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Herein, the effects of electroslag remelting (ESR) and impurities in ESR slag on the composition, microstructure, and properties of lightweight steel with a nominal composition in wt% of Fe‐20Mn‐10Al‐1.5C are studied. These results can provide a reference for the production of such steels using ESR and the design of the composition of such steels. The results show that ESR can make the contents of Si increase and that of S decrease, make the grain size decrease, make the phase transformation of austenite at about 540 °C change from spinodal decomposition to ordered transformation, make the contents of MnS and SiO2 and inclusions greater than 5 μm decrease, make the distribution of inclusions homogenize, and make the shape of inclusions change from long strip with sharp corners to spherical shape. ESR can improve its strength, plasticity, and antiballistic penetration properties. [ABSTRACT FROM AUTHOR]

Vacuum induction melting has proven to be a cost-efficient way to fabricate TiNi alloys with excellent compositional homogeneity and uniformity. However, the high reactivities of TiNi alloys generate aggressive melt attacks with a particular ceramic crucible. Here, the performance of AlN crucible for melting TiNi alloys was investigated, and the underlying mechanisms for the interfacial interactions were revealed. The results demonstrated the feasibility of using AlN crucibles for induction melting of TiNi alloys. Specifically, melt infiltration was suppressed and thus physical erosion was diminished by reducing the apparent porosity of the crucible. Further investigations combined with a theoretical analysis revealed that the TiN barrier layer distributed on the crucible surface was formed in situ due to crucible/melt interactions, which protected the ceramic matrix from further melt attack and limited the contaminant levels. Our work provides a viable pathway for the preparation of high-quality TiNi alloys via induction melting.

Understanding the as-cast structure acts as a precursor, providing insights for alloy processing into a candidate structural material. The recent developments in high-entropy alloys (HEAs) draw attention to explore such domains for their suitability for commercial structural applications. The present work investigates the correlation between the macro-, microstructure, and mechanical properties of a cast single-phase Al0.2CoCrFeNi HEA. The alloy was produced using a vacuum induction melting route and subsequently characterized using X-ray diffraction (XRD), optical microscopy, and field-emission scanning electron microscopy (FESEM). Mechanical properties were evaluated through uniaxial tensile tests and nanoindentation. The macrostructure of the ingot displayed classical solidification features in both the top and bottom portions. Notably, no macrosegregation was observed in the ingot. However, microsegregation of Al and Ni was detected between the dendritic and interdendritic regions in the top part. Despite the absence of significant variation in macrohardness, the tensile tests revealed noteworthy differences in tensile strength between the top center (330 MPa) and bottom center (464 MPa) of the ingot. This variation in strength was attributed to differences in dendrite arm spacing. Further nanoindentation studies supported the observed tensile behavior, with the top center showing relatively high hardness. This high hardness was found to be correlated with the composition of the dendritic and interdendritic regions. [ABSTRACT FROM AUTHOR]

Vacuum induction melting is a commonly used method for preparing AlV55 alloys. However, this method results in high Al evaporation losses, leading to poor cost control. Moreover, the influence of the process parameters on the alloy composition remains unclear. In this study, the evaporation pattern of Al in the melting and preparation processes of AlV55 alloys is studied, and measures for controlling the system pressure are proposed to effectively reduce Al evaporation. The experimental results show that smelting under an Ar gas atmosphere of 2000 Pa can reduce the evaporation loss of Al from 11.48% under vacuum conditions (60 Pa) to 0.58% of the amount of raw material added, effectively improving the metal utilization rate and reducing production costs. The influence of various process parameters on the alloy composition and Al volatilization are investigated to enable the effective control of the compositional uniformity and impurity content of the resulting alloys. Under optimal conditions, the impurity contents of C, O, and N are 0.03%, 0.0073%, and 0.013%, respectively; this reduces the amount of Al lost by evaporation compared to conventional methods, and the alloy produced meets commercial standards. [ABSTRACT FROM AUTHOR]

Calcia refractory exhibits considerable potential owing to its capacity to purify melts. This work analyzes different purity calcia for their microstructure, crystal size distribution, and bonding phases. The pilot-scale calcia crucibles were prepared from two calcia refractories of different purity using cold isostatic pressing. The findings show that calcia refractory purity affects the properties of calcia crucibles. Fewer Ca 3 Al 2 O 6 and Ca 3 SiO 5 results in well-developed calcia grains and improved hydration resistance. The high-purity calcia crucible has better high-temperature strength and thermal shock resistance than the low-purity one. The high-purity crucible possesses a low strength reduction of 69% after thermal shock and a high hot modulus of rupture of 4.2 MPa at 1400 ℃. In contrast, the low-purity crucible displays inferior properties, with strength loss reaching 80% and a hot modulus of rupture measuring 0.73 MPa. Therefore, high-purity calcia is considered a potential refractory for manufacturing oxide crucibles. [ABSTRACT FROM AUTHOR]

In this paper, the effects and the mechanisms of melt superheating treatment (MST) on a directionally solidified alloy were investigated. The mass loss rate of the superalloy becomes severe as the MST temperature rises. The chromium, tantalum, and hafnium are the primary evaporation elements during MST. As the MST temperature increases from 1500 to 1600 °C, the secondary dendrite arm spacing is reduced by 13.3%, and the average size of γ′ particles are reduced by 11.5% and 18.2% in the dendrite core and inter-dendritic area, respectively. The content of oxygen and nitrogen gradually reduces with the increase in the MST temperature. However, the sulfur content is not significantly affected by the MST temperature. The essential cause of γ′ phases transition is supposed to be the MST-induced changes in solute distribution and the decomposition of atomic clusters. In addition, the nitrides and Ti (N, C)-type carbides are continuously dispersed as the MST temperature increases, which promotes the removal of nitrogen impurities. [ABSTRACT FROM AUTHOR]

Molten Ti possesses significantly high chemical activity, causing it to react with crucible materials; this renders the induction melting of Ti alloys extremely challenging. Therefore, fabricating effective and inexpensive crucibles suitable for this process is vital. In this study, an aluminum nitride ceramic crucible with excellent TiAl-induction-melting performance was manufactured. TiAl alloys melted in this crucible showed high purity with an ultra-low oxygen content (<0.1 wt%), and the melting process involved negligible crucible/metal interactions. Subsequently, the performance of the AlN crucible was systematically investigated, with particular emphasis on its anti-corrosion mechanism. The excellent induction-melting performance of the crucible could be ascribed to the formation of a dense TiN barrier film and an Al-rich layer on the crucible surface during melting. The following interfacial reaction (predicting the generation of both TiN and Al-rich phases) was proposed: 3TiAl (l) + 2AlN (s)→TiN + Ti 2 AlN + 4TiAl [Al]. This study provides an in-depth understanding of the fabrication and physical properties of AlN crucibles, which can aid future research on the induction melting of Ti-based alloys. [ABSTRACT FROM AUTHOR]

Today, shape-memory alloys have already taken their place in various fields of science and technology. The most used alloy is titanium nickel or nitinol. When manufacturing alloys based on NiTi in order to use them for various products, it is necessary to know the conditions, under which it is possible to obtain alloys with previously known parameters of the phase transformation. In the work, the dependence between the Ni/Ti ratio, preliminary thermomechanical treatment (TMT) and the temperature of the beginning of the martensitic transformation (Ms) is obtained. [ABSTRACT FROM AUTHOR]

Nickel-based superalloys are widely employed to manufacture aero-engine turbines due to their high mechanical strength and resistance to corrosion and creep. Vacuum Induction Melting (VIM) is a suitable manufacturing technology because of the reactive nature of the alloying elements; however, the melting process is time-consuming and energy-demanding. This research focuses on increasing the overall efficiency of the process in two ways. Initially, studying the influence of metal-containing crucible composition and thermal properties on the melting. In a semi-industrial VIM facility, 2 kg of Inconel 718 alloy was melted employing Al2O3, ZrO2, MgO, and Al6Si4O13-based crucibles. The Al6Si4O13 and ZrO2-based crucibles reduced energy consumption by 28% and 23%, respectively, compared to the reference crucible of Al2O3. Subsequently, an optimized melting procedure is proposed to reduce the process cycle time and energy demand, saving 10%–20% for all crucibles compared to the standard melting procedure. In addition, the ZrO2 and Al6Si4O13 crucibles reduced total cycle time by 13% and 21%, respectively. During melting, intense dross formation was detected for all crucibles, dissipating faster for Al6Si4O13 and MgO crucibles. Therefore, the metal-crucible interface product was analyzed to understand these mechanisms better, and the four crucibles' chemical reactivity was examined.

Vacuum induction melting is a commonly used method for preparing AlV55 alloys. However, this method results in high Al evaporation losses, leading to poor cost control. Moreover, the influence of the process parameters on the alloy composition remains unclear. In this study, the evaporation pattern of Al in the melting and preparation processes of AlV55 alloys is studied, and measures for controlling the system pressure are proposed to effectively reduce Al evaporation. The experimental results show that smelting under an Ar gas atmosphere of 2000 Pa can reduce the evaporation loss of Al from 11.48% under vacuum conditions (60 Pa) to 0.58% of the amount of raw material added, effectively improving the metal utilization rate and reducing production costs. The influence of various process parameters on the alloy composition and Al volatilization are investigated to enable the effective control of the compositional uniformity and impurity content of the resulting alloys. Under optimal conditions, the impurity contents of C, O, and N are 0.03%, 0.0073%, and 0.013%, respectively; this reduces the amount of Al lost by evaporation compared to conventional methods, and the alloy produced meets commercial standards.

An automatic scanning electron microscope (SEM) analysis system and a self-designed superalloy inclusion analysis module were utilized to characterize the inclusions in the GH4068 Ni–Co-based superalloy prepared by vacuum induction melting (VIM). The morphologies, compositions, and distribution of the inclusions as well as the relationship between the contents of oxygen/nitrogen and inclusion were analyzed. The results indicate that the inclusions in the GH4068 alloy mainly include oxides, carbides, nitrides, carbonitrides and complex inclusions. The oxides are mainly concentrated in the top center of the cast ingots, and their content is higher than that at the bottom and edge. Nitrides and complex inclusions are mainly distributed near the bottom and edge of ingots. The analyses of thermodynamics indicate that the homogeneous nucleation of Al2O3 is spontaneous during the solidification although TiN prefers to wrap on the nucleated particles rather than homogeneously precipitate from the melt. The increase of oxygen/nitrogen content results in the increase of oxides, nitrides and complex inclusions. However, when the concentration of nitrogen is in the range of 3–12 ppm, the increase of nitrogen content shows negligible influence on the content of nitride inclusions.

In this paper, the effects and the mechanisms of melt superheating treatment (MST) on a directionally solidified alloy were investigated. The mass loss rate of the superalloy becomes severe as the MST temperature rises. The chromium, tantalum, and hafnium are the primary evaporation elements during MST. As the MST temperature increases from 1500 to 1600 °C, the secondary dendrite arm spacing is reduced by 13.3%, and the average size of γ′ particles are reduced by 11.5% and 18.2% in the dendrite core and inter-dendritic area, respectively. The content of oxygen and nitrogen gradually reduces with the increase in the MST temperature. However, the sulfur content is not significantly affected by the MST temperature. The essential cause of γ′ phases transition is supposed to be the MST-induced changes in solute distribution and the decomposition of atomic clusters. In addition, the nitrides and Ti (N, C)-type carbides are continuously dispersed as the MST temperature increases, which promotes the removal of nitrogen impurities.

The radiochronometric model age is an important signature in nuclear forensic analysis. Recent studies have illustrated the need for controlled experiments on the behavior of decay products during uranium metal casting to provide a foundation for interpretation of discordant model ages. A variety of uranium metal and alloy samples cast under known conditions were analysed by three laboratories. This work is the first multi-laboratory study of its kind to explore how these progeny isotopes are chemically fractionated from uranium metal during casting. The intercomparison allowed for capability demonstration and method development on samples and provided data to increase our understanding of the behavior of decay progeny in these complex systems. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the present study, the microstructure and mechanical properties of various CoCrFeMnNi high-entropy alloys were investigated. Analytical studies were conducted to determine the optimal chemical composition, mixing entropy, mixing enthalpy, atomic radii, valence electron concentration (VEC), dimensionless parameter, and melting point on the Co-Cr-Fe-Mn-Ni system. The microstructure of the alloys was analyzed using FESEM, XRD, and TEM. The results showed that the microstructure of all HEAs had dendritic and interdendritic regions, with secondary precipitations detected along the grain boundaries of the alloy, mainly composed of Mn and Ni. High-density dislocation structures and nano-precipitates were predominantly present in the alloy. The mechanical characteristics such as microhardness and tensile properties are conducted at room temperature. The HEA Co25Cr25Fe10Mn30Ni10 exhibited the highest average microhardness, while the Co20Cr20Fe30Mn10Ni20 HEA had the lowest mean hardness value. This significant difference of 7.2 % may be attributed to the hard phases composed of Mn and Ni. The results of the tensile experiments indicate that the Co20Cr20Fe20Mn20Ni20 alloy has the most favorable overall properties, with an ultimate tensile strength of 441 MPa. This represents a significant increase of 37.8 % compared to 20Cr20Fe20Mn20Ni20. Furthermore, the study examines the instability of the solid-solution state caused by differences in the valence electron concentrations of the constituent elements and phase stability. • The microstructure and mechanical properties of various compositions of the CoCrFeMnNi system are investigated. • The instability of the solid solution state due to the change in valance electron concentration (VEC) was analyzed. • Enhanced microhardness was observed in C025cr25fe10mn30ni10 due to the presence of Mn and Ni in dendritic branches. • The precipitated phase distributed around the grains is mainly responsible for changes in elastic modulus and tensile strength. [ABSTRACT FROM AUTHOR]

AerMet100 steel has strict composition and inclusion requirements. Therefore, its reaction with MgO refractory during vacuum induction melting cannot be ignored. In this study, the reaction mechanism between the MgO refractory and AerMet100 steel during the refining stage was investigated using a MgO crucible. The influence of the MgO crucible on AerMet100 steel composition and inclusions under refining vacuum pressures of 50–100 and 5–10 Pa was compared. The results indicate that SiO 2 , Al 2 O 3 , and MgO in the crucible decompose and are reduced by C in the liquid steel, which results in the increase of Si, dissolved Al (Als), and dissolved Mg (Mgs) content in the liquid steel. The increase of Ca content is due to the reduction of CaO in the crucible by C in the liquid steel. The reaction of Al 2 O 3 inclusions and Mgs in the liquid steel is the primary generation method of MgO·Al 2 O 3 spinel inclusions. As the Mgs content in the liquid steel increases, Al 2 O 3 inclusions transform into MgO·Al 2 O 3 spinel inclusions along the path Al 2 O 3 + Mgs → Al 2 O 3 with a small amount of MgO + Mgs → MgO·Al 2 O 3 spinel. In contrast, the vacuum pressure of 50–100 Pa is more effective at controlling the composition and inclusions of AerMet100 steel and is a more appropriate choice for the refining vacuum pressure. [ABSTRACT FROM AUTHOR]

The metallurgical preparation and microstructure of as-cast Ti-45Al-2W-xC (in at.%) alloys were investigated. Five alloys with carbon content ranging from 0.38 to 1.96 at.% were prepared by vacuum induction melting (VIM) in graphite crucibles, followed by centrifugal casting into graphite moulds. A master 15W-85Al (at.%) alloy with a relatively low melting point and TiC powder were used to facilitate fast dissolution of W during VIM and to achieve the designed content of C in the as-cast alloys, respectively. The increase in the content of C affects the solidification path of the studied alloys. Differential thermal analysis (DTA) and microstructural observations show that the alloys with carbon content up to 0.75 at.% solidify with β primary phase and their dendritic as-cast microstructure consists of the α2(Ti3Al) + γ(TiAl) lamellar regions, retained B2 phase enriched by W and single γ phase formed in the interdendritic region. The increase in the content of C above 0.75 at.% leads to the formation of primary lathe-shaped Ti2AlC carbides, which act as effective heterogeneous nucleation sites of β dendrites during the solidification and grain refinement of the alloys with 1.15 and 1.96 at.% C. The increase in the content of C leads to an increase in Vickers hardness and elastic modulus in the alloys containing 1.96 at.% C. [ABSTRACT FROM AUTHOR]

The absence of appropriate melting method and expensive cost of high-purity Zr raw material limit the commercial application of Zr-based bulk metallic glass. In the present study, using high oxygen industrial grade sponge Zr as raw material and the metal Y as additive, the low-cost and high-purity master alloys were successively prepared using a VIM method with a BaZrO 3 refractory crucible. The results indicate that the BaZrO 3 refractory exhibited good erosion resistance to the alloy melt, the Y additive formed the Y 2 O 3 barrier layer on the surface of crucible, which prevented the melt permeation into the crucible, then effectively reduced the thickness of the erosion layer. In addition, the metal Y deoxidizer could remove the oxygen of melts, finally the low oxygen Zr-based master alloy (about 0.02 wt%) was prepared. These results may provide a promising preparing technique prototype of low-cost Zr-based bulk metallic glass. [ABSTRACT FROM AUTHOR]

The corrosion resistance of refractory materials to the titanium alloy melts is vital for the production of titanium alloys by vacuum induction melting. In this study, the corrosion behavior of calcia-stabilized zirconia, solid state synthesized calcium zirconate, and fused calcium zirconate refractory suffering Ti-5 wt% Cu melts were investigated at 1680 ℃ for 15 min of soaking time by the cup test method. It was found that the three crucibles directly dissolved into the titanium melt, then generated Ti (Zr, O) and CaZrO 3 in the infiltration layer, and eventually developed a porous Ti 3 O layer in the lining. Besides, the contamination of Ti-5 wt% Cu alloy (oxygen: 5.3 wt%; zirconium: 6.01 wt%; calcium: 0.42 wt%) by fused calcium zirconate crucible was significantly less than the solid state synthesized one (oxygen: 5.83 wt%; zirconium: 6.14 wt%; calcium: 0.43 wt%), implying that the production method of calcium zirconate notably affected the impurity of titanium alloys. [ABSTRACT FROM AUTHOR]

Ni–tungsten carbide (WC) composites were prepared using cast WC as hard particles. In this study, the thermal damage behaviour of cast WC particles and its effects on the microstructure and mechanical properties of Ni–WC composites were investigated. Results show that cast WC particles undergo edge dissolution and particle disintegration at 1600 °C and 1800 °C, respectively. The degree of thermal damage to cast WC particles increases from 30.55% to 48.84% when the melting temperature increases from 1600 °C to 1800 °C. In this process, the Ni-based melt gradually erodes the cast WC particles from the edge towards the centre. This leads to severe dissolution of the W 2 C phase, while the WC phase only dissolves partially. Notably, the degree of thermal damage to cast WC directly correlates with the W content in the melt. An increase in the W content enhances the volume fraction and nano-hardness of the M 23 (B, C) 6 compound, improving the wear resistance of the composites. • Elevated temperature rises thermal damage degree of cast WC particle. • Ni-based melt invades from particle edge towards its center during thermal damage process. • High nano-hardness and volume-fraction of block-like M 23 (B,C) 6 compound • Thermal damage behaviour improves wear resistance of composite. [ABSTRACT FROM AUTHOR]

The high Nb-containing TiAl-based alloy ingot beyond laboratory scale with a composition of Ti-46Al-8Nb (at.%) was prepared by a vacuum induction melting process based on a BaZrO3 refractory crucible. A round bar ingot with a diameter of 85 mm and a length of 430 mm was finally obtained, and the chemical composition, solidification pathway, microstructure and tensile properties of the ingot were investigated. The results show that the deviations of Al and Nb content along a 430 mm long central part of the ingot are approximately ±0.39 at.% and ±0.14 at.%, and the oxygen content in the ingot can be controlled at around 1000 ppm. The structure of the alloy ingot is a full lamellar structure composed of γ and α2 phases, and the thickness of the lamellae is approximately 0.53 μm. In case of the α2 phase, the surface content of the ingot is higher than the middle region and the centrical region; also, it indicated a decreasing trend. During cooling, the alloy solidified from a peritectic reaction (L + β→α) rather than the solidified via β phase (β→α). In addition to Al segregation and Nb segregation, β-phase particles associated with γ phase at the triple junction of the colonies were observed. Moreover, the tensile properties of the longitudinal-cut sample in the ingot is significantly better than those of the transverse-cut sample, with a tensile strength of up to as high as 700 MPa and a corresponding fracture elongation of 1.1%. However, the tensile strength of the transverse-cut sample is only 375 MPa, and the fracture elongation is 0.52%. [ABSTRACT FROM AUTHOR]

In this study, yttrium as desulfurizer on the purification of Ni–20Co–20Cr–10Al–Y alloy during vacuum induction melting (VIM) process using Y2O3 crucibles was investigated experimentally. It is found that Y plays an important role on the desulfurizing of the NiCoCrAlY alloy. Without any addition of Y, merely the employment of Y2O3 crucibles could effectively reduce S content of the alloy melts from 28 × 10−6 to 6 × 10−6–7 × 10−6. With addition of 0.8 wt% Y in the alloy, the concentration of S could further reduce 2 × 10−6–3 × 10−6. The primary interactive mechanism between Y and molten alloy was concluded to be the synthesis reaction of Ni3Y phase, Y2S3 phases and YAlO3 phase. In the desulfurize slags, Y2S3 phases and YAlO3 phase are found. No secondary contamination is present in the alloy melts after addition of Y. [ABSTRACT FROM AUTHOR]

Austenitic-ferritic steel, as suggested by its name, has an equal fraction of austenite and ferrite phases, also known as duplex stainless steels (DSS), are one of the highly used materials for subsea pipelines applications. The presence of slurries is inevitable in subsea pipelines. This technical work elucidates the slurry erosive wear behavior of duplex stainless steel and the impact of the addition of niobium (Nb) on the phenomena. Vacuum induction melting was used to produce duplex stainless steel, and its Nb added casts. The aim of the work is to compare both castings' for erosive wear behavior using a slurry jet erosion tester. Computational thermodynamic software Thermo-calc was used to investigate the presence of numerous phases in the system. X-ray diffraction (XRD) has confirmed the formation of niobium carbide in the steel, indicated by Thermo-calc. The effect of slurry velocity (30, 40, and 50 m/s) and impingement angle of slurry (30°, 45°, and 90°) on wear characteristics of these castings were analyzed using volume loss measurements, optical profilometry, and scanning electron microscopy (SEM). The erosion rate of both the materials increased with increasing velocity, whereas erosion was more at shallow angles of impact and increased significantly at the slurry jet's normal incidence. Refinement of austenitic grains in the ferritic pool hints at an increase in heterogeneous nucleation in Nb-doped samples; at the same time, the samples have shown increased hardness and superior erosion resistance against the slurry jet impact. [ABSTRACT FROM AUTHOR]

Maraging steel is a special alloy exhibiting excellent combination of ultra-high strength with considerable ductility. Thus, such steel become significant worldwide for strategic sectors (like nuclear, aerospace and defence) where stringent quality standards with respect to chemistry and properties is compulsory. Manufacturing of these steel is extremely difficult, and vacuum induction melting (VIM) furnace plays most significant part as a primary melting unit. There are a large number of processing parameters to manufacture these special alloys and on top of that, these type of vacuum furnaces are connected with various valves, motors, sensors along with safety systems, which lead to involvement of additional interdependent process variables. Accordingly, building logical agent is often difficult because the developer requires possessing the complete and intricate knowledge of all the agents, which is viable only for deterministic environment. In case of nonlinear condition, the data generation and collection in digital form is a very useful resource of valuable information for meaningful process optimization-related investigation by developing intelligent model from databases. In this perspective, data-driven optimization using evolutionary algorithms is effective tool in order to optimize parameters related to melting time of manufacturing maraging steel through critical analysis of the data. Data of 130 heats collected from VIM 6.5 Tonne furnace and the considered parameters are weight of carbon added, leak rate of system, complete meltdown time, carbon–oxygen–nitrogen pct in opening sample, carbon–oxygen–nitrogen pct in final stages of melting, refining time, leak rate during melting, tapping temperature, melt duration and tap to start time between previous and present melting and lining life. Out of aforementioned fifteen parameters, minimization of refining time and melt duration is the objectives of the present investigation. Evolutionary neural network has been used as a primary optimization algorithm for present investigation which is coupled with predator–prey genetic algorithm (PPGA). Optimization using PPGA has been achieved successfully and obtained the trade-off between refining time and melt duration. The analyses of all input parameters reveal that the complete meltdown time and carbon addition at start are the two main parameters which can affect the melting and refining time greatly. Putting extra care on these two parameters will greatly affect the melting time of maraging steel in VIM furnace. [ABSTRACT FROM AUTHOR]

The metallurgical preparation and microstructure of as-cast Ti-45Al-2W-xC (in at.%) alloys were investigated. Five alloys with carbon content ranging from 0.38 to 1.96 at.% were prepared by vacuum induction melting (VIM) in graphite crucibles, followed by centrifugal casting into graphite moulds. A master 15W-85Al (at.%) alloy with a relatively low melting point and TiC powder were used to facilitate fast dissolution of W during VIM and to achieve the designed content of C in the as-cast alloys, respectively. The increase in the content of C affects the solidification path of the studied alloys. Differential thermal analysis (DTA) and microstructural observations show that the alloys with carbon content up to 0.75 at.% solidify with β primary phase and their dendritic as-cast microstructure consists of the α2(Ti3Al) + γ(TiAl) lamellar regions, retained B2 phase enriched by W and single γ phase formed in the interdendritic region. The increase in the content of C above 0.75 at.% leads to the formation of primary lathe-shaped Ti2AlC carbides, which act as effective heterogeneous nucleation sites of β dendrites during the solidification and grain refinement of the alloys with 1.15 and 1.96 at.% C. The increase in the content of C leads to an increase in Vickers hardness and elastic modulus in the alloys containing 1.96 at.% C.

The high Nb-containing TiAl-based alloy ingot beyond laboratory scale with a composition of Ti-46Al-8Nb (at.%) was prepared by a vacuum induction melting process based on a BaZrO3 refractory crucible. A round bar ingot with a diameter of 85 mm and a length of 430 mm was finally obtained, and the chemical composition, solidification pathway, microstructure and tensile properties of the ingot were investigated. The results show that the deviations of Al and Nb content along a 430 mm long central part of the ingot are approximately ±0.39 at.% and ±0.14 at.%, and the oxygen content in the ingot can be controlled at around 1000 ppm. The structure of the alloy ingot is a full lamellar structure composed of γ and α2 phases, and the thickness of the lamellae is approximately 0.53 μm. In case of the α2 phase, the surface content of the ingot is higher than the middle region and the centrical region; also, it indicated a decreasing trend. During cooling, the alloy solidified from a peritectic reaction (L + β→α) rather than the solidified via β phase (β→α). In addition to Al segregation and Nb segregation, β-phase particles associated with γ phase at the triple junction of the colonies were observed. Moreover, the tensile properties of the longitudinal-cut sample in the ingot is significantly better than those of the transverse-cut sample, with a tensile strength of up to as high as 700 MPa and a corresponding fracture elongation of 1.1%. However, the tensile strength of the transverse-cut sample is only 375 MPa, and the fracture elongation is 0.52%.

FGUP VIAM has developed a technology for producing cast billets of a high-temperature composite material based on the Nb–Si system. This technology includes the fabrication of a Si–Cr–Al–Y master alloy, the assembling of a consumable electrode, its remelting a vacuum arc furnace, and the subsequent remelting of the resulting ingot in a vacuum induction furnace in an yttrium oxide–based crucible. This technology can be used to achieve a homogeneous chemical composition of an alloy close to the calculated one and low content of oxygen impurities. [ABSTRACT FROM AUTHOR]

This study documents laboratory-scale observation of the interactions between the Ni-based superalloy FGH4096 and refractories. Three different crucibles were tested—MgO, Al2O3, and MgO-spinel. We studied the variations in the compositions of the inclusions and the alloy-crucible interface with the reaction time using scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction. The results showed that the MgO and MgO-spinel crucibles form MgO-containing inclusions (Al-Mg oxides and Al-Mg-Ti oxides), whereas the inclusions formed when using the Al2O3 crucible are Al2O3 and Al-Ti oxides. We observed a new MgAl2O4 phase at the inner wall of the MgO crucible, with the alloy melted in the MgO crucible exhibiting fewer inclusions. No new phase occurred at the inner wall of the Al2O3 crucible. We discuss the mechanism of interaction between the refractories and the Ni-based superalloy. Physical erosion was found to predominate in the Al2O3 crucible, whereas dissolution and chemical reactions dominated in the MgO crucible. No reaction was observed between three crucibles and the Ti of the melt although the Ti content (3.8wt%) was higher than that of Al (2.1wt%). [ABSTRACT FROM AUTHOR]

Corona discharge, or gas breakdown, is undesired in superalloy vacuum induction melting (VIM) applications as it can damage insulation, produce ozone and subsequently oxidize and contaminate the melt. Gas breakdown also introduces uncontrolled variations to the casting process and increases the risk of needing to scrap the end product. To reduce the risk of corona, a rule-of-thumb of 150 to 1000 micron (150 mTorr to 1 Torr) was developed in the past as a No-Go Pressure Zone. Operating within this zone has been observed to create an unwanted, readily ionizable environment. An analytical model is developed within this work to evaluate the historical rule-of-thumb. The analytical model incorporates the following elements: Paschen's law, gas compressibility, gas and insulation permittivity, and electric field non-uniformity. The model is then applied to a sampling of VIM furnace designs to evaluate the shifts of the No-Go Pressure Zone due to variations in configuration and other operating conditions. In the end, the objective is to improve VIM furnace design and operation to reduce the risk of corona discharge—thereby improving the casting process, practice of alloy melting and quality of the end product. [ABSTRACT FROM AUTHOR]

Ａｉｍｉｎｇ ａｔ ｅｘｐｌｏｒｉｎｇ ｔｈｅ ｃｏｍｐｌｅｘ ｒｅｌａｔｉｏｎｓｈｉｐ ｂｅｔｗｅｅｎ ｖａｃｕｕｍ ｉｎｄｕｃｔｉｏｎ ｇａｓ ａｔｏｍｉｚａｔｉｏｎ (ＶＩＧＡ) ｐｒｏｃｅｓｓ ｐａｒａｍｅｔｅｒｓ ａｎｄ ｐａｒｔｉｃｌｅ ｓｉｚｅｓ ｏｆ ｓｕｐｅｒａｌｌｏｙ ｐｏｗｄｅｒｓꎬ ｔｈｅ ＡＮＳＹＳ￣ Ｆｌｕｅｎｔ ｓｏｆｔｗａｒｅ ｗａｓ ｕｓｅｄ ｔｏ ｓｉｍｕｌａｔｅ ｔｈｅ ｂｒｅａｋｉｎｇ ｂｅｈａｖｉｏｒ ｏｆ ｄｒｏｐｌｅｔｓ ｄｕｒｉｎｇ ｔｈｅ ＧＨ４１６９ ｓｕｐｅｒａｌｌｏｙ ＶＩＧＡ ｐｒｏｃｅｓｓ. Ｔｈｅ ｉｎｆｌｕｅｎｃｅ ｏｆ ａｔｏｍｉｚａｔｉｏｎ ｐｒｅｓｓｕｒｅ ｏｎ ｔｈｅ ａｔｏｍｉｚａｔｉｏｎ ｐｒｏｃｅｓｓ ａｎｄ ｐａｒｔｉｃｌｅ ｓｉｚｅ ｄｉｓｔｒｉｂｕｔｉｏｎｓ ｏｆ ｔｈｅ ｍｅｌｔ ｍｅｔａｌ ｗａｓ ａｎａｌｙｚｅｄ. Ｔｈｅ ｒｅｓｕｌｔｓ ｓｈｏｗｅｄ ｔｈａｔ ｔｈｅ ｔｈｉｃｋｎｅｓｓ ｏｆ ｔｈｅ ｓｔｒｉｐ￣ｓｈａｐｅｄ ｌｉｑｕｉｄ ｆｉｌｍ ａｎｄ ｔｈｅ ｄｒｏｐｌｅｔ ａｒｅａ ｉｎ ｔｈｅ ｆｉｒｓｔ ａｔｏｍｉｚａｔｉｏｎ ｐｒｏｃｅｓｓ ｇｒａｄｕａｌｌｙ ｄｅｃｒｅａｓｅｄꎬ ｗｈｉｌｅ ｔｈｅ ｃｒｕｓｈｉｎｇ ｅｆｆｅｃｔ ｏｆ ｔｈｅ ｓｅｃｏｎｄａｒｙ ａｔｏｍｉｚａｔｉｏｎ ｏｎ ｔｈｅ ｍｅｌｔ ｗａｓ ｇｒａｄｕａｌｌｙ ｅｎｈａｎｃｅｄ. Ｔｈｅ ｐａｒｔｉｃｌｅ ｓｉｚｅ ｏｆ ｔｈｅ ａｔｏｍｉｚｅｄ ｐｏｗｄｅｒｓ ｗａｓ ｒｅｄｕｃｅｄ ｆｒｏｍ ８１. １０ ｔｏ ６９. ８０ꎬ ６４. ７７ꎬ ５２. ３０ ａｎｄ ｆｉｎａｌｌｙ ｔｏ ４１. ８０ μｍ. Ｃｏｒｒｅｓｐｏｎｄｉｎｇｌｙꎬ ｔｈｅ ｙｉｅｌｄ ｏｆ ｆｉｎｅ ｐｏｗｄｅｒｓ ｗａｓ ｇｒａｄｕａｌｌｙ ｉｍｐｒｏｖｅｄ ｆｒｏｍ １. ７２％ ｔｏ １２. ６２％ ꎬ １８. ８９％ ꎬ ５６. ５０％ ꎬ ａｎｄ ｆｉｎａｌｌｙ ｔｏ ７１. ５４％ . [ABSTRACT FROM AUTHOR]

The effect of Zr addition on the melting temperature of the CoCrFeMnNi High Entropy Alloy (HEA), known as the “Cantor’s Alloy”, is investigated, together with its micro-structure, mechanical properties and thermomechanical recrystallization process. The base and Zr-modified alloys are obtained by vacuum induction melting of mechanically pre-alloyed powders. Raw materials are then cold rolled and annealed. recrystallization occurred during the heat treatment of the cold-rolled HEA. The alloys are characterized by X-ray diffraction, electron microscopy, thermal analyses, mechanical spectroscopy and indentation measures. The main advantages of Zr addition are: (1) a fast vacuum induction melting process; (2) the lower melting temperature, due to Zr eutectics formation with all the Cantor’s alloy elements; (3) the good chemical alloy homogeneity; and (4) the mechanical properties improvement of re-crystallized grains with a coherent structure. The crystallographic lattice of both alloys results in FCC. The Zr-modified HEA presents a higher recrystallization temperature and smaller grain size after recrystallization with respect to the Cantor’s alloy, with precipitation of a coherent second phase, which enhances the alloy hardness and strength.

The nitrogen behavior of superalloy melt GH4169 during the vacuum induction melting (VIM) process was clarified by using different proportions of returned materials including block-shaped returned material, chip-shaped returned material, and pure materials to produce a high–purity superalloy melt and provide guidance for the purification of the superalloy melt. For the nitrogen removal during the VIM process, the denitrification rate in the refining period reached 10 ppm per hour on average, which is significantly higher than 1 ppm per hour on average in the melting period. The denitrification reaction of superalloy melt GH4169 under extremely low vacuum pressure is controlled by both the mass transfer of nitrogen in the melt and the chemical reaction of the liquid–gas interface. The nitrogen removal of superalloy melts during VIM occurs through the two methods of gasification denitrification and nitride floatation because the nitrides begin to precipitate in the liquid phase at 1550 °C. A higher nitrogen removal rate can be obtained by increasing the proportion of chip-shaped material or decreasing the proportion of block-shaped material.

Features of the structure and phase composition of alloys with a shape memory effect of the Ni-Ti-Nb and Ni-Ti-Nb-Zr systems, melted in graphite and inert ceramic crucibles in a vacuum are considered. Cast metal qualitative and quantitative structural and phase analysis data are provided, and the dependence of the amount of "parasitic" phase Ti2Ni on melting method is demonstrated. The possibility of melting highly active materials based on titanium nickelide alloyed with niobium and zirconium in ceramic crucibles based on ZrO2 is demonstrated. [ABSTRACT FROM AUTHOR]

The possibilities of metallurgical preparation of 40Nb-60Al and 15W-85Al intermetallic compounds (in at.%) by plasma arc melting (PAM) and vacuum induction melting (VIM) were studied. Both methods allow easy preparation of Nb–Al alloys; however, significant evaporation of Al was observed during the melting, which affected the resulting chemical composition. The preparation of W–Al alloys was more problematic because there was no complete re-melting of W during PAM and VIM. However, the combination of PAM and VIM allowed the preparation of W–Al alloy without any non-melted parts. The microstructure of Nb–Al alloys consisted of Nb2Al and NbAl3 intermetallic phases, and W–Al alloys consisted mainly of needle-like WAl4 intermetallic phase and Al matrix. The effects of melting conditions on chemical composition, homogeneity, and microstructure were determined. Differential thermal analysis was used to determine melting and phase transformation temperatures of the prepared alloys.

In recent years, biodegradable magnesium alloys have attracted considerable attention in medical devices, such as permanent implants and stents. However, poor corrosion resistance is a major problem limiting the practical application of magnesium alloys. In this study, Mg _67 Zn _28 Ca _5 alloys were prepared via two different methods, namely, vacuum induction melting and ulfur hexafluoride shielded melting. The effect of melting method on the bio-corrosion resistance of MgZnCa cast magnesium alloy was also studied. The microstructure and phase composition of Mg _67 Zn _28 Ca _5 alloys were investigated by optical microscopy and X-ray diffraction. The element distribution and surface morphology of Mg _67 Zn _28 Ca _5 alloys were examined by scanning electron microscopy and energy-dispersive spectroscopy. The corrosion resistance of Mg _67 Zn _28 Ca _5 alloys was measured via electrochemical and immersion tests. Results showed uniform composition of the Mg _67 Zn _28 Ca _5 alloy melted by vacuum induction. Immersed in the simulated body fluid, the corrosion rate of Mg _67 Zn _28 Ca _5 by vacuum induction melting (0.2618 mm/ a ) was lower than that by ulfur hexafluoride shielded melting (0.9686 mm/ a ); the corrosion potential of Mg _67 Zn _28 Ca _5 melted by vacuum induction (−1313 mV) was nobler than that by ulfur hexafluoride shielded melting (−1483 mV); the corrosion current of Mg _67 Zn _28 Ca _5 by vacuum induction melting (1.202 × 10 ^−5 A) was lower than that by ulfur hexafluoride shielded melting (4.332 × 10 ^−5 A). The Mg _67 Zn _28 Ca _5 by vacuum induction melting showed uniform corrosion behavior.