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1.
Evaluation of vanadium carbide coatings on AISI H13 obtained by thermo-reactive deposition/diffusion technique 总被引:1,自引:0,他引:1
Vanadium carbide coatings on AISI H13 steel were prepared by thermo-reactive deposition/diffusion process (TRD) in molten salt bath for 1 to 6 h at 920 °C and 1000 °C, respectively. The obtained coatings were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and X-ray diffraction analysis (XRD). Equiaxed grains were observed throughout the coatings. The grain size gradually increased from the coating/substrate interface to the top surface. The coatings were composed of ordered state V6C5 phase and disordered state VCx (x = 0.83-0.88) phases and had a preferential orientation of (111) and (200) planes. The values of nano-indentation hardness and elastic modulus of the coating are 28.1 ± 0.7 GPa and 421 ± 14 GPa, respectively. The growth of the vanadium carbide coating by the TRD process followed a parabolic kinetics with an activation energy of 199.3 kJ/mol. The variation of the coating thickness on the AISI H13 steel with treating time and temperature can be determined. 相似文献
2.
Dongju LeeHeesub Park Hojin RyuSeokwoo Jeon Soonhyung Hong 《Journal of Alloys and Compounds》2011,509(37):9060-9064
The effect of an addition of SiC nanowire on the microstructure and mechanical properties of tungsten-based composites is investigated in this study. SiC-nanowire-augmented tungsten composites were prepared by a spray-drying process and an in situ spark plasma sintering process. Three distinctive reaction phases, tungsten, tungsten carbide (W2C) and rod-type tungsten silicide (W5Si3) were formed during the sintering process. The flexural strength was significantly increased from 706 MPa to 924 MPa in tungsten composites augmented with SiC nanowires, as was the formation of W2C and W5Si3 phases. The rod-type W5Si3 bears significant stress by both sharing a portion of the load and providing a bridging mechanism. Furthermore, a high ablation resistance at an elevated temperature was observed for tungsten composites augmented with SiC nanowires. 相似文献
3.
J.K. Sonber T.S.R.Ch. Murthy C. Subramanian Sunil Kumar R.K. Fotedar A.K. Suri 《International Journal of Refractory Metals and Hard Materials》2010
This paper presents the results of investigation carried out on synthesis and densification of monolithic HfB2 and the effect of TiSi2 as sinter additive. Pure phase HfB2 was prepared by boron carbide reduction of HfO2 and hot pressed to full density with the addition of TiSi2. Isothermal oxidation study of this composite was carried out at 850 °C up to 64 h. Formation of HfB2 was seen at 1200 °C but pure HfB2 was formed at a much higher temperature of 1875 °C in vacuum. Hot pressing of HfB2 at 1850 °C and 35 MPa pressure gave a compact of 80% TD. Addition of TiSi2 helped in achieving a much higher density at a lower temperature of 1600 °C and a pressure of 20 MPa. A fully dense composite of HfB2 and TiSi2 was obtained with 15% TiSi2. Hardness and fracture toughness of this composite were 27.4 ± 1.9 GPa and 6.6 ± 0.2 MPa m1/2, respectively. Considerable deflection was observed in the crack propagation in composites. Oxidation studies indicated the formation of HfO2, SiO2, TiO2 and HfSiO4 with some glassy phase and the composite with 15% TiSi2 was seen to be completely covered with a protective glassy layer. 相似文献
4.
In this study, the effect of infiltration parameters on composition of W-ZrC composites produced by displacive compensation of porosity (DCP) method was investigated. For this purpose, a porous tungsten carbide preform was prepared by cold isostatic pressing (CIP) of tungsten carbide powder and polyvinyl alcohol (PVA). The porous preform was debinded for 4 h at 400 °C and sintered for 4 h at 1400 °C. The sintered preform was then infiltrated by molten Zr2Cu at 1300 °C and 1200 °C for 1, 3, 5 and 7 h. Scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectrometer (EDS) and X-ray diffraction (XRD) were used to study the cross section of infiltrated specimens. The results indicated that the amount of tungsten and zirconium carbide phases increased by increasing the infiltration temperature, whereas the effect of infiltration time on composition of W-ZrC composite was negligible. 相似文献
5.
T.S.R.Ch. Murthy J.K. Sonber C. Subramanian R.K. Fotedar Sunil Kumar M.R. Gonal A.K. Suri 《International Journal of Refractory Metals and Hard Materials》2010
A new composite of TiB2 with CrSi2 has been prepared with excellent oxidation resistance. Dense composite pellets were fabricated by hot pressing of powder mixtures. Microstructural characterization was carried out by XRD and SEM with EDAX. Mechanical and physical properties were evaluated. Extensive oxidation studies were also carried out. A near theoretical density (99.9% TD) was obtained with a small addition of 2.5 wt.% CrSi2 by hot pressing at 1700 °C under a pressure of 28 MPa for 1 h. The microstructure of the composite revealed three distinct phases, (a) dark grey matrix of TiB2, (b) black phase – rich in Si and (c) white phase – Cr laden TiB2. Hardness and fracture toughness were measured as 29 ± 2 GPa and 5.97 ± 0.61 MPa m1/2, respectively. Crack branching, deflection and bridging mechanisms were responsible for the higher fracture toughness. With increase in CrSi2 content, density, hardness and fracture toughness values of the composite decreased. Thermo gravimetric studies revealed the start of oxidation of the composite at 600 °C in O2 atmosphere. Isothermal oxidation of these composites showed better oxidation resistance by formation of a protective oxide layer. TiO2, Cr2O3 and SiO2 phases were identified on the oxidized surface. Effects of CrSi2 content, temperature and duration of oxidation on the oxide layer formation are reported. Activation energy of the composite was calculated as ∼110 kJ/mol using Arrhenius equation. Diffusion controlled mechanism of oxidation was observed in all the composites. 相似文献
6.
Mechanical properties (Young's modulus E, hardness H, degree of plasticity) of all three components of thermal barrier coatings systems, prepared by electron beam physical vapour deposition (EB PVD), have been investigated by nanoindentation. The power-law exponents n and m, describing the shapes of the loading and unloading nanoindentation curves, increase with peak load for the yttrium-stabilized zirconia top coat (TC), containing 4 mol% Y2O3, and the NiCoCrAlY bond coat (BC). The variations of m are correlated to the degree of plasticity. Decrease of the hardness with increasing peak load, generally known as indentation size effect (ISE), is observed only for the TC and the BC. The ISE in the TC is explained using a new empirical equation based on the concept of elastic recovery. The average Young's moduli of the Ni-based superalloy substrate, the BC and the TC are 189 ± 11 GPa, 166 ± 7 GPa, and 126 ± 25 GPa, respectively. The corresponding average hardness values are 3.3 ± 0.3 GPa, 5.5 ± 0.2 GPa, and 6.2 ± 1.7 GPa, respectively. The mechanical properties of the TC show complex behaviour upon annealing at 1000°°C in air, which can be explained by changes in the porosity and the residual stresses. 相似文献
7.
Mostafa Roosta Hamidreza Baharvandi 《International Journal of Refractory Metals and Hard Materials》2010
In this study the W/Cu and W/ZrC composites have been fabricated by hot-press and then their mechanical properties were compared in addition to their ablation resistance. To produce W-20vol.%Cu composite at first stage the elemental W and Cu powders were ball milled for 3 h in rotation speed of 200 rpm, in which 2% nickel was added in order to reduce the density. The mixed powders were hot-pressed for 1 h at 1400 °C and compact pressure of 30 MPa. Additionally W/40vol.%ZrC composite has been fabricated by hot-pressing of mixed W and ZrC powders in 30 MPa and 2200 °C for 1 h. Since these materials are used at elevated temperature applications, where ablation is the main source of material failure, after producing the composites their ablation resistance was evaluated in a real condition. The results show that not only W–ZrC composite is better than W–Cu composite in mechanical properties, but also in ablation resistance. 相似文献
8.
Young Jun HongDae Soo Jung Hye Young KooJung Hyun Kim You Na KoYun Chan Kang 《Journal of Alloys and Compounds》2011,509(31):8077-8081
ZnO-B2O3-SiO2-CaO glass frits were directly prepared by high temperature spray pyrolysis for use in Cu electrodes. The frits prepared at temperatures above 1400 °C were spherical, amorphous, of fine size and dense structure. The mean particle size and geometric standard deviation of the frits prepared at 1400 °C were 0.87 μm and 1.37, respectively. The temperatures of glass transition, crystallization and melting were 454, 534 and 800 °C, respectively. The glass layer fired at 800 °C had a dense structure due to the material's complete melting, despite some crystals being observed by SEM. A copper electrode formed from copper paste with glass frits had a dense structure when fired at 800 °C. The specific resistances of electrodes formed from copper paste with and without glass frits were 2.5 and 8.5 μΩ cm, respectively. 相似文献
9.
Bulk WC-Al2O3 composites prepared by spark plasma sintering 总被引:1,自引:0,他引:1
Donghai ZhengXiaoqiang Li Xuan AiChao Yang Yuanyuan Li 《International Journal of Refractory Metals and Hard Materials》2012,30(1):51-56
WC and WC-Al2O3 materials without metallic binder addition were densified by spark plasma sintering in the range of 1800-1900 °C. The densification behavior, phase constitution, microstructure and mechanical properties of pure WC and WC-Al2O3 composite were investigated. The addition of Al2O3 facilitates sintering and increases the fracture toughness of the composites to a certain extent. An interesting phenomenon is found that a proper content of Al2O3 additive helps to limit the formation of W2C phase in sintered WC materials. The pure WC specimen possesses a hardness (HV10) of 25.71 GPa, fracture toughness of 4.54 MPa·m1/2, and transverse fracture strength of 862 MPa, while those of WC-6.8 vol.% Al2O3 composites are 24.48 GPa, 6.01 MPa·m1/2, and 1245 MPa respectively. The higher fracture toughness and transverse fracture strength of WC-6.8 vol.% Al2O3 are thought to result from the reduction of W2C phase, the crack-bridging by Al2O3 particles and the local change in fracture mode from intergranular to transgranular. 相似文献
10.
High-temperature application above 1600 °C of C/SiC composites requires evaluation of the ablation properties. The C/SiC composites were prepared by low pressure chemical vapor infiltration using CH3SiCl3 as precursor. As-prepared C/SiC composites were ablated by oxy-acetylene flame with the temperature of 2900 and 3550 °C. Above 3550 °C, subliming of carbon fiber and silicon carbide matrix was the main ablation behaviour. At 2900 °C, thermal decomposition and oxidation of SiC matrix were the main ablation behaviour. A carbon coating resulted from the pyrolysis of the acetylene prevented the C/SiC from oxidizing dramatically. 相似文献
11.
A.S. Kurlov A.I. GusevA.A. Rempel 《International Journal of Refractory Metals and Hard Materials》2011,29(2):221-231
The effect of sintering temperature and particle size of tungsten carbide WC on phase composition, density and microstructure of hardmetals WC-8 wt.% Co has been studied using X-ray diffraction, scanning electron microscopy and density measurements. The sintering temperature has been varied in the range from 800 to 1600 °C. The coarse-grained WC powder with an average particle size of 6 μm, submicrocrystalline WC powder with an average particle size of 150 nm and two nanocrystalline WC powders with average sizes of particles 60 and 20 nm produced by a plasma-chemical synthesis and high-energy ball milling, respectively, have been used for synthesis of hardmetals. It is established that ternary Co6W6C carbide phase is the first to form as a result of sintering of the starting powder mixture. At sintering temperature of 1100-1300 °C, this phase reacts with carbon to form Co3W3C phase. A cubic solid solution of tungsten carbide in cobalt, β-Co(WC), is formed along with ternary carbide phases at sintering temperature above 1000 °C. Dependences of density and microhardness of sintering hardmetals on sintering temperature are found. The use of nanocrystalline WC powders is shown to reduce the optimal sintering temperature of the WC-Co hardmetals by about 100 °C. 相似文献
12.
Fancheng MengCheng Liu Fan ZhangZhongqing Tian Weijiu Huang 《Journal of Alloys and Compounds》2012,512(1):63-67
Alumina matrix composites containing 5 and 10 wt% of ZrO2 were sintered under 100 MPa pressure by spark plasma sintering process. Alumina powder with an average particle size of 600 nm and yttria-stabilized zirconia with 16 at% of Y2O3 and with a particle size of 40 nm were used as starting materials. The influence of ZrO2 content and sintering temperature on microstructures and mechanical properties of the composites were investigated. All samples could be fully densified at a temperature lower than 1400 °C. The microstructure analysis indicated that the alumina grains had no significant growth (alumina size controlled in submicron level 0.66-0.79 μm), indicating that the zirconia particles provided a hindering effect on the grain growth of alumina. Vickers hardness and fracture toughness of composites increased with increasing ZrO2 content, and the samples containing 10 wt% of ZrO2 had the highest Vickers hardness of 18 GPa (5 kg load) and fracture toughness of 5.1 MPa m1/2. 相似文献
13.
I. Khobta O. PetukhovO. Vasylkiv Y. SakkaA. Ragulya 《Journal of Alloys and Compounds》2011,509(5):1601-1606
The simultaneous synthesis and densification of TiN/TiB2 ceramic composites via reactive spark plasma sintering (RSPS) was investigated. Different component ratios (TiH2/BN (TiN, B)) and heating rates (112.5-300 °C/min) were used to initiate the chemical reaction for TiN/TiB2 synthesis. The omit RSPS process was revealed to have three stages, which are described separately. The relationships between the RSPS conditions, the microstructure and the properties of sintered ceramic composites were established. A Vickers hardness of 16-25 GPa and a fracture toughness of 4-6.5 MPa m1/2 were measured for various compositions. Sintered ceramic composites containing 36 wt% TiB2 with the highest relative density of 97.4 ± 0.4% and an average grain size of 150-550 nm have been obtained. 相似文献
14.
Moonsu SeoJiwoong Kim Shinhoo Kang 《International Journal of Refractory Metals and Hard Materials》2011,29(4):424-428
(Ti0.7W0.3)C solid solution powder was synthesized by high-energy ball milling. We investigated the effect of excess carbon in this system on the microstructure, pore level, and mechanical properties of (Ti0.7W0.3)C?-20 wt.% Ni cermet. We also report the variations in the carbon stoichiometry of the (Ti0.7W0.3)Cx phase in the powder and in the (Ti0.7W0.3)Cx?-20 wt.% Ni cermet after carbothermal reduction and liquid phase sintering, respectively. The particle size of the solid-solution carbide decreased with increasing carbon content in the (Ti0.7W0.3)C-?20 wt.% Ni cermets. This occurred because the dissolution of the solid solution (Ti,W)C is hindered by the high activity of carbon. However, an increase in the carbon content generated pores and carbon segregation, resulting in poor mechanical properties, as also observed in other carbide cermets. 相似文献
15.
To protect carbon/carbon (C/C) composites against oxidation, a SiC nanowire-toughened MoSi2-SiC coating was prepared on them using a two-step technique of chemical vapor deposition and pack cementation. SiC nanowires obtained by chemical vapor deposition were distributed random-orientedly on C/C substrates and MoSi2-SiC was filled in the holes of SiC nanowire layer to form a dense coating. After introduction of SiC nanowires, the size of the cracks in MoSi2-SiC coating decreased from 18 ± 2.3 to 6 ± 1.7 μm, and the weight loss of the coated C/C samples decreased from 4.53% to 1.78% after oxidation in air at 1500 °C for 110 h. 相似文献
16.
Yongsheng Liu Litong Zhang Laifei Cheng Wenbin Yang Weihua Zhang Yongdong Xu 《Corrosion Science》2009,51(4):820-826
An amorphous boron carbide (a-BC) coating was prepared by LPCVD process from BCl3-CH4-H2-Ar system. XPS result showed that the boron concentration was 15.0 at.%, and carbon was 82.0 at.%. One third of boron was distributed to a bonding with carbon and 37.0 at.% was dissolved in graphite lattice. A multiple-layered structure of CVD SiC/a-BC/SiC was coated on 3D C/SiC composites. Oxidation tests were conducted at 700, 1000, and 1200 °C in 14 vol.% H2O/8 vol.% O2/78 vol.% Ar atmosphere up to 100 h. The 3D C/SiC composites with the modified coating system had a good oxidation resistance. This resulted in the high strength retained ratio of the composites even after the oxidation. 相似文献
17.
J.K. SonberR.K. Fotedar A.K. Suri 《International Journal of Refractory Metals and Hard Materials》2011,29(1):21-30
This paper presents the results of experimental investigations carried out on the synthesis of pure ZrB2 by boron carbide reduction of ZrO2 and densification with the addition of HfB2 and TiSi2. Process parameters and charge composition were optimized to obtain pure ZrB2 powder. Monolithic ZrB2 was hot pressed to full density and characterized. Effects of HfB2 and TiSi2 addition on densification and properties of ZrB2 composites were studied. Four compositions namely monolithic ZrB2, ZrB2 + 10% TiSi2, ZrB2 + 10% TiSi2 + 10% HfB2 and ZrB2 + 10% TiSi2 + 20% HfB2 were prepared by hot pressing. Near theoretical density (99.8%) was obtained in the case of monolithic ZrB2 by hot pressing at 1850 °C and 35 MPa. Addition of 10 wt.% TiSi2 resulted in an equally high density of 98.9% at a lower temperature (1650 °C) and pressure (20 MPa). Similar densities were obtained for ZrB2 + HfB2 mixtures also with TiSi2 under similar conditions. The hardness of monolithic ZrB2 was measured as 23.95 GPa which decreased to 19.45 GPa on addition of 10% TiSi2. With the addition of 10% HfB2 to this composition, the hardness increased to 23.08 GPa, close to that of monolithic ZrB2. Increase of HfB2 content to 20% did not change the hardness value. Fracture toughness of monolithic sample was measured as 3.31 MPa m1/2, which increased to 6.36 MPa m1/2 on addition of 10% TiSi2. With 10% HfB2 addition the value of KIC was measured as 6.44 MPa m1/2, which further improved to 6.59 MPa m1/2 with higher addition of HfB2 (20%). Fracture surface of the dense bodies was examined by scanning electron microscope. Intergranular fracture was found to be a predominant mode in all the samples. Crack propagation in composites has shown considerable deflection indicating high fracture toughness. An oxidation study of ZrB2 composites was carried out at 900 °C in air for 64 h. Specific weight gain vs time plot was obtained and the oxidized surface was examined by XRD and SEM. ZrB2 composites have shown a much better resistance to oxidation as compared to monolithic ZrB2. A protective glassy layer was seen on the oxidized surfaces of the composites. 相似文献
18.
Blended elemental W–xTiC (x = 0, 5, 10, 15 wt%) powders were mechanically alloyed (MA’d) for 30 h in a SPEX Mixer/Mill at room temperature. About 1 wt% Ni was added to each MA’d batch as sintering aid which were further milled for 1 h. MA’d powders were sintered at 1400 °C for 2 h under Ar, H2 gas flowing conditions and annealed at 1600 °C for 6 h under Ar atmosphere. Microstructural characterizations of as-sintered and annealed samples were conducted using XRD and SEM. XRD patterns of the as-sintered and annealed samples revealed the presence of the matrix W and Ni phases, whereas (Tix,W1−x) solid solution phase came into existence after annealing. In addition to XRD patterns, hot combustion and infrared detection measurements revealed the decarburization of TiC. Relative density values varied between 85.2% and 96.4% after sintering. The density values of sintered samples decreased with increasing TiC content. After annealing, a maximum relative density value of 99.8% was achieved. Vickers microhardness values varied between 5.11 GPa and 10.79 GPa for as-sintered samples and a maximum microhardness value of 8.1 GPa was measured after annealing. Wear resistance of the as-sintered samples increased with increasing TiC content. 相似文献
19.
WuBian Tian Hideki KitaHideki Hyuga Naoki Kondo 《Journal of Alloys and Compounds》2011,509(5):1819-1823
TiB2-C preforms formed with different compositions and processing parameters were reactively infiltrated by Si melts at 1450 °C to fabricate TiB2-SiC-Si composites. Phase constituent and microstructure of these composites were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The resulting composites are generally composed of TiB2 and reaction-formed β-SiC major phases, together with a quantity of residual Si. Unreacted carbon is detected in the samples with a starting composition of 2TiB2 + 1C formed at higher pressure and in all of the ones at the composition of 1TiB2 + 1C. The distribution of these phases is fairly homogeneous in microstructure. TiB2-SiC-Si composites show good mechanical properties, with representative values of 19.9 GPa in hardness, 395 GPa in elastic modulus, 3.5 MPa m1/2 in fracture toughness and 604 MPa in bending strength. The primary toughening and strengthening mechanism is attributed to the crack deflection of TiB2 particles. 相似文献
20.
Recession behavior of Yb2Si2O7 phase was examined under high speed steam jet environment between 1300 °C and 1500 °C. Yb2SiO5 phase was formed on the bulk surface by the decomposition of Yb2Si2O7 phase and the elimination of silica component at elevated temperatures. The phase ratio of Yb2SiO5/Yb2Si2O7 increased up to 1400 °C and then decreased above 1400 °C. The relative intensity of 2 2 0 peak for Yb2Si2O7 phase increased with increasing the temperatures. Fine grains were generated on the bulk surface at 1300 °C. The phase decomposition caused on the grain interior. A porous structure was formed on the bulk surface during the test at 1400 °C. Surface cracks were generated for 1400 °C test sample. A smooth surface was generated on the surface of 1500 °C test sample. The triple points of the grains were bridged with a glassy phase. 相似文献