Surface segregation in a dilute copper–silver alloy

1986 ◽  
Vol 1 (5) ◽  
pp. 646-651 ◽  
Author(s):  
S.W. Bronner ◽  
P. Wynblatt
Keyword(s):  
Surface Segregation ◽  
Single Phase ◽  
Surface Composition ◽  
Surface Concentration ◽  
Lattice Diffusion ◽  
Silver Surface ◽  
Silver Alloy ◽  
Two Phase ◽  
Diffusion Controlled ◽  
Kinetics Of

The equilibrium surface composition of a Cu-0.83 at. % Ag alloy has been studied over the range from 600°–400°C. Above 450°C the alloy consists of a single phase, whereas below that temperature the material separates into copper-rich and silver-rich phases. The kinetics of equilibration appear to be controlled by grain boundary diffusion, leading to more rapid equilibration than expected on the basis of lattice diffusion-controlled kinetics. In the single-phase regime, silver segregates to the surface with an average enthalpy of segregation of −24 kJ/mol and an entropy of segregation of 0.94 J/mol K, and displays a trend of increasing equilibrium silver surface concentration with decreasing temperature. Theoretical estimates of the enthalpy of segregation yield the somewhat more negative values of −60 and −47 kJ/mol, respectively. In the two-phase regime, the surface continues to be enriched in silver, but the silver surface concentration decreases with decreasing temperature as a result of the rapidly decreasing equilibrium solubility of silver in copper.

Tensile Property Improvements of Spinodal Cu-15Ni-8Sn by Two-Phase Heat Treatment

1982 ◽  
Vol 104 (3) ◽  
pp. 234-240 ◽  
Author(s):  
T. J. Louzon
Keyword(s):  
Heat Treatment ◽  
Single Phase ◽  
Phase Region ◽  
Two Phase ◽  
Heat Treated ◽  
Slow Kinetics ◽  
Increased Strength ◽  
Kinetics Of ◽  
Phase Solution ◽  
Strength And Ductility

A heat treatment has been developed which produces significant improvements in the tensile properties of Cu-15Ni-8Sn spinodal alloy. The treatment involves solution heat treatment in the two-phase region rather than the single-phase region normally used. After quenching and aging, increased strength and ductility of the alloy over single phase solution heat-treated and aged values were found. The mechanical properties obtained were superior to any previously observed for material of the compositions studied in the solution treated, quenched, and aged condition. Also, the alloys’ transformation kinetics were greatly slowed by the two phase heat-treatment. It is suggested that the increase in strength and slow kinetics of transformation observed are caused by grain size effects and by grain boundary modifications. Resistivity data and etching response corroborate these arguments.

scholarly journals Kinetics of Arsenic Surface Segregation in Scrap-Based Silicon Electrical Steel

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 1
Author(s):  
Darja Steiner Petrovič
Keyword(s):  
Surface Segregation ◽  
Surface Engineering ◽  
Electrical Steel ◽  
Bulk Material ◽  
Steel Matrix ◽  
Two Phase ◽  
Temperature Range ◽  
Residual Elements ◽  
Site Competition ◽  
Kinetics Of

The segregation kinetics of surface-active, residual elements are investigated in an in situ study of annealing scrap-based silicon electrical steel sheet where the arsenic (As) surface segregation is highlighted. During annealing in the temperature range of 300–950 °C, different kinds of interactions between the segregated residual elements were observed. Attractive interactions between the segregands produced co-segregation, e.g., between Sn and Sb, whereas repulsive interactions resulted in site competition, e.g., between Sn and As. These competing interactions are strongly time dependent. In spite of there being twice as much Sn compared to As in the bulk material, the As prevailed in the surface enrichments of the polycrystalline silicon steel at 950 °C. The intensity of the As surface segregation in the temperature range 800–950 °C is proportional to the calculated amount of γ-austenite phase in the (α + γ) steel matrix. The detected phenomenon of the As versus Sn site competition could be valuable for the texture design and surface engineering of silicon steels with a thermodynamically stable two-phase (α + γ) region.

Kinetic mechanisms for mullite formation from sol-gel precursors

1990 ◽  
Vol 5 (9) ◽  
pp. 1963-1969 ◽  
Author(s):  
Dong X. Li ◽  
William J. Thomson
Keyword(s):  
Activation Energy ◽  
Reaction Kinetics ◽  
Single Phase ◽  
Sol Gel ◽  
Mullite Formation ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffusion Controlled ◽  
Kinetic Mechanisms ◽  
Kinetics Of

The reaction kinetics for the formation of mullite (3Al2O3 · 2SiO2) from sol-gel derived precursors were studied using dynamic x-ray diffraction (DXRD) and differential thermal analysis (DTA). The reaction kinetics of diphasic and single phase gels are compared and different reaction mechanisms are found for each gel. Mullite formation in the diphasic gel exhibits an Avrami type, diffusion-controlled growth mechanism with initial mullite formation temperatures of about 1250 °C and an activation energy on the order 103 kJ/mole. On the other hand, mullite formation from the single phase gel is a nucleation-controlled process with an initial formation temperature of 940 °C and a much lower activation energy of about 300 kJ/mole.

Optimisation of Precipitation for the Development of Improved Wrought Fe3Al-based Alloys

2004 ◽  
Vol 842 ◽  
Author(s):  
Satoru Kobayashi ◽  
Stefan Zaefferer ◽  
André Schneider
Keyword(s):  
Grain Refinement ◽  
Hot Deformation ◽  
Single Phase ◽  
Fine Particles ◽  
Phase Region ◽  
Air Cooling ◽  
Two Phase ◽  
Kinetics Of ◽  
Very High ◽  
Grain Refinement Strengthening

ABSTRACTEffect of TiC precipitates on the kinetics of static recrystallisation has been studied by using a Fe-26Al-5Cr (at%) single-phase (α:A2/B2/D03) alloy and two-phase (α+TiC) alloys with different amounts of TiC precipitates. Based on the results, a desirable thermo-mechanical processing is proposed for the development of wrought Fe3Al-based alloys with strengthening MC carbides.In the alloys with a high amount of TiC, needle-like TiC precipitates with 1–10 μm in length formed during air-cooling after homogenisation. Hot deformations with such large precipitates cause inhomogeneous deformation around the particles, leading to particle stimulated nucleation (PSN) and hence accelerate recrystallisation.The occurrence of PSN is harmful for the embrittlement problem, i.e. ductility drastically decreases when recrystallisation occurs, but useful for grain refinement. The following process is proposed to accomplish grain refinement, strengthening by precipitates and avoidance of the embrittlement: hot deformation with a large amount of precipitates to make grain refinement possible by using PSN, followed by hot deformation with a small amount of precipitates near α single-phase region and a subsequent heat treatment to obtain fine precipitates. The fine particles would also act to pin the boundaries of growing grains, thus leading to extended recovery rather than recrystallisation. This process is difficult to carry out in the (Fe-26Al-5Cr)-TiC system because the temperature necessary to enable precipitation is very high and the kinetics is quick. The precipitation temperature is significantly decreased by replacing TiC by VC or MoC.

scholarly journals Fractional-differential approach to describe the process of feeding metals and alloys solidifying under controlled gas pressure

2021 ◽  
Vol 4 (135) ◽  
pp. 149-155
Author(s):  
Tatjana Selivyorstova ◽  
Vadim Selivyorstov ◽  
Yuliia Mala
Keyword(s):  
Single Phase ◽  
Metals And Alloys ◽  
Phase Zone ◽  
Two Phase ◽  
Diffusion Type ◽  
Different Types ◽  
Fractional Differential ◽  
The Given ◽  
Kinetics Of ◽  
Independent Thought

To describe the processes of filtration in the folding dendritic-porous middle of the proponation, a number of fractional-differential mathematical models of the diffusion type. Described non-linear, how to take the shot of the abducted Riman-Leeuwill for an hour, as it can be stuck for a correct description of the single-phase filtration of not Newtonian age in the porous middle.The two-phase zone, which is established during the transition from melting from hard to hard mill, can often be characterized by abnormal kinetics of resistance. The peculiarities of kinetics in the whole range of winners are related to the issues of widespread nonlocality, in a number of types, memory defects, which adhere to the progressive laws. The mathe-?atical apparatus, which allows to adequately describe such processes, is the theory of integration-differentiation of the fractional order.Victorians in robotic thinking have a phenomenological character, so the possibility of their dependence in a specific, practical dermal condition is blamed on the basis of experimental results, so that the validity of other differences is confirmed. Stagnation of the given approach for describing the dynamics of the process of vitality of the two-phase zones and metals and alloys, which solidifies in the minds of a regulated gas vice. Presented in the fractional-differential robotic model of filtration are classified as abnormal diffusion. A characteristic feature of the ryvnyan, which is derived from different types of differential models of filtration, is not the same. With a whole model, they preserve the structure of the classical lines of filtration in the whole order and pass into them in boundary drops, if the order of the other differentiation is old.Vivchennya yakіsnyh authorities otrimanih іvnyans, and also prompts їh numerical decisions є to finish nontrivial zavdannyi, as vimagayut in the skin okremomu vampad of independent thought.

SURFACE SEGREGATION ON Au3Cu(001)

1996 ◽  
Vol 03 (05n06) ◽  
pp. 1823-1829 ◽  
Author(s):  
S. SCHÖMANN ◽  
E. TAGLAUER
Keyword(s):  
Temperature Dependence ◽  
Surface Segregation ◽  
Surface Composition ◽  
Exchange Process ◽  
Surface Concentration ◽  
Ion Scattering ◽  
Elemental Concentrations ◽  
Low Energy Ion Scattering ◽  
Segregation Process ◽  
Ordered Alloys

In relation to investigations of the surface composition of ordered alloys in the region of their critical temperature, the elemental concentrations of the top two atomic layers of a Au 3 Cu (001) alloy surface were determined with low energy ion scattering in the temperature range of 300–925 K. Up to 550 K the first layer consists only of Au atoms and the second layer of Cu atoms. Above this temperature desegregration occurs; from the temperature dependence a segregation enthalpy of 47 kJ/mole could be deduced. The segregation results in a contraction of the top layer distances compared to the bulk values. The segregation kinetics can be described as an exchange process between the top atomic layers with an activation energy of 0.2–0.3 eV. The temperature dependence of the surface concentration of this alloy is determined by the segregation process rather than by the bulk ordering phase transition.

Investigations of α + β → β Phase Transformation in Monotonically Heated Ti6Al7Nb Alloy / Badania Przemiany Fazowej α + β → β W Stopie Ti6Al7Nb Przy Nagrzewaniu Ciągłym

2012 ◽  
Vol 57 (4) ◽  
pp. 995-1000 ◽  
Author(s):  
R. Dąbrowski
Keyword(s):  
Phase Transformation ◽  
Single Phase ◽  
Continuous Heating ◽  
Critical Temperatures ◽  
Two Phase ◽  
Fine Needle ◽  
Β Phase ◽  
Phase Range ◽  
Alloy Microstructure ◽  
Kinetics Of

This paper presents an evaluation of critical temperatures of α + β → β phase transformation in an Ti6Al7Nb alloy occurring during heating performed by dilatometric and metallographic methods. Also, changes in the alloy microstructure during cooling down from the two-phase (α + β) and single phase (β) ranges have been analysed. In the microstructure of the alloy quenched from temperature above 1010°C (one-phase range) in water, the very fine, needle-like precipitates (presumably α’) were observed as well as abnormal grain growth of the primary β phase. The obtained results may serve for the interpretation of phase transformation occurring in the Ti6Al7Nb alloy during tempering. In future, the kinetics of the phase transformation during tempering will be investigated by original CHT (Continuous-Heating-Transformation) charts, which are commonly applied for iron-base alloys.

A TEM study of the influence of microstructure on the superplastic behavior of a U-5.8 wt.% Nb alloy

1986 ◽  
Vol 44 ◽  
pp. 568-569
Author(s):  
G. Mackiewicz Ludtka
Keyword(s):  
Grain Size ◽  
Heating Rate ◽  
Phase Field ◽  
Single Phase ◽  
Superplastic Behavior ◽  
Two Phase ◽  
Single Phase Field

Historically, metals exhibit superplasticity only while forming in a two-phase field because a two-phase microstructure helps ensure a fine, stable grain size. In the U-5.8 Nb alloy, superplastici ty exists for up to 2 h in the single phase field (γ1) at 670°C. This is above the equilibrium monotectoid temperature of 647°C. Utilizing dilatometry, the superplastic (SP) U-5.8 Nb alloy requires superheating to 658°C to initiate the α+γ2 → γ1 transformation at a heating rate of 1.5°C/s. Hence, the U-5.8 Nb alloy exhibits an anomolous superplastic behavior.

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