Study on the Natural Convection and Formation of Periodic Diphase Dendrite in Al-La Alloys

2010 ◽  
Vol 129-131 ◽  
pp. 1308-1312
Author(s):  
Ya Hong Zheng ◽  
Yan Lin Wang ◽  
Zi Dong Wang
Keyword(s):  
Crystal Growth ◽  
Natural Convection ◽  
Concentration Distribution ◽  
Concentration Field ◽  
Growth Direction ◽  
Liquid Interface ◽  
Dendrite Morphology ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Interface Edge

In the crystal growth process, the temperature distribution and concentration distribution at the solid-liquid interface edge are always the hot problems. In this paper, we study the concentration distribution at the solid-liquid interface edge under the natural convection conditions, we find that the concentration field is oscillating exponential decline or rose along the crystal growth direction. We also study the dendrite morphology of Al-La alloys using the experimental method, the results show that the microstructure of Al-35%La alloys is different from the common microstructure of hypereutectic alloy during the conventional casting process, the first crystalline phase is Al11La3, which composition is discontinuous along the growth direction, the main dendrite is composed of α-Al alternating with Al11La3, the results of SEM and XRD show that the chemical composition along the main dendrite exhibits periodic behavior, therefore, this microstructure is named as periodic diphase dendrite structure.

Mechanics of shaped crystal growth from the melt

1996 ◽  
Vol 11 (9) ◽  
pp. 2163-2176 ◽  
Author(s):  
John C. Lambropoulos ◽  
Chien-Hsing Wu
Keyword(s):  
Crystal Growth ◽  
Dislocation Density ◽  
Growth Parameters ◽  
Growth Direction ◽  
Liquid Interface ◽  
Dislocation Generation ◽  
Crystalline Anisotropy ◽  
Initial Dislocation Density ◽  
Solid Liquid Interface ◽  
Solid Liquid

We present the numerical formulation of the thermal stress driven steady-state dislocation generation during the growth of shaped crystals from the melt, with Czochralski (CZ) growth of solid cylinder III–V compound semiconductors as an example. We use and compare the Haasen–Alexander model, coupling dislocation multiplication and creep strain rates, and the Jordan model, based on thermoelastic stresses. Growth parameters may be chosen so as to produce an overall approximately flat interface, leading to reduced dislocation density in the majority of the crystal's cross section. Calculation of final dislocation density requires the initial dislocation density and all stress components along the solid-liquid interface, microstructural features which depend on the physical processes leading to solidification. The final dislocation density is not sensitive to the initial dislocation density along the solid-liquid interface, but strongly depends on the interface stress. Significant stress relaxation at the interface is required to produce experimentally observed “W” shaped dislocation patterns. Crystal growth direction and crystalline anisotropy couple elastic (lattice) and plastic (slip systems) crystalline anisotropy.

scholarly journals Numerical Analysis of Difficulties of Growing Large-Size Bulk β-Ga2O3 Single Crystals with the Czochralski Method

Crystals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 25
Author(s):  
Xia Tang ◽  
Botao Liu ◽  
Yue Yu ◽  
Sheng Liu ◽  
Bing Gao
Keyword(s):  
Crystal Growth ◽  
Single Crystals ◽  
Czochralski Method ◽  
Liquid Interface ◽  
Spiral Growth ◽  
Growth Time ◽  
Large Size ◽  
Crystal Diameter ◽  
Solid Liquid Interface ◽  
Solid Liquid

The difficulties in growing large-size bulk β-Ga2O3 single crystals with the Czochralski method were numerically analyzed. The flow and temperature fields for crystals that were four and six inches in diameter were studied. When the crystal diameter is large and the crucible space becomes small, the flow field near the crystal edge becomes poorly controlled, which results in an unreasonable temperature field, which makes the interface velocity very sensitive to the phase boundary shape. The effect of seed rotation with increasing crystal diameter was also studied. With the increase in crystal diameter, the effect of seed rotation causes more uneven temperature distribution. The difficulty of growing large-size bulk β-Ga2O3 single crystals with the Czochralski method is caused by spiral growth. By using dynamic mesh technology to update the crystal growth interface, the calculation results show that the solid–liquid interface of the four-inch crystal is slightly convex and the center is slightly concave. With the increase of crystal growth time, the symmetry of cylindrical crystal will be broken, which will lead to spiral growth. The numerical results of the six-inch crystal show that the whole solid–liquid interface is concave and unstable, which is not conducive to crystal growth.

Solidification parameters of the solid-liquid interface in crystal growth in response to vibration

1994 ◽  
Vol 29 (15) ◽  
pp. 3997-4000 ◽  
Author(s):  
Wang Fengquan ◽  
Chen Shiyu ◽  
He Deping ◽  
Wei Bingbo ◽  
Shu Guangji
Keyword(s):  
Crystal Growth ◽  
Liquid Interface ◽  
Solidification Parameters ◽  
Solid Liquid Interface ◽  
Solid Liquid

Modeling Coupled Conduction–Convection Ice Formation on Horizontal Axially Finned and Unfinned Tubes

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Hassan M. S. Al-Sarrach ◽  
Ghalib Y. Kahwaji ◽  
Mohamed A. Samaha
Keyword(s):  
Natural Convection ◽  
Liquid Interface ◽  
Ice Formation ◽  
Finite Difference Schemes ◽  
Freezing Process ◽  
Liquid Region ◽  
Water Density ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
The Impact

The freezing of water around immersed unfinned and finned horizontal tubes is simulated numerically. The impact of natural convection as well as the water density inversion with temperature is considered. The equations governing both fluid flow and heat transfer around the tubes and through the solid–liquid interface are solved using finite difference schemes. To follow the moving solid–liquid boundary, dynamic grid generation is performed using the elliptic partial differential equation method with iterative interpolating smoothing to avoid divergence. For validation, the present results for unfinned tubes are compared with experimental studies reported in the literature. The present numerical simulations are aimed at improving our understanding of the parameters affecting the freezing process around both finned and unfinned tubes. The results showed that the flow patterns are similar in both tube configurations with one main vortex in the liquid region when there is no inversion in the water density. The presence of fins complicates the distribution of local Nusselt number along the solid–liquid interface in comparison with the unfinned tube. The impact of natural convection on the rate of ice formation is limited to the initial period of the freezing process. The results also show the freezing enhancement when utilizing fins. An accumulated ice mass correlation is developed for each tube configuration. This model can be used to optimize the design of both finned and unfinned tubes in energy storage systems, which are viable tools for air conditioning load shifting and leveling.

In Situ Visualization Of A Solid-Liquid Interface During Crystal Growth

1988 ◽  
Author(s):  
S B. Trivedi ◽  
T S. Ananthanarayanan ◽  
R G. Rosemeier ◽  
J J. Kennedy
Keyword(s):  
Crystal Growth ◽  
Liquid Interface ◽  
In Situ Visualization ◽  
Solid Liquid Interface ◽  
Solid Liquid

scholarly journals Numerical Analysis of Solidification Behavior during Laser Welding Nickel-based Single-crystal Superalloy Part IV: Optimization of Thermo-metallurgical Factors

2021 ◽  
Vol 1996 (1) ◽  
pp. 012004
Author(s):  
Zhiguo Gao
Keyword(s):  
Single Crystal ◽  
Welding Speed ◽  
Laser Power ◽  
Liquid Interface ◽  
Solidification Behavior ◽  
Dendrite Morphology ◽  
Grain Formation ◽  
Solid Liquid Interface ◽  
Solid Liquid ◽  
Stray Grain

Abstract Important metallurgical factors, such as alloying aluminum redistribution, supersaturation and undercooling of dendrite tip around solid/liquid interface, are separately optimized to alleviate stray grain formation and columnar/equiaxed transition (CET) with series of welding conditions and provide a very efficient method for microstructure control through modification of growth kinetics of dendrite tip under nonequilibrium solidification conditions of ternary Ni-Cr-Al molten pool. Asymmetrical (001)/[110] welding configuration is inferior to symmetrical (001)/[100] welding configuration, because overall area-weighted alloying redistribution, supersaturation and undercooling of dendrite tip throughout the solid/liquid interface of weld pool are consistently severer to exacerbate solidification behavior and microstructure development and incur morphology instability of columnar/equiaxed transition. High heat input, such as combination of higher laser power and slower welding speed, monotonically increases aluminum enrichment, supersaturation and undercooling of dendrite tip near solidification interface to simultaneously deteriorate nucleation and growth of stray grain formation and weaken columnar dendrite morphology, while low heat input, such as combination of lower laser power and faster welding speed, decreases solute buildup, relieves supersaturation and beneficially suppresses dendrite tip undercooling to minimize equiaxed dendrite morphology in the crack-susceptible region, and thereby facilitate single-crystal epitaxial growth with decrease of thermo-metallurgical factors for columnar/equiaxed transition in order to provide prerequisite for optimization of welding conditions. Favorable solidification conditions are obtainable with preferential crystallographic orientation to eliminate columnar/equiaxed transition under which the epitaxy of single-crystal metallurgical properties across fusion boundary of substrate is predominantly promoted to essentially reduce stray grain formation in (001)/[100] welding configuration, and is kinetically capable of significant reduction of microstructure anomalies and nonuniform solidification behavior. The useful relationship among welding conditions, alloying aluminum redistribution, supersaturation and undercooling of dendrite tip is properly established within dendrite stability range through thorough analysis. In addition, the validation of theoretical predictions is fairly reasonable by the experiment results. It is worth that the contributions of kinetics-related solidification phenomena with advancement of solid/liquid interface are imposed altogether to understand why stray grain formation occurs on the basis of controlling mechanism of minimum undercooling or minimum velocity by the reproducible methodology procedure.

Sign in / Sign up

Export Citation Format

Share Document