Structure Of Ingots Research Articles

Electrical Activity of Extended Defects in Multicrystalline Silicon

The excess carrier lifetime (τ) distribution in multicrystalline silicon grown by the Bridgman technique from high-purity metallurgical silicon (HPMG-Si) is studied. The features of the variation in τ, caused by the grain-boundary structure of ingots, are revealed. The grain boundaries, dislocations, and impurity microinclusions are studied by electron probe microanalysis (EPMA) and scanning electron microscopy (SEM) using selective acid etching. The electrical activity of extended defects is measured by the electronbeam- induced-current (EBIC) method.

Электрическая активность протяженных дефектов в мультикремнии

AbstractThe excess carrier lifetime (τ) distribution in multicrystalline silicon grown by the Bridgman technique from high-purity metallurgical silicon (HPMG-Si) is studied. The features of the variation in τ, caused by the grain-boundary structure of ingots, are revealed. The grain boundaries, dislocations, and impurity microinclusions are studied by electron probe microanalysis (EPMA) and scanning electron microscopy (SEM) using selective acid etching. The electrical activity of extended defects is measured by the electronbeam- induced-current (EBIC) method.

The Influence of Casting Velocity on Structure of Al Continuous Ingots

AbstractThe aim of paper was determination of influence of the casting velocity in horizontal continuous casting process on solidification phenomenon and next primary structure of aluminum ingots. In the range of studies was conducted the experiment concerning continuous casting of Al ingots with diameter 30 mm at velocity from 30 to 80 mm/min. Moreover was developed adequate to the real the virtual model of cooled water continuous casting mould, which was used in simulation of solidification process of Al continuous ingot, made in ANSYS Fluent software. In result was determined the influence of casting velocity and temperature of cooling water on position of crystallization front inside the continuous casting mould. While the shape and size of grains in primary structure of Al continuous ingots were determined on the basis of metallographic macroscopic studies. On the basis of the results analysis was affirmed that increase of casting velocity strongly influences on position of crystallization front and causes increase of temperature of ingot leaving the continuous casting mould. In result the increase of casting velocity supposedly leads to decrease of temperature gradient on crystallization front what creates coarse grains in primary structure of aluminum continuous ingots and caused low usable properties i.e. suitability to plastic deformation.

Review on Modeling and Simulation of Electroslag Remelting

The Electroslag Remelting (ESR) is an advanced technology for the production of high quality materials, for example, hot work tool steels or nickel base alloys. In the past years, several models are developed aiming to predict the way in which the operational parameters affect the structure and chemical composition of the final ESR ingot. Proper modeling of this process depends on the ability of the model to predict the Multiphysics resulting from the complex coupling between many physical phenomena. This review includes the main findings starting from the 1970's, with a special focus on the results obtained in the period of 1999–2017. The difficulties related to the poorly known physical properties of ESR slags are discussed. Then, the main achievements in the field of electromagnetism, fluid flow, heat transfer, and solidification are also summarized. The review finishes by presenting the special topics representing the actual scientific frontiers, such as the physics of mold current, the importance of multiphase phenomena, and the difficulties in predicting the electrode melting rate.

Distinctive features of the structure and characteristics of long-length light gauge ingots from aluminium alloys, cast into electromagnetic crystallizer

Distinctive features of the structure and characteristics of long-length light gauge ingots from aluminium alloys, cast into electromagnetic crystallizer

Study of the structure and properties of heat-resistant alloys based on titanium aluminides with gadolinium microadditives

The results of the research works on the development, study, and approbation of promising heatresistant REE-containing intermetallic alloys based on ortho- and gamma-titanium aluminides (Ti2AlNb, TiAl) performed at the All-Russian Scientific Research Institute of Aviation Materials (VIAM) for solving the current problems of aircraft engine construction within the implementation of the complex scientific direction 7.1 “Intermetallic Alloys Based on Titanium” (“Strategic Directions of the Development of Materials and Technologies of Their Processing for the Period until 2030”) [1] are presented. The energy-efficient technological regimes of vacuum arc melting of ingots made of ortho and gamma alloys and having a homogeneous chemical composition and structure are developed; it is shown that the introduction of gadolinium microadditives in the amount of 0.05–0.2 at % into the studied alloys gives a significant modifying effect and forms a finely lamellar structure in ingots, which is favorable from the point of view of the combination of heat-resistant and performance properties. The structural changes and the combination of mechanical characteristics of new VIT5 ortho alloy depending on the heat treatment regimes are studied.

Primary Structure and Mechanical Properties of AlSi2 Alloy Continuous Ingots

AbstractThe paper presents the research results of horizontal continuous casting of ingots of aluminium alloy containing 2% wt. silicon (AlSi2). Together with the casting velocity (velocity of ingot movement) we considered the influence of electromagnetic stirring in the area of the continuous casting mould on refinement of the ingot’s primary structure and their selected mechanical properties, i.e. tensile strength, yield strength, hardness and elongation. The effect of primary structure refinement and mechanical properties obtained by electromagnetic stirring was compared with refinement obtained by using traditional inoculation, which consists in introducing additives, i.e. Ti, B and Sr, to the metal bath. On the basis of the obtained results we confirmed that inoculation done by electromagnetic stirring in the range of the continuous casting mould guarantees improved mechanical properties and also decreases the negative influence of casting velocity, thus increasing the structure of AlSi2 continuous ingots.

Fabrication of Gasar ingots with straight parallel pores by a Bridgman method

Multi-step withdrawal schemes with varying speeds of Bridgman method were designed and studied by numerical simulation and experimental methods in order to improve the pore straightness and parallelism of Gasar ingots. When the starting withdrawal speed v is larger than the expected reference v of 1mm/s, a subsequent decelerated withdrawal process is necessary, and v should go down to cross 1mm/s. When the starting v is smaller than 1mm/s, a hybrid-speed withdrawal process with a quickly accelerating stage first and a gradually decelerating stage afterwards is necessary, and v should also cross 1mm/s. The optimized varying speed withdrawal schemes should conform to the natural decreasing trend of the solidification rate. Compared with the optimized constant speed withdrawal scheme, the optimized varying speed withdrawal schemes can not only improve the pore straightness, but also adjust the pore structure of Gasar ingots.

Effect of temperature conditions on grain refinement of Mg–Al alloy under ultrasonic field

The effects of temperature conditions on the grain refinement of a Mg–Al alloy by ultrasonic treatment were investigated. It was found the grain refinement strongly depended on the temperature. When the ultrasonic treatment was performed above the liquidus temperature, the better grain refinement was achieved in the ingot treated at 700 °C rather than at lower temperature. While for the cases of the ultrasonic treatment being ended below the liquidus temperature, the better refinement can be achieved at lower ending temperature. The undendritic structrue of UST ingots is obviously different with the dendritic structure of UMT ingots. The ultrasonic cavitation improves the nucleation temperature, resulting in greater undercooling to benefit the nucleation. The acoustic streaming accelerates the release of latent heat of solidification and shorten the time for grain growth. Both of the two factors contribute to achieve the grain refinement.

Influence of withdrawing speed on the porous structures of Gasar ingots fabricated by Bridgman method

The pore straightness of Gasar ingots was investigated through experiments and numerical simulation. The pore growth direction changes from diverging to convergent as the withdrawing speed increases, and straight pores are obtained when the solid/liquid interfaces are almost planar. The optimum withdrawing speed to obtain straight pores increases as the sample size decreases. Under optimum conditions, the average pore diameter of the small ingot is smaller than that of the large ingot, while the penetrative porosity of the large ingot is superior. The shape of the solid/liquid interfaces at the bottom of the ingot can be improved effectively by modifying the structure of the mold. Bridgman method is applicable for the fabrication of Gasar ingots with large size and high quality, and suitable sample size should be considered for different structural requirements.

Mathematical modeling of the steel ingot teeming and the solidification process

The paper presents computer simulation-based findings on the teeming speed effect on the formation of the ingot structure and inner defects. It is reported that for a top-poured ingot, the average teeming speed (1.4-2.0 m/sec) proves to be the best choice as it is accompanied with a decreased number of surface defects and an increased metal yield resulting from a decreased shrinkage cavity.

On the magnetic anisotropy in Fe78Si9B13 ingots and amorphous ribbons: Orientation aligning of Fe-based phases/clusters

Magnetic anisotropy in Fe-based amorphous ribbon plays an important role in various applications and is still not fully understood. To gain an in-depth understanding of this phenomenon, the structure and magnetic properties of Fe78Si9B13 master alloy ingots and melt-spun amorphous ribbons were measured by various techniques. For the ingot samples, both the <100>α-Fe and <001>Fe2B axes are aligned parallel with the radial direction (RD) of the original cylindrical ingot, i.e. the maximum temperature gradient direction, and their other orthogonal axes have several preferred directions in the plane vertical to RD. The hard magnetic axis of the ingot samples is parallel to RD, which is due to the large magnetocrystalline anisotropy energy difference between <001> and {001} of the Fe2B phase. For the amorphous ribbons, there is an in-plane magnetic anisotropy: the easy or hard axis of magnetization is aligned on the plane of the ribbon, and parallel to or at an angle of about 60° to its width direction, respectively. According to the structural heredity between the melts and glasses/crystals during solidification, we deduce that the magnetic anisotropy in the ribbon plane is ascribed to the orientation alignment of Fe-Si and Fe-B clusters, i.e. a hidden order beyond short-range order, in Fe78Si9B13 amorphous ribbons.

Evolution of grain structure and recombination active dislocations in extraordinary tall conventional and high performance multi-crystalline silicon ingots

In this work one high performance multi-crystalline silicon ingot and one conventional multi-crystalline silicon ingot, each with an extraordinary ingot height of 710mm, were replicated by the successive growth of eight G1 ingots to evaluate the potential advantage of extraordinary tall HPM ingots in industrial production. By analyzing different grain structure parameters like mean grain size, grain orientation and grain boundary type distribution as well as the recombination active dislocation area over the complete ingot height, it was observed that the material properties strongly differ in the initial state of growth for the two material types. However, at ingot heights above 350mm, the difference has vanished and the grain structure properties for both materials appear similar. It is shown that the evolution of the grain structure in both material types can be explained by the same grain selection and grain boundary generation/annihilation mechanisms whereas the current grain structure determines which mechanisms are the most dominant at a specific ingot height. Since the grain structure directly influences the dislocation content in the silicon material, also the recombination active dislocation area becomes equal in high performance and conventional multi-crystalline silicon material at ingot heights above 350mm. From these results it is concluded that the advantage of high performance silicon material is limited to the first grown 350mm of the ingot.

Effect of Melt Rate on Surface Quality and Solidification Structure of Mn18Cr18N Hollow Ingot during Electroslag Remelting Process

A new method for manufacturing Mn18Cr18N steel applied to retaining ring has been developed based on hollow ESR ingot. The ESR hollow ingot not only keep away from upsetting and punching, provide hollow billet for forging directly, but also meet the need of high quality of the raw material. ESR hollow ingot of Mn18Cr18N steel has been produced successfully in our lab. Melt rate is the most important technological parameter of electroslag remelting (ESR) process, which influences ingot quality and production efficiency. To further investigate the influence of surface quality on melt rate, the experimental results comparing to the simulations results have been implemented in this paper. A mathematical model to describe the temperature distribution and the solidification structure of ESR hollow ingot of Mn18Cr18N steel has been established. The change of metal pool profile, pool cylinder part height, and grain growth angles during hollow ESR process are calculated based on the coupled technology of CAFE method and the moving boundary method, which are consistent with the experimental results. The experiment of hollow ESR Mn18Cr18N steel at the most suitable melt rate obtained by numerical simulation results has been carried out to reveal the law of cylinder part height of metal pool changing with the withdrawal speed. The optimal technological parameters applied in the experiment of hollow ESR process can reasonably control the surface quality of Mn18Cr18N hollow ingot.

Study of the solidification structure of compacted graphite cast iron

This investigation focuses on the study of the solidification mechanism of compacted graphite cast iron (CGI). The solidification macrostructure was revealed in cast samples using a special technique known as direct austempering after solidification (DAAS). The microstructure was revealed by colour etching. The results were compared with earlier investigations of the solidification of spheroidal (SGI) and lamellar (LGI) graphite irons, and show that, similarly to other free graphite cast irons, the solidification of CGI is dominated by the presence of relatively large grains of austenite that can be observed with bare eyes. The CGI cast samples show a typical ingot structure, containing columnar and equiaxed grains, with a narrow columnar to equiaxed transition. The microstructure analysis showed that a dendritic substructure and a large number of eutectic colonies form the grains. Microsegregation is located inside the grains, mostly between secondary dendrite arms. The results indicate that the growth mechanism during solidification of CGI resembles that of LGI, but not the mechanism of SGI.

Influence of complex ladle modifying on the structure of aluminium ingots

Influence of complex ladle modifying on the structure of aluminium ingots

Features of Structure and Solidification of Extended Double Ingots for Hollow Forgings. Part 1

Results are provided for a study of features of the structure of extended double hot-topped ingots. In the upper half of a test ingot, there is significant development of defects of shrinkage origin (closed secondary shrinkage cavities and zone of axial porosity), and they are significantly developed over the height and insignificantly over the diameter. Defects of shrinkage origin are concentrated within the upper half of an ingot body. It is established that within a double ingot nonmetallic inclusion distribution and cast structure parameters differ from the distribution for an ingot of normal geometry. Comparison of mathematical modeling data with results of studying ingot structure shows that a higher temperature in a narrow axial part of an actual ingot slows down solidification. This leads to an increase in dendrite parameter, a reduction in dendrite structure density, an increase in porosity, the amount of readily melting sulfide and complex oxysulfide nonmetallic inclusions, and also formation of a closed secondary shrinkage cavities. This position of defects of shrinkage and liquation origin facilitates their removal during ingot forging, and provides the possibility of obtaining hollow forgings from them. In test ingot forgings, there is a fourfold reduction in their chemical inhomogeneity and an increase in mechanical property stability over an object’s length. Use of extended double ingots for preparing hollow billets makes it possible to increase output of finished metal in a forging by 8%.

Thermodynamic design of electroslag remelting slag for high titanium and low aluminium stainless steel based on IMCT

The advantages of the electroslag remelting (ESR) process as to cleanness and homogeneity of the ingot structure are well known. As to homogeneity of composition, the control of titanium in stainless steel with high titanium and low aluminium contents during the ESR process has not been resolved well so far. The current work focuses on designing appropriate slag for controlling titanium content during 1Cr21Ni5Ti remelting based on the interaction of the slag/metal interface. Several kinds of slag containing different CaO contents combined with steel samples of 1Cr21Ni5Ti were employed to investigate the effect of slag on titanium content in an electrical resistance furnace, and metal samples were taken at different times for investigating the change of titanium and aluminium contents in steel. The results show that slag with low CaO content at low temperature has excellent capacity for avoiding loss of titanium content caused by its reaction with the alumina in slag, especially in case of remelting of stainless steel with high titanium and low aluminium contents. The CaO in slag has great effect on the activities of TiO2 and Al2O3, and thermodynamic analysis was applied to investigate the CaO behaviour based on the ion and molecule coexistence theory of slag. The thermodynamic analysis results show that the increases as CaO content in slag decreases, which is better for preventing loss of titanium caused by its reaction with the alumina in the ESR slag. The slag with low CaO content at low temperature is suitable for ESR of 1Cr21Ni5Ti.

Observation of drastic change of generalized phonon density-of-states in nanostructured half-Heusler using inelastic neutron scattering

To understand the role of the nanophase in reducing the lattice contribution of the thermal conductivity of thermoelectrics, the structure and phonon density of a p-type half-Heusler thermoelectric ingot (ingot-HH, nominal composition of (Hf0.5Zr0.5)Co(Sb0.8Sn0.2)), and its nano form prepared from ball milling (nano-HH), were studied using neutron diffraction and neutron inelastic scattering techniques. They are both cubic, F4¯3m, with lattice parameters a = 6.0649(3) Å (nano) and 6.0629(1) Å (ingot), but the nano and ingot materials exhibit markedly different generalized phonon density-of-states (GDOS) at 300 K due to the substantially reduced grain size in the nano sample. These overall changes in GDOS, together with the increase in grain boundary scattering, account for the sharp reduction of the thermal conductivity in the nano-hot-pressed (nano-hp-HH) sample, which has a similar average grain size to that of nano-HH.

Smelting and Casting Technologies of Fe-25Mn-3Al-3Si Twinning Induced Plasticity Steel for Automobiles

The technologies for producing twinning induced plasticity (TWIP) blank in large scale with argon oxygen refining (AOD)-ingot casting-electroslag remelting (ESR) processes were studied. It was found that it was difficult to refine the low carbon Fe-25Mn-3Al-3Si TWIP steel using hot metal of high Mn content in AOD refining by a technology of decarburization and manganese retaining. However, it is practicable to perform decarburization and manganese retaining with the hot metal of lower Mn content in the early stage of AOD refining and do alloying with electrolytic manganese in the late stage. To overcome the problem of castability of TWIP steel, high superheat casting process was applied in ingot casting process, and the solidification structure of TWIP ingot was not compact and even, mainly composed of rough and long columnar and central random oriental dendrite. Due to the Ar protection and low current remelting processes applied in ESR procedure, the solidification structure was significantly improved and the inclusions were well controlled after ESR.