Formation Of Equiaxed Crystals Research Articles

Simulation of the solidification organization of X15CrNiSi20-12 alloy castings during investment casting based on the CAFE model

In this work, the CAFE (Cellular Automata Finite Element) model was used to simulate the grain growth of X15CrNiSi20-12 austenitic stainless steel during the investment casting process, and the effects of shell thickness, shell temperature, casting temperature, and cooling rate on the solidification organization were investigated by orthogonal tests. The results show that the cooling method has an important effect on the formation of equiaxed crystals. However, the shell temperature, shell thickness, and casting temperature have a smaller effect on the formation of equiaxed crystals. A more equiaxed fine grain structure can be obtained by using a shell thickness of 7 mm, shell temperature of 1143.15 K, casting temperature of 1913.15 K, and water-cooling conditions. In addition, a decrease in the shell thickness, shell temperature, and casting temperature can lead to an increase in the grain size, while an increase in the cooling rate will lead to smaller grain size and increase the number of equiaxed fine crystals, thus improving the mechanical properties of the material.

Mechanism of Electromagnetic Field in the Sub-RapidSolidification of High-Strength Al-Cu-Li Alloy Produced by Twin-Roll Casting

In this work, a Al-Cu-Li alloy plate with outstanding mechanical properties was successfully prepared with electromagnetic twin-roll casting (TRC) technology. The microstructure of Al-Cu-Li alloy manufactured by conventional mold casting, TRC, and electromagnetic TRC was studied in detail. The action mechanism of electromagnetic oscillation field (EOF) in the TRC process was studied by systematic experimental characterization and numerical simulation. The results show that the EOF will enlarge the circumfluence area in the cast-rolling zone, accelerate the mass transfer and heat transfer in the molten pool, and make the solute field and flow field in the liquid cavity tend to be evenly distributed. Further, the introduction of the EOF will produce the electromagnetic body force F with the maximum strength of 14 N/m3. The F acting on the solidification front will eliminate the accumulation and deposition of Cu2+, Li+, Mg2+, Zn2+, Mn2+ at the dendrite tip and inhibit the growth of dendrites. At the same time, the F can refine the microstructure of the TRC plate, promote the formation of equiaxed crystals, improve the supersaturated solid solubility of solute elements in the α(Al) matrix, and avoid the appearance of obvious solute segregation area or the formation of excessive solute enrichment area. Therefore, the macro-segregation in TRC plate was significantly reduced, the solidification structure was dramatically refined, and the comprehensive properties of the alloy were remarkably improved.

Study of Structure and Properties of Fe-Based Amorphous Ribbons after Pulsed Laser Interference Heating

The paper is devoted to the study of microstructural and magnetic properties of the Fe-based amorphous ribbons after interference pulsed laser heating. The ternary amorphous alloy FeSiB, as well as the multi-component alloys FeCuSiB and FeCuNbSiB, was subjected to laser pulses to induce crystallization in many microislands simultaneously. Structure and properties changes occurred in laser-heated dots. Detailed TEM analysis from a single dot shows the presence of FeSi(α) nanocrystals in the amorphous matrix. The FeSiB alloy is characterized after conventional crystallization by a dendritic structure; however, the alloys with copper as well copper and niobium additions are characterized by the formation of equiaxed crystals in the amorphous matrix. Amorphous alloys before and after the laser heating are soft magnetic; however, conventional crystallization leads to a deterioration of the soft magnetic properties of the material.

Improvement of Dielectric Breakdown Strength in (1-x)Sr<sub>0.7</sub>Ba<sub>0.3</sub>Nb<sub>2</sub>O<sub>6</sub>-xSr<sub>0.7</sub>Bi<sub>0.2</sub>TiO<sub>3</sub> Ceramics

In this work, a series of (1-x)Sr0.7Ba0.3Nb2O6-xSr0.7Bi0.2TiO3 ceramics were formulated by a phase-mixed sintering, the microstructure and energy storage performance were studied. The introduction of SBT induces the formation of equiaxed crystals leading to the denser microstructure, thus improving the dielectric breakdown strength. In addition, the enhancement of relaxor behavior improves the energy storage performance. For 0.94Sr0.7Ba0.3Nb2O6-0.06Sr0.7Bi0.2TiO3, an energy storage density of 0.49J/cm3 and an efficiency of 94.2% were achieved.

The Formation Mechanism of Equiaxed Crystals in Pure Aluminum Solidification Structure under the Al-Ti-C Master Alloy

The influence of different solidified velocities on the structure of pure aluminum during the process of refinement by Al-5Ti-0.6C master alloy was studied and the impact mechanism was discussed. The results show that at the same solidified velocity, with the increase of the amount of Al-5Ti-0.6C master alloy, in the solidified structure of pure aluminum, columnar crystals will gradually decrease, while equiaxed crystals will gradually increase. But in the case when the level of addition is the same, the faster the solidified velocity, the greater the number of equiaxed crystals will be in the ingot microstructure. The formation of equiaxed crystals is the result of the dual role of dissociation of crystal particles and heterogeneous nucleation of “TiC particle---Ti transition zone”.

Modeling of Columnar-to-Equiaxed Transition in Solidified Al-Si Alloys

A Cellular-Automaton Finite-Volume-Method (CAFVM) algorithm has been developed, coupling with macroscopic model for heat transfer calculation and microscopic models for nucleation and growth. The solution equations have been solved to determine the timedependent constitutional undercooling and interface retardation during solidification. The constitutional undercooling is then coupled into the CAFVM algorithm to investigate both the effects of thermal and constitutional undercooling on columnar growth and crystal selection in the columnar zone, and formation of equiaxed crystals in the bulk liquid. The model cannot only simulate microstructures of alloys but also investigates nucleation mechanisms and growth kinetics of alloys solidified with various solute concentrations and solidification morphologies.

等軸晶の生成について

等軸晶の生成について

Metallography of aluminum and it's alloys solidified under high hydrostatic pressure

This paper reports macroscopic and microscopic metallography of aluminum and its alloys solidified in a cylindrical die under high hydrostatic pressure of 1000-6000kg/cm2.When the pressure was applied at 50-60°C higher than the melting temperature, columnar crystals, which had originated on the surface of die, easily developed towards the center of die, although other conditions were selected to allow the formation of equi-axed crystals under normal pressure. Less superheating, on the other hand, often generated a center zone of equi-axed crystals, and the zone was wider with the increase of pressure. Preferential linear growth of dendrite stems in columnar zone remarkably occurred under high pressure, and exclusion of solute to liquid side of solid/liquid interface was facilitated by the application of high pressure. It resulted in normal segregation in aluminum-silicon and aluminum-copper alloys. When the pressure was constant and the temperature at which pressure was applied was lower, the equiaxed zone was wider, and the crystals were finer by the effects of undercooling (accompanied by the rise of the melting temperature) and rapid cooling. It was found that pure aluminum solidified at 11°C higher than normal melting temperature under applied pressure of 1500kg/cm2.