scholarly journals Grain Growth Control of Dielectric and Magnetic Ceramics

Ceramist ◽  
2021 ◽  
Vol 24 (3) ◽  
pp. 260-272
Author(s):  
Kyoung-Seok Moon
Keyword(s):  
Growth Rate ◽  
Grain Growth ◽  
Driving Force ◽  
Growth Control ◽  
Interface Reaction ◽  
Ceramic Materials ◽  
Interface Energy ◽  
Diffusion Control ◽  
Interface Mobility ◽  
Interface Curvature

The sintering process transported the atoms in the materials by decreasing the total interface energy. The microstructure changes as a result of grain growth and densification under the capillary driving force due to the interface curvature among grains. The grain growth rate is expressed as the product of the interface mobility and the driving force. According to grain growth theories, the mobility of the interface governed by diffusion control is constant but interface mobility is nonlinear when the movement of an interface is governed by interface reaction. As the growth rate is nonlinear for the regime of interface reaction control, the grain growth is nonstationary with annealing time. The microstructure can be controlled by changing the growth rate of an individual grain with the correlation between the maximum driving force and the critical driving force for appreciable growth. The present paper discusses applications of the principle in the fabrication of dielectric and magnetic ceramic materials.

Principles of Microstructural Design in Two-Phase Systems

2007 ◽  
Vol 558-559 ◽  
pp. 827-834 ◽  
Author(s):  
Suk Joong L. Kang ◽  
Yang Il Jung ◽  
Kyoung Seok Moon
Keyword(s):  
Growth Rate ◽  
Grain Growth ◽  
Driving Force ◽  
Driving Forces ◽  
Interface Reaction ◽  
Processing Parameters ◽  
Microstructural Development ◽  
Two Phase ◽  
Interface Mobility ◽  
Microstructural Design

When a polycrystal is in chemical equilibrium, the microstructure evolves as a result of grain growth under the capillary driving force arising from the interface curvature. As the growth rate of an individual grain is the product of the interface mobility and the driving force, the growth of the grain can be controlled by changing these two parameters. According to crystal growth theories, the growth of a crystal with a rough interface is governed by diffusion and its interface mobility is constant. In-contrast, the growth of a crystal with faceted interfaces is governed by the interface reaction and diffusion for driving forces below and above a critical value, respectively. As the growth rate is nonlinear for the regime of interface reaction control, the grain growth is nonstationary with annealing time. Calculations reveal that the types of nonstationary growth behavior including pseudo-normal, abnormal, and stationary are governed by the relative value of the maximum driving force, gmax, to the critical driving force for appreciable growth, gc. Recent experimental observations showing the effects of critical processing parameters on microstructural development also support the theoretical prediction. The principles of microstructural design are deduced in terms of the coupling effects of gmax and gc.

A Simulation of the Abnormal Grain Growth in a Nano-Structural AZ31 Mg Alloy by Phase Field Model

2009 ◽  
Vol 633-634 ◽  
pp. 697-705 ◽  
Author(s):  
Yan Wu ◽  
B.Y. Zong ◽  
M.T. Wang
Keyword(s):  
Grain Growth ◽  
Phase Field ◽  
Field Model ◽  
Boundary Energy ◽  
Phase Field Model ◽  
Annealing Treatment ◽  
Interface Energy ◽  
Az31 Alloy ◽  
Abnormal Grain Growth ◽  
Interface Mobility

Abnormal grain growth was simulated by phase field model in order to find ways of producing scattered a few enormous grains in a nano-structural single phase AZ31 alloy to improve its ductility. It is shown that the abnormal grain growth is controlled by the three keys factors of interface energy, strain restored energy and interface mobility. Therefore, the microstructure with scattered a few enormous grains in the nano-structural matrix can be achieved after an annealing treatment if there is a small group of specially orientated nano-size grains in the original nao-structure with local low grain boundary energy or local high strain energy or local high interface mobility. The morphology of abnormal grains is also examined as function of annealing time to optimize the microstructure.

scholarly journals Phase Field Simulation of AA6XXX Aluminium Alloys Heat Treatment

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 241
Author(s):  
Antonis Baganis ◽  
Marianthi Bouzouni ◽  
Spyros Papaefthymiou
Keyword(s):  
Heat Treatment ◽  
Grain Growth ◽  
Phase Field ◽  
Interface Energy ◽  
Pinning Force ◽  
Artificial Ageing ◽  
Interface Mobility ◽  
Ageing Treatment ◽  
Secondary Particles ◽  
Ageing Condition

Heat treatment has a significant impact on the microstructure and the mechanical properties of Al-Mg-Si alloys. The present study presents a first Phase-Field modelling approach on the recrystallisation and grain growth mechanism during annealing. It focuses on the precipitate fraction, radius, and Mg-Si concentration in the matrix phase, which are used as input data for the calculation of the yield strength and hardness at the end of different ageing treatments. Annealing and artificial ageing simulations have been conducted on the MultiPhase-Field based MICRESS@ software, while the ThermoCalc@ software has been used to construct the pseudo-binary Al-Mg phase-diagrams and the atomic-mobility databases of MgxSiy precipitates. Recrystallisation simulation estimates the recrystallisation kinetics, the grain growth, and the interface mobility with the presence/absence of secondary particles, selecting as annealing temperature 400 °C and a microstructure previously subjected to cold rolling. The pinning force of secondary particles decelerates the overall recrystallisation time, causing a slight decrease in the final grain radius due to the reduction of interface mobility. The ageing simulation examines different ageing temperatures (180 and 200 °C) for two distinct ternary systems (Al-0.9Mg-0.6Si/Al-1.0Mg-1.1Si wt.%) considering the interface energy and the chemical free energy as the driving force for precipitation. The combination of Phase-Field and the Deschamps–Brechet model predicted the under-ageing condition for the 180 °C ageing treatment and the peak-ageing condition for the 200 °C ageing treatment.

Lengthening Kinetics of Pro-Eutectoid Ferrite Ledge in Fe-C Alloy under Interface-Diffusion Mixed Control Mode

2011 ◽  
Vol 172-174 ◽  
pp. 1134-1139 ◽  
Author(s):  
Zhi Gang Yang ◽  
Zhao Dong Li ◽  
Zhi Yuan Liu ◽  
Zhen Qing Liu ◽  
Zhi Xin Xia ◽  
...  
Keyword(s):  
Growth Rate ◽  
Carbon Concentration ◽  
Driving Force ◽  
Carbon Diffusion ◽  
Control Mode ◽  
Interface Migration ◽  
Interface Mobility ◽  
Ferrite Growth ◽  
Mixed Control ◽  
Steady Level

A mixed control mode is developed to model the ledge growth of pro-eutectoid ferrite, considering coupled effects of migration of austenite/ferrite interface and carbon diffusion in austenite. Carbon concentration of austenite at the austenite/ferrite interface increases from the bulk carbon concentration to a steady level, which is lower than that in local equilibrium, during the ferrite growth process. Correspondingly, ferrite grows rapidly at the beginning since all the driving force of ferrite transformation is dissipated on the interface migration. In the later stage of isothermal transformation, the growth rate of ferrite decreases towards a steady level since a part of driving force is dissipated on carbon diffusion in austenite. The effect of interface migration on ferrite growth rate by changing the interface mobility is emphatically discussed. In the case of the low interface mobility, the growth rate of ferrite is very small while the growth is dominated by the carbon diffusion ability in the case of large interface mobility. When a medium interface mobility is obtained, the growth rate of ferrite may reach a maximum value, which exceed the limitation of diffusion control and interface control modes. After comparing the modeled growth rate of ferrite with the experimental data of 0.11-0.49 wt% C alloy at 973-1113 K, the pre-expontential factor (M0) of interface mobility is estimated within the range of 0.1-1 mol m J-1s-1, around the value 0.5 mol m J-1s-1theoretically estimated.

scholarly journals Evolutionary economics: Crisis, transformation and metamorphosis

2021 ◽  
pp. 1-8
Author(s):  
Milan Zeleny
Keyword(s):  
Growth Rate ◽  
Productivity Growth ◽  
Driving Force ◽  
Evolutionary Economics ◽  
Regional Economies ◽  
Economic Evolution ◽  
Economic Sectors ◽  
Advanced Economies ◽  
First Time

Most world economies are undergoing fundamental transformations of economic sectors, shifting their employed workforce through the secular sequence of (1. Agriculture⟶2. Industry⟶3. Services⟶4. Government). The productivity growth rate is the driving force. Most advanced economies have reached the final stages of the sequence. Assorted recessions, crises and stagnations are simply cofluent, accompanying phenomena. Crises might be cyclical, but economic evolution is unidirectional. Traditional economics can hardly distinguish phenomena of crisis from those of the transformation. Because there is no “fifth sector”, some economies are entering the phase of metamorphosis, for the first time in history. Metamorphosis is manifested through deglobalization, relocalization and autonomization of local and regional economies. We are entering the Age of Entrepreneurship.

scholarly journals Mean Field Analysis of Orientation Selective Grain Growth Driven By Interface-Energy Anisotropy

1994 ◽  
Vol 343 ◽  
Author(s):  
J. A. Floro ◽  
C. V. Thompson
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Growth ◽  
Texture Evolution ◽  
Mean Field ◽  
Orientation Distribution ◽  
Interface Energy ◽  
Abnormal Grain Growth ◽  
Field Analysis ◽  
Energy Anisotropy

ABSTRACTAbnormal grain growth is characterized by the lack of a steady state grain size distribution. In extreme cases the size distribution becomes transiently bimodal, with a few grains growing much larger than the average size. This is known as secondary grain growth. In polycrystalline thin films, the surface energy γs and film/substrate interfacial energy γi vary with grain orientation, providing an orientation-selective driving force that can lead to abnormal grain growth. We employ a mean field analysis that incorporates the effect of interface energy anisotropy to predict the evolution of the grain size/orientation distribution. While abnormal grain growth and texture evolution always result when interface energy anisotropy is present, whether secondary grain growth occurs will depend sensitively on the details of the orientation dependence of γi.

A Model of Wheat Grain Growth and Its Applications to Different Temperature and Carbon Dioxide Levels

1995 ◽  
Vol 22 (5) ◽  
pp. 843 ◽  
Author(s):  
YP Wang ◽  
RM Gifford
Keyword(s):  
Growth Rate ◽  
Grain Growth ◽  
Temperature Response ◽  
Rate Sensitivity ◽  
Temperature Sensitive ◽  
Potential Growth ◽  
Carbon Supply ◽  
The Difference ◽  
Carbon Dioxide Levels ◽  
Kernel Growth

Kernel growth after anthesis is simulated as a function of the potential kernel growth rate, current photosynthate production and mobilisation of stored reserves. The potential growth rate of the kernel is simulated as two temperature-sensitive processes, cell production and cell growth. The difference between the potential and actual growth rates of the kernel depends on the carbon supply to the free space of the kernel endosperm, while the carbon supply is itself affected by the actual kernel growth rate. Sensitivity analysis showed that the growth rate of the grain per plant is most sensitive to the potential growth rate of the kernel and number of kernels per plant. This model is able to simulate the observed rates of grain growth and leaf senescence from anthesis to physiological maturity for wheat plants grown in two CO2 concentrations. The simulated temperature response of grain growth agrees well with the experimenal observations.

scholarly journals Endogenous hormonal content during grain development in hexaploid and tetraploid wheat

1970 ◽  
Vol 33 (3) ◽  
pp. 493-502 ◽  
Author(s):  
Sridhar Gutam ◽  
Virendra Nath ◽  
GC Srivastava
Keyword(s):  
Growth Rate ◽  
Acetic Acid ◽  
Abscisic Acid ◽  
Gibberellic Acid ◽  
Grain Growth ◽  
Indole Acetic Acid ◽  
Tetraploid Wheat ◽  
Weight Basis ◽  
Ploidy Levels ◽  
Hormonal Content

A pot experiment was conducted in the rabi (post rainy) seasons of 2001 and 2002 to study the genotypic differences in grain growth rate and endogenous hormonal content in the developing grains of hexaploid and tetraploid wheat. The endogenous hormonal contents of grains in both the ploidy levels had changed in sequence. At 5 days after anthesis (DAA), gibberellic acid (GA3); at 15 DAA (rapid growth phase), indole-acetic acid (IAA); at 25 DAA (dough stage), abscisic acid (ABA) were maximum. At 35 DAA, all the endogenous hormonal level decreased and among the hormones, ABA was highest followed by IAA and GA3. Hexaploids recorded higher concentrations of endogenous hormones (13.38% IAA, 17.89% GA3, and 14.7% ABA) on fresh weight basis and resulted in higher seed weight (56.99 mg/grain) and grain growth rate (0.009 g/g/day) compared to tetraploids (49.08 mg/grain; 0.008 g/g/day) on dry weight basis by better mobilization of photosynthates during grain filling. Key Words: Grain growth rate, hormones, indole-acetic acid, gibberellic acid, abscisic acid. doi:10.3329/bjar.v33i3.1608 Bangladesh J. Agril. Res. 33(3) : 493-502, September 2008

A Simple Statistical Theory for Grain Growth in Materials.

1990 ◽  
Vol 209 ◽  
Author(s):  
P. Mulheran ◽  
J.H. Harding
Keyword(s):  
Growth Rate ◽  
Monte Carlo ◽  
Statistical Theory ◽  
Stochastic Model ◽  
Grain Growth ◽  
Three Dimensional ◽  
Monte Carlo Procedure ◽  
Short Time ◽  
2D And 3D ◽  
Good Agreement

A Monte Carlo procedure has been used to study the ordering of both two and three dimensional (2d and 3d) Potts Hamiltonians, further to the work of Anderson et al. For the 3d lattice, the short time growth rate is found to be much slower than previously reported, though the simulated microstructure is in agreement with the earlier studies. We propose a new stochastic model that gives good agreement with the simulations.

A Mechanism of Polycrystallization in Fully Lamellar Ti-48Al-8Nb Single Crystal Alloy Aged at Elevated Temperatures

2002 ◽  
Vol 753 ◽  
Author(s):  
Yukinori Yamamoto ◽  
Masao Takeyama ◽  
Takashi Matsuo
Keyword(s):  
Growth Rate ◽  
Diffusion Coefficient ◽  
Single Crystal ◽  
Grain Growth ◽  
Elevated Temperatures ◽  
Volume Diffusion ◽  
Activation Enthalpy ◽  
Lamellar Microstructure ◽  
Aged Sample ◽  
Fully Lamellar

ABSTRACTPolycrystallization mechanism of a fully lamellar microstructure during aging at 1473 and 1273 K has been examined using Ti-48Al-8Nb fully lamellar single crystal, which consists mostly of γ/γ interfaces (variant, perfect-twin and pseudo-twin boundaries). After a certain period of aging, a few γ grains are formed within the lamellae and the lamellar microstructure collapses rapidly to become a γ grained microstructure at both temperatures. An EBSP analysis for aged sample revealed that most of the grains follow the orientation of variant domains in the lamellar microstructure. A kinetic analysis of the grain growth during aging revealed that the activation enthalpy of the growth rate is estimated to be 390 kJ/mol, which is very close to that for volume diffusion coefficient of Al and Nb in γ-TiAl. Based on the results, it is concluded that the formation of the grains is attributed to coarsening of variant domains within the lamellar plates and coalescence of the same variant domains across the lamellae, leading to a γ grained microstructure following the orientation of variant domains. These reactions also make the number of the variant domains decrease during aging, which remains only two variant domains with perfect-twin relationship.

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