An ultrafine grain 304L stainless steel with average grain size of about 650 nm was produced by martensitic process. 10 mm as-received sheets were 80% cold rolled in the temperature of ?15 °C and then annealed at 700 °C for 300 min to obtain ultrafine grained microstructure. The results showed that the ultrafine grained 304L steel has yield strength of 720 MPa, tensile strength of about 920 MPa, and total elongation of 47% which is about twice that of coarse grain structure. The effect of annealing temperature (750-900 °C) on the grain growth kinetics was modeled by isothermal kinetics equation which resulted in the grain growth exponent (n) and activation energy for grain growth of 4.8 and 455 KJ/mol, respectively. This activation energy was also compared with those for other austenitic steels to better understanding of the nature of grain growth and atoms mobility during annealing. It was found that activation energy for grain growth is about twice higher than self-diffusion activation energy of austenite that is related to the Zener pinning effects of the second phase particles. 相似文献
Compressive and wear properties of bulk nanostructured Al2024 alloy prepared by mechanical milling and hot pressing methods were investigated. Al2024 powders were subjected to high-energy milling for 30 h to produce nanostructured alloy. As-milled powders were compacted at 500 °C under 250 MPa in a uniaxial die. Consolidated sample had an average hardness and relative density values of 207.6 HV and 98%, respectively. Uniaxial compression tests at strain rates in the range of 1.67 × 10−4–1.67 × 10−2 s−1 were performed using an Instron-type machine. The wear behavior of nanostructured sample was investigated using a pin-on-disk technique under an applied load of 20 N. The compression and wear experiments were also executed on samples of commercial coarse-grained Al2024-O (annealed) and Al2024-T6 (artificially-aged) alloys, for comparison. The structure of consolidated Al2024 was characterized by X-ray diffraction (XRD). The yield strength and compressive strength of nanostructured Al2024 reached a value of 698 MPa and 712 MPa at strain rate of 1.67 × 10−4 s−1, respectively, which was considerably higher than those for coarse-grained Al2024-O and Al2024-T6 counterparts. Worn surfaces and the wear debris were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and XRD. Nanostructured Al2024 revealed a low friction coefficient of 0.3 and a wear rate of 12 × 10−3 mg/m, which are significantly lower than those obtained for Al2024-O and Al2024-T6 alloys. This enhanced wear resistance was mainly caused by nanocrystalline structure with high hardness value. The dominating wear mechanism of nanostructured Al2024 appeared to be delamination mechanism. 相似文献
The Coulomb barrier is in general much higher than thermal energy. Nuclear fusion reactions occur only among few protons and
nuclei (i.e., deuterium and tritium) with higher relative energies than Coulomb barrier. It is the equilibrium velocity distribution
of these high-energy protons and nuclei that participates in determining the rate of nuclear fusion reactions. In the circumstance
it is inappropriate to use the Maxwellian velocity distribution for calculating the nuclear fusion reaction rate. We use the
relativistic equilibrium has a reduction factor with respect to that based on the Maxwellian distribution, which factor depends
on the temperature, reduced mass and atomic numbers of the studied nuclear fusion reactions. In this paper, we concluded at
energy range 105 (keV) ≤ E ≤ 106 (keV), that is smaller than reduced mass energy of deuterium–tritium, mrc2, the numerical values of R and RM are not different from each other very much, but by increasing energy near the region of mrc2 the difference between them are visible, also by increasing energy for example 9 × 106 (keV) ≤ E ≤ 10 × 106 (keV) the difference is obviously more visible. Therefore, we have to use relativistic equilibrium velocity distribution
instead of Maxwellian velocity distribution. 相似文献
Mechanochemical processing is a novel technique for the synthesis of nano-sized materials. This research is based on the production of Al2O3–TiB2 nanocomposite powder using mechanochemical processing. For this purpose, a mixture of aluminum, titanium and boron oxide powders was subjected to high energy ball milling. The structural evaluation of powder particles after different milling times was conducted by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results showed that during ball milling the Al/B2O3/Ti reacted with a combustion mode producing Al2O3–TiB2 nanocomposite. In the final stage of milling, the crystallite sizes of Al2O3 and TiB2 were estimated to be less than 50 nm. 相似文献
BACKGROUND: The Commission on Cancer of the American College of Surgeons has called upon institutions providing cancer care to compare practice patterns and outcomes with the National Cancer Data Base (NCDB). Using data from the Virginia Mason Tumor Registry (VMTR), we sought to compare our pancreatic cancer care patterns with those reported nationally, while critically evaluating the accuracy and usefulness of our registry. METHODS: A review of the 906 computerized patient files in the VMTR from 1973 to 1995 was performed, with more detailed data on patients from the last 5 years retrieved from 224 manual abstracts. These data were compared with the 1991 NCDB for pancreatic cancer. RESULTS: The percent of cases according to AJCC stage in the NCDB (n = 9,715) versus the VMTR (n = 149), respectively, with cases of unknown stage excluded, were stage I 22% versus 22%, stage II 9% versus 12%, stage III 17% versus 28% (P <0.05) stage IV 52% versus 38% (P <0.05). One-third of the cases in the VMTR 1991 to 1995 were of unknown stage; number of cases with unknown stage for NCDB was 26.6%. The percent of surgical procedures for the NCDB (n = 7,802) versus the VMTR (n = 224), respectively, was pancreatectomy 14% versus 11%, local excision 1% versus 0%, no cancer-directed surgery 83% versus 89% (P <0.05), unknown 2% versus 0% (P <0.05). The actuarial relative survival rates for the 1991 NCDB versus 1987 to 1995 VMTR was 3-year 18% versus 38%, and 5-year 14% versus 35%. CONCLUSIONS: In comparison with the NCDB, VMTR may have fewer stage IV pancreatic cancers, but improvement is needed in decreasing the number of patients for whom the stage is unknown, as many of these likely represent late stage disease. We have a similar resection rate and a higher survival compared with the NCDB, but a mechanism is not in place to statistically compare our survival data with those of the NCDB. Even though all accredited hospitals are required to have a tumor registry, our data were difficult to compare with those of the NCDB because of coding and reporting deficiencies and inability to statistically compare survival data. Before our practice patterns and outcomes can be compared with national standards, both the VMTR and the NCDB must have standardized data collection and better access to the data. 相似文献
In theory, emergence of robustness concept has pushed decision-makers toward designing alternatives, such as resistant against the potential fluctuations fueled by uncertain surrounding environment. This study promotes an objective-based multi-attributes decision-making framework that takes into account the uncertainties associated with the impacts of the climate change on water resources systems. To capture the uncertainties of climate change, Monte Carlo approach has been used to generate a series of ensembles. These generated ensembles represent the stochastic behavior of the hydro-climatic variables under climate change. This framework represents the inherent uncertainties associated with hydro-climatic simulations. Next, a coupled TOPSIS/Entropy multi-attribute decision-making framework has been formed to prioritize the feasible alternatives using system performance measures. The main objective of this framework is to minimize the risk of deceptive and subjective assessments during decision-making process. Karkheh River basin has been selected as a case study to demonstrate the implication of this framework. Using a set of system performance attributes, the performance of two hydropower systems has been estimated during the baseline period and under the future climate change conditions. According to the conducted frequency analysis, the alternative in which both hydropower projects would go under construction emerged as the robust solution (i.e., there was a 99.9% chance that it outperforms other solutions). The results indicate that the construction of these hydropower systems leads to the increase of Karkheh River basin robustness in the future.
Recently fabrication of titanium alloys through solid state processes such as mechanical alloying has been greatly taken into consideration. In the present investigation the effects of common atmospheric impurities, oxygen and nitrogen, on the fabrication procedure and milling behavior of nanostructured Ti–6Al–4V alloy during mechanical alloying (MA) was studied. In this regards, elemental powders were milled under three different protective atmospheres of air, 90% and 99.998% pure Argon. Results indicated that, samples milled under Ar with 90% purity featured the best behavior and reached a nanostructure and subsequent amorphous state in shorter time periods. This was considered to be due to Ti lattice distortion made by interstitial element such as O2 and N2. 相似文献
A simple and cheap spectrophotometric method for the simultaneous determination of Tartrazine, Quinoline Yellow, Sunset Yellow, Carmoisine and Brilliant Blue in commercial food products with the aid of a portable double beam photocolourimeter are described. The method is based on the difference of the absorptivity ratios at maximum absorbances of two compounds or three compounds. The proposed device uses red–green–blue light-emitting diode as light source and light dependent resistor as detector. A programmable microcontroller sequentially turns the emitters on, receives the signals followed by calculating the absorbance and displaying it on a liquid–crystal display. The photometer is capable of performing absorbance measurements in a single wavelength as well as in three wavelengths sequentially, allows its application in simultaneous analysis of binary and ternary mixtures based on the differences of absorbance ratios in two and/or three wavelengths. The method was validated against a standard HPLC method and the results obtained were in a good agreement with those of HPLC method. 相似文献
In this study, the amorphous phase formation in Al80Fe10M10 (M = Ti, V, Ni) (at.%) ternary systems during mechanical alloying has been investigated. The milled samples were characterized
using X-ray diffraction and differential thermal analyses. A thermodynamic analysis of the amorphous phase formation was performed
for these systems using the Miedema model. The obtained results demonstrate that amorphous phases can be formed during the
mechanical alloying process of the Al80Fe10M10 (M = Ti, V, Ni) ternary systems. The produced amorphous alloys exhibit one-stage crystallization during heating, which is
amorphous to the Al13Fe4 intermetallic phases. The thermal stability of the produced amorphous phases decreases in the order of Al80Fe10Ti10 > Al80Fe10Ni10 > Al80Fe10V10. 相似文献