Papers by Keyword: Rapid Solidification

Abstract: The microstructure and tensile properties of TiB₂ particles reinforced A356 composite materials at different cooling rates are investigated. Experimental results show that the composition of the alloy solidification ,eutectic silicon content , morphology and size have undergone significant changes while the cooling rate increased: On one hand, α-phase grains significantly reduced, by a 50 μm average grain size refinement to 1~5μm with the evolution from coarse dendritic to rosette dendritic, or even spherical evolution; On the other hand, eutectic Si content increases, and diameter, aspect ratio also showed a decreasing trend, while the circularity is gradually increasing. Meanwhile, with the increasing of cooling rate, the particle distribution of TiB₂/A356 particle reinforced composite materials can be optimized. Particle aggregation is reduced, as a result TiB₂ particles’ reinforcement is more obvious, and the tensile fracture shows the obvious characteristics of ductile fracture.

Abstract: The molecular dynamics simulation studies on the microstructure evolution properties of liquid Ca-Mg alloys during the rapid solidifications have been performed. The simulated structure factor S(q) of Ca₇Mg₃ is well agreed with the experimental data. Results indicate that the glass transition temperatures of CaMg₂ and Ca₇Mg₃ are 590 K and 550 K respectively with the cooling rate of 1×10¹² K/s. It also found that icosahedron is much easier to form in CaMg₂ system, and Ca-Mg alloys with more Mg content indicate higher glass forming ability.

Abstract: A molecular dynamics simulation study has been performed for a system consisting of 10,000 atoms to investigate the microstructure evolutions during the rapid solidification. Results indicate that the crystallization has not enough time to complete due to the high cooling rate; therefore, a part of crystal structure is formed, in which the hcp and fcc basic clusters and some other metallic type clusters coexist in the final solidified structure.

Abstract: A molecular dynamics simulation study has been performed for a system consisting of 15,000 atoms to investigate the formation and magic number characteristics of various clusters formed during the rapid solidification. Results indicate that the icosahedral cluster (12 0 12 0) plays key role in the glass transition. The size distribution of clusters in the system showing magic number characteristics, and the magic number sequence in the Mg₂Ca system is 13, 19, 25, 36, 37, ....This magic number sequence is quite similar with that of the system of metal Al.

Abstract: The crystallization characteristics of the binary alloys which have InSn4 intermetallic compounds(IMC) were investigated.The influence which high undercooling had caused to the process of lattice formation,the lattice evolution in the later period of solidification,the stabilization process of the alloy property were mainly studied.The results show that the solute redistribution is restrained intensely in the rapidly solidified condition,the components of InSn4 IMC distribute uniformly,the highly undercooling structure have small sub-grain structure.X-ray diffraction analysis show that strong (0001) texture is formed in the alloys,EBSD analysis show that many sub-boundaries exist in the grains.While these unstable structures have an isothermal annealing between 20~140oC,the texure feature of the alloys weaken,and at the same time the microhardness lower in varying degrees.

Abstract: Through solving an extended Fick’s diffusion equation for the solidification front of a paraboloid of revolution, a generalized Ivantsov function is obtained. The relaxation effect of nonequilibrium liquid diffusion is taken into account. The solute profile in the interfacial region and in the bulk liquid during steady-state dendritic solidification is uniquely determined. It is concluded that the consideration of the relaxation effect and the diffuse interface of finite thickness which decreases with increasing of velocities are necessary for achieving the good model predictions.

Abstract: During rapid solidification, interfaces are often driven far from equilibrium and the "solute trapping" phenomenon is usually observed. Very recently, a phase field model with finite interface dissipation, in which separate kinetic equations are assigned to each phase concentration instead of an equilibrium partitioning condition, has been newly developed. By introducing the so-called interface permeability, the phase field model with finite interface dissipation can nicely describe solute trapping during solidification in the length scale of micrometer. This model was then applied to perform a phase field simulation in a Al-Sn alloy (Al-0.2 at.% Sn) during rapid solidification. A simplified linear phase diagram was constructed for providing the reliable driving force and potential information. The other thermophysical parameters, such as interface energy and diffusivities, were directly taken from the literature. As for the interface mobility, it was estimated via a kinetic relationship in the present work. According to the present phase field simulation, the interface velocity increases as temperature decreases, resulting in the enhancement of solute trapping. Moreover, the simulated solute segregation coefficients in Al-0.2 at.% Sn can nicely reproduce the experimental data.

Abstract: Al-11%Si (-0.44%Fe-0.16%Cu-0.14%Mg) was cast into the strip using a vertical type high speed twin roll caster at speed of 60m/min. Cooling rate of the strip was ranging from 2000^OC/s at surface to 1000^OC/s at center of thickness. The eutectic Si was smaller than 2μm. The homogenization, cold rolling down to 1mm, and annealing were carried out before the tension test, 180 degrees bending test and deep drawing test. Tensile stress was 192MPa, 0.2%proof stress was 84MPa, and elongation was 23.8%. Roll cast Al-11%Si had excellent elongation. The specimen was not broken by the 180 degree bending. LDR (Limiting Drawing Ratio) of the deep drawing test was 1.8. The ductility was drastically improved by the high speed twin roll caster. These results show that roll cast Al-11%Si has ability to be used for sheet forming. Moreover, Fe was increased up to 1.0% as the model of recycled alloy. The elongation was 15.9% and LDR was 1.7 in the condition that Fe content was 1.0%. Al-Si-Fe intermetallic became fine by the effect of rapid solidification. As the result, deterioration of the ductility was improved.

Abstract: This study investigates the precipitation behavior of two similar cast Al-Mg-Sc-Zr alloys with different solidification and cooling rates. Microstructural analyses and hardness testing were performed after casting and ageing. In addition, the precipitation and hardness evolution after rapid quenching using electron beam re-solidification were studied. It was shown that the amount of Al₃(Sc,Zr) phases present after casting or re-solidification increases with decreasing solidification and cooling rate. Consequently, the degree of supersaturation in Sc and Zr at room temperature and thus the hardening potential in a subsequent ageing process increases with the solidification and cooling rate. Therefore, the electron beam re-solidified samples revealed the most pronounced hardening.

Abstract: RETRACTED PAPER: High entropy alloys have attracted great interest due to their flexibility in composition accompanied with very interesting properties, which make these materials candidates for further research. The formation of single solid solution phases as a preference to complex mixtures of intermetallic phases leads to good mechanical and thermal properties. Additive manufacturing in the form of Laser deposition presents us with a very unique way to manufacture near net shape metallic components with advanced materials. The present study focusses on the characterization of High entropy alloys manufactured through laser deposition. The alloy system considered for this study is (AlFeCoCrNi). The ratio of aluminum to nickel was decreased to observe the transition of the solid solution from a BCC structure to a FCC structure. The lattice parameter increased from .288 nm to .357 nm and the hardness decreased from Hv 670 to Hv 149 respectively. The effect of composition on thermodynamic variables, microstructure and mechanical properties were analyzed.