共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
Effects of sintering additives on microstructure and mechanical properties of TiB2-WC ceramic-metal composite tool materials 总被引:1,自引:0,他引:1
Jinpeng SongChuanzhen Huang Bin ZouHanlian Liu Lin LiuJun Wang 《International Journal of Refractory Metals and Hard Materials》2012,30(1):91-95
TiB2-WC ceramic-metal composite tool materials were fabricated using Co, Ni and (Ni, Mo) as sintering additives by vacuum hot-pressing technique. The microstructure and mechanical properties of the composite were investigated. The composite was analyzed by the observations of scanning electron microscope (SEM), X-ray diffraction (XRD) and energy dispersive spectrometry (EDS). The microstructure of TiB2-WC ceramic-metal composites consisted of the fine WC grains and uniform TiB2 grains. The brittle phase of Ni3B4 and a few pores were found in TiB2-WC-Ni ceramic-metal composite. A lot of pores and brittle phases such as W2CoB2 and Co2B were formed in TiB2-WC-Co ceramic-metal composite. The liquid phase of Co was consumed by the reaction which led to the formation of the pores and the coarse grains of TiB2. The pores, brittle phases and coarse grains of TiB2 were harmful to the improvement of the mechanical properties of the composite. The sintering additive of (Ni, Mo) had a significant effect on the density and the mechanical properties of TiB2-WC ceramic-metal composite. The formation of intermetallic compound of MoNi4 inhibited the consumption of liquid phase of (Ni, Mo). The liquid phase of (Ni, Mo) not only inhibited the formation of the pores and the coarse grains of TiB2 but also strengthened the interface energy between WC and TiB2 grains. The grain size was fine and the average relative density of TiB2-WC-(Ni, Mo) ceramic-metal composite reached 99.1%. The flexural strength, fracture toughness and Vickers hardness of TiB2-WC-(Ni, Mo) ceramic-metal composite were 1307.0 ± 121.4 MPa, 8.19 ± 0.29 MPa m1/2 and 22.71 ± 0.82 GPa, respectively. 相似文献
3.
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
4.
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
5.
Z.G. YuanJ.F. Yang X.P. WangZ.J. Cheng Q.F. Fang 《Surface & coatings technology》2011,205(10):3307-3312
In this paper the direct current unbalanced reactive magnetron sputtering and composite target techniques were exploited to deposit quaternary Mo-Si-C-N coatings on Si wafer and stainless steel (1Cr18Ni9) in an Ar/N2 gaseous mixture. The chemical composition, microstructure, morphology, hardness, and friction coefficient of these films were characterized by means of X-ray diffraction, XPS, field emission scanning electron microscopy, TEM and nanoindentation. With the increase of C content in the range of C/(C + Mo + Si + N) = 0-12 at.%, the crystallite size decreases from 32 nm to 5 nm and the average friction coefficient of Mo-Si-C-N coatings decreases from 0.24 to 0.17, while the hardness increases at first and then decreases after passing a maximum value of about 27 GPa at 9 at.% C. It was suggested that in the Mo-Si-C-N coatings C atoms substitute for the N atoms in the nano-sized crystalline Mo2N to form Mo2N(C) solid solution phase and the microstructure of the Mo-Si-C-N coatings may be nano-sized crystalline Mo2N(C) embedded in the amorphous SiNx and CNx phases. 相似文献
6.
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
7.
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
8.
Zhiwei Liu Qingyou Han Jianguo LiWeidong Huang 《Journal of Materials Processing Technology》2012,212(2):365-371
Some issues such as clustering of TiB2 particles, formation of long rod-like Al3Ti particles, as well as high porosity level usually associate with the fabrication of in situ TiB2p/Al-alloy composites via conventional stir casting technique using Ti and B as reactants. High-intensity ultrasonic vibration was introduced in our research to solve the above issues. The process involved that the original in situ TiB2p/Al-12Si-4Cu sample with large clusters of TiB2 particles, large long rod-like Al3Ti particles and high porosity was remelted at 850 °C, and then ultrasonic vibration was applied to the melt with an ultrasonic probe. The microstructural evolution of the samples treated by ultrasonic vibration with different time was examined by using SEM. After treated by ultrasonic vibration for 12 min, large clusters of TiB2 particles were broken up effectively and TiB2 particles were dispersed uniformly in the matrix, and long rod-like Al3Ti particles were turned into blocky ones with the size of 10 μm due to the effect of ultrasonic stirring. In the meantime, the porosity in the composites decreased from about 6.5% to 0.86% due to the effect of ultrasonic degassing. Microhardness test suggested that a homogeneous microstructure of the composite was achieved after ultrasonic treatment. An effective approach using high-intensity ultrasonic vibration to optimize the microstructures of the particulate reinforced Al-alloy composites was proposed, and the mechanism of the effect of high-intensity ultrasonic vibration on the microstructural evolution of the reinforcements and degassing of composites was also discussed in our research. 相似文献
9.
NiAl-TiB2 composite coatings with 0, 10 and 20 wt.% TiB2 were synthesized on the Ni-based superalloy substrate using electro-thermal explosion ultrahigh speed spraying technology. The microstructure analysis shows that the coatings consist of submicron grains. The bond between coatings and substrate is metallic cohesion. TiB2 as a powerful reinforcement is doped in NiAl for increasing its hardness. The isothermal oxidation test is carried out for the composite coatings at 1100 °C in air. The result shows that the oxidation resistance of NiAl coating is higher than that of NiAl-10TiB2 and NiAl-20TiB2 coatings. The phases of oxides on the coatings during the process at high temperature have been analyzed by X-ray diffraction. The results show that Al2O3 and Cr2O3 coexistence on surface of NiAl coating, while Al2O3, Cr2O3, TiO2 and a small amount of NiO form on surface of NiAl-10TiB2 and NiAl-20TiB2 coatings after oxidation for 4 h. 相似文献
10.
C.K. Chung T.S. Chen N.W. Chang S.C. Chang M.W. Liao 《Surface & coatings technology》2010,205(5):1268-1272
The oxidation resistance and mechanical properties of Ta-Si-N films at high temperature are important issues for application. In this paper, quasi-amorphous Ta-Si-N thin films were fabricated by using reactive magnetron co-sputtering at different Si/Ta power ratios and nitrogen flow ratios (FN2% = FN2/(FAr + FN2) × 100%). Vacuum rapid thermal annealing at 600-900 °C at 2.6 Pa was performed to investigate the oxidation resistance of films. At the higher Si/Ta power ratio and increased FN2%, there is low oxygen fraction (O/(O + N) ≤ 0.2) of films at high annealing temperature which corresponds to benefit oxidation resistance. The crystalline δ-Ta2O5 phase was formed at 900 °C for all films. The islands of oxide were formed on the surface of films at low-Si-content (≤ 20 at.%) after 900 °C annealing. The hardness of all as-deposited Ta-Si-N films was between 16 and 24 GPa. The low-Si-content Ta-Si-N films has higher hardness than high-Si-content (≥ 20 at.%) ones due to lower fraction of soft amorphous SiNx. The effect of annealing temperature on the correlation among process parameters, microstructure, phase transformation and hardness is discussed. The Ta-Si-N formed at 6 FN2% and Si/Ta power ratio of 2/1 can be the best candidate for good oxidation resistance with appropriate mechanical property. 相似文献
11.
Sung Sic HwangJaeHo Han Dongyun Lee Sang-Whan Park 《Journal of Alloys and Compounds》2011,509(35):L336
High-purity Ti3SiC2 compounds have been fabricated by infiltration of molten Si into a precursor, a partially sintered TiCx (x = 0.67) preform. The Si source and the TiCx preform were placed side by side on carbon cloth, and the system was heated to 1550 °C. Molten Si infiltrated the preform through the carbon cloth, and a direct reaction between TiCx and molten Si immediately occurred at the reaction temperature to yield pure Ti3SiC2. We could observe phase formation and the microstructure of the bulk products with time, which were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS). Pure Ti3SiC2 compounds were formed on the exterior of the TiCx preform at 1550 °C when the sintered TiCx:Si ingot molar ratio was 3:1.4. At 1550 °C, no other minor phases were detected for any of the sintering time ranges. 相似文献
12.
G.B. Raju Bikramjit Basu A.K. Suri 《International Journal of Refractory Metals and Hard Materials》2010
The present communication reports the effect of MoSi2 addition on high temperature thermal conductivity and room temperature (RT) electrical properties of TiB2. The thermal diffusivity and the thermal conductivity of the hot pressed TiB2–MoSi2 samples were measured over a range from room temperature to 1000 °C using the laser-flash technique, while electrical resistivity was measured at RT using a four linear probe method. The reciprocal of thermal diffusivity of TiB2 samples exhibit linear dependence on temperature and the measured thermal conductivity of TiB2-2.5% MoSi2 composites correlate well with the theoretical predictions from Hashin’s model and Hasselman and Johnson’s model. A common observation is that the thermal conductivity of all the samples slightly increases with temperature (up to 200 °C) and then decreases with further increasing temperature. It is interesting to note that both the thermal conductivity and electrical conductivity of TiB2 samples enhanced with the addition of 2.5 wt.% MoSi2 sinter additive. Among all the samples, TiB2-2.5 wt.% MoSi2 ceramics measured with high thermal conductivity (77 W/mK) and low electrical resistivity (12 μΩ-cm) at room temperature. Such an improvement in properties can be attributed to its high density and low volume fraction of porosity. On the other hand, both the thermal and electrical properties of TiB2 were adversely affected with further increasing the amount of MoSi2 (10 wt.%). 相似文献
13.
The double-layer deposition of composite SiC-TiBC (Ti-Si-B-C) films with various Si contents (0, 40, 55, 60 and 100 mol%) on Ti-B-C was achieved from mixtures of titanium tetra-ethoxide, boron tri-ethoxide, and/or hexa-methyl-disiloxane solutions at about 700 °C on WC-Co cutting tools by Ar/H2 thermal plasma CVD. The crystalline phases of TiB2, TiC, and SiC were identified in the coatings by thin film grazing incidence X-ray diffraction. The surfaces and cross-sections of the double-layer coatings were observed by scanning electron microscopy to reveal their microstructure. Cutting tests of the double-layer Ti-Si-B-C/Ti-B-C were carried out by determining the flank and crater wear. The wear rate of the double-layer formed with the Ti-Si-B-C composite over-layer with 55 mol% Si was the slowest of the five samples. In addition, the effect of surface roughnesses (Ra (μm) = 0.03, 0.20 and 0.55) on the coating and wear resistance of the double-layer Ti-Si-B-C/Ti-B-C with 55 mol% Si was investigated by cross-sectional SEM observation and cutting tests. 相似文献
14.
I. Ozdemir S. MuecklichH. Podlesak B. Wielage 《Journal of Materials Processing Technology》2011,211(7):1260-1267
A comparative evaluation has been carried out on the microstructure of aluminum based SiC and Al2O3 particle reinforced composites produced by semi-solid direct squeeze forming of composite powder at temperatures of 635-645 °C. The study is focused on the distribution of the reinforcement and the intermetallic phases, the porosity content, the microstructure of the matrix phase, the interfacial state and mechanical properties. The particle size of the reinforcements, the time of the high-energy ball milling procedure for the fabrication of composite powder and the semi-solid forming temperature had a strong influence on the quality of sample in terms of distribution of reinforcement and interfacial interaction. Ball milling improves the interface formation between reinforcement and matrix and influences the remelting behaviour. Increasing ball milling time and decreasing semi-solid forming temperature with isothermal holding time resulted in relatively homogenous microstructures and in a reduced amount of interaction between SiC and metal matrix. Best results were obtained for 5 vol.% SiCp composites after 3 h ball milling, semi-solid formed at 635 °C and held for 10 min. 相似文献
15.
Si-containing a-C:H and a-C thin films with nitrogen, oxygen and transition metal (Cr and W) additives were deposited on polished single crystalline silicon substrates at room temperature by plasma activated CVD, magnetron-sputtering PVD and also by combined PACVD-PVD techniques.In particular Si-, Si-O- and Si-N-containing a-C:H films (denoted as a-C-Si, a-C-Si-O and a-C-Si-N) were deposited respectively from tetramethylsilane (TMS), hexamethyldisiloxane and hexamethyldisilazane vapourised precursors in He carrier gas by electron cyclotron wave resonance RF plasma. Cr-containing a-C:H films, further denoted as a-C-Si-Cr, were deposited with combined PVD-PACVD by sputtering chromium and carbon targets in argon and introducing TMS vapour. Wcontaining a-C films (denoted as a-C-Si-W) were deposited by PVD with simultaneous sputtering of the constituents in Ar. Detailed characterisation of the composition and chemical state of the elements present in the films were done by X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy. Mechanical properties, hardness (H), reduced modulus (E) and scratch behaviour were studied by depth-sensing nanoindentation and scratch tests.In the a-C:H films, the C/Si ratio varied between 1.5 and 3.5 showing a significant deficiency of C as compared to the composition of the precursors. The Cr and W content in the a-C-Si-Cr and a-C-Si-W films varied in a very broad 2-50 at.% range.The chemical state of carbon was primarily of sp2 and partly of sp3 type C-C with XPS chemical shifts for C 1s at 284.3 eV and 285.0 eV, respectively. The Si in the films is bonded predominantly to carbon (Si 2p at 100.8 eV BE) or to nitrogen in N-containing films (Si 2p at 101.3 eV BE). In the a-C-Si-Cr films Cr-C bonding states were determined (Cr 2p3/2 at 574.5 eV and C 1s at 282.8 eV). Si formed predominantly Si-C and also Si-Cr bonds. In the a-C-Si-W, films C-Si and C-W (W 4f7/2 at 32.3 eV) chemical bonds could be identified.It was discovered that the modified Auger parameter for silicon, αSi (derived from the Si 2p electron and Si KLL Auger line energy), sensitively reflects the entire chemical structure of these films, including crosslinking and densification. These spectroscopic data, supported further by the increase of the bulk plasmon loss energy of the C 1s peak, were directly connected with the mechanical properties of these films. The amorphous nature of the films was deduced from the chemical state analysis and was verified also by transmission electron microscopy (TEM) and electron diffraction (ED) studies.Hardness and elastic modulus of the a-C-Si-(O,N) films could be adjusted in a wide range of approx. 5-15 GPa and 40-140 GPa, respectively. Systematic alteration of these values with the composition (C/Si, O/Si and N/Si atomic ratio) and with the chemical structure (αSi?) was established and their interrelations are discussed. Whilst incorporation of Cr does not alter the mechanical properties, the addition of W increases H and E up to 19 GPa and 210 GPa, respectively. 相似文献
16.
Jianing LiChuanzhong Chen Zhaoqing LinTiziano Squartini 《Journal of Alloys and Compounds》2011,509(14):4882-4886
Laser cladding of the Fe3Al + TiB2/Al2O3 pre-placed alloy powder on Ti-6Al-4V alloy can form the Ti3Al/Fe3Al + TiB2/Al2O3 ceramic layer, which can greatly increase wear resistance of titanium alloy. In this study, the Ti3Al/Fe3Al + TiB2/Al2O3 ceramic layer has been researched by means of electron probe, X-ray diffraction, scanning electron microscope and micro-analyzer. In cladding process, Al2O3 can react with TiB2 leading to formation of amount of Ti3Al and B. This principle can be used to improve the Fe3Al + TiB2 laser cladded coating, it was found that with addition of Al2O3, the microstructure performance and micro-hardness of the coating was obviously improved due to the action of the Al-Ti-B system and hard phases. 相似文献
17.
The effects of adding SiC as a reinforcement and TiN as an additive on TiB2-based composites fabricated by the spark plasma sintering (SPS) technique were investigated. SPS was implemented at the sintering conditions of 1900 °C temperature, 7 min holding time and 40 MPa pressure. Adding these two secondary phases had noticeable effects on the microstructure of TiB2-based composites. A relative densities of 99.9% was obtained for TiB2–SiC–TiN composite. Detection of in-situ formed phases and investigation on them were done using SEM, XRD, EDS and thermodynamic assessment. These evaluations proved the formation of in-situ phases of TiC, BN nano-platelets, TiSi and B4C in the TiB2-based composite codoped with SiC and TiN. Formation of these in-situ phases had fascinating effects on the sinterability and ultimate microstructure of titanium diboride. 相似文献
18.
Microstructure and properties of W-ZrC composites prepared by the displacive compensation of porosity (DCP) method 总被引:1,自引:0,他引:1
Shouming Zhang Song WangWei Li Yulin ZhuZhaohui Chen 《Journal of Alloys and Compounds》2011,509(33):8327-8332
Tungsten-zirconium carbide composites were fabricated at different temperatures by the displacive compensation of porosity (DCP) method, the microstructure, mechanical properties, and ablation resistance were investigated. It was found that no WC phase was left in the composites prepared at 1400 °C, and a few residual W2C particles were surrounded in W product. Microstructure analyses revealed that zirconium atoms diffused into tungsten carbide to form ZrC and W2Zr besides carbon diffused into the Zr2Cu melt. Composites fabricated at 1400 °C had a flexural strength of 356.7 ± 15.2 MPa, an elastic modulus of 193.7 ± 9.8 GPa, a fracture toughness of 7.0 ± 0.7 MPa m1/2, and a hardness of 13.6 ± 0.7 GPa. After ablated by an oxyacetylene flame for 30 s, the higher temperature prepared composites had a better ablation resistance, the linear ablation rate was 0.0033 ± 0.0004 mm/s, and the mass ablation rate was 0.0012 ± 0.0001 g/s. 相似文献
19.
In this study, we introduce a rapid boriding technique that can produce very thick titanium diboride (TiB2) layers on titanium substrates. We also discuss the effects of process duration on boride layer thickness, chemistry and, morphology. In our experiments, the boriding of commercial purity titanium (CP-Ti) substrates was carried out in an electrochemical cell in which we used a mixture of sodium tetraborate and sodium carbonate as the base ingredients of molten electrolyte at 950 °C and at current density of 300 mA/cm2. The titanium test pieces were attached to the cathode holder of the electrochemical cell while a graphite crucible served as the anode. Both TiB and TiB2 phases were detected by X-ray diffraction method even after 5 min of treatment. Scanning electron microscopy (SEM) images verified that the production of 4.5 µm thick TiB2 layers was feasible after boriding for an hour. The boride layers consisted of a homogeneous TiB2 phase on the top and TiB whiskers toward the substrate. The micro-indentation studies indicated that the layer on top has hardness values as high as 40 GPa. The main advantages of this technique are its ability to produce very thick and hard TiB2 quickly and to create no gaseous emissions or solid wastes during or after the treatment. 相似文献
20.
Titanium diboride (TiB2) and its ceramic composites were prepared by hot pressing process. The sintering process, phase evolution, microstructure and mechanical properties of TiB2 ceramics prepared by using different milling media materials: tungsten carbide (WC/Co) or SiAlON was studied. It was found that the inclusion of WC/Co significantly improved the sinterability of the TiB2 ceramics. A core/rim structure with pure TiB2 as the core and W-rich TiB2, i.e. (Ti,W)B2 as the rim was identified. Microstructure analysis revealed that this core/rim structure was formed through a dissolution and re-precipitation process. In addition, silicon carbide (SiC) was also introduced to form TiB2–SiC composites. The addition of SiC as the secondary phase not only improved the sinterability but also led to greatly enhanced fracture toughness. The optimum mechanical properties with Vickers hardness ~ 22 GPa, and fracture toughness ~ 6 MPa m1/2 were obtained on TiB2–SiC composites milled with WC/Co. 相似文献