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991.
Vladimir Brailovski Patrick Terriault Sergei Prokoshkin 《Journal of Materials Engineering and Performance》2002,11(6):614-621
Shape memory alloys (SMA) suffer from the same impairing mechanisms experienced during cycling loading by classic alloys.
Moreover, SMA fatigue behavior is greatly influenced by thermomechanical cycling through the zone of thermoelastic phase transformation,
which is the basis of shape memory and superelasticity effects. Since the fatigue resistance of any material can be improved
by an appropriate thermomechanical treatment, in the present work combined differential scanning calorimetry and microhardness
testing were used to determine an optimum annealing temperature for the cold-worked Ni-50.1%Ti alloy. The optimization is
based on the assumption that latent heat of transformation is proportional to the mechanical work generated by SMA upon heating,
while material hardness is related to the yield stress of the material. It is supposed that an optimum trade-off in these
two properties guarantees the best dimensional and functional stability of SMA devices. The level and stability of the mechanical
work generated by the material during low-cycle fatigue testing are considered criteria for the material performance and thus
of the validity of the proposed optimization procedure. 相似文献
992.
Elevated temperature Mg-Al-Sr: Creep resistance,mechanical properties,and microstructure 总被引:13,自引:0,他引:13
Eric Baril Pierre Labelle Mihriban Pekguleryuz 《JOM Journal of the Minerals, Metals and Materials Society》2003,55(11):34-39
Mg-Al-Sr-based alloys (AJ alloys) have shown superior creep performance and tensile strength at temperatures as high as 175°
with stresses up to 70 MPa. Mg-6Al-2.4Sr (AJ62x) exhibits an optimum combination of creep resistance and excellent castability,
while AJ62Lx (strontium <2.1) has better ductility than other AJ formulations. The AJ alloy microstructure is characterized
by the Al4Sr-α(Mg) lamellar phase that forms at the interdendritic/grain boundary region of the primary magne sium matrix. Mg-5Al-2Sr
(AJ52x) contains a ternary phase that was tentatively named Al3Mg13Sr. When the strontium level is low in AJ62x, the volume fraction of Al4Sr is reduced, the aluminum supersaturation of the magnesium primary phase increases, and Mg17Al12 forms. In this article, a mechanism is proposed whereby the creep resistance decreases with the strontium level but the tensile
strength and ductility increase.
For more information, contact Eric Baril, Noranda, Noranda Technologies Centre, 240 Hymus Pointe-Claire (Montréal), Québec,
H9R 1G5 Canada; (514) 630-9347; fax (514) 630-9379; e-mail eric.baril@ntc.noranda.com. 相似文献
993.
Polarization and impedance measurements were performed on steel in deaerated 5% HCl solution with and without Schiff base additives within the concentration range 1 × 10−4–5 × 10−3 mol/dm3. The Schiff base compounds used were salicylaldimine, R, N-(2-chlorophenyl)salicyaldimine, 2Cl-R, N-(3-chlorophenyl)salicyaldimine, 3Cl-R, and N-(4-chlorophenyl)salicyaldimine, 4Cl-R. It was found that when the concentration of the inhibitors were increased the inhibitor efficiencies, η, also increased with increasing surface coverage. The results indicated that the ortho-substituted (2Cl-R) compound had the highest inhibition efficiency. All the Schiff base additives studied obeyed the Langmuir isotherm. 相似文献
994.
995.
To investigate the effects of introducing the iron compound on the carbonization behavior polyacrylonitile (PAN)-based electrospun nanofibers were carbonized with or without iron(III) acetylacetonate (AAI) over the temperature range of 900–1500 °C in nitrogen atmosphere. The morphological characteristics of the carbon nanofibers were investigated using X-ray diffractometer (XRD), Raman spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The electrical conductivity of the carbon nanofiber web was measured by four-point probe method. The iron catalyst had a profound effect on the crystal structure of the carbonized nanofiber. In the presence of AAI the nanofibers carbonized at 1300 °C developed graphite structure, which could be obtained at the temperature higher than 2000 °C in the absence of the catalyst. The in-plane size of the graphite crystals (La) was measured to be about 6.5 nm by Raman spectroscopy and the (0 0 2) spacing by XRD was 0.341 nm. 相似文献
996.
The need for new, improved solder alloys and a better understanding of reactions during the soldering process grows steadily
as the need for smaller and more reliable electronic products increases. Information obtained from phase equilibria data and
thermodynamic calculations has proven to be an important tool in the design and understanding of new lead-free solder alloys.
A wide range of candidate alloys can be rapidly evaluated for proper freezing ranges, susceptibility to contamination effects,
and reactions with substrate materials before the expensive process of preparing and testing candidate alloys is initiated. 相似文献
997.
Terry C. Lowe Ruslan Z. Valiev 《JOM Journal of the Minerals, Metals and Materials Society》2004,56(10):64-68
Severe plastic deformation (SPD) has emerged as a promising method to produce ultrafine-grained materials with attractive
properties. Today, SPD techniques are rapidly developing and are on the verge of moving from lab-scale research into commercial
production. This paper discusses new trends in the development of SPD techniques suchas high-pressure torsion and equal-channel
angle pressing, as well as new alternative techniques for introducing SPD. The paper also contains a comparative analysis
of SPD techniques in terms of their relative capabilities for grain refinement, enhancement of properties, and potential to
economically produce ultrafine-grained metals and alloys.
For more information, contact Terry C. Lowe, Science and Technology Base Programs, Los Alamos National Laboratory, Los Alamos,
NM 87545; (505) 667-7824; fax (505) 665-3199; e-mail tlowe@lanl.gov. 相似文献
998.
Casting/mold thermal contact heat transfer during solidification of Al-Cu-Si alloy (LM 21) plates in thick and thin molds 总被引:1,自引:0,他引:1
K. Narayan Prabhu Bheemappa Chowdary N. Venkataraman 《Journal of Materials Engineering and Performance》2005,14(5):604-609
Heat flow at the casting/mold interface was assessed and studied during solidification of Al-Cu-Si (LM 21) alloy in preheated
cast iron molds of two different thicknesses, coated with graphite and alumina based dressings. The casting and the mold were
instrumented with thermocouples connected to a computer controlled temperature data acquisition system. The thermal history
at nodal locations in the mold and casting obtained during experimentation was used to estimate the heat flux by solving the
one-dimensional inverse heat conduction problem. The cooling rate and solidification time were measured using the computer-aided
cooling curve analysis data. The estimated heat flux transients showed a peak due to the formation of a stable solid shell,
which has a higher thermal conductivity compared with the liquid metal in contact with the mold wall prior to the occurrence
of the peak. The high values of heat flux transients obtained with thin molds were attributed to mold distortion due to thermal
stresses. For thin molds, assumption of Newtonian heating yielded reliable interfacial heat transfer coefficients as compared
with one-dimensional inverse modeling. The time of occurrence of peak heat flux increased with a decrease in the mold wall
thickness and increase in the casting thickness. 相似文献
999.
Wen-Fung Wang 《Journal of Materials Engineering and Performance》2007,16(5):533-538
Two types of Hoganas iron powders—sponge (NC), and highly compressible (SC) were investigated. These specimens were compacted
with a pressure of 300, 400, 500, 600, and 700 MPa, before sintering in a production belt-type furnace. Steam treatment of
the specimens was at 570 °C for 30 min. The sintered density and as-sintered hardness increase with increasing compaction
pressure, and are significantly influenced by the powder structural characteristics. During steam treatment the type of powder
and compaction pressure have an important influence on the extent of pore closure and weight gain. The maximum hardness was
obtained for the components compacted at a pressure of 500 MPa for both groups of iron powders. Surface pore closure and oxidation
resistance of the steam-treated components are improved with increasing compaction pressure. 相似文献
1000.
E. E. Abd El Aal W. Zakria A. Diab S. M. Abd El Haleem 《Journal of Materials Engineering and Performance》2003,12(2):172-178
The anodic dissolution of nickel was studied galvanostatically in hydrochloric acid solutions of various concentrations. The
reaction orders of chloride ion and hydrogen ion concentrations were found to be 0.5 and 1.0, respectively. An anodic Tafel
slope equal to 120 ± 10 mV · decade−1 was obtained. The dissolution rate of nickel at constant acid concentration was increased with stirring of the solution and
increasing temperature. The activation energy, ΔH, for the anodic dissolution process was found to be 12 kcal · mol−1. The presence of oxygen in solutions assisted the passivation process. The effect of addition of aniline and some of its
derivatives (o-, m-, and p-anisidine) as inhibitors on the dissolution kinetics of Ni in 1 M HCl was also investigated. These
compounds inhibited the anodic dissolution of nickel without affecting the Tafel slope, indicating that the adsorption of
such inhibitors could not interfere with the mechanism of metal dissolution. 相似文献