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991.
J.S. Huo J.T. Gou L.Z. Zhou X.Z. Qin G.S. Li 《Journal of Materials Engineering and Performance》2007,16(1):55-62
Creep properties of the experimental superalloy were investigated in the temperature range 1073–1223 K and stress range 110–550 MPa.
The observations of dislocation structures during different creep conditions reveal that in the high stress region, particle-shearing
mechanisms including stacking fault formation and antiphase boundary creation are operative and in the low stress region,
the dislocation climb mechanism is dominant. From the plot of minimum creep rate versus applied stress, a very low stress
region with exponent n < 2, which is related to diffusional creep, is found. Based on the experimental results, a stress–temperature creep deformation
mechanism map for the alloy is constructed. On the basis of particle hardening theories and various dislocation-creep theories,
the dislocation-creep transitions in terms of internal stress are discussed and calculated threshold stresses of various creep
deformation mechanisms indicates that the particle shearing is easier to operate than Orowan looping at high stresses, and
general climb is easy to happen at low stresses. 相似文献
992.
The rate of corrosion of rotating copper discs was measured as a function of the concentration of oxygen in metal. It was found that the catastrophic acceleration of the corrosion of the sample occurs at 3 × 103 ppm of oxygen in metal. In the temperature range 5–75°C, the corrosion resulting from the presence of the oxygen in the metal occurs in the regime of activational control, and it is not influenced by the oxygen dissolved in the acid. The corrosion resulting from the oxygen depolarization occurs in the activational control regime in the temperature range 5–35°C, in the mixed kinetics regime in the range 45–55°C, and in the range 65–75°C in the diffusional regime with respect to the oxygen dissolved in the acid. The overall rate of corrosion of copper containing 8 × 103 ppm of oxygen is about 20 times greater than the rate of corrosion of copper with oxygen depolarization. 相似文献
993.
Effect of rhenium addition on isothermal oxidation behavior of single-crystal Ni-based superalloy 总被引:1,自引:0,他引:1
The isothermal oxidation behavior of a nickel-based superalloy, which we designate as DD32, containing 4 wt.% rhenium and another alloy (DD32M) without rhenium were investigated at 900, 1000 and 1100 °C. Oxidized alloys were characterized by SEM, EDX, EPMA and XRD. The two alloys revealed similar oxidation rates at 900 °C, while the DD32 alloy showed a slightly higher mass gain than that of the DD32M alloy during 1000 and 1100 °C exposure. Surface and cross-sectional examination indicated that DD32 alloy showed nonuniform oxidation between dendritic and interdendritic areas at all temperatures. Similar different oxidation behavior between dendritic and interdendritic regions was also observed in the DD32M alloy at 900 °C. However, DD32M showed relatively uniform oxidation at 1000 and 1100 °C exposure. Therefore, Re addition clearly induced the nonuniform oxidation of the alloy. 相似文献
994.
995.
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
996.
The dissolution rate of mild steel in 1 N H2SO4 without and with different additions of Cl?, Br? and I? has been measured. Analysis of the results indicates that halide ions adsorbed on the metal surface inhibit the dissolution reaction. Adsorption occurs according to the Frumkin isotherm. 相似文献
997.
The objective of this study is to experimentally investigate the cutting mechanisms of polycrystalline diamond compacts (PDC) using two different lasers: (a) a near infrared Nd:YAG laser (Neodymium-doped Yttrium Aluminum Garnet) of 1064 nm wavelength and 100 μs pulse width; and (b) a green light KTP (Potassium Titanyl Phosphate)/Nd:YAG laser of 532 nm wavelength and 120 ns pulse width. To realize the objective, the study applies polishing, lapping and etching processes to the cut-surfaces of the PDC samples. It further observes and analyzes the processed cut-surfaces with scanning electron microscopy (SEM) and Raman spectroscopy. A discussion is provided to reveal the underlying physics of the laser cutting mechanisms, and a conclusion is drawn based on the outcomes from the experimental investigation and the discussion. 相似文献
998.
Ennoblement of stainless steel (SS) by microbially deposited manganese oxides can lead to pitting corrosion at low chloride concentrations, causing unexpected material failures. We exposed 316L SS to manganese oxidizing bacteria Leptothrix discophora under well-defined laboratory conditions, and then placed the ennobled coupons in a 0.5 M sodium chloride solution until pitting developed. Using time-of-flight secondary ion mass spectroscopy we demonstrated that the pits and their immediate vicinity associated with microbial influenced corrosion had different chemical signatures than those associated with electrochemically induced pitting, suggesting a possibility that the microorganisms were directly involved in pit initiation. Based on the differences in the chemical signatures we were able to distinguish the microbially induced pits from those induced by anodic polarization. 相似文献
999.
Conclusion In the process of heat treatment at the austenitization temperature, on the grain boundaries of steel 10 segregations of manganese and of substitutional impurities form, the adsorbed layers being about 200 nm thick. Long-term aging (up to 250,000 h) at 245°C does not lead to a noticeable change in the concentration of these layers.Leningrad Technological Institute of the Refrigeration Industry. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 54–56, October, 1987. 相似文献
1000.
An Al-3% Mg solid solution alloy was subjected to intense plastic deformation, using either equal-channel angular (ECA) pressing or torsion straining, to produce grain sizes in the submicrometer range. Static annealing at elevated temperatures led to grain growth and average grain sizes of up to > 100 μm. As-fabricated and statically annealed specimens were used to determine the variation in microhardness with grain size, and results confirm that the Hall-Petch relationship persists down to at least the finest grain size examined experimentally (∼90 nm). The results provide no evidence to support the claims of a negative Hall-Petch slope when the average grain size is very small, but there is evidence of a decrease in the slope of the Hall-Petch plot at the very finest grain sizes (< 150 nm); this is attributed to the increased participation of mobile extrinsic dislocations in the boundary regions when taking the hardness measurements. 相似文献