Directional Solidification Technique Research Articles

Effect of Ce and solidification cooling rate on the microstructure and mechanical properties of AA2017 aluminum alloy

Controlling dendritic growth and grain size in new Ce-containing Al-based alloys becomes crucial due to new envisioned applications and Ce rising demand in casting processes. In the present work Ce effect on the 2xxx Al series microstructures at various industrial-scale solidification cooling rates was investigated. The directional solidification technique is crucial in this endeavor since can generate several solidified samples related to several cooling rates. The AA2017 alloy and a modified version containing 3wt.% of Ce were both produced under directional solidification and various microstructure aspects were characterized. The mechanical behavior was analyzed by microhardness and compression tests. The Ce addition reduced primary and secondary dendritic spacing without impacting grain size. Cells were only observed to form on the Ce-containing alloy at cooling rates of approximately 19°C/s; while dendritic configurations dominated all other conditions. While round pockets composed of Al+Al2Cu+Mg2Si ternary eutectic formed the interdendritic zones in the AA2017 alloy, the AA2017-Ce alloy microstructure was mainly constituted by elongated AlCeSi + Al8CeCu4 interdendritic phases. Finally, the addition of Ce favored an increase in the microhardness and compressive strength values of the AA2017 alloy, which is attributed to the refinement of the solidification structure, as well as the formation of a greater fraction of secondary reinforcement phases.

Compressive Property and Toughening Mechanism of Directionally Solidified Fe(Al, Ta)/Fe2Ta (Al) Eutectic Composites

In present study Fe(Al, Ta)/Fe2Ta(Al) eutectic composites were prepared using the electron beam floating zone melting directional solidification technique. The compression and fracture toughness properties of Fe(Al, Ta)/Fe2Ta(Al) eutectic composites at different solidification rates were studied with compression and three‐point bending experiments. The toughening mechanism of the material was also analyzed from morphology, composition and microstructure. The results show that the yield strength and compression properties of the Fe(Al, Ta)/Fe2Ta(Al) eutectic composite are increased with the increase of the solidification rate. The room temperature fracture toughness reaches 30.5 MPa·m1/2 when the solidification rate is 4 mm/min. In addition, the material exhibits high strength performance at room temperature. However, it exhibits poor strength and excellent plasticity due to the softening effect of recrystallization at 600°C. The toughening mechanism of the Fe(Al,Ta)/Fe2Ta(Al) eutectic composites can be summarized as crack blunting, crack branching, crack deflection, and local deformation.This article is protected by copyright. All rights reserved.

Featuring vertical channel structure through directional solidification method to endow GNP-aerogels with enhanced ultra-electromagnetic wave absorption

Three-dimensional (3D) carbon-based electromagnetic waves absorbing materials (EWAMs) have garnered significant attention due to high electrical conductivity, high dielectric loss, low density, and improved characterization of impedance matching. However, there is a paucity of research on the design of material structures. In this regard, we proposed the graphene nanoplates (GNPs) EWAMs featuring a vertically aligned channel structure through liquid nitrogen rapid directional solidification and freeze-drying techniques. By utilizing methyl cellulose (MC) as a binder to modify the internal ice crystal structure, an exceptional electromagnetic waves (EWs) absorption material exhibiting excellent impedance matching characteristics and demonstrating multiple polarization phenomena were created. Notably, the material showcased superior absorption performance with a minimal reflection loss (RLmin) of −57.20 dB. Furthermore, the pre-solidification slurry possesses remarkable plasticity, facilitating the fabrication of various complex structures for EWAMs during directional solidification. This method provides novel insights for future exploration and fabrication of tuneable frequency band EWAMs.

Application of Ni-based superalloy in aero turbine blade: A review

A superalloy is a high-performance alloy used for achieving stability and strength at elevated temperatures. Generally, a temperature of about 800°C is developed at the first stage of the aero turbine blade. So it is a challenge to choose a material that can withstand such high temperatures. Nowadays advanced generation single crystal Ni-based superalloys are being used for the fulfillment of high-temperature requirements in aero turbine components. But the continuous effort is being carried out to manufacture new materials that can withstand more and more temperatures generated at aero turbine because the high-temperature operation of the turbine is directly proportional to the efficiency of a turbine engine. The requirement of high-temperature application upgraded the Ni-based superalloy and different generations of alloys were prepared from time to time those were discussed in the paper. Recent developments of superalloys in the paper mainly include fifth and sixth generations of superalloys those incorporate Hf, Re, and Ru-like elements in significant amounts. A brief extension discussion has been placed on the types, processing, and hot deformation characteristics of Ni-based superalloys. VIM melting, single crystal growth, directional solidification, and powder metallurgy techniques for manufacturing Ni-based superalloys are discussed in detail. The strengthening mechanism and machinability behavior depict the characteristics of superalloys in a mechanical direction. Heat treatment and hot deformation behavior of Ni-based superalloy was precisely discussed in the context so as to correlate the strength of the material with the temperature change. Overall, the paper describes the origin, processing and characteristics of Nickel based superalloy in detail.

Fabrication of single-crystal Fe-Mn-Al-Cu alloys by cyclic heat treatments

In general, single crystal shape memory alloys exhibit superior shape memory effect and superelasticity when compared to their polycrystalline counterparts. However, it is challenging and costly to prepare a single crystal in traditional ways, such as the Czochralski method and directional solidification technique. Recently, cyclic heat treatment (CHT) has emerged as a facile and cost-effective method to fabricate single crystal by inducing abnormal grain growth. In the present work, we aimed to fabricate Fe-Mn-Al-Cu single crystals utilizing the CHT technique. Single crystal Fe-Mn-Al-Cu shape memory alloys were successfully prepared, and the effect of CHT parameters on abnormal grain growth was investigated. It was revealed that increasing the cooling rate resulted in a non-monotonic response in the maximum grain size, which initially increased and was followed by a subsequent decrease. This behavior was attributed to the subgrain refinement, increase in subgrain misorientation angles, and the narrowing of the low density zones (LDZs) of subgrains. Decreasing the lower temperature of CHT caused similar trends in maximum grain size, due to the increase in subgrain misorientation angle and the expansion of the LDZs. Extending the holding time at the lower temperature of CHT had minimal impact on grain size. Increasing the heating rate of CHT resulted in a reduction in the maximum grain size because of the narrowing of the LDZs. Moreover, the addition of 2 wt% Cu led to a reduction of the maximum grain size, attributing to the decreased solvus temperature of the γ phase as a result of Cu addition. Consequently, the γ phase and subgrains were refined, and the LDZs were narrowed.

Solidification analysis for variable thickness aluminum castings: simulation and chill design insights

Manufacturing high-quality casting parts with complex geometries requires high engineering skill and precision. One essential quality concern is isolated hot spots within the castings, often in thick sections. Each hot spot must be consistently fed or mitigated through directional solidification techniques. The impact of various mold sands and the geometry of chill parts on solidification direction was investigated using specialized casting and general-purpose simulation programs. A parametric optimization method was employed to analyze directional solidification to adjust the geometry of the chill parts. The results indicate that employing diverse mold sands to enhance cooling in the thick sections was a viable strategy for achieving directional solidification in parts where the feeding pathway is obstructed due to changes in cross-section. Furthermore, the study revealed that intricate details in the chill part’s geometry are not critical; however, a minimum volume (or weight) was necessary for adequate directional solidification. Lastly, an easily applicable mathematical model has been developed to determine the required volume of chill parts to ensure successful directional solidification.

Strong cooperation growth of two phases in the ternary eutectic

The growth mechanism and tensile performance of ternary Ni40.6Fe36.4Ti23 alloy were investigated using directional solidification technique. The ternary Fe2Ti+γ-Fe(Ni)+Ni3Ti eutectic formed a lamellar structure under the steady state growth. After quenching, the Fe2Ti phase transformed into independently grown fiber while the γ-Fe(Ni) and Ni3Ti phases kept lamellar structure. It was confirmed that the solid/solid interfacial energy anisotropy contributed to the strong cooperation growth of the two phases in the ternary eutectic. The γ-Fe(Ni)/Ni3Ti interface preferred to be parallel to the common planes of {111}γ and {0001}Ni3Ti with low interfacial energy, leading to the formation of the stable lamellar structure under different solidification conditions. Owing to the reduction of transverse grain boundaries and grain refinement, the alloy solidified at 10 μm/s growth velocity showed the highest tensile strength and Young's modulus with translamellar fracture mechanism.

Insight into tuning of ZrO2 distribution and mechanical properties of directionally solidified Al2O3/(5Re0.2)AG/ZrO2 eutectic ceramic composites

A novel Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12((5Re0.2)AG)/ZrO2 eutectic high entropy oxide ceramic composite (HEOC) was prepared by the directional solidification technique. The Al2O3/(5Re0.2)AG/ZrO2 eutectic HEOCs had a refined microstructure and different crystallographic orientation relationships of <10-10>Al2O3 || <103>(5Re0.2)AG || <100>ZrO2, {11–20}Al2O3 || {100}(5Re0.2)AG || {100}ZrO2, {0001}Al2O3 || {103}(5Re0.2)AG || {100}ZrO2 compared to Al2O3/YAG/ZrO2 eutectic ceramic composites. ZrO2 was distributed more uniformly and dispersedly in Al2O3/(5Re0.2)AG/ZrO2 eutectic HEOCs than in Al2O3/YAG/ZrO2 due to the similar volume strain of Al2O3/(5Re0.2)AG, (5Re0.2)AG/ZrO2 and Al2O3/ZrO2. As a result, mechanical performance including hardness, elastic modulus, and fracture toughness had been greatly improved because of the refined microstructure, tailored interfacial structure, and homogeneous distribution of ZrO2 caused by the introduction of the high entropy (5Re0.2)AG.

Recycling of kerf loss silicon: An optimized method to realize effective elimination of various impurities

Photovoltaic solid waste, particularly diamond-wire sawing silicon powder (DWSSP), has emerged as a significant concern in the industry. Consequently, the recycling and reuse of such waste have become a prominent research focus. In this study, focusing on achieving direct recycling and reuse of DWSSP, the key driving factors for effective purification were identified. It was found that simply increasing the melting temperature and time was insufficient to completely remove volatile impurities, and the migration process in the melt had to be taken into consideration. Additionally, this study focused on analyzing the instability model of inter-granular grain growth and its impact on the stable migration of impurities, with particular attention to the microstructure of inter-granular micro-regions. The thermal control directional solidification technique focused on controlling the temperature gradient during the melt solidification process. This approach helped stabilize the microstructure, enhance impurity migration, and ultimately led to a more effective purification of DWSSP.

Ceramics with eutectic microstructure in the ZrO2–PrOx system

AbstractPraseodymium oxides present redox properties analogous to those of Ce‐based systems and have been proposed for catalytic applications in combination with CeO2, ZrO2, or both. However, uncertainties remain concerning the nature and redox behavior of Pr‐rich mixtures, especially with ZrO2. Here we study the eutectic composites of the ZrO2–PrOx system, focusing on the sensitivity of their microstructure, phase symmetry, and composition to variations of the processing atmosphere from oxidizing to reducing. Mixed oxides have been produced by a laser‐assisted directional solidification technique in O2, air, N2, or 5%H2(Ar) environment, and the resulting materials have been analyzed by scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, X‐ray diffraction, Raman spectroscopy, and magnetic susceptibility. In air, N2, or 5%H2(Ar) atmosphere, a lamellar, eutectic‐like microstructure forms, the major phase being the one with less Pr content. Both the Pr concentration in each phase as the PrOx molar percentage of the eutectic composites decrease as the atmosphere becomes more reducing. Both eutectic phases are fluorite‐like when processing in air, whereas in N2 or 5%H2(Ar), the phase with high Pr content is of the A‐R2O3 type, and the phase with low Pr content can be described as a fluorite phase containing C‐R2O3‐like short‐range‐ordered regions. The results obtained for samples processed in O2 suggest that for high enough pO2 no eutectic forms, in analogy with the ZrO2–CeO2 system. The evolution of the phase composition and symmetry is discussed in terms of the limited stability of the phases found in the ZrO2–Pr2O3 system, namely, A‐ or C‐R2O3‐like, beyond a certain Pr oxidation degree and oxygen content.

Solidification microstructure and mechanical properties of an Al-11wt%Si alloy modified with Nb and Sb

It is important to understand the effects of adding Nb and Sb in order to improve the applied properties of Al–Si alloys. Thus, a nonsteady-state directional solidification technique was used in the present study to evaluate the effects of Nb and Sb microaddition and the solidification cooling rate on the dendritic microstructure of an Al-11 wt% Si alloy and their relationships with the tensile and hardness properties. Sb was shown to reduce the primary dendritic spacing (λ1) at the same solidification velocity or cooling rate, whereas Nb did not have these effects. Modification of the eutectic Si was shown to occur at high cooling rates, where the acicular Si transformed into fibrous, branched, and globular forms, instead of being attributed to the addition of alloying elements. The hardness profile for the Nb-containing alloy was the highest among all alloys examined in this study. The tensile properties were correlated with the changes in λ1 along the length of the directionally solidified castings. Al–Si alloy with added Nb obtained the best performance in terms of the ultimate tensile strength and elongation to fracture due to the better distribution of Si combined with aluminum-rich phase strengthening in solid solution with Nb.

Indium segregation in bulk GaInSb crystal grown using vibration assisted vertical directional solidification technique

Indium segregation in bulk GaInSb crystal grown using vibration assisted vertical directional solidification technique

Directional growth effect on magneto-mechanical properties of Fe81Al19 alloy

Directional growth effect on magneto-mechanical properties of Fe81Al19 alloy is studied. The ideal model of heat flux for directional solidification (DS) technique is proposed, and the tuned A/L (the ratio of cross-sectional area and length for the ingot) and ΔT (temperature difference) are adopted to increase heat flux (q). The experimental result shows that the increase of q effectively promotes the degree of (011)[100] Goss texture and therefore helps to form an oriented stripe domain structure. Large λ100 of 93.8 ppm attained for this optimized Fe81Al19 alloy prepared by DS method is very close to that of the Fe81Al19 single crystal (95.0 ppm). For the optimized DS prepared Fe81Al19 alloy, high magnetostriction sensitivity (dλ/dH) of 0.45 ppm/Oe leads to huge ΔEs/E0 of ∼10% and attractive ΔE/E0 of 8.2% at small H = 0.25 kOe. The above remarkable magneto-mechanical properties, low cost of Fe81Al19, and simple process of DS favor for applications. This work proposes an ideal model to emphasize the importance of heat flux in DS, and experimentally attains the remarkable magneto-mechanical properties for Fe81Al19 alloy prepared by DS.

Influence of Minor Additions of Be on the Eutectic Modification of an Al-33wt.%Cu Alloy Solidified under Transient Conditions

Al-based alloys are often selected for use in various engineering applications as well as in the aircraft and aerospace industry. The improvement of their performances under severe conditions have required the use of alloying elements. In the present work, Be is added to the eutectic Al-33 wt.%Cu alloy with a view to investigating the resulting effects on microstructural features and hardness. A directional solidification technique is used, yielding a wide range of solidification cooling rates. This permits microstructural features to be investigated with emphasis on the role of Be on the eutectic morphology. The directionally solidified microstructures are formed by eutectic colonies for the Al-33 wt.%Cu alloy, however, with additions of both 0.05 and 0.5 wt.% Be, the original cell-like morphology is transformed into a trefoil-like morphology. This together with the α-Al dendritic pattern characterize the microstructure of the Al-33Cu-Be alloys examined. Solidification growth laws are experimentally derived relating dendritic and eutectic colony spacings to solidification cooling rates and growth rates. The length scale of such spacings is shown not to affect the Vickers hardness of the Al-33Cu-Be alloys examined; however, the additions of Be are shown to improve the brittle behavior of the Al-33 wt.%Cu alloy.

Microstructure characteristics of a René N5 Ni-based single-crystal superalloy prepared by laser-directed energy deposition

This work focused on the microstructure and mechanical properties of nickel-based single crystal (SX) superalloy René N5 prepared by laser-directed energy deposition (L-DED) using a flat-top laser beam. A comparison was conducted with the conventional directional solidification technique. Results show that the crack-free single-crystal superalloys with a fraction of low-angle grain boundary (LAGB) higher than 98.5% were obtained by epitaxial growth under different laser powers. The flat fusion line using a flat-top laser beam can suppress the formation of stray grain and high-angle grain boundaries (LAGB) during the L-DED process. Microstructure observation shows the extremely refined dendrites in L-DED SX superalloys with primary dendrite arm spacing (PDAS) values around 20–30 µm, which is significantly lower than as-cast ones (∼350 µm). PDAS increases with the increasing laser power. Segregation of refractory elements of Re, W, and Ta increases with increasing laser power, and the SX specimens with laser power of 1100 W and 1300 W have lower elemental segregation compared with as-cast specimens. The SX specimens exhibit a uniform square γ′ phase at the dendrite core, with an average size of 79–101 nm and a volume fraction of 57–68%. Besides, the carbides with discontinuous and refined shapes show a uniform distribution in the L-DED specimens in comparison with as-cast specimens. The microhardness of as-deposited specimens increases with the increasing laser power, which is higher than that of as-cast ones. This work can provide potential guidance for the microstructure control in the laser additive manufacturing of Ni-based SX superalloys and a further improvement in high-temperature mechanical performance.

Dry Sliding Wear Features of an Al-20Sn-5Zn Alloy Affected by Microstructural Length Scales

Al-Sn-Zn alloys are attractive options for use as wear-resistant materials. While Sn promotes self-lubricating characteristics, Zn strengthens the Al-rich matrix. Conventionally, the manufacturing of these alloys involves casting. However, there is still a paucity of studies that associate the solidification microstructure with the wear resistance of these alloys. Inspired by such considerations, this work aims at investigating the wear behavior of an Al-20Sn-5Zn [wt.%] alloy produced by a directional solidification technique. A set of samples with different microstructure length scales was subjected to ball cratering tests using a normal contact load of 0.25 N and six test times. The results show that the dependence of the wear behavior on the microstructure length scale becomes more expressive for longer sliding distances. It was found that coarser microstructures provide an improved wear resistance. In view of that, a possible spectrum of specific wear rates was determined as a function of the sliding distance, considering different microstructure length scales. Finally, experimental equations are proposed to represent a possible range of wear volume and wear coefficient according to the dendrite arm spacings.

Enhancing the elastocaloric effect and thermal cycling stability in dendritic-like Ni50Mn31.6Ti18.4 single crystal

Solid-state cooling based on elastocaloric effect possesses potential for refrigeration. The improvement of elastocaloric effect and thermal cycle stability is beneficial to enhance the refrigeration efficiency and service life of refrigeration equipment. Here, single-crystal Ni50Mn31.6Ti18.4 shape-memory alloys were successfully prepared using directional solidification technique. The microstructure, martensitic transformation, isothermal stress-strain responses and elastocaloric effect of the single crystals with different solidification rates have been systematically studied. The single crystal solidified at 10 µm s−1 exhibits lower stress hysteresis Δσhy and much more superior adiabatic temperature |ΔTad| than those of alloys solidified at 100 µm s−1 and 500 µm s−1, with the values of 34 MPa and 24.8 K. In addition, the single crystal at low solidification rate also performs excellent cyclic stability. All these results show that the single crystal with larger austenite primary dendrite arm spacing (PDAS) can effectively enhance the elastocaloric effect and thermal cycling stability in Ni50Mn31.6Ti18.4 alloys. This work sheds a bright light on the relationship between the elastocaloric performance and microstructure for shape-memory alloys.

Distinct difference between peri-eutectic and eutectic growth in ternary Fe-Ni-Ti alloy

Peri-eutectic transition L+δ-Fe→γ-Fe(Ni)+Fe2Ti in ternary Fe66.5Ni17.6Ti15.9 alloy was investigated using directional solidification technique. We found that the primary phase and the peri‑eutectic in the solid region had a common orientation relationship, while the eutectic in the mushy zone had multiple orientation relationships. This firstly provided the evidence for the different growth mechanisms of peri-eutectic and eutectic, and secondly clarified that the peri‑eutectic nucleated from the primary phase and grew cooperatively. These orientation relationships related with interface structure and solidification kinetics. The peri‑eutectic had complicated interface structure characterized by a quaternary junction and grew under near equilibrium, whereas the eutectic had fewer interfaces and formed during quenching. Besides, the primary δ-Fe phase transformed to the lamellar α-Fe phase with different orientations after peri‑eutectic transition. This work is helpful for further understanding the peri‑eutectic transition as well as the connection between growth mechanism and crystallographic orientation in ternary alloys.

Effect of metastable phase content controlled by heat-treatment on corrosion behavior of directionally solidified Ni-12 wt%Si hypereutectic composites

The Ni-12 wt%Si hypereutectic composites with solidification rates of 6 μm/s, 9 μm/s, 25 μm/s and 40 μm/s were prepared by an improved Bridgman directional solidification technique. However, the metastable phase Ni31Si12 was inevitably formed during solidification process. This is usually unfavorable to the stability of the microstructure and properties of alloy. The content of metastable phase was decreased by different annealing heat treatment processes in this paper. Moreover, the effect of metastable phase content on the corrosion behavior of Ni-12 wt%Si hypereutectic composites in 10% H2SO4 solution was investigated as well.

Extraordinary mechanical properties and successive caloric effects with ultrahigh cyclic stability in directionally solidified Ni36.6Co12.8Mn34.7Ti15.9 alloy

Caloric effects based on multiferroic phase transformation have attracted extensive attention for their great potential to replace the conventional vapor-compression technique. However, most multiferroic phase transforming materials are inherently brittle and their caloric effects exhibit poor cyclic stability. Here, the Ni36.6Co12.8Mn34.7Ti15.9 alloy was manufactured by the directional solidification technique. The alloy can reach maximum compressive strength and strain of 2823 MPa and 17.7% at room temperature, respectively. Under magnetic field changes of 7 T, the maximum magnetic entropy change induced by a magnetic field is 28.1 J·kg−1·K−1. A large adiabatic temperature change of 20.1 K can be obtained by applying a stress field. Besides, the adiabatic temperature change between loading and unloading cycles can be maintained at ∼11.3 K for more than 10,000 cycles. A broad refrigeration temperature range of over 80 K can be realized by combining magnetocaloric and elastocaloric effects. With the simultaneously achieved extraordinary mechanical properties and large successive caloric effects with excellent cyclic stability, the present alloy has a great prospect for solid-state refrigeration applications.