Grain Refinement Mechanism of Al-5Ti-1B Master Alloy by Ab Initio Calculations

2014 ◽  
Vol 794-796 ◽  
pp. 746-751
Author(s):  
Han Long Zhang ◽  
Yan Feng Han ◽  
Jun Wang ◽  
Yong Bing Dai ◽  
Bao De Sun

To exactly understand the grain refining mechanism of α-Al by the Al-5Ti-1B master alloy, the structural properties of α-Al/solid-TiB2(S/S) and liquid-Al/solid-TiB2(L/S) interfaces were studied using the first-principles method. Different ordered structures were formed on the interfaces with different terminations of TiB2(0001) surface, which determines the nucleant potency of TiB2. The heterogeneous nucleation of α-Al on the B-terminated surface is frustrated by an AlB2-like structure formed at the interface. In contrast, a five-layer quasi-solid region with stacking sequence of fcc-Al (111) planes forms on the Ti-terminated TiB2(0001) surface, which is the basis of successful heterogeneous nucleation of α-Al. Moreover, when redundant Ti solute being added into the liquid Al region of Ti-terminated liquid-Al/TiB2interface, the quasi-solid Al region further extends until entire solidification. The reason for using the Al-5Ti-1B master alloy rather than TiB2powders as the commercial refiner in Al industry lies in two aspects: the excessive Ti atoms in the master alloy could guarantee sufficient Ti chemical potential to form Ti-terminated surface of TiB2, and the redundant Ti solute in inoculated melts could facilitate the growth of quasi-solid Al region at the solid/liquid interface.

2005 ◽  
Vol 475-479 ◽  
pp. 313-316
Author(s):  
Jian Guo Li ◽  
Min Huang ◽  
Zimu Shi ◽  
Dong Yu Liu

The AlTiC master alloy has been prepared in different components to refine 99.8%Al and 99.98%Al, then compared to two typical Al5Ti1B in refining efficiency and the grain nuclear. The result showed that the refining efficiency seemed better if the nucleation of high pure aluminum revealed complexity and variety. It may due to that the latency heterogeneous nucleation was efficient on the whole, consequently accelerated refining efficiency.


2005 ◽  
Vol 483-485 ◽  
pp. 541-546 ◽  
Author(s):  
A. Catellani ◽  
G. Cicero ◽  
M.C. Righi ◽  
C.A. Pignedoli

We review some recent investigations on prototypical SiC-based interfaces, as obtained from first-principles molecular dynamics. We discuss the interface with vacuum, and the role played by surface reconstruction in SiC homoepitaxy, and adatom diffusion. Then we move to the description of a buried, highly mismatched semiconductor interface, the one which occurs between SiC and Si, its natural substrate for growth: in this case, the mechanism governing the creation of a network of dislocations at the SiC/Si interface is presented, along with a microscopic description of the dislocation core. Finally, we describe a template solid/liquid interface, water on SiC: based on the predicted structure of SiC surfaces covered with water molecules, we propose (i) a way of nanopatterning cubic SiC(001) for the attachment of biomolecules and (ii) experiments to reveal the local geometry of adsorbed water.


2014 ◽  
Vol 574 ◽  
pp. 391-395
Author(s):  
Li Mi ◽  
Jun Jun Wang ◽  
Zhi Liu Hu

Al-Ti-B master alloy is the most widely used grain refiner in the aluminum fabrication industry, while it’s refinement mechanism is not clearly understand yet. The TiB2 in Al-Ti-B master alloy is one of important phase to grain refining, which intimately related to the generation of initial nucleus, the “fading” phenomenon of refining effect declines with the increase of holding or standing time in grain refining process. Besides, TiB2 is analyzed in several studies about the “poisoning” phenomenon, a large extent weaken of refining effect when Zr, Cr, Mn etc. exists. In this article, the impact of TiB2 to the refining effect of Al-Ti-B master alloy is discussed aiming at the roles and phenomenon mentions above.


1992 ◽  
Vol 114 (1) ◽  
pp. 12-19 ◽  
Author(s):  
J. Marn ◽  
I. Catton

The concept of an unsteady control volume is used to predict the onset of instability for a simple array of cylinders. The array consists of a flexible cylinder placed amidst rigid cylinders. The fluid is assumed to be incompressible with a “slip” boundary condition used on the solid/liquid interface. The equations derived for the model from first principles are solved in the complex plane. The results are compared to experimental data. The paper is concluded with a discussion of the advantages and disadvantages of the model and an assessment of the accuracy of the predictions.


2005 ◽  
Vol 12 (05n06) ◽  
pp. 753-758 ◽  
Author(s):  
SEN-JIANG YU ◽  
QUAN-LIN YE ◽  
LIANG-NENG WU ◽  
JIANG-XING CHEN ◽  
YU-JIAN CUI ◽  
...  

In this paper, we present the spontaneous formation of an unusual type of ordered structures in thin metal film systems deposited on silicon oil surfaces by a thermal evaporation method. These structures are composed of a large number of parallel rectangular-shaped domains and exhibit anti-symmetric characteristic. The experiment shows that thin solid films can move freely on liquid surfaces due to the near-zero adhesion of the solid–liquid interface, resulting in superposition of the films and formation of the ordered structures. Compressive stress gradient in the films is shown to be the driving force for self-organization. All characteristics of the ordered structures are discussed in detail based on special mechanical behaviors of these near-free sustained films.


2012 ◽  
Vol 706-709 ◽  
pp. 1743-1748
Author(s):  
Jiao Zhang ◽  
Qing Dong ◽  
Yong Bing Dai ◽  
Bao De Sun ◽  
Hong Lan Xie

In the present work, solidification of hypoeutectic, eutectic and hypereutectic Al-Cu alloys was illustrated by synchrotron X ray imaging, and the CET of hypoeutectic alloy was picked out to thorough investigated. The mechanism of hypoeutectic dendrites fragment behaviors among the nucleation area was studied by in-situ imaging and first-principles computation. The results show that the density difference between the fragments and the enriched melt leads to the movement of the fragments. The ejected fragments contributed to the columnar-eutectic transition and expanded the breadth of mush zone in front of the solid/liquid interface.


Author(s):  
P.C. Shieh ◽  
J.M. Howe

Determining the atomic structures of solid/liquid interfaces is important for understanding mechanisms of solidification of crystalline materials. To date, research in this area has largely been theoretical in nature because of the difficulty of determining the atomic structure of a solid/liquid interface experimentally. This study has employed HRTEM and image simulations to investigate the atomic structure of crystalline/amorphous interfaces in directionally crystallized Pd80Si20 amorphous ribbons. The crystalline/amorphous interface is similar to a solid/liquid interface in many respects. The HRTEM analyses of directionally crystallized samples have shown that the amorphous Pd80Si20 alloy crystallizes into a lamellar mixture of faceted Pd3Si and nonfaceted Pd9Si2. Interpretation of the HRTEM images requires knowledge of the visibility of ordered structures imbedded in amorphous surroundings. This paper reports the results of a computer simulation study undertaken to determine this visibility.Computer simulations were performed in two parts: 1) construction of a model atomic structure, and 2) simulation of HRTEM images of the model structure. The atomic model was started with a crystalline seed of Pd3Si several unit-cells thick and new atoms were deposited on to the seed according to the dense random packing model for metal-metalloid systems. A unit cell of appropriate size was cut from the resulting composite structure and sliced into layers for input into the image simulations. The HRTEM images were calculated using the TEMPAS multislice program with the following parameters for a JEOL 4000EX: 400kV accelerating potential, 1.0 mm spherical aberration coefficient, 5.0 nm half-width of Gaussian spread of defocus, 0.5 mrad semi-angle of beam convergence, 6.5 nm−1 objective aperture radius, −50.0 nm defocus (near Scherzer defocus) and diffracted beams out to 4.0 nm−1


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