共查询到20条相似文献,搜索用时 12 毫秒
1.
Theoretical analysis of the influence of the temporal profile (rectangular, triangular, Gaussian) of the laser pulse on heating/cooling and phase transition velocities and quantity of ablated material was performed on the basis of a multifront Stephan problem. Modeling showed that material removal under stationary conditions (that correspond to long pulses) is entirely controlled by specific heat and material density, while in the case of transient regimes (short pulses) thermal conductivity and heat capacity play a predominant role. Interaction of the melting and evaporation fronts characterized by an evaporation front velocity far exceeding the melting front one is one of the examples of the transient nature of the phenomena influenced by the laser pulse parameters. 相似文献
2.
《Journal of magnetism and magnetic materials》1987,68(2):233-237
Temperature and magnetic field dependences of the thermal expansion between 4 and 300 K and in fields up to 6 T were made on Fe80-xNixCr20 for 14⩽x⩽49 at%. This concentration range covered the regions in which the samples were antiferromagnetic, paramagnetic and ferromagnetic as well as spin glass and reentrant spin glass at low temperatures. We develop a method of determining the lattice contribution to the thermal expansion for such systems showing mixed magnetic behavior and analyze the present data accordingly. We find in ferromagnetic samples large magnetic contributions to the thermal expansion even at temperatures much higher than the Curie temperature. The field dependence of the lenght change shows behavior which is characteristic of the magnetic state of the system. 相似文献
3.
M. Laridjani R. Krishnan E. Okoniewska Pszczołkowska M. Dancygier J. F. Sadoc 《Applied Physics A: Materials Science & Processing》1984,34(2):111-115
Ductile amorphous foils of Fe80B20 have been sputter-deposited. We report here the results of structural and magnetic studies on these samples. Structural analysis shows slight differences between amorphous foils and ribbons. From the high-field measurements (H<15 T) the magnetic moment of Fe is estimated as 2.1±0.02 at 4.2 K in agreement with the value reported for ribbons. However, the magnetization is less temperature dependent in the foil, as compared to the ribbon. This result would indicate a lesser fluctuation in the exchange integralJ and hence lesser variations in the local environment of Fe. Finally the thermal stability is shown to be higher in the foils. It is suggested that sputtering technique could be used to prepare amorphous foils of large area for certain applications. 相似文献
4.
We have studied the influence of the relaxation effects on the different kinds of short range order structures which can be distinguished inFe 80 B 20 amorphous alloys by Mössbauer spectroscopy. The analysis of the distribution function of the hyperfine fields gives results on the variations of the chemical and topological short-range orders in good agreement with those known in literature. Attempt to give quantitative results is made. 相似文献
5.
《Applied Surface Science》1986,27(2):180-198
Recent studies of catalysis by amorphous metals have prompted an interest in their surface properties. We have utilized Auger electron spectroscopy, X-ray photoelectron spectroscopy and low energy alkali ion scattering to study the surface composition, electronic properties and topography of amorphous and crystallized Fe80B20 ribbons. The majorresults are that the surface stoichiometry is approximately that of the bulk, unaltered by segregation. Bulk crystallization results in the diffusion of impurities to the surface, but does not change the Fe/B ratio. A small shift in the B1s core level binding energy was observed on crystalline, annealed surfaces relative to amorphous or sputtered surfaces, but no shifts were observed in the iron core level energies. A weak feature due to the B2p levels was observed in the valence band spectra from sputtered surfaces. The surfaces exhibit atomic scale roughness which is not altered by bulk crystallization. Finally, there were no observable differences in the structure, composition or electronic properties between the two sides of the ribbons. 相似文献
6.
S. K. Sharma S. Banerjee Kuldeep Animesh K. Jain 《Applied Physics A: Materials Science & Processing》1988,45(3):217-220
Diffusion rates (D) of Au in two amorphous alloys, Fe80B20 and Fe82B18, and of Cu in amorphous Fe82B18 alloy were measured in the temperature range 546–645 K by using the technique of Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES), respectively. The diffusion of Au was found to be 3 to 6 times faster in Fe80B20 than in Fe82B18, though both the alloys had almost similar crystallization temperatures. The observed differences in the diffusion rates corroborate the fact that Fe80B20 has a more open structure than Fe82B18 as revealed from the reported values of the metal packing fractions of these two alloys. Also, the diffusivities of smaller sized Cu atoms (radius: 0.128 nm) were found to be higher by more than an order of magnitude than those of larger sized Au atoms (radius: 0.146 nm), suggesting a dependence ofD on the size of the diffusing species. 相似文献
7.
V. A. Burdovitsin E. S. Dvilis A. V. Medovnik E. M. Oks O. L. Khasanov Yu. G. Yushkov 《Technical Physics》2013,58(1):111-113
The structural transformations that occur in the near-surface layer in alumina ceramics during irradiation by a pulsed electron beam generated by a forevacuum plasma electron source are studied. The modification of the surface properties of the ceramics is shown to be caused by the formation of regions consisting of close-packed and identically oriented crystallites within every grain. The crystallites are elongated: their length and width are 0.5–1.5 μm and the transverse size is 0.1–0.2 μm. 相似文献
8.
Janusz Oleniacz Przemysław Duda Włodzimierz Zych Jan Grabski 《Hyperfine Interactions》2005,165(1-4):227-230
Amorphous alloys of the type Fe80???xPdxB20 and type Fe80???xPtxB20 for 0?≤?x?≤?50 have been investigated by means of 57Fe Mössbauer spectroscopy and magnetisation measurements in temperatures from 4.2 up to 300 K. Curie temperatures and crystallisation temperatures are found by DTMG-DTA method. Mössbauer spectroscopy magnetic field is observed to visible increase for x?=?1 and 1.5% at room temperature for Pd, while a decrease is observed for higher x values. Curie temperature for Pd alloys has a maximum at x?=?4 with T C?=?753 K, which supports enforcing influence of Pd at low concentrations of Pd for magnetic interactions. We discuss different explanations for these measurements and compare with other findings for high Pd concentrations and alloys with Pt instead of Pd. 相似文献
9.
Summary The electrical resistivity of Fe80B20 and Fe78B13Si9 amorphous glasses as a function of temperature from 293 K down to 15 K was measured, and it was found to fit quite well with
the model given by Cote and Meisel. Comparison between our resistivity measurements of Fe80B20 and others was made, where some differences were found. These resistivity differences are evidence for a variety of amorphous
atomic arrangements of the samples. The longitudinal magnetoresistance of Fe80B20 and Fe78B13Si9 at 293K and 77K was measured in a low magnetic field. The observed magnetoresistance shows a typical field dependence known
for ferromagnetic materials. 相似文献
10.
利用强流脉冲电子束(HCPEB)装置对金属纯钛进行轰击,采用X射线衍射,扫描电子显微镜及透射电子显微镜技术详细分析了轰击样品表层的结构和缺陷. X射线衍射分析表明, HCPEB能够在材料表层诱发幅值为 GPa量级的压应力,并在(100), (102)和(103)晶面出现择优取向.表层微观结构的观察表明: HCPEB轰击后材料表层发生了马氏体相变,形成了大量的片状马氏体组织; 此外, HCPEB轰击还在辐照表面诱发了强烈的塑性变形,一次轰击后,晶粒内部的塑性变形以(100)晶面的位错滑移为主,位错密度显著提高;多次轰击后,样品变形结构发生变化,变形孪晶的数量明显增多. 这些变形微结构不仅影响表层的织构演化行为,而且还能细化晶粒,进而提高材料表面硬度, 为HCPEB技术进行纯钛表面强化提供了一条有效的途径. 相似文献
11.
V. V. Efimov E. A. Efimova Yu. S. Kovalev S. I. Tyutyunnikov 《Physics of Particles and Nuclei Letters》2006,3(5):290-295
Results of the measurement of Raman scattering spectra (RSS) using the laser scanning confocal microscope (LSCM) with the excitation line λ = 441.6 nm of the relaxor PLZT 8/65/35 ceramics irradiated by different doses of laser and high current pulsed electron beams are given. The two-dimensional images and layered scanning data for unirradiated and irradiated parts of the sample were obtained using the Raman-active mode $v_{TO_4 } $ = 536 cm?1. Space regions with an anomalously high intensity of the $v_{TO_4 } $ mode were found in the irradiated sample. Possible mechanisms of the effect of high current pulsed electron irradiation for the PLZT 8/65/35 are discussed. 相似文献
12.
利用强流脉冲电子束 (HCPEB) 技术对金属纯锆进行表面处理, 采用X射线衍射, 扫描电子显微镜及透射电子显微镜详细分析了辐照诱发的表层微观结构和缺陷. X射线分析结果表明, HCPEB辐照后在材料表层诱发幅值为GPa量级的压应力, 并形成{0002}, {1012}, {1120}及{1013}织构. 表层微观结构观察表明, 与其他金属材料不同, HCPEB辐照在材料表层诱发的熔坑数量极少, 多次轰击甚至几乎没有表面熔坑的形成. 此外, 在快速的加热和冷却状态下, 在表面熔化层形成大量的超细晶粒结构, 同时诱发马氏体相变和强烈的塑性变形. 1次HCPEB辐照后表层内形成的变形微结构以位错为主, 孪晶数量较少; 5 次辐照样品的位错密度迅速增高, 孪晶数量也显著增加; 10次辐照后样品中的变形微结构以变形孪晶为主, 且出现二次孪晶现象. 表层晶粒内部变形的晶体学特征不仅决定了表层的织构演化行为, 而且还起到细化晶粒的作用, 为纯锆及锆合金表面强化提供了一条有效的途径.
关键词:
强流脉冲电子束
纯锆
微观结构
应力状态 相似文献
13.
Amorphous metals (Metglass Fe80B20) have been studied by Mössbauer spectroscopy. In the analysis the radial distribution function of Bernal's liquid-structure model has been correlated with the distribution of magnetic hyperfine spectra. 相似文献
14.
Farit Vagizov Roman Kolesov Silviu Olariu Yuri Rostovtsev Olga Kocharovskaya 《Hyperfine Interactions》2006,167(1-3):917-921
We report the first observation of a laser-produced vibration with the aid of Mössbauer techniques. Thin platelets of MgO single crystals were doped by diffusion of 57Fe atoms. The illumination of the MgO:57Fe sample with a pulsed Nd:YAG laser produced a significant broadening of the Mössbauer spectrum. In order to find out what caused these changes, we performed a series of time-domain experiments, in which the Mössbauer spectra were collected only during a 2.5 μs gate interval. This gate interval was swept from 5 μs to 190 μs over the time interval between the two laser pulses. After laser irradiation, the position of the Mössbauer line was found to be changing in time as a decaying oscillations of well-defined frequency, which can be due to the vibration of the sample induced by the laser pulse. 相似文献
15.
Hypereutectic Al-20Si (Si 20 wt.%, Al balance)alloy surface was treated with high current pulsed electron beam (HCPEB) under different pulse numbers. The results indicate that HCPEB irradiation induces the formation of metastable structures on the treated surface. The coarse primary Si particle melts, producing a “halo” microstructure with primary Si as the center on the melted surface. A supersaturated solid solution of Al is formed in the melted layer caused by Si atoms dissolving into the Al matrix. Cross-section structure analysis shows that a 4 μm remelted layer is formed underneath the top surface of the HCEPB-treated sample. Compared with the matrix, the Al and Si elements in the remelted layer are distributed uniformly. In addition, the grains of the Al-20Si alloy surface are refined after HCPEB treatment, as shown by TEM observation. Nano-silicon particles are dispersed on the surface of remelted layer. Polygonal subgrains, approximately 50-100 nm in size, are formed in the Al matrix. The hardness test results show that the microhardness of the α(Al) and eutectic structure is increased with increasing pulse number. The hardness of the “halo” microstructure presents a gradient change after 15 pulse treatment due to the diffusion of Si atoms. Furthermore, hardness tests of the cross-section at different depths show that the microhardness of the remelted layer is higher than that of the matrix. Therefore, HCPEB technology is a good surface modification method for enhancing the surface hardness of hypereutectic Al-20Si alloy. 相似文献
16.
The most prominent phenomena on the target surface induced by laser irradiation in pulsed laser deposition is the formation of conical morphologies in the irradiated area. The conical morphologies formed under different laser fluences and the ambient oxygen pressures in KrF laser ablation of Pb(Zr0.53Ti0.47)O3 were studied in detail by using scanning electron microscopy. The results indicate that, depending on the melting extent of the irradiated surface, there are two kinds of cones: one type with well-defined cone tip and cone body and the other having only a cone tip. Pb is very deficient in cone tip. The gas ambient pressure plays a remarkable role in the laser-target interaction. These results are interpreted by employing the impurity shielding mechanism and the surface instability mechanism. 相似文献
17.
Properties of the color and emission centers induced with an electron pulse beam at temperature within 80-300 K have been studied in CsI(Tl) crystals. It has been established by optical spectrometry with time resolution that initial color centers in this crystal are only Tl0 and Vk centers, which spontaneously recombine emitting visible light at 2.25 and 2.55 eV. It has been shown that the emission decay kinetics at 80 K include two fast exponential components with decay constants 3 and 14 μs as well as slow hyperbolic component with the power index depending on the wavelength of the emitting light. The temperature effect on the emission kinetics has been studied and it has been directly proved that the emission rise stage at the temperature above 170 K is caused by the recombination of electrons, which are thermally released from single Tl0 centers, with VkA centers. The origin of scintillations in CsI(Tl) crystal is discussed in terms of the tunnel electron transitions from ground state of Tl0 centers to ground state of Vk centers at different distances from each other. 相似文献
18.
A prototype pulsed electron beam irradiation facility for radiation processing of food and medical products is being commissioned
at our centre in Indore, India. Analysis of surface dose and uniformity for a pulsed beam facility is of crucial importance
because it is influenced by various operating parameters such as beam current, pulse repetition rate (PRR), scanning current
profile and frequency, scanning width and product conveying speed. A large number of experiments are required to determine
the harmonized setting of these operating parameters for achieving uniform dose. Since there is no readily available tool
to set these parameters, use of Monte Carlo methods and computational tools can prove to be the most viable and time saving
technique to support the assessment of the dose distribution. In the present study, Monte Carlo code, MCNP, is used to simulate
the transport of 10 MeV electron beam through various mediums coming into the beam path and generate an equivalent dose profile
in a polystyrene phantom for stationary state. These results have been verified with experimentally measured dose profile,
showing that results are in good agreement within 4%. The Monte Carlo simulation further has been used to optimize the overlapping
between the successive pulses of a scan to achieve ±5% dose uniformity along the scanning direction. A mathematical model,
which uses the stationary state data, is developed to include the effect of conveyor speed. The algorithm of the model is
discussed and the results are compared with the experimentally measured values, which show that the agreement is better than
15%. Finally, harmonized setting for operating parameters of the accelerator are derived to deliver uniform surface dose in
the range of 1–13 kGy/pass. 相似文献
19.
D.J. Hwang N. Misra C.P. Grigoropoulos A.M. Minor S.S. Mao 《Applied Physics A: Materials Science & Processing》2008,91(2):219-222
Lasers have proved to be effective tools for material processing at the micron and nanometer scales. In particular, laser
interaction with nanostructures offers the unique advantage of highly localized excitation and heating. In this study, a short-pulsed
laser beam is coupled to a scanning electron microscope, without disturbing the microscopy function, in order to study in
situ laser cleaning of individual submicron particles from a silicon substrate. The substrate conditions before and after
particle removal were inspected by electron microscopy. The mechanisms of particle removal and the underlying dynamic coupling
of the laser radiation associated with particle cleaning are investigated.
PACS 42.62.Cf; 42.82.Gw; 81.65.Cf; 07.78.+s 相似文献