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排序方式: 共有277条查询结果,搜索用时 15 毫秒
41.
The development of the microstructure on aging of an (α + β) type titanium alloy containing 6A1-1.6Zr-3.3Mo-0.3Si (VT9) (in
weight percent) has been studied. The β-transus temperature of this alloy is approximately 1243 K. Solution treatment in the
β-phase field of the alloy followed by quenching in water at room temperature resulted in the formation of a single-phase
martensite struc-ture. The martensitic structure was confirmed to be orthorhombic (α″) using X-ray diffraction. The water-quenched
(WQ) specimens were subjected to aging treatments at temperatures of 823, 873, and 973 K for various lengths of time. Aging
at 823 K for times between 24 and 100 hours did not bring about any noticeable change in the microstructure. Aging at 823
K for 200 and 300 hours resulted in the heterogeneous precipitation ofs
2 silicide particles and thin films of β sandwiched between the interplatelet boundaries of martensite. Electron diffraction
analysis confirms that the crystal structure of silicide particles is hexagonal with lattice parameters α= 0.70(1) nm andc = 0.36(8) nm. Aging at 873 K for 12 and 24 hours resulted only in the precipitation ofs
2 silicide particles, while aging at the same temperatures for longer times (48, 100, and 200 hours) and also at 973 K for
6 to 100 hours resulted in the precipitation of silicides and also thin films of β and acicular martensite. The relative sizes
of silicide precipitates and width of thin films of β phase increase with increasing aging time. The sites for silicide precipitation
are mainly at α′-α′ boundaries, α-β interfaces, and sometimes within regions of transformed β. The kinetics ofs
2 silicide precipi-tation in this alloy is faster than in commercial near-α titanium alloys. This is attributed to the presence
of Mo, a strong β stabilizer.
Formerly Reader, Department of Metallurgical Engineering, Centre of Advanced Study, Institute of Technology, Banaras Hindu
University, Varanasi-221 005, India 相似文献
42.
Thanuja Ranawaka 《Journal of Constructional Steel Research》2009,65(2):249-259
In recent times, light gauge cold-formed steel sections have been used extensively since they have a very high strength to weight ratio compared with thicker hot-rolled steel sections. However, they are susceptible to various buckling modes including a distortional mode and hence show complex behaviour under fire conditions. Therefore, a research project based on detailed experimental studies was undertaken to investigate the distortional buckling behaviour of light gauge cold-formed steel compression members under simulated fire conditions. More than 150 axial compression tests were undertaken at uniform ambient and elevated temperatures. Two types of cross sections were selected with nominal thicknesses of 0.60, 0.80, and 0.95 mm. Both low (G250) and high (G550) strength steels were used. Distortional buckling tests were conducted at six different temperatures in the range of 20-800 °C. The ultimate loads of compression members subject to distortional buckling were then used to review the adequacy of the current design rules at ambient and elevated temperatures. This paper presents the details of this experimental study and the results. 相似文献
43.
The present study investigates the effect of ball milling on thermal conductivity and viscosity of stable nanofluid of fly ash from Indian coal. The particle size of fly ash decreased from micron size to 89, 55.5, and 11.5 nm with reduction by 55, 90, and 434 times, respectively, due to ball milling for 30, 40, and 60 hours. The surfactant Triton X-100 was used to attain stability of 0.1% and 0.5% volume concentration of fly ash nanofluid. The samples were characterized by using scanning electron microscopy, dynamic light scattering, and zeta potential analysis. The outcome reveals that the thermal conductivity of fly ash nanofluid increases with temperature, volume concentration, and reduction in particle size. A maximum enhancement in thermal conductivity of 11.9% with 11.5-nm nanofluid sample and 5.4% with 89-nm nanofluid sample for 0.5% concentration at 60°C is observed. The viscosity of fly ash nanofluid increases with concentration and varies inversely with particle size and temperature. A difference of 1.6% in viscosity is observed between the values obtained with 11.5 and 89 nm nanofluid samples for 0.5% concentration at 30°C. 相似文献
44.
Barium strontium alumino silicate (BSAS); (Ba0.6Sr0.4Al2Si2O8) was synthesized through solid state reaction between BaCO3, SrCO3, Al2O3 and SiO2 subjected to wet milling in isopropanol for about 24 h. The sequence of the solid state reaction was studied by subjecting to DG/DTG from room temperature to 1550 °C. The crystallographic phase evolution was confirmed by X-ray diffraction of the powders calcined in the range 1000 to 1300 °C for 2 h. The monoclinic celsian phase obtained at 1300 °C, pelletized through uniaxial pressing was sinterable to 67 to 78% density in the temperature range of 1300 to 1500 °C. The density improved to 75 to 94% after ball milling for 76 h, while ZrO2 addition further improved the density by 2%. The celcian phase of BSAS was dispersed in isopropyl alcohol, milled for about 24 h and spray coated on to plain SiC and mullite precoated SiC substrates. Sintering of coated samples and characterization for weight gain/loss, microstructure, scratch test prove that mullite + BSAS coating is more effective than single layer coating of BSAS on SiC substrates. 相似文献
45.
Shibnath Samanta Miryala Muralidhar V. Sankaranarayanan K. Sethupathi M. S. Ramachandra Rao Masato Murakami 《Journal of Materials Science》2017,52(22):13012-13022
Nb and Fe co-doped PLZT (Pb0.97La0.02(Zr0.52Ti0.48)1?2x (Nb0.5Fe0.5)2x O3 for x = 0.00, 0.02, 0.04, 0.06 and 0.08) samples have been prepared using sol–gel method. X-ray diffraction (XRD) and Raman spectroscopy studies confirmed that the samples are single phase even for the highest tested doping of 8 mol% of Nb and Fe. Incorporation of Nb and Fe atoms into PLZT lattice has been confirmed by XRD study where a systematic peak shift has been observed with increasing dopant concentration. The lattice parameters are found to decrease gradually with increase in Nb and Fe contents. From Raman spectroscopic investigation, redshift of several modes has been observed. Rietveld refinement has been performed to correlate XRD results with the fitting of Raman spectra. A total of 14 distinguished modes have been identified by de-convolution of Raman spectra, and they are in good agreement with the theoretically calculated modes for PbTiO3 and also with those reported on PZT and PLZT previously. The Burstein–Moss shift of absorption edge has been observed by diffuse reflectance spectroscopy experiment, and the analysis shows change in band gap from 3.21 eV (for x = 0.00) to 2.59 eV (for x = 0.08). The underlying mechanisms and the observed electronic behavior have been confirmed and analyzed by photoluminescence study which revealed several transitions and supported the effect of Nb and Fe co-doping as observed from XRD and Raman spectroscopy. 相似文献
46.
Chintamani Nagesa Ramachandra Rao Manjeet Chhetri 《Advanced materials (Deerfield Beach, Fla.)》2019,31(13)
Hydrogen generation by water splitting is clearly a predominant and essential strategy to tackle the problems related to renewable energy. In this context, the discovery of proper catalysts for electrochemical and photochemical water splitting assumes great importance. There is also a serious intent to eliminate platinum and other noble metal catalysts. To replace Pt by a non‐metallic catalyst with desirable characteristics is a challenge. Borocarbonitrides, (BxCyNz) which constitutes a new class of 2D material, offer great promise as non‐metallic catalysts because of the easy tunability of bandgap, surface area, and other electronic properties with variation in composition. Recently, BxCyNz composites with excellent electrochemical and photochemical hydrogen generation activities have been found, especially noteworthy being the observation that BxCyNz with a carbon‐rich composition or its nanocomposites with MoS2 come close to Pt in electrocatalytic properties, showing equally good photochemical activity. 相似文献
47.
Enhancement in electrical and magnetodielectric properties of Ca‐ and Ba‐doped BiFeO3 polycrystalline ceramics 下载免费PDF全文
Ramachandran Balakrishnan Ambesh Dixit Ratna Naik Mamidanna Sri Ramachandra Rao 《Journal of the American Ceramic Society》2018,101(2):782-788
We carried out a comparative study on the electrical and magnetodielectric properties of polycrystalline BiFeO3, Bi0.9Ca0.1FeO2.95, Bi0.9Ba0.05Ca0.05FeO2.95, and Bi0.9Ba0.1FeO2.95 ceramics. The two dielectric anomalies, near 25 K and 281 K, are observed for BiFeO3. Interestingly, the anomaly near 25 K shifts towards a higher temperature above 60 K with Ca and/or Ba doping, attributed to the doping induced chemical pressure. In addition, the room temperature switchable magnetodielectric effect is witnessed for the doped BiFeO3 compounds, due to the quadratic magnetoelectric coupling. This indicates the improved magnetoelectric coupling in BiFeO3 with the Ca and Ba doping. This is essentially due to the enhanced magnetic ordering and reduced leakage current in BiFeO3 after the doping. 相似文献
48.
Lue N Choi W Popescu G Ikeda T Dasari RR Badizadegan K Feld MS 《Applied optics》2007,46(10):1836-1842
Using the decomposition of an image field in two spatial components that can be controllably shifted in phase with respect to each other, a new quantitative-phase microscope has been developed. The new instrument, referred to as the fast Fourier phase microscope (f-FPM), provides a factor of 100 higher acquisition rate compared with our previously reported Fourier phase microscope. The resulting quantitative-phase images are characterized by diffraction limited transverse resolution and path-length stability better than 2 nm at acquisition rates of 10 frames/s or more. These features make the f-FPM particularly appealing for investigating the structure and dynamics of live cells over a broad range of time scales. In addition, we demonstrate the possibility of examining subcellular structures by digitally processing the amplitude and phase information provided by the instrument. Thus we developed software that can emulate phase contrast and differential interference contrast microscopy images by numerically processing FPM images. This approach adds the flexibility of digitally varying the phase shift between the two interfering beams. The images obtained appear as if they were recorded by variable phase contrast or differential interference contrast microscopes that deliver an enhanced view to the subcellular structure when compared with the typical commercial microscope. 相似文献
49.
The characterisation of aqueous silicon slips 总被引:1,自引:0,他引:1
R. Ramachandra Rao H. N. Roopa T. S. Kannan 《Journal of the European Ceramic Society》1999,19(16):874-2771
The optimum conditions of aqueous silicon slips for slip casting was achieved by employing various experimental techniques like zeta potential, particle/floc size distribution, sedimentation, viscosity and rheological measurements as a function of pH of the slips in the pH range of 2–11. Silicon suspensions display a maximum in zeta potential values and a minimum in sedimentation height and viscosity in two pH regions of 4–5 and 8. The slips behaved as near-newtonian at these pH values up to a solid loading of 52 wt% and as non-newtonian with thixotropic behaviour above this solid loading. Samples with highest green density (68%) were produced from 72 wt% solid loaded slips which were conditioned at a pH of 8 and milled for 26 h. The cast bodies of these slips were nitrided to obtain reaction bonded silicon nitride products which were also characterised. 相似文献
50.
H
R Hemantha Kumar P Vincent Monteiro Gajanan S Bhat H
G Ramachandra Rao 《Journal of the science of food and agriculture》2001,81(1):42-45
Milk proteins were enzymatically modified, using neutrase and trypsin immobilised on CM‐Sephadex C‐50, to the extent of 3, 4 and 5% degrees of hydrolysis. The neutrase‐treated milk and the trypsin‐treated milk were used separately to prepare set yoghurt. The set yoghurt prepared from neutrase‐treated milk showed an improvement in body, texture and flavour, a faster rate of acid development and a reduction in setting time compared with the control. However, the set yoghurt prepared from trypsin‐treated milk showed either a small or no improvement in textural and sensory properties. © 2000 Society of Chemical Industry 相似文献