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1.
Si–C–Ti ceramics were synthesized by reactive pyrolysis of polycarbosilane (PCS) precursor filled with metal Ti powder. Pyrolysis of mixture with atomic ratio of Ti:Si through 3:1–3:2 was carried out in argon atmosphere at given temperature up to 1500 °C. The metal–precursor reactions, and phase evolution were studied using X-ray diffraction and scanning electron microscopy with EDX. The Ti3SiC2 phase was obtained firstly from reaction of PCS and Ti. Ti3SiC2 formation starts at 1300 °C and its amount increases significantly in a narrow temperature range between 1400 °C and 1500 °C. In addition, addition of CaF2 can promote the formation of Ti3SiC2 phase. 相似文献
2.
《Composites Part A》2003,34(1):17-24
Structural characterizations based on transmission electron microscopy observations were carried out on as-fabricated and heat-treated Al-2024/TiC composites. These composites types reinforced with TiC particles were produced with a pressureless melt infiltration route at 1200 °C for 2 h under argon atmosphere. The composites were heat-treated at 530 °C during 150 min, cold-water quenched and subsequently artificial and natural aged at 190 °C for 12 h in an argon environment and at room temperature for 96 h, respectively. Different precipitate types were obtained and they were identified as CuAl2, Al3Ti, Ti3AlC and Ti3Al. Most of the precipitates were found to be uniformly distributed in the matrix and some regions show precipitates which have a cubic morphology (Ti3Cu). High-resolution electron microscopy images were partially used for the characterization of the precipitates in these composites. 相似文献
3.
Low-cycle fatigue (LCF) tests are carried out on TP347H stainless steel at a strain rate of 8 × 10−3 s−1 with total strain amplitudes (Δεt/2) of ±0.4% and ±1.0%, at room temperature (RT) and 550 °C. It is found that the stress responses and dislocation structures under cyclic loading strongly depend on the value of strain amplitude at 550 °C. Compared with those at the same strain amplitude at RT, the material shows a rapid strain softening, and finally attains a stabilized state at Δεt/2 = ±0.4% and 550 °C, but the one presents an anomalous behavior, i.e., first a rapid hardening to the maximum stress, followed by a reducing softening at Δεt/2 = ±1.0% and 550 °C. More cells resulting from dislocation cross-slip and planar structures due to dynamic strain ageing (DSA) restricting cross-slip develop at low strain amplitude of ±0.4% at the first cycle. However, there are more complicated dislocation structures, such as cells, elongated cells, walls/channels and planar structures at Δεt/2 = ±1.0%. The observations of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) exclude the effects of martensitic transformation, creep, oxidation, and precipitations on these stress responses and microstructure evolutions, which result from DSA appearing at 550 °C. 相似文献
4.
《Materials Research Bulletin》2006,41(3):628-634
Amorphous Ni3(SbTe3)2 compound was prepared from a metathesis between Zintl phase K3SbTe3 and NiBr2 in solution and its oxidation behavior was investigated in the temperature range of 200–700 °C in air. To characterize the sample, thermogravimetry (TG), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive analysis by X-ray (EDAX) analyses were performed and electrical conductivity was measured as a function of temperature in the range of 25–800 °C in air. The specimen showed a metallic conducting-like behavior below 585 °C while a semiconducting-like behavior above 585 °C. At a first oxidation step of Ni3(SbTe3)2 below 500 °C, TeO2 phase is formed. Above 500 °C, NiO phase is formed, then some NiO reacts with TeO2 to form NiTeO3 and NiSb2O6 is simultaneously formed. Above 700 °C, NiTeO3 is further reacted with TeO2 to form NiTe2O5. Both NiTeO3 and NiTe2O5 are decomposed above 774 °C. 相似文献
5.
In the present study, diffusion bonding of titanium alloy and micro-duplex stainless steel with a nickel alloy interlayer was carried out in the temperature range of 800–950 °C for 45 min under the compressive stress of 4 MPa in a vacuum. The bond interfaces were characterised by scanning electron microscopy, electron probe microanalyzer and X-ray diffraction analysis. The layer wise Ni3Ti, NiTi and NiTi2 intermetallics were observed at the nickel alloy/titanium alloy interface and irregular shaped particles of Fe22Mo20Ni45Ti13 was observed in the Ni3Ti intermetallic layer. At 950 °C processing temperature, black island of β-Ti phase has been observed in the NiTi2 intermetallics. However, the stainless steel/nickel alloy interface indicates the free of intermetallics phase. Fracture surface observed that, failure takes place through the NiTi2 phase at the NiA–TiA interface when bonding was processed up to 900 °C, however, failure takes place through NiTi2 and β-Ti phase mixture for the diffusion joints processed at 950 °C. Joint strength was evaluated and maximum tensile strength of ∼560 MPa and shear strength of ∼415 MPa along with ∼8.3% ductility were obtained for the diffusion couple processed at 900 °C for 45 min. 相似文献
6.
This paper reports on a comparative study of tribological and corrosion behavior of plasma nitrided 34CrNiMo6 low alloy steel under modern hot wall condition and conventional cold wall condition. Plasma nitriding was carried out at 500 °C and 550 °C with a 25% N2 + 75% H2 gas mixture for 8 h. The wall temperature of the chamber in hot wall condition was set to 400 °C. The treated specimens were characterized by using scanning electron microscopy (SEM), X-ray diffraction (XRD), microhardness and surface roughness techniques. The wear test was performed by pin-on-disc method. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were also used to evaluate the corrosion resistance of the samples. The results demonstrated that in both nitriding conditions, wear and corrosion resistance of the treated samples decrease with increasing temperature from 500 °C to 550 °C. Moreover, nitriding under hot wall condition at the same temperature provided slightly better tribological and corrosion behavior in comparison with cold wall condition. In consequence, the lowest friction coefficient, and highest wear and corrosion resistance were found on the sample treated under hot wall condition at 500 °C, which had the maximum surface hardness and ε-Fe2–3N phase. 相似文献
7.
T.S. Huang M.N. Rahaman B.S. Bal 《Materials science & engineering. C, Materials for biological applications》2009,29(6):1935-1941
Dense composite laminates of alumina (Al2O3) and tantalum (Ta) were fabricated by hot pressing and tested in vitro for potential use as a femoral head material in total hip arthroplasty (THA). Al2O3–Ta composite laminates hot pressed at 1450 °C and 1650 °C had flexural strengths of 940 ± 180 MPa and 1090 ± 340 MPa, respectively, which were far larger than the values of 420 ± 140 MPa and 400 ± 130 MPa for Al2O3 hot pressed at 1450 °C and 1650 °C, respectively. The interfacial shear strength, determined by a double-notched specimen test, was 310 ± 80 MPa for the composite laminate hot pressed at 1650 °C, indicating strong interfacial bonding between Al2O3 and Ta. Scanning electron microscopy (SEM), energy dispersive X-ray (EDS) analysis, and X-ray mapping of polished sections of the hot-pressed laminates showed the presence of an interfacial region formed presumably by diffusion of O (at 1450 °C) or O and Al (1650 °C) from Al2O3 into Ta. Composite femoral heads of Al2O3 and Ta could combine the low wear of an Al2O3 articulating surface with the safety of a ductile metal femoral head. 相似文献
8.
This study discusses the effects of a CrPt3 alloy underlayer on the magnetic properties and microstructure of FePt films. The L12 CrPt3 phase was chemical long-range ordered at a temperature above 600 °C, and the 120-nm thick CrPt3 film annealed at 800 °C, resulting in ferrimagnetic behavior. The long-range ordered CrPt3 underlayer slightly increased the ordering of the L10 FePt film, as evidenced by the individual L12 CrPt3 and L10 FePt (0 0 1) superlattice peaks. An X-ray slow scan of the [FePt/CrPt3(T °C)]400°C bilayer shows that the integrated intensity of the L10 FePt (0 0 1) peaks was higher on the long-range order L12-type CrPt3 (T = 600, 800) underlayer and lower on the partial short-range order L12 and A1-types CrPt3 (T = 400) underlayer. However, optimal magnetic properties were obtained in the [FePt/CrPt3(400 °C)]400°C bilayer. When a FePt film is deposited on a ferrimagnetic CrPt3(800 °C) underlayer, the resulting bilayer shows isotropic magnetic hysteresis loops and cannot be saturated at 1.8 T. Atomic force microscopy (AFM) and transition electron microscopy (TEM) show that the L12 CrPt3(800 °C) underlayer exhibits coarse surface roughness and plate-like grains, respectively. From TEM images, all the FePt grains were isolated uniformly by CrPt3 matrix. 相似文献
9.
Yan’gai Liu Yu Zhou Dechang Jia Zhaohui Huang Minghao Fang 《Materials Chemistry and Physics》2011,125(1-2):143-147
Characterization of domain configurations in 15 vol% LiTaO3/Al2O3 ceramic composites hot-pressed sintered at 1300 °C was carried out using transmission electron microscopy and high-resolution transmission electron microscopy. Mainly banded- and wedge-shaped 90° domains, with few 180° domains, were formed in the LiTaO3 grains within the composite. The formation of 90° domains was attributed to the large stress caused by residual polarization. Many dark dots, distributed along the 90° domain boundaries, were detected and it was confirmed that they were not a deposited second phase but a type of contrast induced by high strain. The 90° domain boundaries presented an α-type fringe contrast and no δ-type fringes were observed, indicating that they were of the non-conventional type. 相似文献
10.
Li Yun Yang Gui Peng Feng Tian Xi Wang Jia Min Zhang Tian Jun Lou 《Materials Letters》2011,65(17-18):2601-2603
An alternative low cost method was proposed for the low temperature (600 °C) preparation of CdTiO3 nanoplates, using low-melting-point Cd(NO3)2 · 4H2O and high-reactive-activity TiO2 nanocrystals as the reactants. The structure, composition, specific surface area, thermal stability and optical properties of the as-synthesized products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, field emission scanning electron microscopy, Brunauer–Emmett–Teller surface area analysis, UV–vis absorption and room temperature photoluminescence spectra. The as-synthesized CdTiO3 nanoplates were thermally stable at temperatures ≤ 900 °C, and their phase changed from ilmenite to perovskite when heated in air at 1000 °C for 2 h. Besides, they exhibited a strong and broad visible light emission in the range of about 470–750 nm upon laser excitation at 325 nm, enabling their use as a luminescent material. 相似文献
11.
Novel biomaterials are of prime importance in tissue engineering. Here, we developed novel nanostructured Al2TiO5–Al2O3–TiO2 composite as a biomaterial for bone repair. Initially, nanocrystalline Al2O3–TiO2 composite powder was synthesized by a sol–gel process. The powder was cold compacted and sintered at 1300–1500 °C to develop nanostructured Al2TiO5–Al2O3–TiO2 composite. Nano features were retained in the sintered structures while the grains showed irregular morphology. The grain-growth and microcracking were prominent at higher sintering temperatures. X-ray diffraction peak intensity of β-Al2TiO5 increased with increasing temperature. β-Al2TiO5 content increased from 91.67% at 1300 °C to 98.83% at 1500 °C, according to Rietveld refinement. The density of β-Al2TiO5 sintered at 1300 °C, 1400 °C and 1500 °C were computed to be 3.668 g cm?3, 3.685 g cm?3 and 3.664 g cm?3, respectively.Nanocrystalline grains enhanced the flexural strength. The highest flexural strength of 43.2 MPa was achieved. Bioactivity and biomechanical properties were assessed in simulated body fluid. Electron microscopy confirmed the formation of apatite crystals on the surface of the nanocomposite. Spectroscopic analysis established the presence of Ca and P ions in the crystals. Results throw light on biocompatibility and bioactivity of β-Al2TiO5 phase, which has not been reported previously. 相似文献
12.
《Materials Research Bulletin》2006,41(9):1775-1782
GaN crystals were grown on graphite and sapphire substrates at 990–1050 °C by reaction of Ga2O with flowing NH3. Ga2O gas was produced at a constant rate (1.3 wt% min−1) by reaction of Ga2O3 with carbon at 1000–1060 °C. The effect of NH3 concentration (3–100 vol%) and the nature of the substrate on the morphology and orientation of the GaN crystals were determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and selected area electron diffraction. It was found that sheet and plate-like crystals grew at different orientations to the substrate with different NH3 concentrations and substrates. 相似文献
13.
Nipin Kohli Onkar Singh Kanika Anand Ravi Chand Singh 《Materials Research Bulletin》2012,47(8):2072-2076
Nanoparticles of chromium oxide have been synthesized following a precipitation technique at reaction temperatures 5, 27 and 65 °C. Synthesized powders were characterized using X-ray diffraction, transmission electron microscope and Brunauer–Emmett–Teller techniques to carry out structural and morphological analysis. The reaction temperature has been found to be playing a crucial role in controlling particle size. It has been observed that Cr2O3 nanoparticles synthesized at 27 °C were smaller as compared to those synthesized at 5 and 65 °C. Chromium oxide samples thus prepared were deposited as thick films on alumina substrates to act as gas sensors and their sensing response to ethanol vapour was investigated at different operable temperatures. It has been observed that all the sensors exhibited optimum response at 250 °C. The investigations revealed that sensing response of Cr2O3 nanoparticles synthesized at 27 °C was exceptionally higher than that of Cr2O3 nanoparticles synthesized at 5 and 65 °C. 相似文献
14.
Siwei Li Bin Zeng Zude Feng Yongsheng Liu Wenbin Yang laifei Cheng Litong Zhang 《Thin solid films》2010,519(1):251-258
A two-layer boron carbide coating is deposited on a graphite substrate by chemical vapor deposition from a CH4/BCl3/H2 precursor mixture at a low temperature of 950 °C and a reduced pressure of 10 KPa. Coated substrates are annealed at 1600 °C, 1700 °C, 1800 °C, 1900 °C and 2000 °C in high purity argon for 2 h, respectively. Structural evolution of the coatings is explored by electron microscopy and spectroscopy. Results demonstrate that the as-deposited coating is composed of pyrolytic carbon and amorphous boron carbide. A composition gradient of B and C is induced in each deposition. After annealing, B4C crystallites precipitate out of the amorphous boron carbide and grow to several hundreds nanometers by receiving B and C from boron-doped pyrolytic carbon. Energy-dispersive spectroscopy proves that the crystallization is controlled by element diffusion activated by high temperature annealing, after that a larger concentration gradient of B and C is induced in the coating. Quantified Raman spectrum identifies a graphitization enhancement of pyrolytic carbon. Transmission electron microscopy exhibits an epitaxial growth of B4C at layer/layer interface of the annealed coatings. Mechanism concerning the structural evolution on the basis of the experimental results is proposed. 相似文献
15.
Chihiro Mochizuki Hiroki Hara Ichiro Takano Tohru Hayakawa Mitsunobu Sato 《Materials science & engineering. C, Materials for biological applications》2013,33(2):951-958
The fabrication and characterization of a carbonate-containing apatite film deposited on a Ti plate via an aqueous spray method is described. The mist of the spray solution emitted from a perpendicularly oriented airbrush was made to strike a warmed Ti substrate. The thicknesses of the sprayed film and those heat-treated at 400 °C–700 °C under Ar gas flow were in the range 1.21–1.40 μm. The results of elemental analyses and Fourier transform infrared spectroscopy of the powders that were mechanically collected from the surface of the sprayed film suggest that the film was Ca10(PO4)6(CO3) · 2CO2 · 3H2O. The presence of the carbonate ion and the lattice CO2 molecule was confirmed via the aforementioned analyses; the finding was also consistent with the X-ray diffraction patterns of the films and the chemical identity of the sprayed and heat-treated films that were measured using X-ray photoelectron spectroscopy. The sprayed film comprises a characteristic network structure, which contains round particles within the networks, as was observed by field-emission scanning electron microscopy. A scratch test indicated that the shear stress of the sprayed film (21 MPa) significantly improved to 40 and > 133 MPa after heat-treatment at 600 °C and 700 °C, respectively, under Ar gas flow for 10 min. 相似文献
16.
《Composites Part A》2007,38(10):2102-2108
Three groups of SiCf/Ti/Cu composites were prepared under conditions of 650 °C + 105 min (sample 1#), 750 °C + 85 min (sample 2#) and 840 °C + 50 min (sample 3#), respectively, by foil-fiber-foil method (FFF), and their room temperature tensile strengths were established. The aim is to model the reactive bonding states between Ti and SiC fiber and between Ti and Cu when Ti is used as interfacial adhesion promoters in SiCf/Cu–matrix composites. The fracture surfaces, SiCf/Ti interfaces and Ti/Cu interfaces were investigated by scanning electron microscopy (SEM), optical microscopy and energy dispersive spectroscopy (EDS). The tensile tests show that the tensile strengths of samples 1# and 2# are not obviously enhanced due to the weak bonding strength between SiC fiber and Ti, while those of sample 3# are achieved above 90% of ROM (the rule of mixtures) strength because of excellent bonding between SiC fiber and Ti. However, there are distinct Ti/Cu interfacial reaction zones after the three processes, which are approximately 5.4, 9.0 and 13.3 μm thick, respectively. The Ti/Cu interfacial reaction products are mainly distributed in four layers. In samples 1# and 2#, the products are predicted to be Cu4Ti, Cu3Ti2, CuTi and CuTi2 according to their chemical compositions determined by EDS, while in sample 3#, the products are Cu4Ti, Cu4Ti3, CuTi and CuTi2. Additionally, the relationships between the thickness of Ti interlayer and its reaction with C and Cu are also discussed, and an optimal thickness of Ti is introduced. 相似文献
17.
Atomic force microscopy (AFM) studies of the dimensional changes of cellulose microfibril materials, called cellulose aggregate fibrils (approx. 100 µm × 3 µm × 300 nm), exposed to two distinct relative humidities of 80% and 23% for 24 h and then suddenly subjected to 50% RH and 23 °C show that the fibrils are responsive to the surrounding environments in a nonspecific fashion. AFM images (10 µm × 10 µm) of the individual straight cellulose aggregate fibrils were taken as a function of elapsed time during both desorption and adsorption of moisture. The longitudinal distance between discrete natural defects observed on the cellulose aggregate fibrils as well as the width, cross-sectional area, and height of the cellulose aggregate fibril were measured from the AFM images. The length of the cellulose aggregate fibrils was found to have reduced after exposure to either high or low relative humidity, and then placement in ambient conditions. Over time in ambient conditions, the cellulose aggregate fibrils progressively relaxed to their original length during both desorption and adsorption of moisture. However, the relaxation rate during adsorption was faster than that during desorption. The possible explanations for this phenomenon are discussed including the sample preparation method, volume conservation, entropy elasticity, and free volume theory. The changes in the width, height, and cross-sectional area are also discussed. 相似文献
18.
Neveen A. Hassan Sahar A. El-Molla Ghada M. Mohamed Gehan A. Fagal 《Materials Research Bulletin》2012,47(9):2655-2661
Fe2O3/MgO system was prepared by wet impregnation method followed by treatment with different amounts of Zr-dopant salt then heating at 500 and 700 °C. The dopant concentrations were 0.48, 0.95 and 1.4 mol% ZrO2. Pure and variously doped solids were characterized using XRD, N2-adsorption isotherms carried out at ?196 °C and catalytic decomposition of H2O2 in aqueous solution at 25–35 °C. The results revealed that the nanosized MgO phase was only detected in the diffractograms of pure and doped solids calcined at 500 °C. Heating pure and doped solids at 700 °C produced nanosized MgFe2O4 phase together with MgO phase. Pure and ZrO2-doped solids calcined at 500 and 700 °C are mesoporous adsorbents. The doping process brought about a measurable decrease in the SBET of Fe2O3/MgO system with subsequent increase in its catalytic activity. The catalytic activity of the investigated system toward H2O2 decomposition, expressed as reaction rate constant per unit surface area was found to increase as a function of dopant concentration. The maximum increase in the reaction rate constant per unit surface area measured for the reaction carried out at 30 °C attained 125% for the heavily doped samples. This significant increase was based on the catalytic activity of pure catalyst sample measured under the same conditions. 相似文献
19.
Won Seok Choi Yeun-Ho Joung Jinhee Heo Byungyou Hong 《Materials Research Bulletin》2012,47(10):2780-2783
In this paper we introduce mechanical and structural characteristics of diamond-like carbon (DLC) films which were prepared on silicon substrates by radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) method using methane (CH4) and hydrogen (H2) gas. The films were annealed at various temperatures ranging from 300 to 900 °C in steps of 200 °C using rapid thermal processor (RTP) in nitrogen ambient. Tribological properties of the DLC films were investigated by atomic force microscopy (AFM) in friction force microscopy (FFM) mode. The structural properties of the films were obtained by high resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The wettability of the films was obtained using contact angle measurement. XPS analysis showed that the sp3 content is decreased from 75.2% to 24.1% while the sp2 content is increased from 24.8% to 75.9% when the temperature is changed from 300 to 900 °C. The contact angles of DLC films were higher than 70°. The FFM measurement results show that the highest friction coefficient value was achieved at 900 °C annealing temperature. 相似文献
20.
In the present study, Ti–6Al–4V alloy was bonded to electrolytic copper at various temperatures of 875, 890 and 900 °C and times of 15, 30 and 60 min through diffusion bonding. 3 MPa uniaxial load was applied during the diffusion bonding. Interface quality of the joints was assessed by microhardness and shear testing. Also, the bonding interfaces were analysed by means of optical microscopy, scanning electron microscopy and energy dispersive spectrometer. The bonding of Ti–6Al–4V to Cu was successfully achieved by diffusion bonding method. The maximum shear strength was found to be 2171 N for the specimen bonded at 890 °C for 60 min. The maximum hardness values were obtained from the area next to the interface in titanium side of the joint. The hardness values were found to decrease with increasing distance from the interface in titanium side while it remained constant in copper side. It was seen that the diffusion transition zone near the interface consists of various phases of βCu4Ti, Cu2Ti, Cu3Ti2, Cu4Ti3 and CuTi. 相似文献