Vacuum Induction Melting Research Articles

Erosion behaviors of BaZrO3 and BaZrO3/Y2O3 dual-phase refractories within Nb-Si melts during vacuum induction melting

To develop a potential refractory for preparing Nb-Si alloy, the Nb-16Si (at.%) alloy was melted using BaZrO3 and BaZrO3/Y2O3 dual-phase crucibles through vacuum induction melting (VIM). The interfacial behavior of BaZrO3 and BaZrO3/Y2O3 dual-phase refractories against Nb-16Si alloy melts was investigated by utilizing scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and X-ray diffraction (XRD). The results show that the improved performance of the BaZrO3/Y₂O₃ crucible can be attributed to Y replacing Zr in BaZrO3, forming a BaZr1-xYxO₃ solid solution. The Gibbs free energy of BaZr1-xYxO₃ is lower than that of BaZrO3, indicating higher thermodynamic stability. Furthermore, Y2O3 acted as a barrier, isolating BaZrO3 from the Nb-16Si melts. The dissolution of BaZrO3 was the primary mechanism of crucible erosion. The thickness of erosion layer of BaZrO3 crucible caused by Nb-16Si melts was about 186 μm, while the erosion layer of BaZrO3/Y2O3 dual-phase crucible was negligible, resulting in alloy ingots with significantly lower contamination. The BaZrO3/Y2O3 dual-phase refractory exhibited superior high-temperature stability to Nb-16Si melts compared with BaZrO3.

A comparative study on Arc- and vacuum induction-melting for Ti16.6Zr16.6Hf16.6Co10Ni20Cu20 high entropy shape memory Alloy Production

Arc-melting (AM) as a primary method for casting high entropy alloys (HEAs) ensures rapid alloy screening with minimal material input, high cost-effectiveness, and high cooling rates. However, the limitations of AM on a laboratory scale, particularly its constrained sample size and the necessity for remelting steps to ensure homogeneity, hampers thorough mechanical and functional testing of bulk materials. Therefore, this study features a comparative analysis between AM and vacuum induction-melting (VIM) techniques for High Entropy Shape Memory Alloys (HE-SMAs) production, focusing on the senary alloy Ti16.6Zr16.6Hf16.6Co10Ni20Cu20, known for its potential functional applications and high sensitivity to material inhomogeneity. The alloy’s composition, including high-melting point elements like Hf, Ti and Zr, makes it a well-suited candidate for assessing the capabilities of VIM in producing homogeneous bulk materials. The employment of binary pre-alloys in both AM and VIM processes reduced the necessity for remelting steps and ensured better initial quality for subsequent heat treatments. A homogenization treatment at 900 °C for 100 h of an AM-produced senary alloy showed only slight improvements compared to the same alloy produced via VIM, largely due to the slow diffusion of the larger Hf and Zr atoms from the dendrites into the solid solution. This suggests that VIM can achieve comparable levels of homogenization in substantially less time than required for AM-treated samples. The findings finally indicate that by using VIM, when combined with binary pre-alloys, one achieves more homogeneous alloys with reduced heat-treatment time, making it a viable method for HE-SMA production.

Study on interfacial reaction behavior between CaO-Y2O3 ceramic and Ni-based superalloy melt during vacuum induction melting

The reaction mechanism at the interface between CaO-Y2O3 composite oxide refractories and superalloy melt during vacuum induction melting of Ni-based superalloys was investigated. Once the reaction occurred, the interfacial layer consisted of exterior CaS layer and interior CaYAlO4 layer. CaS was formed by the desulfurization reaction of CaO and S from alloy melt. While the CaYAlO4 was formed by the reaction of 12CaO·7Al2O3 or Al2O3 (CaO and Y2O3 were replaced by Al), CaO and Y2O3. The whole interfacial reaction was: CaO(s)+[S]Ni(l)+[Al]Ni(l)+Y2O3(s)=CaYAlO4(s)+ CaS(s)+[Y]Ni(l).

A Simulation Method for Predicting Shrinkage Cavity and Cracking Tendency in Waspaloy Vacuum Induction Melting Ingot

A Simulation Method for Predicting Shrinkage Cavity and Cracking Tendency in Waspaloy Vacuum Induction Melting Ingot

Towards High-Quality Investment Casting of Ti-6Al-4V with Novel Calcium Zirconate Crucibles and Optimized Process Control

The investment casting of titanium and its alloys relies on a high resistance of the crucibles and shell molds in terms of temperature and reactivity. The availability of ceramic crucibles that offer sufficient resistance to the titanium melt enables vacuum induction melting (VIM). CaZrO3 prepared from a mixture of CaO and ZrO2 as a raw material for refractory ceramics shows a high corrosion resistance against metallic melts even under very high temperatures up to 1800 °C. Crucibles and shell molds of CaZrO3 were successfully produced and used in subsequent casting trials. This study is focused on the refractory crucibles suitable for casting Ti-6Al-4V (Ti-64) using a tilt casting machine. In order to evaluate the crucible reaction and, therefore, the quality of the castings, chemical analyses, investigations of the microstructures and hardness measurements were carried out. Careful control of the melting duration is mandatory to avoid crucible reactions that otherwise result in contamination of the cast with oxygen and zirconium. This was achieved by modified coil geometries. Under optimized casting conditions, the oxygen and zirconium impurity limits of ASTM B367-09 for titanium castings were met. Based on the correlations found, optimized casting parameters with regard to material quantity, coil geometry and heating power could be determined in order to provide guidance for a high-quality casting process with VIM.

Using the Radial-Shear Rolling Method for Casted Zirconium Alloy Ingot Structure Improvement

In developing materials for the nuclear industry, it is crucial to enhance both alloy composition and processing methods. This study focuses on investigations of applying radial-shear rolling (RSR) to a Zr-1%Nb alloy ingot, aiming to refine its microstructure and improve its properties for nuclear applications. This method, with complex vortex metal flow inside of a casted workpiece, has not been previously tested for processing zirconium ingots, so experimental verification of its applicability is of scientific interest. The 30 mm diameter ingot, produced by vacuum induction melting, was initially rolled to 20 mm at 800 °C to eliminate defects and refine the cast structure. A second rolling stage reduced the diameter to 13 mm at 530 °C, resulting in an ultrafine-grained structure. The RSR method effectively combines structural refinement and defect healing within fewer cycles, making it suitable for producing components for nuclear reactors. This approach demonstrates a potential reduction in traditional processing steps, providing a more efficient route for preparing high-quality materials for nuclear applications.

Synergistic impact mechanism of particle size and morphology in superalloy powders for additive manufacturing

The particle size and morphology of superalloy powders are crucial parameters that significantly influence the performance of additive manufacturing (AM) processes. This study investigates the effects of atomization pressure on these characteristics through a combination of computational fluid dynamics (CFD) simulations and vacuum induction melting gas atomization (VIGA) experiments. The CFD simulations revealed that increasing the atomization pressure from 2.0 MPa to 3.5 MPa resulted in a rise in maximum gas velocity from 526 m/s to 537 m/s and a reduction in median particle size (D50) from 60.9 μm to 37.5 μm. Subsequent experiments demonstrated a decrease in D50 from 52.9 μm to 35.6 μm, and sphericity from 0.9432 to 0.9377, as pressure increased. The particle size results of the atomization experiments and numerical simulations show strong consistency, validating the accuracy of the numerical simulation results. The volume of hollow particles also increased slightly in specific size fractions. These results suggest that higher atomization pressures produce finer powders with lower sphericity, but also promote particle adhesion, reducing the overall refinement effect. This study provides insights into optimizing atomization conditions for the precise control of superalloy powders in AM.

Fabrication and characterization of novel high-efficiency and high-durability neutron-absorbing Ni-based alloys

New neutron-absorbing Ni-based functional alloys that depend on the gadolinium and dysprosium neutron absorption units were fabricated using vacuum induction melting. The effects of Gd and Dy contents on the microstructure characteristics and properties of Ni-based alloys were investigated. Adding Gd, Dy, and Gd + Dy into Ni-based alloys formed Ni5Gd, Ni5Dy and Ni5(Gd,Dy), respectively, and their volume fraction increased with increasing of Gd/Dy content. Different type of elements, Gd or Dy, had no obvious influence on mechanical properties and corrosion resistance, while the amount of Gd and Dy elements played an important role. The shielding properties were calculated by the Monte Carlo method, and the alloys possessed high efficiency and high durability performance due to the high contents of Gd and Dy elements. The developed alloys are expected to be good functional materials for use in the field of nuclear shielding.

Study on the effect of temperature on the microstructure and mechanical properties of as-cast CoCr2Ni3.5VAl1.5Ti high-entropy alloy

This study investigates the microstructure and mechanical properties of a CoCr2Ni3.5VAl1.5Ti high entropy alloy (HEA) annealed at 500 °C, 700 °C, 900 °C and 1100 °C for 6 h. The alloy was prepared using a vacuum induction melting furnace and annealed at the specified temperatures for 6 h. It was then characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD). The results indicate that with increasing annealing temperature, the alloy's phase structure transitions gradually from multiphase (fcc, bcc, hcp) to predominantly fcc phase, with relatively stable elemental distributions. Annealing at 500 °C–900 °C mainly strengthens the alloy through precipitates and dislocation strengthening, whereas at 1100 °C, strengthening occurs through grain boundary strengthening and precipitate growth, enhancing the material's strength and ductility. The alloy exhibits optimal comprehensive performance after annealing at 1100 °C. This study provides important insights for optimizing the heat treatment process of HEAs.

Effects of Pressure on Nitrogen Content and Solidification Structure during Pressurized Electroslag Remelting Process with Composite Electrode

The nitrogen content and solidification structure of the 1Mn18Cr18N ingots produced by the customized laboratory‐scale vacuum induction melting furnace and the pressure electroslag remelting furnace (PESR) with novel composite electrode under different pressure and the same power consumption are compared and studied. The results show that there are perfectly uniform radial chromium and nitrogen profiles during the PESR process. The nitrogen uptake reaction in the PESR process with composite electrode takes place on the liquid metal film on the electrode. Nitrogen uptake could be improved by increasing the nitrogen partial pressure. In addition, the basin depth at a pressure of 0.1 and 1.22 MPa is about 41 and 38 mm, the angle of the grains with respect to the vertical axis is 35° and 31°, respectively. The flat metal basin profile resulted from the thermal resistance at the slag–mold interface decreasing with increasing pressure. Primary and secondary dendritic arm spacing (PDAS and SDAS) variations exhibit an increasing and subsequently decreasing the trend as they move further away from the center in a horizontal direction. Both PDAS and SDAS decrease with increasing pressure from 0.1 to 1.22 MPa.

Integrated simulation method and experimental validation for the vacuum induction melting process

In Vacuum Induction Melting (VIM), reduction of defects such as porosity and cracking is critical to improve electrode integrity. Traditional simulation method ignores the temperature drop of liquid metal as it passes through the tundish, leading to inaccuracies in predicting the solidification process in the mold. Additionally, the crack of ingot may occur during demolding process, which is always overlooked. This paper presents an integrated simulation method that includes the flow model of liquid metal in the tundish, as well as the solidification model and the stress model of ingot in the mold. Based on these models, the criterion for demolding time is established based on First and Fourth Strength Theories. The entire VIM process from pouring to demolding can be analyzed comprehensively through this simulation method. The method is validated by 500 kg Inconel 718 VIM trial including the temperature measurement of outer mold wall, the height measurement of liquid metal in the tundish and longitudinal sectioned experiment of ingot. The suitable criteria for porosity of 500 kg Inconel 718 ingot, including shrinkage porosity and shrinkage cavity, have been found to be the Niyama criterion threshold of 15 K0.5s0.5cm−1 and Classical porosity model. Finally, the impact of each process parameter on porosity and demolding time is studied through this method for 500 kg Inconel 718 ingot. This method is not only applied to 500 kg ingot but also to larger ingot, thereby providing a basis for the VIM process optimization.

Evaluation of critical temperatures of as-cast Co-based superalloys as a function of alloying elements and their effect on microstructure

Co-based superalloys are of great interest in the aeronautical and aerospace industry due to their superior thermal performance compared to Ni-based superalloys. This work explores the influence of elemental additions (Ni, Al, Cr, Si, and Ti) on the critical temperatures (liquidus, solidus, solvus, and eutectic) and microstructural features of several Co systems fabricated by vacuum induction melting until the final Co-30Ni-10Al-4Cr-2Si-2Ti (wt%) composition was obtained. Differential Scanning Calorimetry results indicated high thermal stability concerning the γ' phase formation. Si and Ti additions suppressed the eutectic presence in the proposed superalloy, which is desirable to avoid the incipient melting of components. Instead, the present work exhibits a low-density Co-based superalloy conformed of a continuous γ/β microstructure with γ' precipitating uniformly. These characteristics make the Co-30Ni-10Al-4Cr-2Si and Co-30Ni-10Al-4Cr-2Si-2Ti superalloys promising candidates to be subjected to high temperatures in comparison with current Co-based superalloys.

Effect of cold-rolling and annealing temperature on microstructure, texture evolution and mechanical properties of FeCoCrNiMn high-entropy alloy

This study investigates the effects of cold rolling and annealing on the microstructure, texture, and mechanical properties of FeCoCrNiMn high-entropy alloys. Utilizing vacuum induction melting, the alloy was initially cast into ingots and hot-rolled into plates, which were subsequently cold-rolled to various thicknesses and annealed at different temperatures. Microstructural analyses were conducted using X-ray diffraction and electron backscatter diffraction techniques, revealing a persistent face-centered cubic structure across all conditions. The texture evolution demonstrated a shift from Copper and S components to dominant Goss and Brass components as cold rolling intensified, suggesting the formation of Brass-type texture in FeCoCrNiMn at high deformation. Mechanical testing showed that the alloy's yield and tensile strengths significantly increased with cold rolling, reaching optimum values at ∼66 % reduction. Annealing at 750 °C enhanced both strength and ductility, primarily through grain refinement and the formation of Σ3 annealing twin boundaries, which dominated the microstructure of recrystallized grains. The study confirms that the low stacking fault energy of the alloy facilitates the activation of twinning and transformation-induced plasticity mechanisms, crucial for the observed enhancements in mechanical properties.

Bulk CoCrFeNiAlMo high entropy alloy as high-efficient electrocatalyst in alkaline environment

Developing cost-efficient catalysts with high efficiency for water splitting has been considered as large challenge. Herein, the bulk high entropy alloys (HEAs) are fabricated through the vacuum induction melting, which could be beneficial to solving the above issues. At the same time, it also enhances the electrocatalysts activity and stability. The alloy composition is discovered to be crucial in the both hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) activity enhancements with the CoCrFeNiAlMo bulk HEA catalyst combination providing the exceptional catalytic activities. Forming the CoCrFeNiAlMo bulk HEA catalyst also significantly promotes the electrocatalytic cycling stabilities. Hence, the CoCrFeNiAlMo bulk HEA catalyst displays a small overpotential (261 mV @ 50 mA cm−2) and a corresponding Tafel slope (48.66 mV dec−1) for the OER in a 1.0 M KOH electrolyte. For HER, CoCrFeNiAlMo bulk HEA catalyst also possess a relatively small overpotential. Furthermore, it exhibits a relatively small cell voltage of 1.83 V at 50 mA cm−2 and superior durable for 14 h. This study presents a universal pathway for preparing sustainable high efficiency electrocatalysts, it demonstrates that the bulk HEAs have the potential to be effective catalysts in alkaline environments.

Influence of texture on anomalous yielding behavior of thermomechanically processed nickel-based superalloy 720Li

Precipitation-strengthened Ni-base superalloys are extensively used for high-temperature load-bearing applications due to their unique combination of yield stress anomaly (YSA), excellent creep, fatigue, and corrosion resistance. However, in line with the previous reported results, it is shown in the present study that 720Li alloy does not exhibit YSA during uniaxial deformation. The investigation explores the role of anti-phase boundary (APB) energy, Zener ratio and break away stress of Kear-Wilsdrof (KW) lock on YSA behavior. It is shown that in spite of meeting all the energetic requirements necessary for YSA (viz. energy for octahedral to cubic cross slip along with high break away shear stress, i.e. ∼ 80 MPa); the thermo-mechanically processed 720Li alloy does not exhibit YSA. In support of the observed absence of YSA, a plausible mechanism is provided for the first time through this work. This unusual absence of YSA has been attributed to the crystallographic texture of the alloy (specifically, the loading direction (LD) being parallel to [11¯1]), which prevents the formation of KW-locks in the first place. The [11¯1] texturing has been shown to rather lead to direct cubic plane slip i.e. {001} <110>, thereby paving way for suppression of KW-locks (and hence YSA). In order to validate this postulate, the study also examines a vacuum induction melt and cast Ni75(Al11, Ti14), L12 compound. The presence of YSA in the L12 compound under conditions of LD not being parallel to [11¯1], confirms that texturing impacts the occurrence of YSA.

Study on the microstructure, mechanical and corrosion behaviors of 2A12 Al matrix composites containing B4C and 50% K2TiF6 flux

This study presents an innovative exploration into the development and characterization of boron carbide (B4C) reinforced aluminum (Al) metal matrix composites (AMMCs), specifically focusing on the 2A12 Al alloy. Utilizing a cutting-edge vacuum induction melting process, the research investigates the effects of varying B4C particle concentrations in conjunction with 50% K2TiF6 flux additions. This novel approach aims to enhance the microstructural integrity, mechanical properties, and corrosion resistance of the AMMCs. The research unveils a significant improvement in microhardness and tensile strength with the increase of B4C content. This enhancement is attributed to the efficient load transfer mechanism from the aluminum matrix to the B4C phase and the thermal expansion coefficient mismatch-induced dislocations. A critical finding of this study is the uniform distribution of B4C particles and the formation of a Ti-rich layer around these particles, facilitated by the K2TiF6 flux. This layer acts as a barrier, minimizing interfacial reactions. Electrochemical testing reveals that there is a slight decrease in corrosion resistance with increased B4C content. The outcomes of this research contribute to the field of metal matrix composites, offering a path forward for the application of B4C-reinforced AMMCs in demanding industrial environments where high strength, stiffness, and durability are critical. The study's findings open new avenues for advanced materials development in aerospace, automotive, and energy sectors.

Interfacial reaction between the nickel-based superalloy and the Al2O3 crucible during vacuum induction melting

The effects of holding time on the interfacial reaction between a nickel-based superalloy and an Al2O3 crucible during the vacuum induction melting process were studied at 1450 °C. The results show that the reaction products at the interface are intermittently distributed and then gradually become dense and continuous as the holding time increases. The average thickness of the reaction layer increases and then decreases when the melting time is extended. Through microstructure characterization, the interfacial reaction layer extending from the boundary to the matrix consists of a continuous Al2O3 reaction layer and a discontinuous TiC layer. Finally, the process of the interface reaction is summarized.

A modified vacuum induction melting technique with argon backfilling to produce pristine Ni–Ti–Si ternary shape memory alloys

A modified vacuum induction melting technique with argon backfilling to produce pristine Ni–Ti–Si ternary shape memory alloys

The influence of aluminum content on thermal properties of copper-aluminum alloys: a first-principles calculation

Abstract Copper-aluminum alloy, also called aluminum bronze, is a type of host material for abradable sealing coatings. The amount of aluminum content obviously affects the properties of the coating. This research uses the density functional theory to calculate the properties of an aluminum bronze with different aluminum content. The copper-aluminum alloy model uses the model of special quasirandom structures (SQS). The elastic constant, melting point, constant pressure specific heat capacity, and thermal expansion coefficient of the copper-aluminum alloys were calculated using the quasi-harmonic approximation (QHA) method. The copper-aluminum alloys with three different nominal components were prepared using vacuum induction melting. The melting point, thermal expansion coefficient, and specific heat capacity of the copper-aluminum alloys were characterized through experiments. The results showed that the melting point of the copper-aluminum alloys decreased with an increase in aluminum content. Additionally, the coefficient of thermal expansion of the copper-aluminum alloy increased with the increase in aluminum content. Furthermore, the specific heat capacity of the copper-aluminum alloy initially increased and then reached a turning point when the β’ phase was generated. The experimental values conform well to the calculated values.

Effect of annealing treatment on the mechanical properties and corrosion behaviour of Co40Cr20Ni30Al4.5Ti5Mo0.5 high-entropy alloy

Cast high-entropy alloys are frequently found to have large internal tensions, compositional segregation, and shrinkage defects, which can directly prevent them from performing as intended. Proper heat treatment can modify the internal structure of an alloy and enhance its overall performance. This study describes a new nonequiatomic proportional cast Co40Cr20Ni30Al4.5Ti5Mo0.5 high-entropy alloy prepared by a vacuum induction melting technique. The impacts of different annealing temperatures (700, 800, 900, and 1000 °C) on the microstructure evolution mechanism, mechanical properties and corrosion behaviour of the alloy are systematically examined. The results show that the heat treatment can successfully improve the overall mechanical properties and corrosion resistance of high-entropy alloys while suppressing casting defects. The alloy exhibits the best overall mechanical properties after annealing at 700 °C, with a yield strength of 923 MPa and a tensile strength of 1090 MPa. After annealing at a temperature of 800 °C, the alloy demonstrates excellent corrosion resistance, characterized by a low passivation current density, a large passivation range, and a high corrosion potential. Specifically, ipass is measured to be 4.59 × 10−7A/cm2, and Ecorr is −319 mV. Furthermore, the maximum Cr2O3 oxide content in the alloy passivation film formed at 800 °C contributes to the passivation film stability.