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1.
T. B. Massalski A. J. Perkins J. Jaklovsky 《Metallurgical and Materials Transactions B》1972,3(3):687-694
Recent studies of massive transformations in systems based on copper or silver have shown that the degree to which the primary
solid solution,a, may be extended into the two-phase field,α+β), during a composition invariant massive transformation, varies from system to system, and depends upon a number of factors.
A systematic study of this point was performed in the Cu-Zn, Cu-Al, and Ag-Cd systems, using quenching and heating techniques.
In each system a series of alloys, increasing by small intervals (0.1 at. pct) of solute content, was examined. Particular
care was taken in the control of composition and homogeneity of these alloys. The results show that the highest solute content
for which the massively-formed phase can be identified metallographically exceeds the equilibriuma-phase boundary value by about 0.45 and 1.2 at. pct in the Cu-Zn and Cu-Al systems, respectively, and by several atomic percent
in the Ag-Cd system. In the latter case, extension of solid solubility into the two-phase region occurs both from the fcca and the hcp ζ equilibrium phase fields. It is suggested that these findings may be interpreted in terms of local nonequilibrium
conditions at the massive transformation interface.
Formerly Fellow, Metal Physics Laboratory, Mellon Institute of Science, Carnegie-Mellon Univ. 相似文献
2.
T. B. Massalski 《Metallurgical and Materials Transactions A》1984,15(3):421-425
As is the case with all solid state transformations, massive transformations have some characteristic distinguishing features.
They are diffusional transformations controlled mainly by diffusion of atoms at the transformation interfaces. There is universal
agreement that composition-invariance is one characteristic feature of massive transformations and that a relatively rapid
movement of the transformation interfaces is another. Other features involved in massive transformations are the subject of
some controversy. Among these is the question of orientation relationships, nucleation features, and the mode of growth. In
this article, some of the controversial aspects are discussed with reference to recent publications.
This paper is based upon a presentation made at a symposium on The Massive Transformation, held at the Pittsburgh meeting
of The Metallurgical Society of AIME and the Materials Science Division of ASM, October 9, 1980, under the sponsorship of
the MSD Phase Transformations Committee. 相似文献
3.
《Acta Metallurgica》1986,34(3):385-393
Some main features involved in the characterization of massive transformations are considered. These features are the crystallographic orientation relationships between matrix and product phase crystals, some aspects of nucleation and growth, and the grain structure of product phases. It is shown that no particular crystallographic OR seems to exist in CuGa between a given matrix β crystal and the ζm product phase crystals nucleated within the bulk volume of the former. From the existing experimental information it is shown that only those nuclei having portions of non-coherent interfaces are likely to grow. This is apparent in the case of crystals nucleated at grain boundaries which often bear a rational OR with one of the adjoining matrix grains but grow within the other matrix grain (with which no special OR is held). Similarity of shapes of different (faceted) product crystals of the massive phase nucleated at a single parent matrix grain boundary is considered as being indicative that planar interfaces with definite orientations (and presumably low energy) can occur even in absence of a special OR (like the Burgers relationship between b.c.c. and h.c.p. structures). The impingement of adjacent growing product crystals is considered within a single matrix grain. A dynamic balance of surface tensions is proposed among the grain boundaries that growing massive grains form with one another, and the two interfaces they form with the matrix grain. This balance is thought to give an additional contribution to the driving force acting on the portions of migrating interfaces near a triple junction. Thus, an anisotropy in properties of the different product phase grain boundaries and migrating interfaces leads to a possible explanation (through this proposal) for such different grain structures as the bubble-shaped pattern in AgGa, and a quite irregular pattern in CuGa. It is concluded that the kinetics of atomic transfer across the interfaces seems to be the most important single factor affecting the crystallographic features of nucleation (indirectly, through selection of interface structures according to their mobilities). Also, it is concluded that the structure and energy of product phase grain boundaries is an important factor affecting the morphology of the observed transformation products. 相似文献
4.
Features of compaction by means of the extrusion of powders of Al-40Sn alloy are investigated. Compaction is carried out in
a temperature range of 25–230°C at a reduction coefficient of 4.5 (ɛ = 1.5). An investigation into the structure along the
length of a sample, including the butt end, has shown that the main part of its change occurs at the steps of formation of
a billet and upon the placement of the latter within an operating channel of a press mold for extrusion. Under pressure operation
in this period of time, a new composite material is formed which consists of aluminum particles dispersed into an unbroken
soft tin matrix. As such material is forced through the die, tin strata act as an interparticle lubricant, making the mutual
displacement of aluminum particles, which do not deform much as a result, easier. As a consequence, oxide films on aluminum
particles remain and prevent the establishment of strong interfaces. The extruded material contains cracks along interfaces
and shows low plasticity. 相似文献
5.
6.
Numerical simulation of three-dimensional heat transfer and plastic flow during friction stir welding 总被引:3,自引:0,他引:3
Three-dimensional visco-plastic flow of metals and the temperature fields in friction stir welding have been modeled based
on the previous work on thermomechanical processing of metals. The equations of conservation of mass, momentum, and energy
were solved in three dimensions using spatially variable thermophysical properties and non-Newtonian viscosity. The framework
for the numerical solution of fluid flow and heat transfer was adapted from decades of previous work in fusion welding. Non-Newtonian
viscosity for the metal flow was calculated considering strain rate, temperature, and temperature-dependent material properties.
The computed profiles of strain rate and viscosity were examined in light of the existing literature on thermomechanical processing.
The heat and mass flow during welding was found to be strongly three-dimensional. Significant asymmetry of heat and mass flow,
which increased with welding speed and rotational speed, was observed. Convective transport of heat was an important mechanism
of heat transfer near the tool surface. The numerically simulated temperature fields, cooling rates, and the geometry of the
thermomechanically affected zone agreed well with independently determined experimental values. 相似文献
7.
Martensitic transformations induced by plastic deformation are studied comparatively in various alloys of three types: Fe-30
pct Ni, Fe-20 pct Ni-7 pct Cr, and Fe-16 pet Cr-13 pct Ni, with carbon content up to 0.3 pct. For all these alloys the tensile
properties vary rapidly with temperature, but there are large differences in the value of the temperature rangeM
s toM
d, which strongly increases with substitution of chromium for nickel or with carbon addition. Using the node method, it is
found that the intrinsic stacking fault energy in the austenite drastically increases with temperature in all the chromium-bearing
alloys investigated. This variation is consistent with the observed influence of temperature on the appearance of twinning
or ε martensite during plastic deformation. Very different α’ martensite morphologies can result from spontaneous and plastic
deformation induced transformations, especially in Fe-20 pct Ni-7 pct Cr-type alloys where platelike and lath martensites
are respectively observed. As in the case of ε martensite, the nucleation process is analyzed as a deformation mode of the
material, using a dislocation model. It is then possible to account for the morphology of plastic deformation induced α’ martensite
in both Fe-20 pct Ni-7 pct Cr and Fe-16 pct Cr-13 pct Ni types alloys and for the largeM
s toM
d range in these alloys.
This paper is based upon a thesis submitted by F. LECROISEY in partial fulfillment of the degree of Doctor of Philosophy at
the University of Nancy. 相似文献
8.
Crystals of copper, Cu+6 wt pct Al, and Ag+4 wt pct Sn were compressed along [111] with flow restricted to [ \(\bar 1\bar 12\) ]. After deformation, four differently oriented regions were observed. Their origin is explained by the instability of the (111)[ \(\bar 1\bar 12\) ] orientation which can rotate to either (112) \(\bar 1\bar 11\) or (110)[001] during the imposed shape change. The direction of rotation is determined by which of two initially equally favored pairs of slip systems operate. Surface friction produces shear stresses which favor one pair over the other (depending on the sign of the shear stress) and thus one of the final orientations. Since the sign of the frictional stress varies systematically with position in the deforming crystal, a systematic variation of orientation results. Another orientation (001)[110] has also been observed to behave similarly. During rolling, the frictional forces drawing the crystal into the roll gap are also expected to lead to the division of the crystal into two misoriented regions. The predictions are generalized to include bcc metals of ( \(\bar 1\bar 12\) )[111] and (110)[001] orientations. Previously reported observations of rolled crystals of FeNi3, Fe-3.5 pct Si, and Fe-2 pct Al are in accord with the present analysis. 相似文献
9.
B. A. Druyanov K. B. Vartanov A. A. Bondarev 《Powder Metallurgy and Metal Ceramics》1985,24(7):517-520
Conclusions As a result of an investigation into the process of compression of a porous annular blank, curves have been constructed of the distribution of density and of the parameter of strengthening of the material of the basis. Radial flow leads to the formation, at the inner surface of the blank, of a zone of maximum intensity of bulk and shear strains. This brings the appearance of a region of solid material (=1), whose boundary shifts during compression toward the side wall of the container. The velocities and stresses at the interface between the solid and porous materials are continuous owing to the dependence of the permissible field of velocities on density. With the results obtained it is possible to determine an optimum starting blank shape, ensuring, at a given degree of deformation, the required final dimensions and density of the part.Translated from Poroshkovaya Metallurgiya, No. 7(271), pp. 16–20, July, 1985. 相似文献
10.
Gu Nanju Song Xiaoyan Zhang Jianxin Yin Fuxing Wang Ruixiang 《Metallurgical and Materials Transactions A》1995,26(8):1979-1985
The effects of self-accommodation and plastic accommodation in martensitic transformations and the displacement vector for
lattice deformation are discussed. The authors propose that the formation of an invariant habit plane is connected with the
self-accomodation between different martensitic variants and results in the formation of internal twinned martensites; the
plastic accommodation, rather than self-accommodation, occurs between parent and new phases when the strength is low or the
dislocation density is high for the parent phase and the invariant habit plane is difficult to form, resulting in the formation
of dislocation martensites. 相似文献
11.
Phase transformations during the annealing of powders produced by the electrodispersion of WC-Co alloys are considered. All
the powders contained various amounts of high-temperature β-WC phase. Eutectoid decomposition β-WC → α-WC + W2C is found to result first in the formation of needle α-WC crystals and then in their destruction due to gliding. 相似文献
12.
Suresh K. Gupta V. Rajakumar Paul Grieveson 《Metallurgical and Materials Transactions B》1991,22(5):711-716
llmenite concentrates were heated in argon and oxygen in the temperature range 700 °C to 1000 °C to study the behavior of
the pseudorutile phase and other changes which occur. Pseudorutile does not persist in argon or oxygen in the temperature
range studied. In argon at 700 °C, pseudorutile decomposes into hematite and rutile, while at 1000 °C, it combines with ilmenite
to form ferrous-ferritic pseudobrookite solid solution. A new phase “Fe2O3-2TiO2” was identified as an intermediate product during the heating of ilmenite or pseudorutile in oxygen. This compound decomposes
into hematite and rutile below 800 °C and to pseudobrookite and rutile above 800 °C. The sequence of reactions during the
heating of ilmenite and pseudorutile in oxygen is proposed.
Formerly with the Department of Metallurgy, Imperial College of Science, Technology and Medicine, London.
Formerly with the Department of Metallurgy, Imperial College of Science, Technology and Medicine, London. 相似文献
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16.
GA Uygur Y Liu RS Hellman RS Tikofsky BD Collier 《Canadian Metallurgical Quarterly》1995,36(4):610-612
Fahr's disease is histopathologically characterized by massive bilateral calcifications of the cerebral basal ganglia, the dentate nuclei of the cerebellum and both the cerebral and cerebellar cortices. We report a case of Fahr's disease in which a 99mTc-hexamethyl-propylenamine oxime (99mTc-HMPAO) brain SPECT study was used to evaluate regional cerebral blood flow to the calcified regions. There was markedly decreased perfusion to the basal ganglia bilaterally as well as decreased perfusion to the cerebral cortices that correlated well with the patient's clinical condition. 相似文献
17.
In this paper a theory is developed for Kiscc based on hydrogen induced fracture due to plastic flow on a localized scale within the crack-tip plastic zone. The theory
is qualitatively and quantitatively consistent with experimental data on the influence of yield strength and hydrogen content
on the threshold level and is also able to explain the effect of material composition and microstructure on Kiscc. Evaluation of the yield strength dependence of Kiscc. using this theory, appears to indicate that secondary cracks should initiate a few μm’s from the main crack tip, that is,
at a scale usually finer than grain size, suggesting that carbide and inclusion interfaces or martensite lath boundaries could
play a role in the fracture initiation. Analysis of the hydrogen concentration dependence of Kiscc by means of this theory indicates that this dependence may be a direct result of the interaction of hydrogen with hydrogen
traps in the material through terms involving the binding energy of hydrogen to the traps responsible for initiating fracture.
Formerly Associate Research Scientist, Henry Krumb School of Mines, Columbia University 相似文献
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19.
《Acta Metallurgica Materialia》1991,39(11):2943-2949
The initiation of unstable plastic deformation associated with dynamic strain ageing in controlled load rate tests has been studied. Experimental measurements on an AlMgSi alloy show the existence of two regimes of instability: temporal and spatial. The initiation of the instability is found to occur by the growth of spatially uniform (temporal) strain rate oscillations. At a larger strain, spatial strain localization is found to develop. The existence of an intermediate regime of purely temporal instability is confirmed by a (linear) stability analysis, taking into account stress triaxiality due to non-uniform deformation. Interaction between adjacent material elements via dislocation cross-slip is also considered. Both effects are shown to cause a delay in the onset of spatial instabilities relative to purely temporal instabilities. 相似文献
20.
Instability in the plastic deformation of laminar materials is theoretically studied. The initial formulas in the analytical
model are consistent with the theory of a third contacting body, taking account of the change in the geometric and energy
instability of plastic deformation. The basic solution is in good agreement with experimental data on the deformation of laminar
aluminum-copper and aluminum-steel composites. 相似文献