Solid State Phenomena Vol. 330

Abstract: Based on the theory of grain refinement, the microstructures and simulations of A356 semi-solid aluminum alloy under different cooling mediums were studied. The experiment and simulation results show that water cooling is better than any other cooling mediums. Combined with the simulation of stirring and heat dissipation in SIT device, the changes of temperature field and solid fraction of the melt were studied to help understand the nucleation, growth and solidification behavior under the SIT process. During the process, the temperature field of the melt becomes relatively uniform from a larger temperature gradient and the continuous cooling speed is increased. The results also indicate that compared with traditional casting, the microstructure cooled by water are composed of refined rosiness and nearly spherical particles. With the increase of cooling degree, the average grain size decreased from 206μm to 186μm. The solid fraction increases from 4.4% to 12.2% under the no-cooling and air-cooling conditions, while it is more uniform, increasing from 5.1% to 8.8% due to the water cooling.

Abstract: The relation between the annealing temperature dependence of the structural inhomogeneity and the diffusion coefficient in a metallic glass forming system Zr-Ti-Cu-Ni-Be is studied by using reported experimental data. It is shown that the diffusion coefficient increases with the increase of the correlation length of the structural inhomogeneity. Interestingly, the result found resembles the behavior known in superionic glasses. A discussion on the found relationship is given by exploiting the model for the superionic glasses proposed by the author. Based on the model, an inhomogeneity dependent diffusivity maximum is predicted.

Abstract: This article reviews the research methods and research progress of metal melt structures at home and abroad in recent years. Through liquid XRD, synchrotron radiation X-ray diffraction experiments, X-ray fine structure absorption spectroscopy, sensitive physical property testing and other experimental methods, as well as computer simulations, a lot of information about the structure of metal melts has been obtained. These studies are liquid-solid The structural transformation, the improvement of alloy structure and performance, and the preparation of amorphous provide theoretical guidance.

Abstract: The solid-liquid mixture of Al-5Fe-xRE alloy is "frozen" through rapid cooling technology to prepare solid samples (the weight percentage of Rare Earth Ce added in x: 0%, 0.9%, and 5%). The effect of Ce on the growth of primary Al₁₃Fe₄ phase is studied by means of differential scanning calorimetry (DSC) and field emission transmission electron microscopy (TEM).The results show that with the increase in the amount of Ce in the alloy, the transition temperature of the primary Al₁₃Fe₄ phase increases. The addition of Ce changes the crystallization process of the primary phase. When Al-5Fe-xRE alloy is rapidly cooled at 690°C, the primary phase interface of Al-5Fe-5Ce alloy has more Rare Earth enrichment than that of Al-5Fe-0.9Ce alloy. However, the primary phase of Al-5Fe-5Ce alloy is still relatively coarse. Obviously, excessive Ce does not play a role in modification, so the enrichment of Ce at the interface may not be the main reason for refining the primary iron-rich phase When the Al-5Fe-5Ce alloy is rapidly cooled at 750°C and 690°C, respectively, the Ce at the interface tends to increase. The enrichment area of Ce forms a "film" at the interface of the primary phase, and then it transform into Al₈CeFe₂ phase after solidification. The interface structure of the primary and Al₈CeFe₂ is semi-coherent.

Abstract: Utilizing the common sheet metal forming method has many challenges in the field of sheet metal forming. Higher product quality with the lower quantities is an important requirement in this manufacturing field. The incremental forming process (IPF) is an innovation technology that can satisfy these requirements. In this paper, the single point incremental forming (SPIF) with different roller ball tool was researched. The results show that the smaller ball could provide a better product quality. However, the bigger ball could create a deeper geometry

Abstract: This article introduces four rubber-pad formation techniques for the pressing and drawing of components from thin sheet metals. The Guerin process is the simplest technique of rubber formation, which enables the production of shallow sheet metal parts with complex contours and bends. Free formation is another technique used to draw near-hemispherical shells using a rubber medium. Different bending processes can also be conducted using a rubber pad as a flexible die. Multipoint formation is applied to form complex three-dimensional sheet metal parts with discrete dies and rubber cushions. The fundamentals of these techniques as well as the influence of process parameters on the results are investigated in this paper

Abstract: In this paper the issues of modeling the process of forming sheet materials using method of incremental forming for the manufacture of thin-walled non-axisymmetric parts. The proposed method of forming implemented by deformation of sheet material by providing the required trajectory of movement of the working tool in order to obtain the surface of a product of a given shape. Simulation and analysis of all experiment results are carried out.

Abstract: To pertinently balance growth kinetics, solidification thermodynamics and dendrite expitaxy of multicomponent nickel-based single-crystal supralloy during laser processing, effect of thermometallurgy determinant factors, including laser power, welding speed and welding configuration, on solidification behavior, such as nonequilibrium solidification temperature range, and dendrite growth, such as dendrite trunk spacing, are progressively advanced to forestall solidification cracking phenomena. Symmetric developments of dendrite trunk spacing and solidification temperature range alongside solid/liquid interface are crystallographically driven by useful (001)/[100] welding configuration to auspiciously bring about crack-insusceptible and well-oriented dendrite growth. Dissimilarly, unsymmetrical developments of dendrite trunk spacing and solidification temperature range alongside solid/liquid interface are crystallographically driven by (001)/[110] welding configuration to insidiously favor crack-unresistant and disoriented dendrite growth. Higher heat input thermodynamically and kinetically boosts wide solidification temperature range, appalling stray grain growth with excess of solute ahead of dendrite tip and large size of crack-unresistant region to thermometallurgically disintegrate epitaxial growth for untoward solidification cracking, and therefore should be strictly withstood. Although geometry of symmetrical weld pool both sides is the same in infelicitous (001)/[110] welding configuration, [100] region of dendrite growth is more liable to ruinous stray grain growth and extensive solidification temperature range than [010] region of dendrite growth to complicate dendrite growth and exacerbate weld integrity. The determinant mechanism of crystallography-aided amelioration of solidification cracking resistance as result of kinetics-and thermodynamics-driven dendrite growth is propitiously proposed. Furthermore, the credible and understandable theoretical predictions are in conformity with the experiment results.

Abstract: The effect of thermo-metallurgical factors, such as heat input and welding configuration, on solidification cracking driving forces nearby dendrite tip, such as solidification temperature range and columnar/equiaxed transition (CET) was thermodynamically and kinetically discussed with aid of comprehensive numerical analysis for multicomponent melt-pool solidification during laser processing under non-equilibrium solidification conditions to better understand problematical solidification cracking phenomena. By using (001)/[100] welding configuration, axisymmetrical distributions of columnar/equiaxed transition and solidification temperature range alongside solidification interface are homogeneously produced on both sides of weld pool. By using (001)/[110] welding configuration, nonaxisymmetrical distributions are heterogeneously produced, and are able to bring about infelicitous microstructure degradation. Unidirectional region of [001] columnar dendrite is more prone to epitaxial growth without morphology transition to conservatively better crystallography-assisted single-crystal growth. Unidirectional epitaxial growth is collapsed, and onset of stray grain nucleation and solidification cracking eventuates in [100] region of equiaxed dendrite growth. Low heat input relatively broadens portion of unidirectional columnar dendrite, where stray grain is infrequently nucleated and grown, and thus morphology transition seldom happens, as long as undercooling and solidification temperature range alongside dendrite tip are sufficient low to challengingly develop crackless dendrite growth and high-quality weld by thermometallurgy-aided single-crystallinity control. Auspicious (001)/[100] welding configuration simultaneously abates overall stray grain nucleation and constricts solidification temperature range nearby fusion boundary to wane microstructure heterogeneity. Conversely, plenteous stray grain formation is kinetically attained and extensive solidification temperature range nearby fusion boundary is thermodynamically obtained by problematical (001)/[110] welding configuration to metallurgically induce pernicious equiaxed dendrite and disintegrate dendrite growth. Moreover, the mechanism of solidification cracking diminution as consequence of appropriate optimization of thermo-metallurgical determinants during multicomponent nickel-based single-crystal superalloy melt-pool non-equilibrium solidification is also proposed. The potent consistency between the predicted and experimented results is exceedingly tenable.