TRS.
基金supported by the National Natural Science Foundation of China(No.50074017)the Natural Sci-ence Foundation of Hubei Province(No.2003ABA092)the Doctoral Education Fundation of China(No.1999048714).
文摘Spark plasma sintering(SPS)and conventional vacuum sintering(VS)wereemployed to fabricate ultrafine Ti(C,N)-based cermets.The shrinkage behavior,microstracture,andporosity and mechanical properties of the samples fabricated by SPS were compared with those of thesamples sintered by VS using optical microscopy,scanning electron microscopy,universal testingmachine,and rockwell tester.The results are as follows:(1)The shrinkage process occurred mainlyin the range of 1000-1300 deg C during the VS process,and only a 0.2 percent linear shrinkage ratioappeared below 800 deg C;during the SPS process,a 60 percent dimensional change occurred below800 deg C as a result of pressure action.(2)By utilizing the SPS technique,it is difficult forobtaining fully dense Ti(C,N)-based cermets.Due to the much existence of pores and un-combinedcarbon,the mechanical properties of the sintered samples by SPS are inferior to sintered ones byVS.(3)grain size of the samples sintered by SPS is still below 0.5 urn,but not by VS;because oflow sintering temperature,there are no typical core/rim structures formed in the sintered samplesby SPS1;the main microstructures of the sintered samples by SPS2 are a white core/grey shellstructure,whereas by VS show a typical black core/grey shell structure.
文摘Effect of two-stage sintering parameters such as heating rate, top sintering temperature and holding time, sintering temperature and holding time at the second stage on relative density, transverse rupture strength(TRS) and microstructures of powder injection molded Ti(C, N)-based cermets were investigated, by means of Archimedes’s method, three-point bending test and micrographic analysis. The results show that the optimum sintering cycle for powder injection molded Ti(C, N)-based cermets comprises rapid heating (10℃/min) at low temperatures, slow heating (5℃/min) at intermediate temperatures, holding at the highest sintering temperature (1420℃) for a short time (10min), and holding at the second stage (1360℃) for a longer time (6h) to avoid grain coarsening, and that its TRS reaches 624MPa, and there are little pores in their microstructures.
文摘The microstructure and mechanical properties of Ti(C, N)-based cermets with different content Mo were studied. Different Mo contents were added into Ti(C, N)-based cermets. Effect of sintering temperature on mechanical properties of the cermets was also investigated. Specimens were fabricated by conventional powder metallurgy techniques and vacuum sintered at different temperatures. The microstructure and the fracture morphology were investigated using scanning electron microscope. Transverse strength and hardness were measured. The results show that the microstructure is uniform and the thickness of rim phase is moderate when the content of Mo is 8%. The mechanical properties are the best when the content of Mo is 8% and the sintering temperature is 1450℃.
基金Project(50323008) supported by the National Natural Science Foundation of China
文摘The availability using oxygen-rich powders to prepare ultrafine Ti(C,N)-based cermets was investigated. The deoxidation process, denitrification phenomenon and the effect of deoxidation on microstructure and mechanical properties of sintered samples were discussed, respectively. The results show that oxygen in the samples prepared even with high oxygen contained in starting powders can be almost completely cleaned away through suitable sintering process. The ultrafine oxygen-rich powders have a significant effect on microstructure, which promotes the formation of white core phase. A ultrafine Ti(C,N)-based cermet with mean particle size of 0. 30 μm, uniform microstructure and excellent mechanical properties is successfully prepared. It is also found that there exists severe denitrification phenomenon in the preparation process of ultrafine Ti(C,N)-based cermet.
基金The authors wish to acknowledge the financial support from the National Natural Science Foundation of Chinathe Natural Science Foundation of Anhui Provincethe Project of Key Teachers of University of Education Ministry of China under contract No.50072003,No.03044902 and No.GG-805-10359-1840,respectively.
文摘The wettability and bonding in Ni/Ti(C, N) systems with multiple carbide additions were studied by sessile drop technique and vacuum brazing technique, respectively. The phase characterizations of substrates and fracture surfaces were conducted by XRD. The microstructures at metal/ceramic interfaces and fracture surfaces were observed via SEM in back scattered mode and second electron mode, respectively. Furthermore, an X-ray energy-dispersive spectrometer (EDS) attached to SEM was used to study the elements diffusion in interfacial regions. The results reveal that diffusion and dissolution mechanism controlled reactive wetting takes place in the system in high temperature wetting. Results also show that the contact angles decrease with multiple carbide additions, and the effect of multiple carbide additions is stronger than that of single additions. The contact angle reaches the lowest value in the lowest TiC content case. The enhancement of the wettability is due to alloying procedure during high tempe
基金financially supported by the Science and Technology Department of Fujian Province under Project No.2014H0037the Production,Education and Research of Fujian Provincial Education Department under Project No.JK2016040the Key Subject Project of Fujian Province
文摘The surface modification of multi-walled carbon nanotubes(MWCNTs) was carried out using plasma treatment. The microstructures of the prepared cermets with different additions of MWCNTs were investigated by scanning electron microscopy(SEM), transmission electron microscopy(TEM), energy dispersive X-ray analysis(EDX), and X-ray diffraction(XRD). Mechanical properties such as transverse rupture strength(TRS), fracture toughness(K_(IC)), and hardness(HRA) were measured. The results showed that some reactive groups were successfully modified on the surface of MWCNTs, resulting in the improvement of dispersibility. Most of the amorphous carbons and impurities were peeled from the MWCNTs. Increasing MWCNT addition decreased the dissolution of tungsten, titanium, and molybdenum in the binder phase. The cermet with 0.5 wt% MWCNT addition showed the highest TRS and fracture toughness. The strengthening mechanisms were attributed to the finer grain size, the homogeneous microstructure, and the higher volume fraction of binder phase in the binder. The toughening mechanisms were characterized by bridging and pulling-out.
