Directional Solidification Device Research Articles

Recent progress on apparatus development and in situ observation of metal solidification processes via synchrotron radiation X-ray imaging: A review

The solidification process of metals plays a critical role in their final microstructure and, correspondingly, in their performance. It is therefore important to probe the solidification behavior of metals using advanced in situ techniques. Synchrotron radiation X-ray imaging is one of the most powerful techniques to observe the solidification process of metals directly. Here, we review the development of the solidification apparatus, including the directional solidification device, resistance furnace, multi-field coupling device, semisolid forming device, aerodynamic levitation apparatus, and laser additive manufacturing apparatus. We highlight the recent research progress on the use of synchrotron radiation X-ray imaging to reveal the solidification behavior of metals in the above circumstances. The future perspectives of synchrotron radiation X-ray imaging in metal research are discussed. Further development of this technique will contribute to improve the understanding of the solidification process of metals and other types of materials at different scales.

Solidification thermal parameters, microstructural evolution and dendritic growth in an AlCuNi alloy

ABSTRACT Unsteady-state upward solidification experiment was carried out with the Al-3Cu-3Ni (wt.%) alloy. Temperature profiles were obtained through a water-cooled directional solidification device. Analysis on the resulting as-cast microstructure and its adaptation to thermal solidification parameter, such as growth and cooling rates and solidification local time, VL, TR and tSL, respectively, was carried out. The results showed that the resulting microstructure is constituted by an Al-rich primary phase (Al α ), characterised by a dendritic network, and by second phases that take place within the interdendritic regions, forming a eutectic mixture composed by the β-Al3Ni + θ-Al2Cu intermetallic compounds (IMCs), whose size and morphology have been affected by VL and TR. The length of the microstructural scale of the Al α phase was measured by the secondary dendritic spacing (λ 2). The experimental mathematical expression of λ 2 obtained in this work was compared with mathematical models proposed in the literature that associate tSL-λ 2 for non-equilibrium and equilibrium solidification conditions.

Study of Dry Wear Behavior and Resistance in Samples of a Horizontally Solidified and T6/Heat-Treated Automotive AlSiMg Alloy

To investigate dry wear behavior in an aluminum-based automotive alloy, transient horizontal solidification experiments using a water-cooled directional solidification device have been performed with the Al7Si0.3Mg alloy (wt%). Samples of the as-cast ingot at positions (P) 2, 4, 6, 40, and 80 mm from the cooled interface were subjected to precipitation hardening heat treatment (T6-type). The heat treatment has been applied under the following conditions: solution treatment for 3 h at 520 ± 2 °C, followed by quenching in warm water (70 ± 2 °C), aging for 3 h at 155 ± 2 °C and air-cooling. Dry wear tests were performed on both the as-cast and heat-treated samples. The wear tests were carried out by rotary-fixed ball wear machine means. The analyzed parameters were solidification growth and cooling rates (VL and TR), secondary dendritic spacings (λ2), and wear volume and rate (WV and WR). An interrelation between these parameters has been conducted and experimental mathematical equations have been proposed to characterize the WV and WR dependence on P, VL, TR and λ2. The T6-heat treatment has affected the length of the as-cast dendritic scale, increasing the λ2 values as well as the wear features of the investigated automotive alloy. Finer and coarser dendritic microstructures inherited better wear resistance for the as-cast and heat-treated samples, respectively. An evaluation by occupied area fraction (%IRAF) of interdendritic regions on wear resistance in the as-cast and heat-treated samples has been performed. It has been observed higher and lower IRAF values in the as-cast and heat-treated samples, respectively.

Effect of solidification process parameters on dry sliding wear behavior of AlNiBi alloy

Abstract As-cast samples of the Al–3wt.%Ni–1wt.%Bi alloy resulting from the horizontal directional solidification process were subjected to the micro-abrasive wear test. The effects of the solidification thermal and microstructural parameters, such as the growth and cooling rates and the cellular and primary dendritic spacings (VL and TR; λ1 and λc; respectively), were evaluated in the wear resistance of the investigated alloy. The tribological parameters analyzed were the wear volume and rate (Vw and Rw). The solidification experiments and the wear tests were carried out by means of a water-cooled horizontal directional solidification device and a rotary-fixed ball wear machine, respectively. The results show lower Vw and Rw values correspond to finer microstructures and the Vw dependence on λ1 is characterized by an experimental mathematical equation. A better distribution of Bi soft droplets and Al3Ni hard intermetallic particles is observed within the finer interdendritic region and, in consequence, the better wear resistance is achieved in as-cast samples with dendritic morphology rather than cellular morphology. A transition of wear mechanism from adhesive to abrasive is observed.

Tailoring of Processing Parameters, Dendritic Microstructure, Si/Intermetallic Particles and Microhardness in As-cast and Heat-Treated Samples of Al7Si0.3Mg Alloy

In this work, solidification and T6-heat treatment experiments were performed with the Al7Si0.3Mg alloy in order to investigate the effect of processes parameters on the microstructure and microhardness (HV). A directional solidification device was used, and the solidification thermal parameters investigated were the growth and cooling rates (VL and TR). The heat treatment applied was the T6 (T6-HT), under the following conditions: solution treatment for 3 h at 520????????2 ??C, followed by quenching in warm water (70????????20 ??C), aging for 1, 2, 3 and 4 h at 155????????2 ??C and air-cooling. The microstructure observed in both as-cast and T6-heat treated samples is composed of a primary phase consisting of an Al-rich dendritic network and secondary eutectic phases, located within the interdendritic regions, formed by Si and Mg2Si particles and Fe-intermetallic phases. The dendritic microstructure was characterized by secondary dendritic spacing (??2) and, for both investigated samples, a single mathematical expression was proposed on the ??2 dependence with the position in the ingot. Spheroidized-like eutectic Si particles have been found in both analyzed samples for finer microstructures. Elements quantitative and qualitative microanalysis by SEM/EDS as well as HV measurement at the dendritic and interdendritic regions attest to the effectiveness of the T6-heat treatment. It is highlighted in this work that mathematical expressions have been proposed to characterize the HV dependence on aging time.

Traveling Waves Induced by Sweeping Flows on Solidification Interfaces

Solidification of alloys in a thermal gradient usually involves the generation of flows by thermal or thermosolutal convection. We experimentally study their effects on the dynamics of a solidification interface by inducing a controlled sweeping flow in a directional solidification device. Flow is induced in the sample from an external thermosiphon. Downstream inclination of microstructures and downstream sidebranch development are observed. However, the major outcome is the evidence of large scale travelling waves on the solidification interface. They are induced by the coupling between solidification and flow and yield repetitive striations of the solid phase. Two waves are observed and characterized.

Microstructural Development of an AlNiBi Alloy and Influence of the Transient Horizontal Solidification Parameters on Microhardness

The combination of the structural and tribological properties presented by AlNiBi alloys has motivated us to establish, as the main objective of this study, the investigation of the microstructural evolution and its influence on the microhardness (HV) of Al-3wt pct Ni-1wt pct Bi alloy horizontally solidified via a water-cooled directional solidification device. Temperature mapping by thermocouples inserted in the metal has been performed for experimental determination of the solidification thermal parameters, such as the growth rate and cooling rate (VL and TR, respectively). The microstructure has been characterized by optical and scanning electron microscopy and by microanalysis of the composition via dispersive energy spectroscopy (EDS composition). The macrostructure of the as-solidified ingot is characterized by columnar grains, and the final microstructure consists of an Al-rich primary phase (α-Al) and a eutectic mixture composed of two phases: α-Al + Al3Ni intermetallic (β) with Bi particles anchored on the β phase. The Bi droplet scale is affected by the thermal parameters. The primary phase (α-Al) is characterized by a reverse cellular-to-dendritic microstructural transition. Cellular and dendritic microstructures have been quantified by the cell, primary dendrite arm, secondary dendrite arm, and tertiary dendrite arm spacings (λC, λ1, λ2, and λ3, respectively). The relationships of λC, λ1, λ2, and λ3 with VL and TR have been established via power-type mathematical expressions. The HV dependence on λC, λ1, λ2, and λ3 has been analyzed in both cellular and dendritic microstructural zones. It has been observed that the HV values do not vary in the dendritic zone; however, Hall–Petch’s mathematical equations characterize the HV variation with these thermal and microstructural parameters in the cellular zone.

Microstructural evolution during unsteady-state horizontal solidification of Al-Si-Mg (356) alloy

Abstract The increasing demand for reducing vehicle weight in the automotive and aerospace industries has raised the need to develop improved structural aluminum-based alloys. Thus, horizontal solidification experiment with the Al-7%Si-0.3%Mg (mass fraction) alloy was carried out. A water-cooled horizontal directional solidification device was developed and used. Microstructural characterization was carried out using traditional techniques of metallography, optical microscopy and SEM microscopy. The Thermo-Calc software was used to generate the solidification path of the investigated alloy with addition of 0.17% Fe (mass fraction). The effects of the thermal parameters such as the growth rate (VL), cooling rate (TC) and solidification local time (tSL) on the formation of the macrostructure and on the dendritic microstructure evolution were evaluated. A columnar to equiaxed transition (CET) was found for VL and TC values from 0.82 to 0.98 mm/s and from 1.71 to 2.55 °C/s, respectively. The microstructure was characterized by the measurement of the primary and secondary dendrite arm spacings (λ1 and λ2, respectively). Experimental laws of λ1 =f(VL, TC) and λ2 =f(tSL) were proposed. It is observed that the interdendritic region is composed of the following eutectic mixture: α(Al)+Si+π-Al8Mg3FeSi6+θ-Mg2Si.

Effect of the T6 Heat Treatment on Microhardness of a Directionally Solidified Aluminum-Based 319 Alloy

Aluminum alloys of the ANSI series 319 present Si and Cu as the main alloying elements and the mechanical strength of these alloys can be improved by the precipitation of the metastable Al2Cu phase during the ageing heat treatment. In this paper, the Al-5.5wt.%Si-3wt.%Cu alloy was elaborated and solidified in a water-cooled horizontal directional solidification device. The as-cast ingot was subjected to the precipitation hardening heat treatment (T6 heat treatment), which consisted of: solution for 5 h at 490°C±2°C, followed by quenching in water at 60°C±2°C and ageing for 3 h at 155°C±2°C, and cooling-air. Secondary dendrite arm spacing (λ2) measurements were carried out before and after T6 heat treatment. The mechanical strength of the alloy was investigated by the microhardness test. It has been found that the heat treatment did not influence the λ2 values, however, highest HV values have been observed for the heat-treated samples.

Modelling analysis and experiments of polycrystalline silicon directional solidification in an annular heating field

Abstract As a solution to the low convection strength of the Bridgman method and the convection control difficulties of the electromagnetic induction melting method, a novel, large directional solidification device with annular heaters arranged above the crucible is designed. The inhomogeneous heating field causes differences in melt density, intensifies controllable natural convection and accelerates the moving of impurities from the solid–liquid interface to the surface of the melt, thereby improving purification efficiency and reducing energy consumption. Although the temperature field is inhomogeneous, vertical crystal growth can still be achieved. Mathematical analytic modelling is used to explain the principle, and the feasibility is verified by experiments. The results show that high-quality and large bulk silicon ingot (1 m × 1 m × 0.45 m) can be produced at an average solidification rate of 3.68 μm s−1.

The Role of Si and Cu Alloying Elements on the Dendritic Growth and Microhardness in Horizontally Solidified Binary and Multicomponent Aluminum-Based Alloys

Horizontal directional solidification (HDS) experiments were carried out with Al-3wtpctCu, Al-3wtpctSi, and Al- 3wtpctCu-5.5wtpctSi alloys in order to analyze the interrelation between the secondary dendrite arm spacing (λ 2) and microhardness (HV). A water-cooled horizontal directional solidification device was applied. Microstructural characterization has been carried out using traditional techniques of metallography, optical, and SEM microscopy. The ThermoCalc software was used to generate the phase equilibrium diagrams as a function of Cu and Si for the analyzed alloys. The effects of Si and Cu elements on the λ 2 and HV evolution of the hypoeutectic binary Al-Cu and Al-Si alloys have been analyzed as well as the addition of Si in the formation of ternary Al-Cu-Si alloy. The secondary dendrite arm spacing was correlated with local solidification thermal parameters such as growth rate (V L), cooling rate (T R), and local solidification time (t SL). This has allowed to observe that power experimental functions given by λ 2 = Constant (V L)−2/3, λ 2 = Constant (T R)−1/3 and λ 2 = Constant (t SL)1/3 may represent growth laws of λ 2 with corresponding thermal parameters for investigated alloys. Hall–Petch equations have also been used to characterize the dependence of HV with λ 2. A comparative analysis is performed between λ 2 experimental values obtained in this study for Al-3wtpctCu-5.5wtpctSi alloy and the only theoretical model from the literature that has been proposed to predict the λ 2 growth in multicomponent alloys. Comparisons with literature results for upward directional solidification were also performed.

Interconnection between microstructure and microhardness of directionally solidified binary Al-6wt.%Cu and multicomponent Al-6wt.%Cu-8wt.%Si alloys.

An experimental study has been carried out to evaluate the microstructural and microhardness evolution on the directionally solidified binary Al-Cu and multicomponent Al-Cu-Si alloys and the influence of Si alloying. For this purpose specimens of Al-6wt.%Cu and Al-6wt.%Cu-8wt.%Si alloys were prepared and directionally solidified under transient conditions of heat extraction. A water-cooled horizontal directional solidification device was applied. A comprehensive characterization is performed including experimental dendrite tip growth rates (VL) and cooling rates (TR) by measuring Vickers microhardness (HV), optical microscopy and scanning electron microscopy with microanalysis performed by energy dispersive spectrometry (SEM-EDS). The results show, for both studied alloys, the increasing of TR and VL reduced the primary dendrite arm spacing (l1) increasing the microhardness. Furthermore, the incorporation of Si in Al-6wt.%Cu alloy to form the Al-6wt.%Cu-8wt.%Si alloy influenced significantly the microstructure and consequently the microhardness but did not affect the primary dendritic growth law. An analysis on the formation of the columnar to equiaxed transition (CET) is also performed and the results show that the occurrence of CET is not sharp, i.e., the CET in both cases occurs in a zone rather than in a parallel plane to the chill wall, where both columnar and equiaxed grains are be able to exist.

Corrosion and wear resistance of hypoeutectic Zn–Al alloys as a function of structural features

The aim of the present research was to investigate the role of the type of grain macrostructure (columnar, columnar-to-equiaxed transition–CET -, and equiaxed) and microstructure (secondary dendrite arm spacing - λ2) in the wear and electrochemical behavior of hypereutectic Zn–Al alloys (Zn-1wt%Al, Zn-2wt%Al, Zn-3wt%Al and Zn-4wt%Al) directionally solidified in a vertical upward directional solidification device. We also aimed to, correlate the thermal parameters with the electrochemical and wear properties. The results obtained in this alloy system indicate that the corrosion resistance decreases as the concentration of aluminum increases, but that at the highest concentrations (near the eutectic concentration) this resistance depends on the structure. For the same wear conditions, the wear rate of the equiaxed region is lower than the columnar and transition regions. Independently of the type of structure, wear resistance increases as the aluminum concentration increases.For each alloy concentration, the wear resistance increases from the columnar to the equiaxed structure. A clear inverse relation is observed between the wear resistance and λ2, which may explain the increase in wear resistance in the equiaxed region. At low spacings, the wear rate converges to a single value.

Nucleation and growth of high purity aluminum grains in directional solidification bulk sample without electromagnetic stirring

Abstract A self-made directional solidification device was used to fabricate d80 mm high purity aluminum ingots. SEM and AFM were used to detect the shape of grain boundaries. The orientation of the grain was studied by X-ray diffractometry. The results show that the nucleation points locate at the intersections of three adjacent grains. The lattice orientation of grains does not alter in the horizontal direction, but gradually approaches the optimum growth direction in the vertical direction during the growth process. All the grains suffer the competition and only the one whose orientation is closest to the preferred direction can occupy the final growth space.

Development of a Directional Solidification Device for Cell Cryopreservation

The objective of this study was to develop a reliable, low-cost, and practical directional solidification device (DSD) for cryopreservation of biological cells and tissues. In this study, a linear temperature distribution was established in an aluminum block between a higher temperature source (Th = -5 to 30°C) and a lower temperature sink (Tc = -60 to -85°C). Liquid nitrogen vapor was used to maintain Tc. Two cartridge-heaters were used to maintain Th. Various cryopreservation media (with glycerol, ranging from 0 to 4 M) were placed in long-cylindrical plastic straws (0.5 mL in volume, 2 mm in outer diameter, 150 mm in length, 0.02 mm in wall thickness). The straws were pushed (through a cylindrical channel in the block) from the warm end of the block (Th) to the cold end (Tc) at a constant speed to achieve a corresponding constant cooling rate (up to -200°C/min depending on the speed and the source/sink temperatures). Thermocouples were used to measure/monitor temperature distributions in both the block...

Investigation on the formation of the preferred orientations in a TbDyFe alloy with directional solidification

The formation of the preferred orientations in a TbDyFe alloy was studied by transmission electron microscopy (TEM). It was found that there were several different preferred orientations in the experimental TbDyFe alloy with directional solidification. 〈110〉, 〈112〉 and 〈113〉 preferred orientations were observed in this alloy solidified by our self-made super high gradient temperature directional solidification device. The preferred orientations changed with the variation of the solidification conditions. Two {111} twinning systems resulted in the 〈110〉 preferred orientation and a single {111} twinning system resulted in the 〈112〉 preferred orientation. The twinning displacement was observed and this formatted the 〈113〉 preferred orientation.