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1.
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
2.
The initially globular-shaped Ti powder particles were flattened to ‘pan-cake’ like shape after 12, 16, and thin flakes after 20 h of mechanical milling. Although no change peak positions of HCP Ti crystal structure, the increase in peak intensity with milling time was evident. It is found that the greater surface to volume ratio of the milled Ti powders accelerated the N2 uptake and subsequent formation of TiN at lower temperatures (884, 856 and 833 °C for 12, 16 and 20 h, respectively) than in the unmilled powder (∼ 1100 °C). Higher nitrogen content of 41–44 at.% by EDS analysis confirmed the high rate of dissolution on the milled powders. 相似文献
3.
Influence of dispersion and alloying by boron upon thermal stability and decomposition temperature of hydride phases of mechanical alloys of the Ti-B-H system that were derived in the conditions of high-energy ball milling either of (TiH1.9 + 9 wt.% B + 13 wt.% Ti) and (TiH1.9 + 50 wt.% TiB2) mixtures (50 h milling, rotation speed 1000 rpm) or of (TiH1.9 + 40 wt.% B) and (TiH1.9 + 50 wt.% TiB2) mixtures (20 milling, rotational speed 1630 rpm) has been studied employing scanning electron microscopy, X-ray diffraction analysis, and thermal desorption spectroscopy. It has been established that, dispersion and boron additives to the TiH1.9 powder followed by mechanical treatment influence thermal stability of the hydride. Mechanical milling the (TiH1.9 + 9 wt.% B + 13 wt.% Ti) mixture for 50 h in argon causes decreasing the decomposition temperature of a Ti(B,H)x hydride phase by more than 300° compared with that of the initial TiH1.9 hydride. Mechanisms of influence of both dispersion and boron alloying upon thermal stability of the TiH1.9 hydride have been studied. 相似文献
4.
Kasonde Maweja L.A. Cornish Nedret Can 《International Journal of Refractory Metals and Hard Materials》2011,29(4):445-451
The annealing behaviour of Ti(C0.5N0.05)-40 wt.% W and Ti(C0.5N0.5)0.6-40 wt.% W mechanically alloyed powders was investigated using XRD, TEM, SEM and DTA techniques. It was observed that the reaction start and finish temperatures between constituents were lower in the system that had higher residual lattice strains after milling. The compositions of the intermetallic compounds and solution phases formed were dependent of the milling conditions and the annealing temperature. Thermal alloying was observed during annealing of Ti(C0.5N0.05)-40 wt.% W mechanically alloyed products, whereas de-mixing of W-rich phases from the metastable solid solution occurred during annealing of the Ti(C0.5N0.5)0.6-40 wt.% W milled powders. 相似文献
5.
Xianzhuo Jie Shuhua Liang Qingxiang Wang Xin Zhao Zhikang Fan Xianhui Wang 《Journal of Materials Engineering and Performance》2012,21(1):101-104
W-10Ti alloy was prepared by hot press sintering using W-TiH2 powders milled for 24 h under argon atmosphere. The effect of sintering temperature on the phase constituents and the microstructure
of the alloys was characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron
microscopy (TEM). The microhardness of W-rich phase, electrical resistivity and impurity (C, O) contents of W-10Ti alloy were
determined. The results show that the amount of W-Ti solid solution, the microhardness of the W-rich solid solution and the
resistance of W-10Ti alloy increase with an increase of sintering temperature. At 1300 °C, W-10Ti alloy has the maximum microhardness
value of 333 HV0.05, the O content of 360 ppm and C content of 200 ppm. 相似文献
6.
Haijun YuYing Liu Yongzhong JinJinwen Ye 《International Journal of Refractory Metals and Hard Materials》2011,29(5):586-590
(Ti, W, Mo, V)(C, N)-based cermets were prepared by mixing Mo2C, WC and TaC with ultrafine (Ti, W, Mo, V)(C, N) powders, and then processed via a conventional P/M technique. The effect of Mo2C, WC and TaC on the microstructure and mechanical properties of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co systems was investigated. The Mo2C content was varied from 0 to 10 wt.% and additive WC or TaC was added at a level of 5 wt.% with Mo2C addition. The results show that the densification of (Ti, W, Mo, V)(C, N)-8 wt.% Ni-7 wt.% Co cermets was improved significantly by the addition of Mo2C. With the increase of Mo2C content, there is a coarsening tendency in the microstructure of (Ti, 20W, 15Mo, 0.2V)(C, N)-8Ni-7Co system, but the refinement for (Ti, 15W, 5Mo, 0.2V)(C, N)-8Ni-7Co. TaC addition decreases the density of (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo2C-8Ni-7Co cermet and thus weakens its bending strength. (Ti, 15W, 5Mo, 0.2V)(C, N)-10Mo2C-5WC-8Ni-7Co cermet has optimal mechanical properties: bending strength of 1999 MPa, hardness (Hv) of 1677 MPa and toughness of 9.95 MPa m1/2 respectively by adding WC, which is due to its ultrafine and weak core/rim structure. 相似文献
7.
A.R. AbbasiM. Shamanian 《Journal of Alloys and Compounds》2011,509(31):8097-8104
A two-step mechanical alloying process followed by heat treatment was developed as a novel approach for fabrication of Mo-12.5 mol%Si-25 mol%B nanocomposite powders. In this regard, a Si-43.62 wt.% B powder mixture was milled for 20 h. Then, Mo was added to the mechanically alloyed Si-B powders in order to achieve Mo-12.5 mol%Si-25 mol%B powder. This powder mixture was further milled for 2,5,10 and 20 h. All of the milled powders were annealed at 1100 °C for 1 h. After first step of milling, a nanocomposite structure composed of boron particles embedded in Si matrix was formed. On the other hand, an α-Mo/MoSi2 nanocomposite was produced after second step while no ternary phases between Mo, Si and B were formed. At this stage, the subsequent annealing led to formation of α-Mo and Mo5SiB2 as major phases. The phase evolutions during heat treatment of powders can be affected by milling conditions. It should be mentioned that the desirable intermetallic phases were not formed during heat treatment of unmilled powders. On the other hand, α-Mo-Mo5SiB2-Mo3Si nanocomposites were formed after annealing of powders milled for 22 h. With increasing milling time (at the second step), the formation of Mo3Si during subsequent heat treatment was disturbed. Here, an α-Mo-Mo5SiB2-MoSi2 nanocomposite was formed after annealing of 30 and 40 h milled powders. 相似文献
8.
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
9.
Xiaoli Xi Xiangyang XuZuoren Nie Shan HeWei Wang Jie YiZuo Tieyong 《International Journal of Refractory Metals and Hard Materials》2010
W–Cu composite materials have been widely used in heat sink apparatus and as electronic packaging materials. The preparation of the materials, especially the synthesis of W–Cu nanopowder, is a subject much more researches on. This paper focuses on the synthesis of W–Cu composite nanopowder using the freeze-drying technique, an environment-friendly and advanced technique for powder manufacturing. The process involved mixing ammonium metatungstate with CuSO4·5H2O as preliminary liquid solution and the use of liquid nitrogen as a cryogenic media; W–5Cu, W–10Cu and W–20Cu composite nanopowders were obtained after vacuum drying and following thermal decomposition reduction. X-ray diffraction, infrared spectroscopy and field emission scanning electron microscopy were used to characterize these nanopowders. The results showed that the freeze-drying precursor was the amorphous matter containing tungstate, sulfate, crystal water and ammonia. Copper appeared at 200 °C, tungsten and β-tungsten could not be obtained until 500 °C, and pure tungsten was found above 700 °C, which meant that the whole reduction process was completed. Crystallized W–Cu composite nanopowder, with particle sizes of 10–20 nm, was produced via a two-stage reduction: 400 °C for 2 h and then 700 °C for 2 h. 相似文献
10.
Q.M. Wang A. Flores Renteria R. Mykhaylonka W. Garkas 《Surface & coatings technology》2010,204(15):2343-598
An ∼ 5 µm Cr2AlC coating was synthesized on near-α titanium alloy Ti6242 using an industrially sized magnetron sputtering coater. Isothermal oxidation at 700 °C and 800 °C, and cyclic oxidation at 700 °C of the bare alloys and coated specimens were investigated in air. The results indicated that the Ti6242 alloy faced serious oxidation problems at 700 °C and 800 °C. Repeated formation and spallation of the multilayered oxide scale on the Ti6242 alloy occurred during oxidation testing. The coated specimens exhibited much better oxidation behaviour as compared to the bare alloy. A continuous Al-rich oxide scale formed on the coating surface during the initial oxidation stages. The oxide scale and coating itself acted as diffusion barriers blocking the further ingress of oxygen and protected the substrate alloy from oxidation. The oxidation mechanisms of the bare alloy and the coated specimens were investigated based on the experimental results. 相似文献
11.
This study investigates the influences of brazing temperature and time on microstructures and mechanical properties of commercially pure (CP) titanium. Bonding was performed in a high-vacuum furnace using Incusil-ABA (Ag–27.2Cu–12.5In–1.25Ti, wt.%), as filler metal. Brazing temperatures employed in this study were 710, 750, and 800 °C. At the same time, the investigated holding times at the brazing temperatures were 5, 30, and 90 min. Microstructure and phase constitution of the bonded joints were analyzed by means of metallography, scanning electron microscope (SEM) and X-ray diffraction pattern (XRD). An intense diffusion of Ti to the interface and a strong reaction between the braze alloy and the base metal were observed especially at a temperature of 800 °C. A number of intermetallic phases such as TiCu, Ti2Cu, Ti3In, Cu–In, and TiAg have been identified. Both brazing temperature and holding time are critical factors to control the microstructure and hence the mechanical properties of the brazed joints. The optimum brazing parameter was achieved at a temperature of 750 °C and a holding time of 90 min. 相似文献
12.
The oxidation behaviour of an intermetallic alloy, Ti-46.7Al-1.9W-0.5Si, was studied in air and Ar-20%O2 atmospheres at 750, 850 and 950 °C. Oxidation of the alloy followed a parabolic rate law at low temperature (750 °C) in both environments. The alloy oxidised parabolically in air and at a slower rate in Ar-20%O2 at 850 °C. Following a parabolic oxidation for a relatively short exposure period (72 h) at 950 °C, the oxidation rate was reduced after prolonged exposure (up to 240 h) in air. The alloy oxidised in a slower manner in the Ar-20%O2 atmosphere at 950 °C. Higher oxidation rates were observed in air than in Ar-20%O2 at all three experimental temperatures. Multi-layered scales developed in both environments. The scale formed in air consisted of TiO2/Al2O3/TiO2/TiN/TiAl2 layers, ranging from the surface to the substrate—whilst the scale developed in the Ar-20%O2 atmosphere comprised of the sequence TiO2/Al2O3/TiO2/Al2O3/Ti3Al/substrate. The two layers of Al2O3 in Ar-20%O2 were more effective in providing protection of the substrate against high temperature corrosion than the single layer of Al2O3 formed in air. 相似文献
13.
Guo-Liang Hou Hui-Di Zhou Yu-Long An Guang Liu Jian-Min ChenJie Chen 《Surface & coatings technology》2011,206(1):82-94
WC-(W,Cr)2C-Ni coating was prepared by high velocity oxy-fuel spraying (HVOF). The microstructure and phase composition of the as-sprayed coating and that after oxidation at high temperature were analyzed by means of scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The oxidation behavior of as-sprayed coating and starting powders was evaluated by thermogravimetry. Dry sliding friction and wear behavior of the WC-(W,Cr)2C-Ni coating sliding against Si3N4 ball at different temperatures (room temperature 20 °C and elevated temperature of 700 °C and 800 °C) was evaluated using an oscillating friction and wear tester. Besides, the microhardness and fracture toughness of the coating was also measured. Results show that sintering agglomerated WC-20 wt.%Cr-7 wt.%Ni powder is an effective method to prepare agglomerated and sintered WC-(W,Cr)2C-Ni composite powder. The excellent oxidation resistance of WC-(W,Cr)2C-Ni coating is mainly resulted from a double-decker shell-core microstructure formed in the coating. The composition of the outer shell is (W,Cr)2C phase and that of the inner shell is Cr3C2. During high-temperature friction and wear test, well remained hard WC phase in the WC-(W,Cr)2C-Ni coating can guarantee its good mechanical properties and wear resistance, and newly generated nano NiWO4, CrWO4 and Cr2WO6 particles can further improve these properties significantly. 相似文献
14.
Yongzhong Jin Ying Liu Yankun Wang Jinwen Ye 《International Journal of Refractory Metals and Hard Materials》2010
(Ti, W, Mo, V)(C, N) nanocomposite powders with globular-like particle of ∼10–100 nm were synthesized by a novel method, namely carbothermal reduction–nitridation (CRN) of complex oxide–carbon mixture, which was made initially from salt solution containing titanium, tungsten, molybdenum, vanadium and carbon elements by air drying and subsequent calcining at 300 °C for 0.5 h. Phase composition of reaction products was discussed by X-ray diffraction (XRD), and microstructure of the calcined powders and final products was studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results show that the synthesizing temperature of (Ti, W, Mo, V)(C, N) powders was reduced greatly by the novel precursor method. Thus, the preparation of (Ti, 15W, 5Mo, 0.2V)(C, N) is at only 1200 °C for 2 h. The lowering of synthesizing temperature is mainly due to the homogeneous chemical composition of the complex oxide–carbon mixture and its unusual honeycombed structure. 相似文献
15.
Q.X. Wang X.H. Wang Y. Yang Z.K. Fan 《International Journal of Refractory Metals and Hard Materials》2009,27(5):847-851
W–15 wt%Ti prealloyed powders were prepared by high-energy milling W and TiH2 powders, and the prealloyed powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The size of W and TiH2 grains was estimated by Williamson–Hall formula from width of XRD peaks. The results show that the grain size decreases with increasing milling time, while the lattice parameter increases. After milling for 40 h, nanocrystalline β-WxTi1−x solid solution with the form of thin laminar exists in the W–TiH2 prealloyed powders. 相似文献
16.
Selim Co?kun M. Lütfi Öveço?luAuthor vitae 《International Journal of Refractory Metals and Hard Materials》2011,29(6):651-655
In this study, the effect of Y2O3 additions on the microstructural and the physical properties of W-SiC composites was investigated. Powder blends of W—4 wt.% SiC, W—4 wt.% SiC—1 wt.% Y2O3 and W—4 wt.% SiC—5 wt.% Y2O3 were mechanically alloyed (MA'd) using a Spex mill for 24 h. MA'd composite powders were sintered under inert Ar and reducing H2 gas conditions at 1680 °C for 1 h. Microstructural and morphological characterizations of composite powders and sintered samples were carried out via SEM and XRD analyses. Furthermore, density measurements and hardness measurements of sintered samples were carried out. A highest Vickers microhardness value of 11.4 GPa was measured for the sintered W—4 wt.% SiC—5 wt.% Y2O3 while W—4 wt.% SiC sample possessed the highest relative density value of 97.7%. 相似文献
17.
Krzysztof Naplocha 《Journal of Alloys and Compounds》2011,509(36):8853-8861
Aluminium matrix composite reinforced with Ti compounds was successfully fabricated by SHS combustion synthesis and squeeze casting course. Prepared samples from mixture containing Ti, C and Al2O3 fibres were heated in microwave reactor to ignite synthesis and produce porous preform for subsequent infiltrating with liquid metal. Studies showed that synthesizing temperature has been remarkably increased by applying higher magnetron power and addition of graphite. Synthesis of specimens prepared from preliminary ball milled Ti and C powders proceeded at the highest propagation wave velocity. Microwave heating of metal Ti powder in the stream of CO2 resulted in formation of corrugated precipitates composed of titanium oxide with carbon inclusions TiO(C) and Ti2O3. The produced preforms were impregnated by squeeze casting with the aluminium alloy AlSi7Mg. Proper interface with slight reduction of Ti oxide between the reinforcement and the matrix was developed. Subsequently, the samples were annealed at 500 and 1000 °C. Annealing at the lower temperature induced creation of Ti3O2(C) and Al2O3. This process was continued at 1000 °C, and additionally some Ti(Al0,8Si0,2)3 pellets appeared in the matrix. With prolonged annealing, oxygen was completely removed from Ti compound and oval grains of Ti(C) were created, enveloped with Al2O3. In the matrix, larger and numerous Ti3AlSi5 pellets were formed. Hardness examination showed that the best strengthening effect was achieved after annealing at 1000 °C. 相似文献
18.
Chia-Cheng Lin Li-Hsiang Lin Jing-Ming Hung Yung-Hsun Shih Ching-Zong Wu Keng-Liang Ou Chih-Yeh Chao 《Journal of Alloys and Compounds》2011,509(37):9038-9044
The microstructural characteristics of the Fe-9Al-30Mn-1C-5Ti (wt.%) alloy were determined by scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectrometry. The microstructure of the alloy was essentially a mixture of (γ + TiCx + (α + B2 + DO3)) phases during solution treatment between 950 °C and 1150 °C. The TiCx carbide had a face-center-cubic structure with a lattice parameter a of 0.432 nm. When the as-quenched alloy was subjected to aging treatment at temperatures of 450-850 °C, the following microstructural transformation occurred: (γ + TiCx + κ + (α + DO3)) → (γ + TiCx + κ + (α + B2 + DO3 + TiCx)) → (γ + TiCx + κ + κ′ + (α + B2 + DO3)) → (γ + TiCx + (α + B2 + DO3)). Addition of Ti promotes the formation of the α phase at high temperatures. 相似文献
19.
H. Abbaszadeh A. MasoudiH. Safabinesh M. Takestani 《International Journal of Refractory Metals and Hard Materials》2012,30(1):145-151
The properties of W-15 wt.%Cu composites were investigated by preparing two distinct composites of micrometer and nanoscale structures. Micrometer composite was produced by mixing elemental W and Cu powders and nanometer one was synthesized through a mechanochemical reaction between WO3 and CuO powders. Subsequent compaction and sintering process was performed to ensure maximum possible densification at 1000-1200 °C temperatures. Finally, the behavior of produced samples including relative density, hardness, compressive strength, electrical conductivity, coefficient of thermal expansion (CTE) and room temperature corrosion resistance were examined. Among the composites, nano-structured sample sintered at 1200 °C exhibited better homogeneity, the highest relative density (94%) and mechanical properties. Furthermore, this composite showed superior electrical conductivity (31.58 IACS) and CTE (9.95384 × 10- 6) in comparison with micrometer type. This appropriate properties may be mainly attributed to liquid phase sintering with particle rearrangement which induced by higher capillary forces of finer structures. 相似文献
20.
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