Horizontal Directional Solidification Research Articles

Influence of Lathe Rotation and Secondary Dendritic Arm Spacing on Surface Roughness of an Al-3wt.%Si Alloy Submitted to the Necking Process

This experimental study aims to analyze the influence of lathe rotation and secondary dendritic arm spacing, λ2, on the surface roughness (arithmetic mean deviation of the surface height from the mean line through the profile, Ra) of an Al3wt.%Si alloy. The samples were obtained by horizontal directional solidification under unsteady heat flow conditions and subsequent necking of the ingot at defined positions from the metal / mold Interface. The roughness analysis was performed using optical microscopy. The results showed that, for all rotations, the roughness variation as a function of the secondary dendritic spacing can be expressed by experimental power function given by Ra= a (λ2 )b , where a and b are constants. It was also observed that, for the same secondary dendritic arm spacing, lower roughness values were obtained for higher rotations.

Mathematical modeling of heat and mass transfer processes in the graphite thermal unit of the crystallization apparatus for Horizontal directional solidification method

The design of ECU has been created, which allows in the process of growing halide crystals to create in the growth and annealing zones, respectively, the high-gradient and low-gradient temperature regions necessary for each of the processes. The mathematical study of the influence of the processes of hydrodynamics, heat and mass transfer inside ECU, between ECU and the crystallization apparatus, is considered. For numerical calculations, the Navier-Stokes equation, the Menter differential k-ω turbulence model SST, the modified Stefan-Boltzmann law, the Fourier law are used. To describe the mechanism of heat transfer and heat conduction in solids, boundary conditions of the third kind were set. The distribution of the axial temperature gradient inside the carbon-graphite heat unit was studied. The mode of flow of the refrigerant inside the cooling jacket was determined. The radiative heat transfer between the surfaces, and the mechanisms of heat transfer and heat conduction in solids were studied.

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.

Microstructures and mechanical properties of Al2O3/YAG:Ce3+ eutectics with different Ce3+ concentrations grown by HDS method

The Al2O3/YAG:Ce3+ eutectics (170 mm × 90 mm × 20 mm) with different Ce3+ concentrations, which could be used as structural members and new type of fluorescent materials, were grown by the horizontal directional solidification method. Variations in the microstructures of the eutectics, such as the three-dimensional cross distribution of coarse and fine microstructure regions caused by Ce doping, were directly presented by μCT. The residual compressive stress in the Al2O3 phases increased with the increase of Ce concentration in the eutectics. Although the Young’s modulus, Vickers hardness, and fracture toughness of our eutectics decreased slightly with the increase of Ce concentration, the values were still in the range of the prior results. The flexural and compressive strength of the eutectics were also measured from room temperature to 1273 K. The flexural strength of these eutectics decreased with an increase in Ce concentration. But the eutectic with Ce/Y = 0.25% exhibited a higher compressive strength (1946 MPa) compared to that of the eutectic with Ce/Y = 0% (∼1200 MPa). Therefore, the controlled use of the Ce ions additive is an attractive option to improve the compressive strength of the Al2O3/YAG eutectics.

Effect of cooling rate on microstructure and inclusion in non-quenched and tempered steel during horizontal directional solidification

In order to investigate the relationship between microstructure and MnS inclusion in non-quenched and tempered steel, and cooling rate during horizontal directional solidification, 49MnVS steel was used to conduct the experiments with a self-designed device. The mathematical effect of cooling rate on dendritic arm spacing and mean diameter of MnS particles (dMnS) were determined by using linear regression method. The results show that the length of dendrite from solid–liquid interface to end-solidification decreased with increasing the withdrawal velocity (ϑ). dMnS has a similar value in the area of the steady directional solidification; the value of dMnS was 4.1, 3.6, 3.3, 2.8 and 2.3 μm at withdrawal velocity of 50, 75, 100, 150 and 200 μm/s, respectively. dMnS increased with reducing ϑ or RC (interface cooling rate). MnS precipitated in the gaps between dendrites and was influenced by secondary dendritic arm spacing. Besides, a new concept of the ‘Precipitation Unit Space’ (PUS) was proposed and the relationships between dMnS, VPUS (volume of PUS) and RC were obtained.

Cellular/dendritic transition, dendritic growth and microhardness in directionally solidified monophasic Sn-2%Sb alloy

Abstract Horizontal directional solidification experiments were carried out with a monophasic Sn-2%Sb (mass fraction) alloy to analyze the influence of solidification thermal parameters on the morphology and length scale of the microstructure. Continuous temperature measurements were made during solidification at different positions along the length of the casting and these temperature data were used to determine solidification thermal parameters, including the growth rate ( V L ) and the cooling rate ( T R ). High cooling rate cells and dendrites are shown to characterize the microstructure in different regions of the casting, with a reverse dendrite-to-cell transition occurring for T R >5.0 K/s. Cellular ( l c ) and primary dendrite arm spacings ( l 1 ) are determined along the length of the directionally-solidified casting. Experimental growth laws relating l c and l 1 to V L and T R are proposed, and a comparative analysis with results from a vertical upward directional solidification experiment is carried out. The influence of morphology and length scale of the microstructure on microhardness is also analyzed.

Mechanisms of Interaction of Molybdenum and Tungsten Polyoxide with Aluminum Oxide Melt under Reducing Conditions

The main chemical reactions between Mo and W polyoxides and Al2O3 melt in a controlled Ar + H2 atmosphere (T = 2400 K, P = 1 bar) during sapphire growth by horizontal directional solidification have been investigated. Under these thermodynamic conditions, the melt and products of its dissociative evaporation may actively react with the tungsten heater and molybdenum thermal screens of the crystallization system. It is shown that the polyoxides formed during evaporation do not directly interact with the melt; this interaction occurs only with participation of reagents exhibiting pronounced reducing properties (Al, H2, H, WO, Al2O, AlH, AlH2, AlH3). It is established that most of processes occur with participation of aluminum hydrides. A particular role of Mo(W) dioxide–W(Mo) polyoxide functional pairs in the interaction with the melt is determined.

Microstructure and microhardness in horizontally solidified Al–7Si–0.15Fe–(3Cu; 0.3Mg) alloys

ABSTRACTTransient horizontal directional solidification (THDS) experiments have been carried out with Al–7wt.%Si–0.15Fe, Al–7wt.%Si–3wt.%Cu–0.15wt.%Fe and Al–7wt.%Si–0.3wt.%Mg–0.15wt.%Fe alloys, to identify experimental relationships between growth rates (GR), cooling rates (CR), tertiary dendrite arm spacings (λ3) and microhardness (HV). Optical microscopy and scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) were used to perform a comprehensive microstructural characterisation of the β-Al5FeSi, ω-Al7Cu2Fe, θ-Al2Cu, π-Al8Mg3FeSi6 and α-Mg2Si intermetallic phases. The addition of Cu and Mg to the Al–7wt.%Si–0.15wt.%Fe alloy led to the precipitation of ω and π phases from the β phase. It has been found for all analysed alloys that power experimental functions given by λ3 = constant.(GR)-1.1 and λ3 = constant.(CR)-0.55 best describe the variation of λ3 with corresponding thermal and microstructural parameters.

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.

Microindentation Hardness-Secondary Dendritic Spacings Correlation with Casting Thermal Parameters in an Al-9wt.%Si Alloy

Experiments were carried out to analyze the effect of growth rates (VL) and cooling rates (TR) on both secondary dendritic arm spacings (λ2) and Vickers microhardness (HV) of an Al-9wt.%Si alloy during the horizontal directional solidification under transient heat flow conditions. A water-cooled solidification experimental apparatus was developed allowing a wide range of TR (from 0.2 to 3.5 oC/s) to be experienced. Five computer guided thermocouples were connected with the metal, and the time-temperature data were recorded automatically. The solidification path was also calculated by Scheil model in Thermo-Calc software. Casting samples were characterized by the combined analyses of optical microscopy (OM) and scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS) revealing a complex arrangement of phases including binary (α-Al + Si) and ternary (α-Al + Si + β-AlFeSi) mixtures within interdendritic regions. It was observed that power law functions characterize the variation of λ2 as a function of VL and TR with exponents of -2/3 and -1/3, respectively. Finally, experimental laws of power and Hall-Petch types are proposed relating the resulting HV to the λ2. According to these results, it was found that, for increasing values of λ2, the results of HV decrease.DOI: http://dx.doi.org/10.5755/j01.ms.24.1.17319

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.

Examination of Thermal Parameters, Primary Dendritic Spacings and Microhardness of a Horizontally Solidified Al-Cu-Mg Ternary Alloy

In this paper, the Al-3wt.%Cu-0.5wt.%Mg alloy was grown by the transient horizontal directional solidification method in a water cooled stainless steel chill. A temperature monitoring system in the metal was used and the registered time-temperature data during the solidification process were applied to determine tip growth rates (VL) and cooling rates (TR) which have been correlated with both primary dendrite arm spacings (λ1) and Vickers microhardness (HV). Characterization techniques by optical and scanning electron microscopy (OM and SEM) were employed and the observed microstructures show an Al-rich dendritic matrix (a-Al) and θ (Al2Cu) and S (Al2CuMg) intermetallic phases within the interdendritic regions. Power and Hall-Petch type experimental equations were proposed to describe the HV profile as a function of the thermal and microstructural parameters (VL, TR, and λ1). In order to investigate the effect of the Mg alloying, a comparative analysis was also performed between the experimental values of this article and the results of previous studies carried out with the Al-3wt.%Cu binary alloy.

Isotropy in large-size Al2O3/Y3Al5O12 eutectic ceramic grown by Horizontal Directional Solidification method

The eutectic Al2O3/Y3Al5O12 with the dimension of 150mm×90mm×20mm was grown in vacuum by Horizontal Directional Solidification (HDS) method. The thermal and mechanical properties were investigated from room temperature to 1273K, on specimens whose longitudinal directions were parallel (L-specimen) and perpendicular (T-specimen) to the solidification direction. Even though new preferred orientations of (1 1 2¯ 3) Al2O3 and (5 3 2) Y3Al5O12 emerged in L-specimen, neither in T-specimen, isotropic properties of residual stresses in Al2O3 phase, thermal expansion coefficients, flexural and compressive strengths appeared. For HDS-Al2O3/Y3Al5O12, the reasons of improved Vickers hardness were discussed.

Growth of YAG:Ce3+-Al2O3 eutectic ceramic by HDS method and its application for white LEDs

The resin-free YAG:Ce3+-Al2O3 eutectic ceramic phosphor for white light emitting diodes (WLEDs) was successfully grown in vacuum by Horizontal Directional Solidification method (HDS). X-ray diffraction and scanning electron microscopy indicate that this material has a typical eutectic structure of interpenetrating sapphire and garnet phases. The excitation spectra, emission spectra and temperature characteristics of the eutectic show that it is characterized by a wide excitation band and it has good stability in high temperature. In X-ray photoelectron spectroscopy, annealing in an air atmosphere could eliminate the oxygen vacancies and didn’t change the Ce3+ valence in the eutectic. The YAG:Ce3+-Al2O3 eutectic ceramic with different thickness was fixed in COB (chip on board) element for researching the performance of the WLEDs with the phosphor. The electroluminescence characterization of the WLEDs show that the WLEDs with the eutectic ceramic are more excellent than the common commercial WLEDs.

Interrelation of Solidification Processing Variables and Microstructure of a Horizontally Solidified Al-based 319.1 Alloy

In this paper, primary ( λ 1 ) and tertiary ( λ 3 ) dendritic arm spacings of a ternary Al – 7wt.% Si – 3 wt.% Cu alloy casting were characterized and correlated with solidification processing variables: growth rates (V L ), cooling rates (T C ) as well as local solidification times (t SL ). Horizontal directional solidification experiments were carried out under transient heat extraction undergoing cooling rates varying from 0.9 o C/s to 22 o C/s to be associated with samples having quite different microstructural length parameters. Techniques of metallography and optical microscopy were applied in order to have λ 1 and λ 3 measured. The obtained as-cast microstructures consisted of dendritic α-Al, with Si particles in the aluminum-rich matrix as well distributed along the interdendritic regions in the eutectic mixture interlinked with θ (Al 2 Cu) intermetallic phase developing the microstructure α -Al + θ + Si. The results showed that power laws – 1.1, – 0 .55 and 0.55 express the variations of both λ 1 and λ 3 with V L , T C and t SL , respectively, for investigated alloy. A comparative study with the Al – 3wt.% Cu alloy from literature was also performed and the results show that the growth law of λ 1 as a function of T C is represented, for both the investigated alloys, by the mathematical expression given by λ 1 = constant (T C ) -0.55 . DOI: http://dx.doi.org/10.5755/j01.ms.23.2.15768

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.

Thermal Parameters, Tertiary Dendritic Growth and Microhardness of Directionally Solidified Al-3wt%Cu Alloy

The main purpose of this paper is to evaluate both tertiary dendritic arm growth and microhardness of Al-3wt%Cu alloy during horizontal directional solidification under transient heat flow conditions. Experimental thermal profiles recorded during solidification process allowed to determine growth rate and cooling rate values which are associated with both tertiary dendritic arm spacings and microhardness. The results show that initial tertiary branches growth only occurs when a cooling rate value of 1.14 K/s is reached. Variation of tertiary spacings is expressed as-1.1 and-0.55 power law functions of growth rate and cooling rate, respectively. A comparative analysis with other studies published in the literature that analyze tertiary dendritic growth of Al-Cu alloys considering transient directional solidification is carried out. Dependence of microhardness on dendritic arrangement is evaluated by experimental laws of power and Hall-Petch types with a view to permitting the applicability of the resulting expressions.

Analysis of the Microstructural Evolution during the Transient Upward, Downward and Horizontal Directional Solidification of the Al-1.2wt%Pb Monotectic Alloy

Monotectic alloys are of great industrial importance because of their favorable tribological behavior. Many studies in order to better understand the morphologies obtained by monotectic reaction have been developed. To better understand the morphologies obtained by monotectic Al-1.2wt%Pb alloy reaction, especially in relation to induced convective flow, this paper aims to compare the microstructural evolution of the alloy obteind by directional solidification in transient heat-flow conditions in upward, downwand and horizontal solidification devices. It was observed a morphology transition from particles to fibers on upward and downward cases and a morphology of only particles on the horizontal case. The classical relationship used for eutectic growth, λ2v = C, which was considered applicable to monotectic reactions, didn’t seemed to be valid in the interphase spacing evolution for the downward device, however power functions (λ = C.va) were found in all cases.

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.

Effect of Interfacial Heat Transfer Coefficient on Dendritic Growth and Microhardness during Horizontal Directional Solidification of an Aluminum-Copper Alloy

This paper presents a theoretical-experimental study for the prediction of the interfacial heat transfer coefficient during the horizontal directional solidification of an Al-3wt.%Cu alloy on water cooled stainless steel chill under transient heat flow conditions. Eight thermocouples were connected with the casting and the time-temperature data were recorded automatically. The thermocouples were placed at 5, 10, 15, 20, 30, 50, 70 and 90 mm from the metal-mold interface. A numerical technique which compares theoretical and experimental thermal profiles was used to measure the heat transfer coefficient values. This has permitted the evaluation of the variation of this thermal parameter along the solidification which is represented by a power equation that shows the time dependence during the process given by hi = constant (t)-n, which represents the best fit between the experimental and calculated curves. The obtained results also include the variation of both primary and secondary dendritic arm spacings of alloy analyzed as a function of heat transfer coefficient. These dendrite arm spacings were found to decrease as the values of this coefficient are increased. Finally, an experimental law of the Hall-Petch type is proposed relating the resulting microhardness to the heat transfer coefficient investigated.