Homogenisation of Cast Microstructures: Thermodynamic Calculation and Kinetic Simulation

2010 ◽  
Vol 654-656 ◽  
pp. 1532-1535
Author(s):  
Zhan Li Guo ◽  
Alfred Peter Miodownik ◽  
Rong Shan Qin
Keyword(s):  
Concentration Profile ◽  
Thermodynamic Calculation ◽  
Solute Concentration ◽  
Solute Segregation ◽  
Kinetic Simulation ◽  
Secondary Phases ◽  
Nickel Based Superalloy ◽  
Segregation Profile ◽  
Type Calculation ◽  
Homogenisation Process

This paper uses a combination of thermodynamic calculation and kinetic simulation to model the homogenisation process of cast microstructure for multi-component alloys. The approach assumes that the solute segregation profile across the half dendrite arm spacing can be scaled to the solute concentration profile during solidification as generated by a Scheil type calculation. When secondary phases dissolve during homogenisation, they are treated as an additional fraction of pseudo-eutectic to the initial solute concentration profile of the primary solution phase. The methodology is compared with the assumptions made by other authors, highlighting the significant advantages in the present treatment. Examples are drawn from a cast nickel-based superalloy.

scholarly journals Flattening of Diluted Species Profile via Passive Geometry in a Microfluidic Device

Micromachines ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 839
Author(s):  
Michael Miles ◽  
Biddut Bhattacharjee ◽  
Nakul Sridhar ◽  
Apresio Kefin Fajrial ◽  
Kerri Ball ◽  
...  
Keyword(s):  
Solute Transport ◽  
Concentration Profile ◽  
Microfluidic Channel ◽  
Region Of Interest ◽  
Solute Concentration ◽  
Cross Sectional ◽  
Driven Systems ◽  
Solute Profile ◽  
Dynamics Simulations ◽  
Pressure Driven

In recent years, microfluidic devices have become an important tool for use in lab-on-a-chip processes, including drug screening and delivery, bio-chemical reactions, sample preparation and analysis, chemotaxis, and separations. In many such processes, a flat cross-sectional concentration profile with uniform flow velocity across the channel is desired to achieve controlled and precise solute transport. This is often accommodated by the use of electroosmotic flow, however, it is not an ideal for many applications, particularly biomicrofluidics. Meanwhile, pressure-driven systems generally exhibit a parabolic cross-sectional concentration profile through a channel. We draw inspiration from finite element fluid dynamics simulations to design and fabricate a practical solution to achieving a flat solute concentration profile in a two-dimensional (2D) microfluidic channel. The channel possesses geometric features to passively flatten the solute profile before entering the defined region of interest in the microfluidic channel. An obviously flat solute profile across the channel is demonstrated in both simulation and experiment. This technology readily lends itself to many microfluidic applications which require controlled solute transport in pressure driven systems.

scholarly journals Carbide Precipitation, Dissolution, and Coarsening in G18CrMo2–6 Steel

Metals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 916 ◽  
Author(s):  
Zhenjiang Li ◽  
Pengju Jia ◽  
Yujing Liu ◽  
Huiping Qi
Keyword(s):  
Constant Temperature ◽  
Microstructural Evolution ◽  
Thermodynamic Calculation ◽  
Carbide Precipitation ◽  
M23c6 Carbide ◽  
Kinetic Simulation ◽  
The Matrix ◽  
Tempering Process

The precipitation, dissolution, and coarsening of different carbides at 680 °C in G18CrMo2–6 steel was investigated experimentally combined with Jmatpro simulation. The G18CrMo2–6 steel was normalized at 940 °C, followed by tempering at different times at a constant temperature of 680 °C. During the tempering process, there are mainly two kinds of carbide, namely M3C and M23C6. Through characterization of microstructural evolution, thermodynamic calculation, and kinetic simulation, it was observed that during the tempering process, the stable M23C6 carbide was growing, whereas the metastable M3C carbide was disappearing. At the end, the M3C carbide was dissolved and the M23C6 carbide was in equilibrium with the matrix.

Atom Probe Tomography Of Interfaces

1999 ◽  
Vol 5 (S2) ◽  
pp. 118-119
Author(s):  
M. K. Miller
Keyword(s):  
Atom Probe Tomography ◽  
Small Volume ◽  
Atom Probe ◽  
Solute Segregation ◽  
Alloy 718 ◽  
Polycrystalline Nickel ◽  
Concentration Gradients ◽  
Precipitate Morphology ◽  
Probe Field ◽  
Nickel Based Superalloy

The technique of atom probe tomography (APT) enables the x, y, and z coordinates and the elemental identities of the atoms in a small volume to be determined at the atomic level. Therefore, the APT technique may be used to characterize solute segregation to interfaces and precipitation in terms of concentration gradients and precipitate morphology. This type of information may be used to optimize the design of alloys.The material that was used to illustrate the capabilities of atom probe tomography is a complex polycrystalline nickel-based superalloy, Alloy 718. The composition of this commercial superalloy is Ni- 3.2 at. % Nb, 0.96% Al, 1.15% Ti, 20.3% Fe, 21.8% Cr, 0.26% Co, 1.8% Mo, 0.16% Mn, 0.21% Si and 0.26% C. The material was characterized after a heat treatment oM h at 1038°C + 8 h at 870°C + 500 h at 600°C. Previous atom probe field ion microscopy characterizations of this material has demonstrated that there is no intragranular precipitation after the anneal at 1038°C.

A Mathematical Model on Macro-Segregation Formation for Popular Bloom Continuous Casting Process

2019 ◽  
Vol 944 ◽  
pp. 770-777 ◽  
Author(s):  
Hai Bo Sun ◽  
Zheng Li ◽  
Lie Jun Li ◽  
Bao Hua Nie
Keyword(s):  
Continuous Casting ◽  
Minimum Degree ◽  
Casting Process ◽  
Solute Segregation ◽  
Carbon Segregation ◽  
Negative Segregation ◽  
Segregation Profile ◽  
Measured Profile ◽  
The Impact ◽  
Strand Center

A segmented 3-D coupled electromagnetic-thermal solute transportation model, aimed to better understand the macro-segregation formation in the strand during a popular continuous casting (CC) process, has been developed. Based on the model validation by industrial tests, the effect of M-EMS and F-EMS running parameters on the segregation distribution were subsequently carried out. It is shown that the simulated solute segregation profile in the W-shape along the casting thickness direction is in a good agreement with the measured profile. In the initial solidification shell with thickness in 0.020 m, the solute segregation degree changes from a positive value to a negative with the increasing distance from strand surface because of the washing effect induced by the impact flow from the nozzle side port and M-EMS. Here, the minimum degree of carbon segregation decreases from 0.976 to 0.875 with the increasing stirring current from 100A to 550A. As the stirring current of F-EMS decreases from 630A to 200A, the minimum segregation degree locating at 0.109 m distance from strand surface increases from 0.805 to 0.967. The carbon segregation degree at the strand center first decreases from 1.10 to the minimum value of 1.06 at the case of 350 A/4 Hz because of the concentration equilibrium for the local decreasing negative segregation induced by F-EMS, and then increases to 1.16 due to the local poor stirring.

scholarly journals Detection of Solute Segregation at Grain Boundaries

1980 ◽  
Vol 38 ◽  
pp. 360-361
Author(s):  
J. Briceno-Valero ◽  
R. Gronsky
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Boundary Segregation ◽  
Solute Concentration ◽  
Boundary Region ◽  
Solute Segregation ◽  
Spectroscopic Techniques ◽  
Concentration Gradients ◽  
X Ray ◽  
Grain Boundary Plane

Studies of grain boundary segregation in metallurgical systems are traditionally based upon the premise that grain boundaries are more likely sites for solute atoms than their surrounding grains. This idea is manifested in experimnental studies which distinguish the solute concentration at boundaries from that of grain interiors using various spectroscopic techniques, including more recently, energy dispersive X-ray analysis in TEM/STEM instruments. A typical study therefore usually consists of spot or line scans across a grain boundary plane in order to detect concentration gradients at the boundary region. It has also been pointed out that there are rather severe problems in quantitatively determining the absolute solute concentration within the grain boundary, and data correction schemes for this situation have been proposed.

Systematics of Grain Boundary Diffusion and Solute Segregation in Copper Poly- and Bicrystals

2008 ◽  
Vol 273-276 ◽  
pp. 168-175 ◽  
Author(s):  
Sergiy V. Divinski
Keyword(s):  
Grain Boundary ◽  
Boundary Diffusion ◽  
Copper Matrix ◽  
Solute Concentration ◽  
Solute Segregation ◽  
Grain Boundary Diffusion ◽  
Dilute Solution ◽  
Boundary Width ◽  
Dilute Limit ◽  
Boundary Diffusivity

Recent results on radiotracer grain boundary diffusion of different solutes in the same high-purity polycrystalline copper are reviewed. The measurements were performed in extended temperature intervals satisfying Harrison’s B and C regime conditions at higher and lower temperatures, respectively. In the B regime, the triple product P = sδDgb was determined, while the grain boundary diffusivity Dgb was directly measured in the C regime (s is the segregation factor and δ the grain boundary width). Consequently, the segregation of different solutes in the copper matrix was determined for the true dilute limit conditions. The results on grain boundary diffusion and segregation are analysed in relation to the solute – solvent binding and solute – vacancy interaction in the bulk and in the grain boundaries. By increasing amount of the applied radiotracer the effect of solute concentration on grain boundary diffusion can thoroughly be examined. Grain boundary diffusion experiments on well-characterised bicrystals have been shown to be most suitable for such a study. In a radiotracer experiment, the complete solute segregation isotherm can be measured beginning already from a dilute solution in both, bulk and grain boundary.

scholarly journals An Efficient Model for Predicting the Segregation Profile of Binary Fluidized Beds

2018 ◽  
Vol 63 (1) ◽  
pp. 147-159
Author(s):  
Mohamed Sobhi Al-Agha ◽  
Pál Szentannai
Keyword(s):  
Concentration Profile ◽  
Fluidized Beds ◽  
Vertical Axis ◽  
3D Models ◽  
Data Sets ◽  
Two Phase ◽  
Main Work ◽  
Fitting Procedure ◽  
Segregation Profile ◽  
Vertical Concentration Profile

In most cases, the stationary fluidized beds are composed of two different particle classes (inert and active particles), and the concentration profile of these binary beds along the vertical axis is crucial regarding the effectiveness of the reactor. The present study introduces a semi-empirical 1D mathematical model for predicting the vertical concentration profile of binary fluidized beds. The proposed model is a developed and applicable version of the so-called Gibilaro and Rowe two-phase model, in which the differential equations describing the jetsam movement in the bulk and wake phases were solved numerically. The main work was to determine the parameters of the basic model, which was carried out by means of an advanced multi-step parameter fitting procedure. A more general form was established, which is based on direct linkage with the operating parameters that can be directly set and measured on the system. Comparisons with very diverse measured data sets available in the literature prove the accuracy of this model. Additional comparisons pointed out that the realization of this model is numerically inexpensive as it is several orders of magnitude faster than the available 2D and 3D models.

Thermo-Kinetic Simulation of the Yield Strength Evolution of AA7075 during Natural Aging

2014 ◽  
Vol 922 ◽  
pp. 406-411 ◽  
Author(s):  
Peter Lang ◽  
Thomas Weisz ◽  
Mohammad Reza Ahmadi ◽  
Erwin Povoden-Karadeniz ◽  
Ahmad Falahati ◽  
...  
Keyword(s):  
Yield Strength ◽  
Room Temperature ◽  
Aluminum Matrix ◽  
Natural Aging ◽  
Binding Energies ◽  
Kinetic Simulation ◽  
Secondary Phases ◽  
Strength Evolution ◽  
Binding Forces ◽  
Aluminum Alloy 7075

The yield strength evolution in aluminum alloy 7075 is investigated during natural aging. The thermo-kinetic simulation, capable of predicting nucleation, growth, coarsening and dissolution of metastable and stable hardening precipitates in Al-Zn-Mg-Cu during natural aging, is outlined briefly. A recent strengthening model for shearing and bypassing of precipitates by dislocations is utilized to calculate the evolution of the macroscopic yield strength at room temperature. The simulation accounts for vacancy-solute binding energies calculated with the help of first principles simulations that influence the diffusivity of the system due to the presence of excess quenched-in vacancies. These results provide predictions about the amount of excess vacancies trapped by solid solution alloying elements and how the lifetime of vacancies changes due to attractive or repelling binding forces between vacancies and different solid atoms in the aluminum matrix. In our approach, we calculate the strength evolution after quenching due to interaction between dislocations and changes in the microstructure by precipitation of different kinds of secondary phases. The predicted evolution of yield strength is finally verified on experimental measurements.

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