scholarly journals Decomposition of the β phase at intermediate temperature in β-metastable Ti-5553 alloy

2020 ◽  
Vol 321 ◽  
pp. 12024
Author(s):  
Morgan Goetz ◽  
Moukrane Dehmas ◽  
Benoît Appolaire ◽  
Elisabeth Aeby-Gautier ◽  
Sandra Andrieu ◽  
...  
Keyword(s):  
Bulk Diffusion ◽  
Intermediate Temperature ◽  
Present Contribution ◽  
Β Phase ◽  
Interfacial Kinetics ◽  
Habit Planes

The present contribution focuses on the nature of the β → α transformation in Ti-5333 alloy at intermediate temperatures. It is indeed still unclear whether this transformation is only controlled by bulk diffusion or whether interfacial kinetics may play a role. To address this issue, we have combined SEM and STEM-EDX to measure the concentrations of Al, Cr, Mo, V and Fe in α intragranular precipitates as well as in the abutting β matrix, paying a particular attention to the concentrations at flat interfaces corresponding to the precipitates habit planes. The comparison with Calphad calculations suggests that interfaces are not at equilibrium during the thickening of the plates.

Plasma-Sprayed (Bi2O3)0.705 (Er2O3)0.245 (WO3)0.05 Electrolyte for Intermediate-Temperature Solid Oxide Fuel Cells (IT-SOFCs)

2021 ◽  
Author(s):  
Rui Chen ◽  
Cheng-Xin Li ◽  
Chang-Jiu Li
Keyword(s):  
Fuel Cells ◽  
Solid Oxide Fuel Cells ◽  
Xrd Analysis ◽  
Fluorite Structure ◽  
Solid Oxide ◽  
Intermediate Temperature ◽  
Oxide Fuel ◽  
Cross Sectional ◽  
Β Phase ◽  
Plasma Sprayed

Abstract Stabilized bismuth oxide with fluorite structure is considered a promising electrolyte material for intermediate temperature solid-oxide fuel cells (SOFCs) due to its high oxygen ion conductivity. The ternary system, Bi2O3-Er2O3-WO3, is of particular interest because it is ionically conductive as well as thermally stable. This study investigates the quality of Bi2O3-Er2O3-WO3 (EWSB) electrolyte produced by plasma spraying. The phase structure and cross-sectional microstructure of plasma-sprayed EWSB were characterized by XRD and SEM. The as-sprayed EWSB was found to have a dense microstructure with well bonded lamellae. XRD analysis showed the formation of EWSB with δ-phase and a trace of β-phase, while the β-phase disappeared after annealing at 750°C for 10h. Electrical property tests revealed that the plasma-sprayed electrolyte also had excellent ionic conductivity (0.26 S cm-1 at 750 °C), making it a strong candidate for use in SOFCs at intermediate temperatures.

Activity of layered swedenborgite structured Y0.8Er0.2BaCo3.2Ga0.8O7+δ for oxygen electrode reactions in at intermediate temperature reversible ceramic cells

2021 ◽  
Vol 9 (1) ◽  
pp. 607-621
Author(s):  
Ji-Seop Shin ◽  
Hyunyoung Park ◽  
Kwangho Park ◽  
Muhammad Saqib ◽  
Minkyeong Jo ◽  
...  
Keyword(s):  
Thermal Expansion ◽  
Diffusion Coefficients ◽  
Bulk Diffusion ◽  
Oxygen Electrode ◽  
Intermediate Temperature ◽  
High Chemical ◽  
New Class ◽  
Electrode Reactions ◽  
Low Thermal Expansion

A new class of layered swedenborgite structured Y0.8Er0.2BaCo3.2Ga0.8O7+δ is proposed for oxygen electrode reactions in reversible ceramic cells because of its low thermal expansion and high chemical bulk diffusion coefficients.

Phenomenological analysis of α′L-to-β martensitic transformation in phosphorus-bearing dicalcium silicate

1999 ◽  
Vol 14 (2) ◽  
pp. 460-464 ◽  
Author(s):  
K. Fukuda
Keyword(s):  
Martensitic Transformation ◽  
Effective Strain ◽  
Twin Structure ◽  
Cell Parameters ◽  
Total Displacement ◽  
Β Phase ◽  
Interphase Boundaries ◽  
Two Phases ◽  
Habit Planes ◽  
Shape Deformations

Crystals of (Ca1.95□0.05) (Si0.9P0.1)O4, where □ denotes a vacancy, composed of both the α′L and β phases, were prepared and examined by the precession method. The β phase was exclusively twinned on (100)β, and the relative volumes of the twin-related variants were almost identical with each other. On the basis of the lattice correspondence between the two phases and their cell parameters, the phenomenological crystallographic theory was applied to determine the habit planes and the shape deformations upon α′L-to-β martensitic transformation. The habit planes, which define the coherent interphase boundaries between α′L and β, were nearly parallel to either (100)α′L or (010)α′L·. The alternate shape deformations that produce the former habit planes resulted in the actual (100) twin structure of the β phase. The total displacement was along [100]α′L with the magnitude of 0.008. Because the transformation involved a very small volumetric shrinkage of 0.6%, the strain accommodation would be almost completed. The coherency at the interface boundaries between the two phases and the effective strain accommodation probably caused the thermoelasticity of the Ca2SiO4 solid solutions.

A Molecular Dynamics Study on Pressure Dependence of Ag Diffusion in Ag3SI

2010 ◽  
Vol 72 ◽  
pp. 337-342
Author(s):  
Masakazu Yarimitsu ◽  
Masaru Aniya
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficient ◽  
High Temperature ◽  
Pressure Dependence ◽  
Distribution Functions ◽  
Intermediate Temperature ◽  
Β Phase ◽  
Α Phase ◽  
Method Of Molecular Dynamics ◽  
Pair Distribution Functions

The pressure dependence of the diffusion coefficient in the superionic α- and β-phases of Ag3SI has been studied by using the method of molecular dynamics. It is shown that in the high temperature α-phase, the Ag diffusion coefficient decreases with pressure. On the hand, in the intermediate temperature β-phase, the Ag diffusion coefficient exhibits a maximum at around 2.8 GPa. The structural origin of this behavior is discussed through the pressure dependence of the pair distribution functions.

Atomic growth mechanisms for lamellar structures

1988 ◽  
Vol 46 ◽  
pp. 756-757
Author(s):  
R.W. Fonda ◽  
L.R. Black ◽  
G.J. Shiflet
Keyword(s):  
Cellular Transformation ◽  
Transformation Product ◽  
Induction Melting ◽  
Growth Interface ◽  
Experimental Procedure ◽  
Β Phase ◽  
Ti Alloys ◽  
Synchronous Growth ◽  
The Relationship ◽  
Habit Planes

The pearlite transformation product is composed of alternating plates resulting from a eutectoid transformation whereas the discontinuous or cellular transformation is also composed of alternating plates due to relief of supersaturation. This paper will describe the relationship between the growth interface and interlamellar structure that results from the pearlite and cellular structures. Some important similarities will be noted that relate to both types of phase transformations.The Cu—4w/o Ti alloy was made by induction melting high purity materials and homogenizing. Samples were then solutionized at 900 C and isothermally transformed at 740 C for 60 m. Details of the experimental procedure for the Fe—.8w/o C—12 w/o Mn alloy are given elsewhere.Cellular precipitation in Cu—Ti alloys consists of the synchronous growth of lamallae of less saturated fcc Cu and an ordered orthorhombic Cu4Ti β phase. The conjugate habit planes between the depleted matrix and β phase is (010)β//(111)α with [001]β//[110]α.

Phase Transformation In Ti-6al-4v Alloys

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.

Microstructural and Microchemical Characterization of Nickel Sulfide Inclusions in Plate Glass

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.

High-resolution observations of metastable γ’ precipitation in Al-15at.%Ag

1996 ◽  
Vol 54 ◽  
pp. 1004-1005
Author(s):  
N. V. Larcher ◽  
I. G. Solorzano
Keyword(s):  
Discontinuous Precipitation ◽  
Equilibrium Phase ◽  
Quantitative Description ◽  
Present Contribution ◽  
Α Phase ◽  
The Matrix ◽  
Aging Sequence ◽  
Matrix Precipitation ◽  
Considerable Detail ◽  
Kinetics Of

It is currently well established that, for an Al-Ag alloy quenched from the α phase and aged within the metastable solvus, the aging sequence is: supersaturated α → GP zones → γ’ → γ (Ag2Al). While GP zones and plate-shaped γ’ are metastable phases, continuously distributed in the matrix, formation of the equilibrium phase γ takes place at grain boundaries by discontinuous precipitation (DP). The crystal structure of both γ’ and γ is hep with the following orientation relationship with respect to the fee α matrix: {0001}γ′,γ // {111}α, <1120>γ′,γ, // <110>α.The mechanisms and kinetics of continuous matrix precipitation (CMP) in dilute Al-Ag alloys have been studied in considerable detail. The quantitative description of DP kinetics, however, has received less attention. The present contribution reports the microstructural evolution resulting from aging an Al-Ag alloy with Ag content higher than those previously reported in the literature, focusing the observations of γ' plate-shaped metastable precipitates.

High-Resolution Image Simulation of a Tilted Crystal

1990 ◽  
Vol 48 (1) ◽  
pp. 68-69
Author(s):  
C. J. D. Hetherington
Keyword(s):  
High Resolution ◽  
Crystal Thickness ◽  
Thin Specimen ◽  
Atomic Structures ◽  
Kikuchi Lines ◽  
High Resolution Images ◽  
Final Estimate ◽  
Simulated Images ◽  
Habit Planes

Most high resolution images are not directly interpretable but must be compared with simulations based on model atomic structures and appropriate imaging conditions. Typically, the only parameters that are adjusted, in addition to the structure models, are crystal thickness and microscope defocus. Small tilts of the crystal away from the exact zone axis have only rarely been considered. It is shown here that, in the analysis of an image of a silicon twin intersection, the crystal tilt could be accurately estimated and satisfactorily included in the simulations.The micrograph shown in figure 1 was taken as part of an HREM study of indentation-induced hexagonal silicon. In this instance, the intersection of two twins on different habit planes has driven the silicon into hexagonal stacking. However, in order to confirm this observation, and in order to investigate other defects in the region, it has been necessary to simulate the image taking into account the very apparent crystal tilt. The inability to orientate the specimen at the exact [110] zone was influenced by i) the buckling of the specimen caused by strains at twin intersections, ii) the absence of Kikuchi lines or a clearly visible Laue circle in the diffraction pattern of the thin specimen and iii) the avoidance of radiation damage (which had marked effects on images taken a few minutes later following attempts to realign the crystal.) The direction of the crystal tilt was estimated by observing which of the {111} planes remained close to edge-on to the beam and hence strongly imaged. Further refinement of the direction and magnitude of the tilt was done by comparing simulated images to experimental images in a through-focal series. The presence of three different orientations of the silicon lattice aided the unambiguous determination of the tilt. The final estimate of a 0.8° tilt in the 200Å thick specimen gives atomic columns a projected width of about 3Å.

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