The effects of ultrafine WC(WC_(UF),0.5μm) or W(1μm) and C(0.3μm)(W+C)_(UF) additives on the densification,microstructure and mechanical properties of coarse-grained cemented carbides were compared systematically.O...The effects of ultrafine WC(WC_(UF),0.5μm) or W(1μm) and C(0.3μm)(W+C)_(UF) additives on the densification,microstructure and mechanical properties of coarse-grained cemented carbides were compared systematically.Overall,the cemented carbides with WC_(UF)/(W+C)_(UF) additives are almost fully densification to be higher than 99%,and the average grain size is kept above 2.8μm.The WC_(UF) additive assists grains to(truncated)trigonal prism shape by two dimensional(2D) growth,whereas the(W+C)_(UF) additive assists grains to rounded shape by three dimensional(3D) growth,lowers WC contiguity and increases face-centered-cubic Co.The hardness and bending strength of(75WC_(C)-15WC_(UF))-10Co are 86.6 HRA and 2 272 MPa,respectively,both higher than those of(75WC_(C)-15(W+C)_(UF))-10Co,which could be ascribed to the enhanced densification and unblemished grains.However,the fracture toughness of the(75WC_(C)-15(W+C)_(UF))-10Co is 23.5 MPa·m^(1/2),higher than that of the(75WC_(C)-15WC_(UF))-10Co due to the uniform WC-Co structure and flexible binder phase.展开更多
The activation of CO on iron-based materials is a key elementary reaction for many chemical processes.We investigate CO adsorption and dissociation on a series of Fe,Fe_(3)C,Fe_(5)C_(2),and Fe_(2)C catalysts through d...The activation of CO on iron-based materials is a key elementary reaction for many chemical processes.We investigate CO adsorption and dissociation on a series of Fe,Fe_(3)C,Fe_(5)C_(2),and Fe_(2)C catalysts through density functional theory calculations.We detect dramatically different performances for CO adsorption and activation on diverse surfaces and sites.The activation of CO is dependent on the local coordination of the molecule to the surface and on the bulk phase of the underlying catalyst.The bulk properties and the different local bonding environments lead to varying interactions between the adsorbed CO and the surface and thus yielding different activation levels of the C-O bond.We also examine the prediction of CO adsorption on different types of Fe-based catalysts by machine learning through linear regression models.We combine the features originating from surfaces and bulk phases to enhance the prediction of the activation energies and perform eight different linear regressions utilizing the feature engineering of polynomial representations.Among them,a ridge linear regression model with2nd-degree polynomial feature generation predicted the best CO activation energy with a mean absolute error of 0.269 eV.展开更多
In our study, stress-rupture tests were conducted at elevated temperatures to examine the impact of high temperature on MarM247 LC (low carbon). Our main objective was to investigate the alterations in the microstruct...In our study, stress-rupture tests were conducted at elevated temperatures to examine the impact of high temperature on MarM247 LC (low carbon). Our main objective was to investigate the alterations in the microstructure, particularly the carbon precipitation, during long-term stress-rupture tests. It was observed that cracks developed near the sample neck, following the path of the carbides and the gamma matrix, rather than occurring in the gamma-gamma prime eutectic. This occurred despite the formation of carbides because of prolonged exposure to high temperature and load, and the crack propagation did not follow that path. Based on these findings, we suggest that a reduction in the carbon content of Mar-M247 LC can enhance the sample's lifespan when subjected to temperatures below 760˚C and a stress of 690 MPa.展开更多
High temperature applications such as turbine blades for aeronautics or molten glass-shaping tools require the use of refractory metallic materials.Among the later ones,cast superalloys based on some transition metals...High temperature applications such as turbine blades for aeronautics or molten glass-shaping tools require the use of refractory metallic materials.Among the later ones,cast superalloys based on some transition metals and reinforced by MC carbides stay in good place and their metallurgy merits to be well known.This work consists in a general exploration of the as-cast microstructures which can be obtained after solidification and solid state cooling down to ambient temperature for a wide series of alloys for which the base element and the MC-former element both vary.For fixed contents in chromium and carbon contents,the compositions of a total of nineteen alloys were considered.These alloys are based on Ni,Co,Fe or Nb and the M content was each time chosen to favor the appearance of TiC,TaC,NbC,HfC or ZrC,as single carbide in a given alloy.After elaboration,metallographic samples were observed by electron microscopy to investigate the obtained microstructures.The obtained results show first that the MC carbides were in many cases successfully obtained at the expense of other possible carbides(for all Co-based alloys for example)but there are also several exceptions(notably for some Nibased alloys).Second,the obtained monocarbides have a eutectic origin and they are script-liked shaped.However they are here too some exceptions,as the rare HfC obtained in a Nb-base).In general,the results obtained in this work show that the principle of dendritic matrix combined with MC carbides with a script-like morphology is not necessarily obtained:the nature of the{base element,MC-former element}combination governs the microstructure of the alloy in its as-cast state for these particular compositions in chromium and carbon.In some cases other carbides may appear and the microstructures may be even of another type.展开更多
Varying the morphology and the structure of γ-phase (Co-base Co-W-C solid solution) by means of altering the cooling rate and the preparing method of liquid sintered WC-Co cemented carbides samples, the mechanism of ...Varying the morphology and the structure of γ-phase (Co-base Co-W-C solid solution) by means of altering the cooling rate and the preparing method of liquid sintered WC-Co cemented carbides samples, the mechanism of fcc→hcp transformation of γ-phase in WC-Co alloy has been explored. The results show that, the cooling rate is an important affecting factor on fcc→hcp transformation of γ-phase and the fcc→hcp transformation is mainly a diffusive type when cooling WC-Co samples above room展开更多
The coatings of W-Ti carbides on the surface of diamond was obtained by using physical vapor deposition (PVD), during which WO3 powders pre-treated with hydrofluoric acid were reduced by titanium hydride in vacuum at ...The coatings of W-Ti carbides on the surface of diamond was obtained by using physical vapor deposition (PVD), during which WO3 powders pre-treated with hydrofluoric acid were reduced by titanium hydride in vacuum at 850 ℃. The resistance of diamond to corrosion at high-temperature was investigated. The formation of W-Ti carbides on the surface of diamond was verified by X-ray diffraction analysis, the interface state between diamond and matrix in metaLbase diamond composite was observed by scanning electron microscope. The results showed that the carbide coating is easy to be formed at low deposition temperature on the surface of diamond, while the resistance of diamond to corrosion at highutemperature and the strength of bonding between diarnond and metal matrix are effectively improved.展开更多
This study aims to investigate the primary carbides precipitation in H13 steel solidified at relatively high cooling rates,ranging from 300 to 6,000℃·min^-1,based on in situ observations with a high temperature ...This study aims to investigate the primary carbides precipitation in H13 steel solidified at relatively high cooling rates,ranging from 300 to 6,000℃·min^-1,based on in situ observations with a high temperature confocal laser scanning microscope.In the cooling rate range investigated,the solidification microstructure becomes more refined as cooling rate increases and the relationship between the secondary dendrite arm spacing(SDAS),λ2,and cooling rate,.T,can be expressed asλ2=128.45.T-0.124.Regardless of cooling rates,two kinds of primary carbides,i.e.,the Mo-Cr-rich and V-rich carbides,are precipitated along the interdendritic region and most of them are the Mo-Cr-rich carbides.The morphology of Mo-Cr-rich carbide is not obviously influenced by the cooling rate,but that of V-rich carbide is obviously affected.The increasing cooling rate markedly refines the primary carbides and reduces their volume fractions,but their precipitations cannot be inhibited even when the cooling rate is increased to 6,000℃·min^-1.Besides,the segregation ratios(SRs)of the carbides forming elements are not obviously affected by the cooling rate.However,compared with the conventionally cast ingot,the SDAS and primary carbides in the steel solidified at the investigated cooling rates are much finer,morphologies of the carbides have changed significantly,and SRs of the carbides forming elements are markedly greater.The variation of primary carbide characteristics with cooling rate is mainly due to the change in SDAS.展开更多
The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experim...The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experimental steel consists of dendrites of iron matrix, networks of eutectic carbides and secondary carbides. The average distance between networks is about 34 μm. The carbides mainly include M_2C, M(C,N) and M_6C, and their relative contents are 58.5%, 30.3% and 11.2%, respectively. The average spacing between the M_2C fibers is 1.5 μm. The decomposition of M_2C occurs from 897.2 to 1221.5 ℃(heating rate of 200 ℃/h). Some precipitated carbide particles occur in the M_2C matrix after holding for 15 min at 1100 ℃. With increasing holding time, the carbide fibers neck down more and more obviously until they are broken down. The spectral peaks of M_2C almost disappear after holding for 60 min. The spectral peaks of M_6C gradually strengthen with the holding time, and the relative content of M_6C increases to 79.8% after holding for 60 min. After holding for 180 min, the carbide fibers disappear, and the decomposition products consist of fine carbide particles(about 300 nm) and short rod-like carbides(about 3.5 μm).展开更多
Tianjin Institute of Hard Alloy,Tianjin 300222,China ABSTRACT The effects of solutes of wolfram and carbon on specific saturation magnetization(4πσ)of cobalt have been examined on the basis of the measurement of Ana...Tianjin Institute of Hard Alloy,Tianjin 300222,China ABSTRACT The effects of solutes of wolfram and carbon on specific saturation magnetization(4πσ)of cobalt have been examined on the basis of the measurement of Ana for hexagonal typeα-Co and cubic typeβ-Co.The Co-W-C solid solution simulative alloys have been fabricated according to binder composition in WC-Co cemented carbides and the effect of its component and structure on its Ana has been discussed too.It is pointed out that the Co phase structural factor must be considered as measuring the Ana of WC-Co cemented carbides.展开更多
The granular carbides formed from hot deformation in multiple alloying wear resistant cast iron were studied through the observation by means of optical microscope, SEM and TEM. The experimental results show that carb...The granular carbides formed from hot deformation in multiple alloying wear resistant cast iron were studied through the observation by means of optical microscope, SEM and TEM. The experimental results show that carbides with large size are formed from original short rhabdoid carbides existing in cast, those with small size directly nucleate in the matrix. Carbides with the size between the above are formed from precipitation induced by hot deformation. The bigger the deformation is, the larger the number of microsized granular carbides is. The mechanisms of nucleation and growth of granular carbides and the function of RE were discussed.展开更多
The experimental regularity and the mechanism of affecting the specific saturation magnetization(4πσ)of WC-Co cemented carbides were studied by varying alloy composition(W and C)and quenching treat-ment.The carbon e...The experimental regularity and the mechanism of affecting the specific saturation magnetization(4πσ)of WC-Co cemented carbides were studied by varying alloy composition(W and C)and quenching treat-ment.The carbon effect was mainly discussed.The results show that there is no strict linear relation be-tween 4πσ and Co content,and the 4ha was affected by alloy composition and binder structure.Consequently,there is no one to one correspondence of 4πσ vs.carbon content in them and,therefore,ex-amining carbon content by 4πσ is conditional.展开更多
Structural characteristics, chemical bonds and thermoelectric properties of Al-doped boron carbides are studied through calculations of various structural unit models by using a self-consistent-field discrete variatio...Structural characteristics, chemical bonds and thermoelectric properties of Al-doped boron carbides are studied through calculations of various structural unit models by using a self-consistent-field discrete variation X. method. The calculations show that Al atom doped in boron carbide is in preference to substituting B or C atoms on the end of boron carbide chain, and then may occupy interstitial sites, but it is difficult for Al to substitute B or C atom in the centers of the chain or in the icosahedra. A representative structural unit containing an Al atom is [C—B—Al]<sup>ε+</sup>—[B<sub>11</sub>C]<sup>ε-</sup>, while the structural unit without Al is [C—B—B（C）]<sup>’-</sup>—[B<sub>11</sub>C]<sup>’+</sup>, and the coexistence of these two different structural units makes the electrical conductivity increased. As the covalent bond of Al—B or Al—C is weaker than that of B—B or B—C, the thermal conductivity decreases when Al is added into boron carbides. With the electrical conductivity increasing and the thermal conductivit y decreases,展开更多
The α phase Mo carbide has been widely investigated recently for its high activity in hydrogen production from water gas shift (WGS) reaction. However, high loading of noble metals as well as high economic and enviro...The α phase Mo carbide has been widely investigated recently for its high activity in hydrogen production from water gas shift (WGS) reaction. However, high loading of noble metals as well as high economic and environmental cost derived from high-temperature ammonification and carbonization process will lead to high cost of hydrogen production. Thus, the efficient controlling of phase transfer is promising. Herein, metals (Au, Pt, Rh, Cu) with a wide range of loadings were impregnated on flame spray pyrolysis (FSP) made MoO_(3) to produce Mo carbides by one-step carbonization. A breakthrough high metal-normalized hydrogen production rate of 213 mmol H2·gmetal^(-1)·s^(-1) was achieved on 0.025 wt% Rh/MoCx, which was much higher than Pt and Au based Mo carbides ever reported. The addition of trace Rh induced direct MoO_(3) transformation to high purity α-MoC_(1-x) in one-step carbonization instead of two-steps ammonification and carbonization process. In comparison to Rh, the addition of Pt, Au and Cu tend to transfer MoO_(3) into β-Mo2C at the same conditions. Besides, the one with 2 wt% Rh exhibited high stability in WGS reaction even at high temperature (300 ℃) due to its inhibition on carbides oxidation induced by H2O. We demonstrate that it is feasible to control phase transfer of Mo carbides even by trace amount of metals to simplify the production process of catalysts. The catalytic performance improved by Rh in aspects of both activity and stability provides a guide for producing more stable Mo carbides catalysts.展开更多
As a new member in two-dimensional materials family,transition metal carbides(TMCs)have many excellent properties,such as chemical stability,in-plane anisotropy,high conductivity and flexibility,and remarkable energy ...As a new member in two-dimensional materials family,transition metal carbides(TMCs)have many excellent properties,such as chemical stability,in-plane anisotropy,high conductivity and flexibility,and remarkable energy conversation efficiency,which predispose them for promising applications as transparent electrode,flexible electronics,broadband photodetectors and battery electrodes.However,up to now,their device applications are in the early stage,especially because their controllable synthesis is still a great challenge.This review systematically summarized the state-of-the-art research in this rapidly developing field with particular focus on structure,property,synthesis and applicability of TMCs.Finally,the current challenges and future perspectives are outlined for the application of 2D TMCs.展开更多
The allotropic transformation process of the γ-phase in WC-Co cemented carbides has been explored.Theconcepts of γ-grain and the γ-domain have been proposed forward:The γ-domain is the residual FCC-typeβ-Co grain...The allotropic transformation process of the γ-phase in WC-Co cemented carbides has been explored.Theconcepts of γ-grain and the γ-domain have been proposed forward:The γ-domain is the residual FCC-typeβ-Co grain that failed to transform when cooling alloy sample and γ-base is the HCP-type x-Co transformedmainly by means of diffusion,the outline of the γ-grain is consistent with the newly fromed β-Co grain formedat high temperature.The quantity and distribution of γ-grain domain are related to the cooling rate after sinter-ing and influence the alloys properties.展开更多
The quantitative analytical method combining the electrolytic extraction with X-raydiffraction analysis to determine the carbides and TCP in a Ni-base superalloy wasdeveloped.The variation of decomposition of MC and p...The quantitative analytical method combining the electrolytic extraction with X-raydiffraction analysis to determine the carbides and TCP in a Ni-base superalloy wasdeveloped.The variation of decomposition of MC and precipitation of M<sub>23</sub>C<sub>6</sub> and M<sub>6</sub>C withhot exposure time at 850—1000℃ is shown to conform to hyperbolic law.The elemental con-stitution of M<sub>23</sub>C<sub>6</sub> changes continutously during the hot exposure process.At the primarystage the constitution of the precipitates is(Cr<sub>0.67</sub>Mo<sub>0.13</sub>Ni<sub>0.13</sub>Co<sub>0.07</sub>)<sub>23</sub>C<sub>6</sub>.Then with in-creasing Cr and decreasing Mo,Ni and Co it finally becomes(Cr<sub>0.88</sub>Mo<sub>0.07</sub>Ni<sub>0.03</sub>Co<sub>0.02</sub>)<sub>23</sub>C<sub>6</sub>.The higher the hot exposure temperature,the faster the final constitution of M<sub>23</sub>C<sub>6</sub> may beachieved.展开更多
The correlation between structure, chemical bond and thermoelectric properties of boron carbides is discussed based on structural calculations with self-consistent-field discrete variation (SCF-DV-Xa) method, one of c...The correlation between structure, chemical bond and thermoelectric properties of boron carbides is discussed based on structural calculations with self-consistent-field discrete variation (SCF-DV-Xa) method, one of calculation methods of molecular orbital in quantum chemistry. Nine different structural models for calculation are proposed. The calculated results show that the chain is negatively charged and the icosahedron is positively charged, i.e. [C-B-B(C)]δ-[B11B(C)]δ. The total strength of the five covalent bonds between an atom展开更多
The abrasive wear behaviour of austeniticmedium manganese steels was studied under weakcorrosion-abrasive wear simulating the linerplate in wet metallic ore bail mill undernon-severe impact-loading working condition.R...The abrasive wear behaviour of austeniticmedium manganese steels was studied under weakcorrosion-abrasive wear simulating the linerplate in wet metallic ore bail mill undernon-severe impact-loading working condition.Results show that the work-hardening mechanismand the wear resistance of high carbon austeniticmedium manganese steels differ from those ofmedium carbon austenitic medium manganese steel.Under non-severe impact and weakcorrosion-abrasive wear,the wear resistancesof high carbon and medium carbon austeniticmedium manganese steels are 50-90% and 20-40%higher than that of Hadfield steel respectively.展开更多
On the basis of the experimental work of adhesion(W)data,the adhesion between transition metal car-bides and pure liquid metals which do not react with carbides is studied.In view of great scattering of the ex-perimen...On the basis of the experimental work of adhesion(W)data,the adhesion between transition metal car-bides and pure liquid metals which do not react with carbides is studied.In view of great scattering of the ex-perimental values of W,a critical analysis of these results is performed.The selected W values for 9copper/carbide systems and 6 metal/TiC systems are used to discuss the various suggestions concerning themechanism of adhesion and to evidence the role of the valence electrons of the both carbide and metal on theinteractions between metals and carbides.The interactions between a metal and a carbide are essentially metal-lic interactions,resulting from the overlapping of the valence electrons at the metal/carbide interface.展开更多
基金Funded by the Technology Innovation Leading Program of Shaanxi(No.2022QFY08-02)。
文摘The effects of ultrafine WC(WC_(UF),0.5μm) or W(1μm) and C(0.3μm)(W+C)_(UF) additives on the densification,microstructure and mechanical properties of coarse-grained cemented carbides were compared systematically.Overall,the cemented carbides with WC_(UF)/(W+C)_(UF) additives are almost fully densification to be higher than 99%,and the average grain size is kept above 2.8μm.The WC_(UF) additive assists grains to(truncated)trigonal prism shape by two dimensional(2D) growth,whereas the(W+C)_(UF) additive assists grains to rounded shape by three dimensional(3D) growth,lowers WC contiguity and increases face-centered-cubic Co.The hardness and bending strength of(75WC_(C)-15WC_(UF))-10Co are 86.6 HRA and 2 272 MPa,respectively,both higher than those of(75WC_(C)-15(W+C)_(UF))-10Co,which could be ascribed to the enhanced densification and unblemished grains.However,the fracture toughness of the(75WC_(C)-15(W+C)_(UF))-10Co is 23.5 MPa·m^(1/2),higher than that of the(75WC_(C)-15WC_(UF))-10Co due to the uniform WC-Co structure and flexible binder phase.
基金financially supported from the National Natural Science Foundation of China (No.22002008)Ningxia Key Research and Development Project,China (Nos.2022BEE03002 and 2022BSB03056)funding support from Synfuels China,Co.,Ltd.and Beijing Advanced Innovation Center for Materials Genome Engineering。
文摘The activation of CO on iron-based materials is a key elementary reaction for many chemical processes.We investigate CO adsorption and dissociation on a series of Fe,Fe_(3)C,Fe_(5)C_(2),and Fe_(2)C catalysts through density functional theory calculations.We detect dramatically different performances for CO adsorption and activation on diverse surfaces and sites.The activation of CO is dependent on the local coordination of the molecule to the surface and on the bulk phase of the underlying catalyst.The bulk properties and the different local bonding environments lead to varying interactions between the adsorbed CO and the surface and thus yielding different activation levels of the C-O bond.We also examine the prediction of CO adsorption on different types of Fe-based catalysts by machine learning through linear regression models.We combine the features originating from surfaces and bulk phases to enhance the prediction of the activation energies and perform eight different linear regressions utilizing the feature engineering of polynomial representations.Among them,a ridge linear regression model with2nd-degree polynomial feature generation predicted the best CO activation energy with a mean absolute error of 0.269 eV.
文摘In our study, stress-rupture tests were conducted at elevated temperatures to examine the impact of high temperature on MarM247 LC (low carbon). Our main objective was to investigate the alterations in the microstructure, particularly the carbon precipitation, during long-term stress-rupture tests. It was observed that cracks developed near the sample neck, following the path of the carbides and the gamma matrix, rather than occurring in the gamma-gamma prime eutectic. This occurred despite the formation of carbides because of prolonged exposure to high temperature and load, and the crack propagation did not follow that path. Based on these findings, we suggest that a reduction in the carbon content of Mar-M247 LC can enhance the sample's lifespan when subjected to temperatures below 760˚C and a stress of 690 MPa.
文摘High temperature applications such as turbine blades for aeronautics or molten glass-shaping tools require the use of refractory metallic materials.Among the later ones,cast superalloys based on some transition metals and reinforced by MC carbides stay in good place and their metallurgy merits to be well known.This work consists in a general exploration of the as-cast microstructures which can be obtained after solidification and solid state cooling down to ambient temperature for a wide series of alloys for which the base element and the MC-former element both vary.For fixed contents in chromium and carbon contents,the compositions of a total of nineteen alloys were considered.These alloys are based on Ni,Co,Fe or Nb and the M content was each time chosen to favor the appearance of TiC,TaC,NbC,HfC or ZrC,as single carbide in a given alloy.After elaboration,metallographic samples were observed by electron microscopy to investigate the obtained microstructures.The obtained results show first that the MC carbides were in many cases successfully obtained at the expense of other possible carbides(for all Co-based alloys for example)but there are also several exceptions(notably for some Nibased alloys).Second,the obtained monocarbides have a eutectic origin and they are script-liked shaped.However they are here too some exceptions,as the rare HfC obtained in a Nb-base).In general,the results obtained in this work show that the principle of dendritic matrix combined with MC carbides with a script-like morphology is not necessarily obtained:the nature of the{base element,MC-former element}combination governs the microstructure of the alloy in its as-cast state for these particular compositions in chromium and carbon.In some cases other carbides may appear and the microstructures may be even of another type.
文摘Varying the morphology and the structure of γ-phase (Co-base Co-W-C solid solution) by means of altering the cooling rate and the preparing method of liquid sintered WC-Co cemented carbides samples, the mechanism of fcc→hcp transformation of γ-phase in WC-Co alloy has been explored. The results show that, the cooling rate is an important affecting factor on fcc→hcp transformation of γ-phase and the fcc→hcp transformation is mainly a diffusive type when cooling WC-Co samples above room
文摘The coatings of W-Ti carbides on the surface of diamond was obtained by using physical vapor deposition (PVD), during which WO3 powders pre-treated with hydrofluoric acid were reduced by titanium hydride in vacuum at 850 ℃. The resistance of diamond to corrosion at high-temperature was investigated. The formation of W-Ti carbides on the surface of diamond was verified by X-ray diffraction analysis, the interface state between diamond and matrix in metaLbase diamond composite was observed by scanning electron microscope. The results showed that the carbide coating is easy to be formed at low deposition temperature on the surface of diamond, while the resistance of diamond to corrosion at highutemperature and the strength of bonding between diarnond and metal matrix are effectively improved.
基金the National Natural Science Foundation of China(Grant No.51904146)the Doctor Start-up Fund of Liaoning Province(Grant No.2019-BS-125)the National Key Laboratory of Marine Engineering of China(Grant No.SKLMEA-USTL-201707)。
文摘This study aims to investigate the primary carbides precipitation in H13 steel solidified at relatively high cooling rates,ranging from 300 to 6,000℃·min^-1,based on in situ observations with a high temperature confocal laser scanning microscope.In the cooling rate range investigated,the solidification microstructure becomes more refined as cooling rate increases and the relationship between the secondary dendrite arm spacing(SDAS),λ2,and cooling rate,.T,can be expressed asλ2=128.45.T-0.124.Regardless of cooling rates,two kinds of primary carbides,i.e.,the Mo-Cr-rich and V-rich carbides,are precipitated along the interdendritic region and most of them are the Mo-Cr-rich carbides.The morphology of Mo-Cr-rich carbide is not obviously influenced by the cooling rate,but that of V-rich carbide is obviously affected.The increasing cooling rate markedly refines the primary carbides and reduces their volume fractions,but their precipitations cannot be inhibited even when the cooling rate is increased to 6,000℃·min^-1.Besides,the segregation ratios(SRs)of the carbides forming elements are not obviously affected by the cooling rate.However,compared with the conventionally cast ingot,the SDAS and primary carbides in the steel solidified at the investigated cooling rates are much finer,morphologies of the carbides have changed significantly,and SRs of the carbides forming elements are markedly greater.The variation of primary carbide characteristics with cooling rate is mainly due to the change in SDAS.
基金Project(E2016203256)supported by the Natural Science Foundation of Hebei Province,China
文摘The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experimental steel consists of dendrites of iron matrix, networks of eutectic carbides and secondary carbides. The average distance between networks is about 34 μm. The carbides mainly include M_2C, M(C,N) and M_6C, and their relative contents are 58.5%, 30.3% and 11.2%, respectively. The average spacing between the M_2C fibers is 1.5 μm. The decomposition of M_2C occurs from 897.2 to 1221.5 ℃(heating rate of 200 ℃/h). Some precipitated carbide particles occur in the M_2C matrix after holding for 15 min at 1100 ℃. With increasing holding time, the carbide fibers neck down more and more obviously until they are broken down. The spectral peaks of M_2C almost disappear after holding for 60 min. The spectral peaks of M_6C gradually strengthen with the holding time, and the relative content of M_6C increases to 79.8% after holding for 60 min. After holding for 180 min, the carbide fibers disappear, and the decomposition products consist of fine carbide particles(about 300 nm) and short rod-like carbides(about 3.5 μm).
文摘Tianjin Institute of Hard Alloy,Tianjin 300222,China ABSTRACT The effects of solutes of wolfram and carbon on specific saturation magnetization(4πσ)of cobalt have been examined on the basis of the measurement of Ana for hexagonal typeα-Co and cubic typeβ-Co.The Co-W-C solid solution simulative alloys have been fabricated according to binder composition in WC-Co cemented carbides and the effect of its component and structure on its Ana has been discussed too.It is pointed out that the Co phase structural factor must be considered as measuring the Ana of WC-Co cemented carbides.
文摘The granular carbides formed from hot deformation in multiple alloying wear resistant cast iron were studied through the observation by means of optical microscope, SEM and TEM. The experimental results show that carbides with large size are formed from original short rhabdoid carbides existing in cast, those with small size directly nucleate in the matrix. Carbides with the size between the above are formed from precipitation induced by hot deformation. The bigger the deformation is, the larger the number of microsized granular carbides is. The mechanisms of nucleation and growth of granular carbides and the function of RE were discussed.
文摘The experimental regularity and the mechanism of affecting the specific saturation magnetization(4πσ)of WC-Co cemented carbides were studied by varying alloy composition(W and C)and quenching treat-ment.The carbon effect was mainly discussed.The results show that there is no strict linear relation be-tween 4πσ and Co content,and the 4ha was affected by alloy composition and binder structure.Consequently,there is no one to one correspondence of 4πσ vs.carbon content in them and,therefore,ex-amining carbon content by 4πσ is conditional.
基金Funded by the National Science Foundation of China Through Outstanding Youth Scientist Foundation (No. 59825102) and Science Foundation of Hubei Province(No. 98J028).
文摘Structural characteristics, chemical bonds and thermoelectric properties of Al-doped boron carbides are studied through calculations of various structural unit models by using a self-consistent-field discrete variation X. method. The calculations show that Al atom doped in boron carbide is in preference to substituting B or C atoms on the end of boron carbide chain, and then may occupy interstitial sites, but it is difficult for Al to substitute B or C atom in the centers of the chain or in the icosahedra. A representative structural unit containing an Al atom is [C—B—Al]<sup>ε+</sup>—[B<sub>11</sub>C]<sup>ε-</sup>, while the structural unit without Al is [C—B—B（C）]<sup>’-</sup>—[B<sub>11</sub>C]<sup>’+</sup>, and the coexistence of these two different structural units makes the electrical conductivity increased. As the covalent bond of Al—B or Al—C is weaker than that of B—B or B—C, the thermal conductivity decreases when Al is added into boron carbides. With the electrical conductivity increasing and the thermal conductivit y decreases,
基金This study was supported by DICP(Grant:DICP 1202012)the Natural Science Foundation of China(22078315)+1 种基金the LiaoNing Revitalization Talents Program(XLYC1907066)the Youth Innovation Promotion Association of Chinese Academy of Sciences(2018214).
文摘The α phase Mo carbide has been widely investigated recently for its high activity in hydrogen production from water gas shift (WGS) reaction. However, high loading of noble metals as well as high economic and environmental cost derived from high-temperature ammonification and carbonization process will lead to high cost of hydrogen production. Thus, the efficient controlling of phase transfer is promising. Herein, metals (Au, Pt, Rh, Cu) with a wide range of loadings were impregnated on flame spray pyrolysis (FSP) made MoO_(3) to produce Mo carbides by one-step carbonization. A breakthrough high metal-normalized hydrogen production rate of 213 mmol H2·gmetal^(-1)·s^(-1) was achieved on 0.025 wt% Rh/MoCx, which was much higher than Pt and Au based Mo carbides ever reported. The addition of trace Rh induced direct MoO_(3) transformation to high purity α-MoC_(1-x) in one-step carbonization instead of two-steps ammonification and carbonization process. In comparison to Rh, the addition of Pt, Au and Cu tend to transfer MoO_(3) into β-Mo2C at the same conditions. Besides, the one with 2 wt% Rh exhibited high stability in WGS reaction even at high temperature (300 ℃) due to its inhibition on carbides oxidation induced by H2O. We demonstrate that it is feasible to control phase transfer of Mo carbides even by trace amount of metals to simplify the production process of catalysts. The catalytic performance improved by Rh in aspects of both activity and stability provides a guide for producing more stable Mo carbides catalysts.
基金This research was supported by grants from by the National Natural Science Foundation of China(52002254)Sichuan Science and Technology Program(2020YJ0262,2021YFH0127)+2 种基金Chunhui plan of Ministry of Education of China,Fundamental Research Funds for the Central Universities,China(YJ201893)State Key Lab of Advanced Metals and Materials,China(Grant No.2019-Z03)the Danish National Research Foundation and EU H2020RISE 2016-MNR4S Cell project.
文摘As a new member in two-dimensional materials family,transition metal carbides(TMCs)have many excellent properties,such as chemical stability,in-plane anisotropy,high conductivity and flexibility,and remarkable energy conversation efficiency,which predispose them for promising applications as transparent electrode,flexible electronics,broadband photodetectors and battery electrodes.However,up to now,their device applications are in the early stage,especially because their controllable synthesis is still a great challenge.This review systematically summarized the state-of-the-art research in this rapidly developing field with particular focus on structure,property,synthesis and applicability of TMCs.Finally,the current challenges and future perspectives are outlined for the application of 2D TMCs.
文摘The allotropic transformation process of the γ-phase in WC-Co cemented carbides has been explored.Theconcepts of γ-grain and the γ-domain have been proposed forward:The γ-domain is the residual FCC-typeβ-Co grain that failed to transform when cooling alloy sample and γ-base is the HCP-type x-Co transformedmainly by means of diffusion,the outline of the γ-grain is consistent with the newly fromed β-Co grain formedat high temperature.The quantity and distribution of γ-grain domain are related to the cooling rate after sinter-ing and influence the alloys properties.
文摘The quantitative analytical method combining the electrolytic extraction with X-raydiffraction analysis to determine the carbides and TCP in a Ni-base superalloy wasdeveloped.The variation of decomposition of MC and precipitation of M<sub>23</sub>C<sub>6</sub> and M<sub>6</sub>C withhot exposure time at 850—1000℃ is shown to conform to hyperbolic law.The elemental con-stitution of M<sub>23</sub>C<sub>6</sub> changes continutously during the hot exposure process.At the primarystage the constitution of the precipitates is(Cr<sub>0.67</sub>Mo<sub>0.13</sub>Ni<sub>0.13</sub>Co<sub>0.07</sub>)<sub>23</sub>C<sub>6</sub>.Then with in-creasing Cr and decreasing Mo,Ni and Co it finally becomes(Cr<sub>0.88</sub>Mo<sub>0.07</sub>Ni<sub>0.03</sub>Co<sub>0.02</sub>)<sub>23</sub>C<sub>6</sub>.The higher the hot exposure temperature,the faster the final constitution of M<sub>23</sub>C<sub>6</sub> may beachieved.
基金National Science Foundation of China Through Outsanding Younth Scientist Foundation (No. 59825102) Science Foundation of Hubei ProvinceCNo. 98J028).
文摘The correlation between structure, chemical bond and thermoelectric properties of boron carbides is discussed based on structural calculations with self-consistent-field discrete variation (SCF-DV-Xa) method, one of calculation methods of molecular orbital in quantum chemistry. Nine different structural models for calculation are proposed. The calculated results show that the chain is negatively charged and the icosahedron is positively charged, i.e. [C-B-B(C)]δ-[B11B(C)]δ. The total strength of the five covalent bonds between an atom
文摘The abrasive wear behaviour of austeniticmedium manganese steels was studied under weakcorrosion-abrasive wear simulating the linerplate in wet metallic ore bail mill undernon-severe impact-loading working condition.Results show that the work-hardening mechanismand the wear resistance of high carbon austeniticmedium manganese steels differ from those ofmedium carbon austenitic medium manganese steel.Under non-severe impact and weakcorrosion-abrasive wear,the wear resistancesof high carbon and medium carbon austeniticmedium manganese steels are 50-90% and 20-40%higher than that of Hadfield steel respectively.
文摘On the basis of the experimental work of adhesion(W)data,the adhesion between transition metal car-bides and pure liquid metals which do not react with carbides is studied.In view of great scattering of the ex-perimental values of W,a critical analysis of these results is performed.The selected W values for 9copper/carbide systems and 6 metal/TiC systems are used to discuss the various suggestions concerning themechanism of adhesion and to evidence the role of the valence electrons of the both carbide and metal on theinteractions between metals and carbides.The interactions between a metal and a carbide are essentially metal-lic interactions,resulting from the overlapping of the valence electrons at the metal/carbide interface.
