共查询到20条相似文献,搜索用时 15 毫秒
1.
Cylindrical specimens of Inconel 713LC in as-received condition and with surface treatment by Al diffusion coating were cyclically strained under strain control at 800 °C in air. Surface treated layer was characterized and the hardness depth profile was measured. Cyclic stress–strain response and fatigue life of both materials were assessed. The stress response of the coated superalloy specimens is lower in comparison with the untreated specimens. Beneficial effect of surface treatment on the Manson–Coffin curve is documented. Specimen sectioning and fracture surface studies revealed fatigue damage mechanisms both in coated and uncoated specimens. Propagation path of the principal crack is predominantly interdendritic. 相似文献
2.
3.
4.
《材料科学技术学报》2019,35(8):1607-1617
GH4169 at 650 °C in atmosphere was investigated by using single edge notch tensile specimens. The number of main cracks and crack initiation mechanisms at the notch surface strongly depended on the grain size. The crack initiation life accounted for more percentages of the total fatigue life for the alloy with smaller grain size. The fatigue life generally increased with increasing crack initiation life. The small crack transited to long crack when its length reached ˜10 times the grain size. 相似文献
5.
XimmiaoPAN ZhanpengJIN 《材料科学技术学报》2002,18(6):532-534
The phase equilibrium relations of the ternary Ni-Cr-Zr system at 900℃have been investigated by means of diffusion triple and electron probe microanalysis(EMPA) techniques.A series of tie lines and triangles have been determined, and the corresponding tentative isothermal section is presented based on the current information. 相似文献
6.
Martti Heinonen Davor Zvizdic Danijel Sestan 《International Journal of Thermophysics》2012,33(8-9):1451-1457
The first European humidity key comparison EURAMET-T.K6 was completed in 2008, and it covered the dew-point temperature range from ?50?°C to +?20?°C. Both LPM and MIKES participated in the comparison, but a new low dew-point generator was introduced at LPM as a result of progress in the EUROMET P912 project. To extend the range of available comparison evidence down to ?70?°C and to study the validity of improved uncertainties of LPM, a bilateral comparison was carried out between LPM and MIKES in 2009?C2010. The applied comparison procedure was similar to that applied in EURAMET-T.K6. However, only one transfer standard was used instead of two units and the measurement point ?70?°C was added in the measurement scheme. The results show that the bilateral equivalence between LPM and MIKES is between (0.00 ± 0.06)?°C and (0.02 ± 0.08)?°C in the range from ?50?°C to +?20?°C and (0.01 ± 0.10)?°C at ?70?°C. Using MIKES results as the link to the EURAMET.T-K6, it is shown that the difference between the results obtained with the new LPM dew-point temperature standard and the EURAMET Comparison Reference Values is between (?0.02 ± 0.08)?°C at 20?°C and (+?0.02 ± 0.07)?° C at ?50?°C. 相似文献
7.
15-15Ti is one of the potential candidate materials for fuel rod cladding of lead-based reactors, and its fatigue properties have been investigated. Low cycle fatigue (LCF) tests of 15-15Ti have been carried out under total strain amplitudes ranging from ±0.3% to ±0.9% at 20 and 550°C in vacuum. The results show the LCF life decreases with the increase of temperature. Crack propagates more tortuously and the fatigue crack propagation (FCP) rate is lower when it is tested at 20°C compared to 550°C. In addition, the effect of twin boundaries (TBs) and stacking fault energy (SFE) on FCP rate is discussed in this paper. 相似文献
8.
During fatigue of Kaowool fiber reinforced aluminum composites at 20°C, cracks are initiated at hollow Kaowool particles. The stress concentrations associated with these particles arise from two sources: (i) residual stresses due to differential thermal contraction of the Kaowool and aluminum and (ii) the applied cyclic fatigue stress. These stresses are calculated from a finite element model which incorporates plasticity of the aluminum matrix. In general, the mechanical stresses are considerably larger than the thermal stresses. The total stress, in both the aluminum matrix and the Kaowool particle, increases with decreasing particle wall thickness and the proximity of the particle to the surface. In general, the stress concentrations in the aluminum matrix are more critical than those in the Kaowool particles, and are predicted to exceed locally the yield strength of 339 aluminum for all values of wall thickness. The particles observed experimentally at the fatigue fracture origins are thin walled and close to the surface, in quantitative agreement with the predictions of the finite element model. 相似文献
9.
Fatigue and creep fatigue crack growth behaviour of alloy 800 at 550°C have been studied to analyse defect assessment in a steam generator. Different grades of alloy 800 have been investigated to reproduce the in service conditions. Fatigue crack growth (FCG) tests were conducted on CT20 and tubular specimens, then on welded tubes. Furthermore the influence of hold times on fatigue crack growth behaviour was studied.The results obtained on material simulating the weld heat affected zone are in agreement with the tests conducted on welded tubes. Fatigue crack growth characteristics of aged and cold-worked aged material seem to be slightly improved in comparison with base material. Finally a hold time of one minute increases strongly the FCG threshold value determined in pure fatigue but has a negligible influence on crack growth rates. 相似文献
10.
《Cold Regions Science and Technology》1987,14(3):273-279
The creep behavior of saline ice (prepared in the laboratory by liquid phase sintering) and frozen saline Ottawa sand has been examined in tests performed at constant load in unconfined compression. The range of stress over which the tests were conducted was 0.345 to 1.034 MPa. In both materials, the salinity of the ice-brine mixture was 32 ppt NaCl. The saline ice was found to be quite plastic and to deform to strains in excess of 25% without failing. The Ottawa sand, on the other hand, was observed to enter into tertiary creep at strains of about 2% and then abruptly fail. Despite these differences, the creep behavior at small strains (< 2%) is remarkably similar. This is evidenced by a comparison of the strain rates at 2% strain and the times to reach 2% strains, both of which are very nearly the same for two materials. The results are discussed with respect to simple ideas about the mechanisms of deformation and the role of the sand in the deformation process. 相似文献
11.
Oxidation and hot corrosion are serious problems in aircraft, marine, industrial, and land-base gas turbines. It is because
of the usage of wide range of fuels coupled with increased operating temperatures, which leads to the degradation of turbine
engines. To obviate these problems, superalloys, viz. Superni 75, Superni 718 and Superfer 800H superalloys (Midhani grade),
are the prominent materials for the high temperature applications. It is very essential to investigate the degradation mechanism
of superalloys due to oxidation and hot corrosion and substantiate the role of alloying elements for the formation of protective
oxide films over the surface of the superalloys. Therefore, the present work investigates the oxidation and hot corrosion
behaviour of superalloys exposed to air and molten salt (Na2SO4–60% V2O5) environment, respectively, at 900°C under cyclic conditions. The weight change measurements made on the superalloys during
the experiments are used to determine the kinetics of oxidation and hot corrosion. X-ray diffraction (XRD), X-ray mapping
and field emission scanning electron microscope (FESEM, FEI, Quanta 200F company) with EDAX Genesis software attachment, made
in Czech Republic are used to characterize the corroded products of the superalloys. It is observed that the formation of
scale rich in Cr2O3, NiO and spinel NiCr2O4 has contributed for the better oxidation and hot corrosion resistance of Superni 75; whereas relatively lesser hot corrosion
resistance of Superfer 800H is due to the formation of non-protective oxides of iron and sulphides of iron and nickel. The
parabolic rate constants calculated for the superalloys show that the corrosion rate is minimum in air as compared to molten
salt environment. 相似文献
12.
Hongyan Zhang Ling Cheng Bo Jiang Wen Sun Jingjing Liu Guangda Hu 《Journal of Materials Science: Materials in Electronics》2012,23(10):1864-1868
BiFe0.995W0.005O3 films were epitaxially deposited on LaNiO3(100)/Si substrates using a metal organic decomposition process at the annealing temperatures below 500?°C. X-ray diffraction measurement reveals that the film can be well crystallized at an annealing temperature as low as 450?°C. The leakage current analysis indicates that the content of grain boundaries in the films is a dominant factor affecting the leakage currents of the BiFe0.995W0.005O3 films. Well saturated polarization–electric field hysteresis loops can be obtained in all the crystallized BiFe0.995W0.005O3 films due to their low leakage currents. The film annealed at 450?°C exhibits a large remanent piezoelectric coefficient d 33 (128?pm/V), which is comparable to that obtained in the BiFe0.99W0.01O3 film annealed at 500?°C. Additionally, the most uniform piezoresponse can be observed in the BiFe0.995W0.005O3 film annealed at 450?°C among all the crystallized films, which can be explained by the uniform domain structure and effective electric field applied on the film owing to the homogeneous grain size in the film. 相似文献
13.
This paper presents a study, by means of isothermal dilatometry, of the often very important (10%) shrinkage phenomenon which occurs when heating clay ceramic materials, and especially of the influence of mineralizers on the shrinkage of kaolinite at 900 and 1050° C. We found that the isothermal shrinkage versus time curve of kaolinite at both temperatures was well described by the following equation: $$\lambda = \frac{t}{{\alpha + \beta t}}$$ where λ is the linear shrinkage (relative to the initial length of the bar),t the time, andα andβ two constants. The presence of various mineralizers at different concentrations did not affect the basic shape of this curve at either 900 or 1050° C, but affected the values of parametersα andβ. A sintering mechanism is proposed which takes into account the most recent data concerning the structural transformation of kaolinite in the 900 to 1050° C temperature range. The kaolinite sintering mechanism is of the viscous-flow type proposed by Frenkel [1] involving an amorphous phase, the viscosity of which increases with time due to its progressive recrystallization. The influence of mineralizers is then explained in terms of their action on the viscosity of the amorphous phase and their action on recrystallization. 相似文献
14.
In this study, an attempt to investigate the role of isothermal aging on the microstructure and dry sliding wear behavior of Co–28Cr–5Mo–0.3C alloy was made. Regarding the results, it is clear that isothermal aging at 850 °C for 8 and 16 h contributed to the formation of lamellar type carbides (γ-fcc + M23C6) at the grain boundary regions. Moreover, at higher aging times (24 h), the lamellar type carbides decreased whereas severe precipitation of carbides was found to occur on the stacking faults. Furthermore, according to X-ray diffraction results, 24 h isothermal aging of solution treated specimens did not lead to complete fcc → hcp transformation. The wear properties of as-cast and heat treated samples were determined at 0.5 ms−1 speed several under normal applied loads such as 50, 80, and 110 N. At the lowest load applied (50 N), isothermally aged specimens for 8 and 16 h have higher wear resistance probably due to more volume fraction of lamellar-type carbides when compared to as-cast for both 4 and 24 h aged specimens. But, at higher applied loads (80 and 110 N) due to the formation of adhesive oxide layer on the as-cast specimen surface, the wear rate of as-cast samples is lower compared with all heat treated specimens. 相似文献
15.
About 3 mm thick five-element equimolar high-entropy alloy(HEA) FeCoCrNiMn was successfully deposited by solid-state cold spraying(CS).The high-temperature oxidation behavior of the CSed HEA was investigated at 700-900℃.Heat treatment was performed on the CSed HEA before oxidation to heal the incomplete interfaces between the deposited particles.Results show that the microstructure of the CSed HEA is characterized by grain refinement and abundant interparticle incomplete interfaces.Post-spray heat treatment promotes recrystallization and grain growth in the CSed HEA.After oxidation testing,the oxide scales are composed of multi-layers:a Mn2O3(or Mn3O4) outer layer,a Mn-Cr spinel intermediate layer and a Cr2O3 inner layer.The CSed HEA exhibits higher parabolic rate constants and more favorable internal oxidation than the bulk HEAs that have similar compositions in the literature.Such a discrepancy becomes pronounced at higher temperatures.The grain refinement and numerous particle boundaries are responsible for such a distinctive performance of the CSed HEA. 相似文献
16.
Three alloys containing 0·25–0·50 wt-%C, 26–28 wt-%Cr and 4–6 wt-%Hf were elaborated by foundry. They contained a dendritic matrix and HfC carbides, which are expected to strengthen the alloy at high temperatures. They were exposed in air at 1100°C during 46 h. The aged microstructures displayed coarsened chromium carbides but no significant changes to the fraction or morphology of the HfC carbides. The surface characterisation of the oxidised samples showed that the alloys behaved well despite some localised instances of fast oxidation. The hardness was modified by the microstructure stabilisation achieved during the high temperature exposure. A preliminary test showed that the reinforcement by HfC may indeed lead to interesting creep resistance at 1100°C as had been hoped. 相似文献
17.
Farzad Sadeghi-Tohidi David Samet Samuel Graham 《Science and Technology of Advanced Materials》2014,15(1)
The fatigue properties of ultrathin protective coatings on silicon thin films were investigated. The cohesive and delamination fatigue properties of 22 nm-thick atomic-layered-deposited (ALD) titania were characterized and compared to that of 25 nm-thick alumina. Both coatings were deposited at 200 °C. The fatigue rates are comparable at 30 °C, 50% relative humidity (RH) while they are one order of magnitude larger for alumina compared to titania at 80 °C, 90% RH. The improved fatigue performance is believed to be related to the improved stability of the ALD titania coating with water compared to ALD alumina, which may in part be related to the fact that ALD titania is crystalline, while ALD alumina is amorphous. Static fatigue crack nucleation and propagation was not observed. The underlying fatigue mechanism is different from previously documented mechanisms, such as stress corrosion cracking, and appears to result from the presence of compressive stresses and a rough coating–substrate interface. 相似文献
18.
Oxidation behavior of Mo≤5Si3C≤1 and its composites 总被引:2,自引:0,他引:2
The oxidation behavior of Mo5Si3C1 and its composites was studied in air over the temperature range of 500°C–1600°C. Experiments revealed poor oxidation resistance of monolithic Mo5Si3C1 at high temperature. The oxidation was quite rapid at 1200°C and above, resulting in complete oxidation of specimens in a short time. The addition of 2.0 wt% boron was found to produce a Mo5Si3C1 composite with three other phases of MoB, MoSi2, and SiC, and showed remarkable improvement in oxidation resistance. The mechanism for the improvement was attributed to the viscous sintering of the scale to close the pores formed during the initial oxidation period. Oxidation tests were also conducted on SiC-Mo5Si3C1 composite at 800°C, 1300°C and 1600°C for more than 100 hours. The oxidation resistance of the composite was found to be very good. The results demonstrate that, though oxidation resistance of monolithic Mo5Si3C1 is far insufficient for high-temperature applications, boron-modification and/or composites with SiC are viable methods to improve oxidation resistance to a practically acceptable level. 相似文献
19.
At 300 °C, when dynamic strain ageing takes place, the fatigue life of AISI 316L for lower strain amplitudes is lower than under equivalent conditions at 20 °C. Exhaustive examination of the changes in: (1) apparent elastic modulus, (2) microstructural condition, and (3) fractographic features has been performed to reveal the reason for the life reduction. The analysis of apparent elastic modulus variations and the results of fractographic observations show that the propagation rates for fatigue cracks at 20 °C are faster than for 300 °C. Crack initiation however occurs earlier at 300 °C, in particular for lower strain amplitude tests, due to the activity of localised deformation bands as a consequence of cyclic loading. In addition to persistent slip bands, a form of ladder-free deformation bands is also present at 300 °C, in particular at low strain amplitudes. When the fatigue life is rather short, the influence of the ladder-free deformation bands on cyclic endurance is negligible. The ladder-free type of localised bands have a strong influence on crack initiation once the material endurance increases with lowering strain amplitude, leading to the relative life reduction at the elevated temperature. In addition, the incidence of secondary cyclic hardening for lower strain amplitude tests at 300 °C partly contributes to the more evident life reduction. The influence of dislocation walls on the propagation of microstructurally short fatigue cracks is also examined. 相似文献
20.
L. Ingemarsson K. Hellström S. Canovic T. Jonsson M. Halvarsson L.-G. Johansson J.-E. Svensson 《Journal of Materials Science》2013,48(4):1511-1523
The oxidation of a Mo(Si,Al)2-based composite is investigated in the temperature range 900–1600 °C in dry air. Exposure time was 72 h. Comparisons are made with the oxidation behavior of a conventional MoSi2-based material. Cross-sections are examined with scanning electron microscopy and transmission electron microscopy; the phase composition is analyzed by X-ray diffraction and convergent beam electron diffraction. The material forms a continuous external α-alumina scale throughout the temperature range. Below the scale, there is a continuous Mo5(Si,Al)3 layer that overlies Mo(Si,Al)2 in the bulk. The Mo(Si,Al)2 phase immediately beneath the Mo5(Si,Al)3 layer is depleted in Al. No indications of MoO3 volatilization could be found for the Mo(Si,Al)2 material. 相似文献