Simulation of the phase transformation front advancement during the swelling of fire retardant coatings

ABSTRACTThe phase transformation between the α- and β-cristobalite modifications of SiO2 were studied using molecular dynamic simulations. The transformation was induced isothermally by control of the pressure within the structure, either through an externally applied constant stress or by changing the simulation box volume. The atomic scale mechanisms of the transformation can best be observed by means of a time-correlation function describing the spatial orientation of the planes containing the Si-O-Si bonds. These planes rotate by 90° over the course of the transition. Both, the bulk modulus, calculated for static structures, as well as the vibrational spectra of the Si-O-Si planes, reflect the softening of acoustic modes in the midst of the transition, which is characteristic of displacive phase transformations. Although the aperiodic shift of atomic positions upon passage of the transformation front could be responsible for a momentary softening of the structure, this is not the only reason, since this behavior persists when maintaining the structure at intermediate densities, which corresponds neither to α-, nor to β- cristobalite.

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The deformation of metals under small stresses during phase transformations

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1965.0029 ◽

1965 ◽

Vol 283 (1394) ◽

pp. 403-422 ◽

Cited By ~ 416

Keyword(s):

Phase Transformation ◽

Flow Stress ◽

Phase Transformations ◽

Plastic Flow ◽

Reasonable Agreement ◽

Creep Behaviour ◽

External Stress ◽

Random Orientation ◽

Transformation Front ◽

Theory And Experiment

Stresses are developed internally in metals when a change in density and strength arises from a phase transformation. It is shown that plastic flow, generally confined to the weaker phase, results from the accommodation of strain due to the transformation front. The form of the plastic flow is considered in terms of the extreme cases of yield and creep behaviour. It is deduced that, for a complete cycle both ways through the transformation temperature, the resultant deformation varies linearly with the applied stress (provided this is small), the fractional volume change on transformation and inversely as the flow stress of the weaker phase. The deformation is not zero in the absence of external stress except where the phase transformation front has random orientation and movement. The theoretically deduced relations are examined experimentally by observing the deformation of specimens with attached weights, giving small tensile stresses, while their temperature was cycled through a transformation point. Phase transformations were examined in a number of metals involving a variety of crystal structures: reasonable agreement between theory and experiment was obtained in all cases.

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Abrupt Softening Phenomenon in a Shape Memory CuAlNi Single Crystal under Uniaxial Compression

Materials Science Forum ◽

10.4028/www.scientific.net/msf.614.181 ◽

2009 ◽

Vol 614 ◽

pp. 181-185 ◽

Cited By ~ 1

Author(s):

Li Sun ◽

W.M. Huang

Keyword(s):

Phase Transformation ◽

Martensitic Transformation ◽

Single Crystal ◽

Shape Memory ◽

Uniaxial Compression ◽

Anomalous Behavior ◽

Good Evidence ◽

The Other ◽

Martensite Variant ◽

Transformation Front

Abrupt softening phenomenon was observed in a shape memory CuAlNi single crystal upon uniaxial compression. Sudden martensite variant(s) reorientation was found to be the reason behind this anomalous behavior. The significance of this finding is twofold. On one hand, it clearly demonstrates that the stress induced transformation can follow a sequence of the phase transformation (martensitic transformation, austenite to martensite) and then reorientation (from one martensite variant to another). On the other hand, the anomalous softening provides a good evidence for explaining the propagation of the phase transformation front.

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Effect of the shape of the phase-transformation front on the texture of beta-quenched uranium

Soviet Atomic Energy ◽

10.1007/bf01122381 ◽

1975 ◽

Vol 39 (3) ◽

pp. 798-802

Author(s):

V. F. Zelenskii ◽

A. I. Stukalov ◽

A. V. Azarenko ◽

G. S. Gaidamachenko ◽

V. V. Kunchenko ◽

...

Keyword(s):

Phase Transformation ◽

Transformation Front

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Peculiarities of Discontinuous Precipitation in the Pb-Sn Alloy

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.261-262.61 ◽

2007 ◽

Vol 261-262 ◽

pp. 61-76 ◽

Cited By ~ 1

Author(s):

Yu.A. Lyashenko ◽

N.V. Zaitzeva ◽

O.A. Shmatko

Keyword(s):

Phase Transformation ◽

Driving Force ◽

Maximum Rate ◽

Discontinuous Precipitation ◽

Maximum Velocity ◽

Independent Determination ◽

Polycrystalline Alloys ◽

Concentration Step ◽

Transformation Front

A model of discontinuous precipitation in binary polycrystalline alloys at low temperatures is presented. The proposed approach allows independent determination of the main parameters, including the interlamellar distance, the maximum velocity of the phase transformation front, and the concentration step at this boundary. This is achieved by using a set of equations for: 1) the mass transfer in the moving interphase boundary; 2) the balance of the entropy fluxes at the phase transformation front, and 3) the maximum rate of the free energy release under constraint of entropy balance. Concepts of mobility and linear interrelation between the driving force and velocity are not used explicitly. Comparison of the model calculation with the experimental results for the Pb-Sn system at different supersaturations is provided.

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Phase Transformation In Ti-6al-4v Alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100096175 ◽

1972 ◽

Vol 30 ◽

pp. 584-585

Author(s):

Shiro Fujishiro

Keyword(s):

Phase Transformation ◽

Grain Boundary ◽

Cryogenic Temperature ◽

Β Phase ◽

Heat Treated ◽

Mixed Microstructure ◽

Ductile Behavior

The Ti-6 wt.% Al-4 wt.% V commercial alloys have exhibited an improved formability at cryogenic temperature when the alloys were heat-treated prior to the tests. The author was interested in further investigating this unusual ductile behavior which may be associated with the strain-induced transformation or twinning of the a phase, enhanced at lower temperatures. The starting materials, supplied by RMI Co., Niles, Ohio were rolled mill products in the form of 40 mil sheets. The microstructure of the as-received materials contained mainly ellipsoidal α grains measuring between 1 and 5μ. The β phase formed an undefined grain boundary around the a grains. The specimens were homogenized at 1050°C for one hour, followed by aging at 500°C for two hours, and then quenched in water to produce the α/β mixed microstructure.

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Application of analytical electron microscopy to the study of partitioning of silicon in a 2 wt% Si eutectoid steel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100110222 ◽

1978 ◽

Vol 36 (1) ◽

pp. 616-617

Author(s):

N. Ridley ◽

S.A. Al-Salman ◽

G.W. Lorimer

Keyword(s):

Electron Microscopy ◽

Electron Microscope ◽

Analytical Electron Microscopy ◽

Eutectoid Steel ◽

Minimum Diameter ◽

Thin Foils ◽

Analytical Electron ◽

Analytical Electron Microscope ◽

Transformation Front

The application of the technique of analytical electron microscopy to the study of partitioning of Mn (1) and Cr (2) during the austenite-pearlite transformation in eutectoid steels has been described in previous papers. In both of these investigations, ‘in-situ’ analyses of individual cementite and ferrite plates in thin foils showed that the alloying elements partitioned preferentially to cementite at the transformation front at higher reaction temperatures. At lower temperatures partitioning did not occur and it was possible to identify a ‘no-partition’ temperature for each of the steels examined.In the present work partitioning during the pearlite transformation has been studied in a eutectoid steel containing 1.95 wt% Si. Measurements of pearlite interlamellar spacings showed, however, that except at the highest reaction temperatures the spacing would be too small to make the in-situ analysis of individual cementite plates possible, without interference from adjacent ferrite lamellae. The minimum diameter of the analysis probe on the instrument used, an EMMA-4 analytical electron microscope, was approximately 100 nm.

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Microstructural and Microchemical Characterization of Nickel Sulfide Inclusions in Plate Glass

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100089123 ◽

1991 ◽

Vol 49 ◽

pp. 962-963

Author(s):

J. Cooper ◽

O. Popoola ◽

W. M. Kriven

Keyword(s):

Thermal Expansion ◽

Phase Transformation ◽

Glass Matrix ◽

Nickel Sulfide ◽

Plate Glass ◽

Thermal Expansion Mismatch ◽

Volume Increase ◽

Β Phase ◽

Microchemical Characterization

Nickel sulfide inclusions have been implicated in the spontaneous fracture of large windows of tempered plate glass. Two alternative explanations for the fracture-initiating behaviour of these inclusions have been proposed: (1) the volume increase which accompanies the α to β phase transformation in stoichiometric NiS, and (2) the thermal expansion mismatch between the nickel sulfide phases and the glass matrix. The microstructure and microchemistry of the small inclusions (80 to 250 μm spheres), needed to determine the cause of fracture, have not been well characterized hitherto. The aim of this communication is to report a detailed TEM and EDS study of the inclusions.

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