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排序方式: 共有243条查询结果,搜索用时 31 毫秒
1.
Belcher Calvin H. Zheng Baolong MacDonald Benjamin E. Langlois Eric D. Lehman Benjamin Pearce Charles Delaney Robert Apelian Diran Lavernia Enrique J. Monson Todd C. 《Journal of Materials Science》2022,57(9):5518-5532
Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic... 相似文献
2.
T. S. Srivatsan I. A. Ibrahim F. A. Mohamed E. J. Lavernia 《Journal of Materials Science》1991,26(22):5965-5978
The critical need for high strength, lightweight and high stiffness materials has, in recent years, resurrected much interest in discontinuously reinforced powder metallurgy metal matrix composites. These hybrid materials have combined both standard wrought alloys of aluminium and a wide variety of discontinuous reinforcements such as particulates and whiskers of ceramic materials. Renewed interest in these materials as attractive candidates for use in the aerospace and transportation industry has resulted from an attractive and unique combination of physical and mechanical properties, and an ability to offer near isotropic properties coupled with the low cost of these materials when compared with existing monolithic materials. In this paper, the primary processing categories for discontinuously-reinforced metal-matrix composites are highlighted and the salient features of the various techniques in each category are discussed. The variables involved in each processing technique are examined, and the influence of alloy chemistry highlighted. Novel processing techniques for these materials such as the variable co-deposition method is presented as a means to process these novel engineering materials in order to improve their overall mechanical performance. 相似文献
3.
Yaojun Lin Yizhang Zhou Enrique J. Lavernia Kevin M. McHugh 《Metallurgical and Materials Transactions A》2004,35(11):3633-3635
From the geometrical standpoint, this article presents a qualitative theoretical analysis and prediction of the transient
to steady-state transition during the spray-rolling process, a novel manufacturing technique for aluminum strips. The analytical
results indicate that, when the deposited materials at the specific points on one roll surface overlap their counterparts
on the other roll surface, spray rolling transits from the transient state to the steady state. The specific points are the
limiting deposition positions of the atomized droplets on the roll surface initially. 相似文献
4.
Y. Xun R. Rodriguez E. J. Lavernia F. A. Mohamed 《Metallurgical and Materials Transactions A》2005,36(10):2849-2859
The present article deals with the processing and microstructural evolution of powder metallurgy (PM) Zn-22Al pct eutectoid
alloy. The powder material was produced through inert gas atomization and then cryomilled in liquid nitrogen. The milled powder
particles were consolidated by hot isostatic pressing (“hipping”) followed by thermomechanical treatment, resulting in a two-phase
microstructure. The microstructures were characterized using scanning electron microscopy (SEM) and transmission electron
microscopy (TEM). The principal processing factors and microstructural characteristics associated with the major processing
steps, including spray atomization, mechanical milling (MM), consolidation, and heat treatment, were evaluated and discussed.
Hot isostatic pressing and extrusion followed by heat treatment to produce the superplastic structure (Al-rich phase and Zn-rich
phase) are effective in elimination porosity. A TEM examination of the microstructure of the alloy after processing reveals
the presence of nanodispersion particles that are not uniformly distributed. The formation of the dispersions was attributed
to the interaction between the powder material (primarily Al phase) and environmental elements such as oxygen and nitrogen
during milling. Moreover, the size and distribution of the dispersions present in the bulk material met the anticipated requirements
for serving as inhibitors for grain growth and barriers for dislocation movement. The TEM observations on crept specimens
reveal extensive dislocation/dispersion interactions. 相似文献
5.
Zhihui Zhang Bing Q. Han Kyung H. Chung Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2006,37(7):2265-2273
The current study aims to provide fundamental insight into the behavior of microstructures containing grain sizes that span
multiple length scales. A commercial 5083 Al alloy was selected as the material of interest to facilitate comparison with
recently published data. The materials studied here were prepared via the thermal consolidation of powders that were cryomilled
for different times (i.e., 0, 2, 4, and 8 hours). Following consolidation, the resultant microstructure was characterized by an equiaxed grain morphology
with a size distribution centered around 200∼300 nm. Dispersed among the 200- to 300-nm grains were coarse-grained regions
or ligaments with a grain size ranging from 600 nm to 2 μm. The occurrence of coarse-grained regions is rationalized on the
basis of recrystallization or subgrain coarsening, whereas the occurrence of equiaxed fine regions is proposed to be a result
of continuous grain growth. Two types of microstructures were selected for study, containing coarse-grained volumes of approximately
28 pct and 43 pct that corresponded to an ultimate tensile strength (UTS) of 566 MPa and 535 MPa, and a fracture strain of
3.2 pct and 3.5 pct, respectively. The observed ductility and the relevant toughening mechanisms were discussed in light of
the presence of multiple length scales. 相似文献
6.
Bing Q. Han Farghalli A. Mohamed Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2003,34(1):71-83
In the present study, the mechanical properties of Fe processed via severe plastic deformation (equal-channel angular pressing (ECAP)) at room temperature were investigated for the first time.
The grain size of annealed Fe, with an initial grain size of about 200 μm, was reduced drastically during ECAP. After eight passes, the grain size reaches 200 to 400 nm, as documented by means of
transmission electron microscopy (TEM). The value of microhardness during pressing increases 3 times over that of the starting
material after the first pass and increases slightly during subsequent pressing for higher-purity Fe. Examination of the value
of microhardness after eight passes as a function of post-ECAP annealing temperature shows a transition from recovery to recrystallization,
an observation that resembles the behavior reported for heavily deformed metals and alloys. The tensile and compression behaviors
were examined. In tension, a drop in the engineering stress-engineering strain curve beyond maximum load was observed both
in the annealed Fe and the ECAP Fe. This drop is related to the neck deformation. The fracture surface, examined by scanning
electron microscopy (SEM), shows vein patterns, which is different from the dimples found on the fracture surface of annealed
Fe. In compression, an initial strain-hardening region followed by a no-strain-hardening region was observed in the ECAP Fe.
The yield strength in tension of the ECAP Fe was observed to be higher than that in compression. The strengthening mechanisms
and softening behavior are discussed. 相似文献
7.
Indranil Roy Manish Chauhan Farghalli A. Mohamed Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2006,37(3):721-730
Thermal stability in bulk ultrafine-grained (UFG) 5083 Al that was processed by gas atomization followed by cryomilling, consolidation,
and extrusion, and that exhibited an average grain size of 305 nm, was investigated in the temperature range of 473 to 673
K (0.55 to 0.79 T
m
, where T
m
is the melting temperature of the material) for different annealing times. Appreciable grain growth was observed at temperatures
> 573 K, whereas there was limited grain growth at temperatures < 573 K even after long annealing times. The values of the
grain growth exponent, n, deduced from the grain growth data were higher than the value of 2 predicted from elementary grain growth theories. The
discrepancy was attributed to the operation of strong pinning forces on boundaries during the annealing treatment. An examination
of the microstructure of the alloy suggests that the origin of the pinning forces is most likely related to the presence of
dispersion particles, which are mostly introduced during cryomilling. Two-grain growth regimes were identified: the low-temperature
region (<573 K) and the high-temperature region (>573 K). For temperatures lower than 573 K, the activation energy of 25 ±
5 kJ/mol was determined. It is suggested that this low activation energy represents the energy for the reordering of grain
boundaries in the UFG material. For temperatures higher than 573 K, an activation energy of 124 ± 5 kJ/mol was measured. This
value of activation energy, 124 ± 5 kJ/mol, lies between that for grain boundary diffusion and lattice diffusion in analogous
aluminum polycrystalline systems. The results show that the strength and ductility of bulk UFG 5083 Al, as obtained from tensile
tests, correlate well with substructural changes introduced in the alloy by the annealing treatment. 相似文献
8.
On the influence of N on residual microstrain in cryomilled Ni 总被引:1,自引:0,他引:1
Kyung H. Chung Entrique J. Lavernia 《Metallurgical and Materials Transactions A》2002,33(12):3795-3801
The factors that influence the development of residual microstrain during milling in a liquid nitrogen atmosphere, defined
hereafter as cryomilling, are investigated. The residual microstrains in cryomilled Ni, processed under various cryomilling
conditions, were examined by X-ray diffraction (XRD) and analyzed through the single line approximation (SLA) method. The
average residual microstrains are determined to be in the range of 2×10−3 to 6×10−3. The residual microstrain on the (200) plane is higher than those on the other planes by 33 pct. The residual microstrain
and its anisotropy in Ni are reduced after heat treatment at 800 °C for 1 hour. The measured microstrain is proposed to evolve
from the presence of N and O as impurity atoms in the Ni lattice. Both N and O are introduced from the environment and then
their solubility in Ni is enriched via the generation of defects that occurs during cryomilling. The stable site for N and O atoms in Ni is the octahedral site,
and the sizes of N and O atoms exceed those of the octahedral site of Ni by 48 and 16 pct respectively. Accordingly, a lattice
strain field is expected around interstitial N atoms that are located at octahedral sites. By comparing the crystal structure
around the octahedral site, the stable site for impurity N atoms, in the Ni lattice with that of Ni3N structure, the lattice strains are estimated to be in the range of 5 to 15 pct. The result shows that the (200) plane has
strains that are 2 times higher than those in other planes, and this is argued to be the reason for the measured anisotropy
of residual strain in Ni after cryomilling. 相似文献
9.
10.
Nanostructure in an Al-Mg-Sc alloy processed by low-energy ball milling at cryogenic temperature 总被引:1,自引:0,他引:1
F. Zhou S. R. Nutt C. C. Bampton E. J. Lavernia 《Metallurgical and Materials Transactions A》2003,34(9):1985-1992
Spray-atomized Al-7.5Mg-0.3Sc (in wt pct) alloy powders were mechanically milled at a low-energy level and at cryogenic temperature
(cryomilling). The low-energy milling effectively generated a nanoscale microstructure of a supersaturated face-centered cubic
(fcc) solid solution with an average grain size of ∼26 nm. The nanoscale microstructure was fully characterized and the associated
formation mechanisms were investigated. Two distinct nanostructures were identified by transmission electron microscopy (TEM)
observations. Most frequently, the structure was comprised of randomly oriented equiaxed grains, typically 10 to 30 nm in
diameter. Occasionally, a lamellar structure was observed in which the lamellas were 100 to 200 nm in length and ∼24 nm wide.
The morphology of the mixed nanostructures in the cryomilled samples indicated that high-angle grain boundaries (HAGBs) formed
by a grain subdivision mechanism, a process similar to which occurs in heavily cold-rolled materials. The microstructural
evidence suggests that the subdivision mechanism observed here governs the development of fine-grain microstructures during
low-energy milling. 相似文献