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1.
Using newly available experimental information, the phenomenological crystallographic theory of martensite transformations has been applied to lath martensite. Experimental observations on the habit plane, orientation relationship, and the interface dislocations are in agreement with the theory using the Bain strain and two lattice invariant shears, one on (lll)[?101]f and the other on (100)[0?11]f. The theoretical approach is based on the maintenance of a glissile interface when experimentally observed misfit dislocations are incorporated in the experimental habit plane. The predicted shape deformation magnitude is 0.96, which is comparatively quite large, but because of extensive accommodation deformation in the martensite, the experimentally observed shape strain magnitude may be considerably smaller than the true value. The large martensite shape deformation appears to be responsible for the intrinsic lath morphology and the restricted growth of the martensite in a direction parallel to the shape deformation. The high density of dislocations in the laths probably arises because of accommodation distortion. Theory predicts a highly coherent martensite/austenite interface consisting of one set of steps on (lll)f with associated dislocations and one set of screw dislocations in the direction [0?11]f. 相似文献
2.
This investigation, using an Fe-20 pct Ni-5 pct Mn (wt pct) alloy, was carried out to provide more detailed and accurate information
on the crystallographic features of ferrous lath martensite than is presently available. The martensite observed was typical
of that found in low carbon steels, but with the present alloy substantial amounts of retained austenite are found, which
can be used as a crystallographic reference basis. Analysis of some twenty laths showe_d_the average austenite-martensite
orientation relationship to be (lll)f ‖ (011)b: [•101]f 3.9 deg from [•1•1l]b, using an electron diffraction method involving an error of only a fraction of a degree. Adjacent laths within a packet of
lath martensite were found to exhibit the same variant of the orientation relationship although such laths may be misoriented
relative to each other by up to 2 deg. Thick layers of austenite found between adjacent laths indicate that the laths do not
form by self-accommodation. The lath martensite habit plane is irrational, close to (575)f [equivalently (•154)b], but since the habit plane is of the type hkh, 12 apparent habit planes are observed although 24 variants of the orientation
relationship may be found. The martensite-austenite interface on one side of a given lath is relatively planar, while that
on the opposite side is irregular, suggesting that the laths thicken mainly in one direction. The martensite laths contain
screw dislocations in all four ( 111 )b directions, but one set of the four with Burgers vector α/2 [•111]b is clearly dominant as a result of accommodation deformation imposed by the large lath martensite shape strain. Austenite
dislocation arrays associated with the straight and irregular lath interfaces are very different, again suggesting that the
thickening of a lath takes place mainly in one direction away from the initial straight interface. 相似文献
3.
The changes in matrix structure that occur during tempering of an Fe-0.2C martensite at 400° to 700°C have been investigated.
Light and electron metallographic observations show that when tempered, the fine martensitic lath structure coarsens while
retaining the elongated packet-lath morphology. The as-quenched hardness 504 Khn and total grain boundary area per unit volume
50,800 cm−1 decrease abruptly at the higher tempering temperatures and in seconds reach relatively stable values that decrease slowly
with time. The decrease in low angle boundaries accounts for most of the initial grain boundary area change, while the large
angle boundary component of total boundary area decreases gradually with tempering time. Recovery processes are responsible
for the initial changes in matrix structure, and carbide boundary pinning suppresses recrystallization until grain growth
dominates in the later stages of tempering. 相似文献
4.
对Q235级低碳钢板条马氏体在550℃多道次单向压缩变形后退火和室温大塑性变形轧制后在此温度退火的显微组织演变规律进行了对比研究,结合未变形板条马氏体在此温度的回火组织演变,讨论了变形对马氏体分解过程、铁素体再结晶晶粒尺寸和析出碳化物形貌的影响.实验结果表明,变形显著影响马氏体分解过程,促进渗碳体的析出和铁素体回复及再结晶.热变形组织铁素体再结晶晶粒尺寸在0.5μm左右;渗碳体形貌从细棒状向球状转变,随变形量增大渗碳体尺寸增大,继续保温60min导致铁素体晶粒长大到1μm左右,晶粒内部的渗碳体消失,原先在铁素体晶界析出的渗碳体球化、粗化.冷轧试样在550℃退火保温时间在30min内得到0.3~0.4μm超细晶粒和尺度小于150nm的弥散渗碳体颗粒组织;随退火保温时间延长到60min,铁素体再结晶晶粒长大到1.9μm,渗碳体颗粒尺寸约160nm. 相似文献
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《Acta Metallurgica》1977,25(9):1027-1030
The interaction of hydrogen with dislocations is well established, but its interaction with other structural features in a material has not been investigated or discussed to any appreciable degree. It is the intent of this discussion to examine the preference of precipitates for hydrogen atoms in a plain carbon steel, which is quenched to a martensitic structure and tempered. This structure represents one of the most susceptible to hydrogen embrittlement in the as-quenched condition and the most resistant in the highly tempered condition. One of the prominent features of this microstructure is the carbide precipitate and its transformational and morphological changes that result on tempering. The ability for trapping hydrogen, from an elastic energy standpoint, is seen to decrease with increasing loss in coherency of the precipitate. An energy for interaction between coherent precipitates and hydrogen atoms is calculated. 相似文献
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LA Steinberg 《Canadian Metallurgical Quarterly》1997,49(1):15-17
General dental practitioners and community dental officers may need to consider several factors when referring patients to the consultant orthodontic service. In Birmingham, a local professional group incorporating representatives from both primary care and secondary care (consultant) services have drawn up a set of formal referral guidelines. The purpose of the exercise was to encourage the most appropriate use of the consultant service so that its resources could be directed towards those in greatest need. In this paper, the factors which determine the patients requiring referral are discussed; a second article will deal with the actual process of referral. 相似文献
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B Nortell 《Canadian Metallurgical Quarterly》1976,236(19):2217-2218
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A research program, sponsored by the Rip Van Winkle Foundation, concerned with mental health in rural areas was started in 1955. A few members of the Hudson Post of the American Legion opposed the organized "mental health movement." Local newspaper articles linked "mental health with 'world citizenship, one worldism, internationalism, communism, and socialism.'… Actually, the ruckus did not blow up until the period of data collection from the children was in its last week. Data from only three children were destroyed in compliance with the wishes of their parents." Details of the background and the problem are presented. From Psyc Abstracts 36:02:2AA37E. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
CL Terrell 《Canadian Metallurgical Quarterly》1999,74(1):78-100
Before 1978, amphotericin B and flucytosine were the only drugs available for the treatment of systemic fungal infections. The imidazoles, miconazole and ketoconazole, were introduced during the next 3 years. Intravenously administered miconazole served a limited therapeutic role and is no longer available. Orally administered ketoconazole, an inexpensive, effective, and convenient option for treating mucosal candidiasis, was widely used for a decade because it was the only available oral therapy for systemic fungal infections. During the 1990s, use of ketoconazole diminished because of the release of the triazoles--fluconazole and itraconazole. Fluconazole is less toxic and has several pharmacologic advantages over ketoconazole, including penetration into the cerebrospinal fluid. In addition, it has superior efficacy against systemic candidiasis, cryptococcosis, and coccidioidomycosis. Despite a myriad of drug interactions and less favorable pharmacologic and toxicity profiles in comparison with fluconazole, itraconazole has become a valuable addition to the antifungal armamentarium. It has excellent activity against sporotrichosis and seems promising in the treatment of aspergillosis. Itraconazole has replaced ketoconazole as the therapy of choice for nonmeningeal, non-life-threatening cases of histoplasmosis, blastomycosis, and paracoccidioidomycosis and is effective in patients with cryptococcosis and coccidioidomycosis, including those with meningitis. Further investigation into the development of new antifungal agents is ongoing. 相似文献
11.
Further improvements to the modified quasi-chemical model in the pair approximation for shortrange ordering (SRO) in liquids
are extended to multicomponent solutions. The energy of pair formation may be expanded in terms of the pair fractions or in
terms of the component fractions, and coordination numbers are permitted to vary with composition. The model permits complete
freedom of choice to treat any ternary subsystem with a symmetric or an asymmetric model. An improved general functional form
for “ternary terms” in the excess Gibbs energy expression is proposed. These terms are related to the effect of a third component
upon the binary pair interaction energies. It is shown how binary subsystems that have been optimized with the quasi-chemical
model can be combined in the same multicomponent Gibbs energy equation with binary subsystems that have been optimized with
a random-mixing Bragg-Williams model and a polynomial expression for the excess Gibbs energy. This is of much practical importance
in the development of large databases for multicomponent solutions. The model also applies to SRO in solid solutions as a
special case, when the number of lattice sites and coordination numbers are constant. 相似文献
12.
MR Yeadon 《Canadian Metallurgical Quarterly》1993,11(3):199-208
A simulation model and a rigid body model are used to investigate twisting initiated during the take-off or contact phase. It is shown that it is possible to produce a full twist solely by building up angular momentum in the arms during the contact phase. This method is only half as effective as building up momentum in the whole body during contact. The introduction of twist into a somersault changes the somersault rate by less than 1%. By timing arm adduction appropriately, it is possible to take advantage of nutation and boost the initial value of the tilt angle and so obtain a greater twist rate. Twist may be stopped by the action of piking, since the motion changes from the twisting mode to the wobbling mode of rigid body motion. Transition to and from these two modes can be used to increase or decrease the tilt angle and twist rate. 相似文献
13.
M. Grujicic G. B. Olson W. S. Owen 《Metallurgical and Materials Transactions A》1985,16(10):1735-1744
The interaction of the twinnedβ
-1-γ
1
′
, martensitic interface with various experimentally observed obstacle particles is analyzed using a specific dislocation model
for the interface. The strain interaction of particles with simple shears and tetragonal distortions and their modulus interactions
are treated as functions of particle crystallographic orientation, particle position with respect to interfacial intersection,
and particle size. Differences from previous predictions of a simple general interface model arise primarily from differences
in the assumed interfacial trajectory relative to the particles. The finite-particle calculations indicate that the point-particle
approximation is valid for a particle radius less than one-tenth the interfacial twin period. Overall agreement with the experimentally
measured interfacial mobility behavior is greatly improved over the previous simple model prediction. The measured athermal
component of the driving force for interfacial motion is consistent with the strain and modulus interaction with 2H-phase
particles. The activation-energy /driving-force relations obtained from the thermally activated component are reasonably represented
by the strain interaction with the fine-scale atomic displacements of the tweed structure. 相似文献
14.
G. X. Wang D. Chandra M. C. Fuerstenau 《Metallurgical and Materials Transactions B》1995,26(3):523-527
A kinetics study has been performed on cobaltite to understand the oxidation processes over a temperature range of 573 to
1173 K using a thermogravimetric method. The results show that oxidation of cobaltite occurs in two stages. In the first stage,
which occurs between 823 and 913 K, the majority of the sulfur is removed. However, the arsenic remains in the lattice of
the reacted region. A pore-blocking kinetic model yields a satisfactory fit to these experimental data. At higher temperatures,
there is a concurrent release of As and S from the crystal lattice of CoAsS. The shrinking-core kinetic model is applicable.
Complementary X-ray diffraction and scanning electron microscopic analyses on these partially oxidized samples support the
kinetic models. The effects of partial pressure of oxygen and particle size on roasting have been evaluated. 相似文献
15.
Donald R. Fosnacht Rajendr P. Goel Jose M. Larrain 《Metallurgical and Materials Transactions B》1980,11(1):69-71
The equilibrium partial pressure of sulfur vapor over Co-S melts has been determined by equilibrating the melts with H2S-H2 gas mixtures at temperatures ranging from 1378 to 1617 °C and for melt compositions ranging from approximately cobalt saturation
up to about 31 wt pct sulfur. As in a previous publication from these laboratories, an optical interferometer was employed
to monitor the system’s approach to equilibrium and to analyze the composition of the equilibrium gas phase. A correlation
based on the experimental data and that of other investigators is described. The correlation is based on the assumption of
species in solution, and reproduces well all thermodynamic properties of Co-S melts.
Formerly Graduate Student, Henry Krumb School of Mines, Columbi University. Formerly Graduate Student, Henry Krumb School
of Mines, Columbi University. 相似文献
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