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The chemical homogeneity and metallurgical structure of vacuum arc remelted (VAR) zirconium ingots are directly responsible for product quality. It is therefore important to understand the relationship between these properties and the operating conditions. An in-depth analysis of the modelling of solidification phenomena during the VAR was carried out. Such model, solves a coupled set of transient equations for heat, momentum, solute transport and turbulence in an axisymmetric geometry. The remelting and cooling of a cylindrical ingot are calculated for time-dependent operating parameters. The solidification mechanisms implemented in the model can be applied to multi-component industrial alloys such as Zircaloy-4, which provides information on the macrosegregation phenomena studied in this paper. The model results were validated, based on the remelting of a specially designed chemically homogeneous Zircaloy-4 electrode. The results illustrate the importance of thermal and solute convection, the importance of the permeability of the partially solid material and the weak influence of nuclei density and solute diffusion in the solid phase on the prediction of macrosegregation in Zircaloy-4 ingots.

A comprehensive numerical model is proposed to study the influence of an axial magnetic field (AMF) on the solidification behavior of a Titanium-based (Ti–6Al–4V) vacuum arc remelting (VAR) ingot. Both static and time-varying AMF are examined. The proposed 2D axisymmetric swirl model includes calculating electromagnetic and thermal fields in the entire system composed of the electrode, vacuum plasma, ingot, and mold. A combination of vector potential formulation and induction equation is proposed to model the electromagnetic field accurately. Calculations of the flow in the melt pool and solidification of the ingot are also carried out. All governing equations are presented in cylindrical coordinate. The presence of a weak AMF, such as the earth magnetic field, can dramatically influence the flow pattern in the melt pool. The “Electro-vortex flow” is predicted ignoring AMF or in the presence of a time-varying AMF. However, the flow pattern is “Ekman pumping” in the presence of a static AMF. The amount of side-arcing has no influence on the pool depth in the presence of an AMF. Modeling results are validated against experiments.

In present work, a novel heavy density matrix alloy (Ni–W–Co) was produced through vacuum induction melting (VIM) and vacuum arc remelting (VAR). The as-cast microstructure, element segregation, and mechanical properties were characterized by optical microscopy, scanning electron microscopy, electron probe microanalysis, and universal tensile testing machine. Results indicated that the present matrix alloy displays a considerable purity and chemical homogeneity. The microstructure exhibits typical dendritic features, which is composed of austenite single-phase structure entirely. The elements Ni and Co are evenly distributed in the matrix, while W shows a distinct segregation trend in the as-cast ingot. The tensile properties of the as-cast alloy at room temperature show that the maximum ultimate tensile strength and fracture elongation are up to 560Mpa and 55.79%, respectively. Tensile fracture morphologies reveal the presence of complex quasi cleavage and ductile fractures. The true stress-plastic strain curves display distinct linear deviation in the region of uniform plastic deformation and exhibit two groups of positive and negative slopes at the lower and higher strains, respectively. The instantaneous work hardening rate-true strain curves depict typical “three stages” hardening characteristics.

In this paper, shape memory alloys (SMAs) (NiTi-based) have been manufactured by casting with a different atomic percentage of a silver element (0, 1, 2 and 3 at. % Ag) using a Vacuum Arc Remelting (VAR) furnace. The silver element is added to the binary alloys due to its excellent properties such as (anti-corrosion, anti-bacterial and high electrical conductivity), which make these alloys using in wider applications. These alloys with different atomic percentages (Ni55Ti45Ag0, Ni55Ti44Ag1, Ni55Ti43Ag2 and Ni55Ti42Ag3) have been manufactured. The successful manufacturing process has been achieved and proved via examinations and tests. The FESEM microscopic examinations show that the silver element has been distributed uniformly and homogeneously in the NiTi matrix. Moreover, the emergence of austenite phase, martensite phase and little amount impurities. Regarding the XRD examination, showed that there is an increase in the number of peaks of Ag phase with an increase in the atomic percentage of the silver element, as well to emergence of phase (Ti2Ni) upon heating, phase (Ti 002) upon cooling, and phase (Ni4Ti3) is not desired. The starting and finishing of the phase transformations have been determined for all samples by the DSC test. The Shape Memory Effect (SME) for the alloy (Ni50Ti42Ag3) is measured to be about 89.99%.

The chemical composition variation of the TiAl-4722 alloys was examined in a batch of the industrial scale master ingots, and in the corresponding castings prepared by conventional vacuum arc remelting (VAR) combined with induction skull melting (ISM) and investment casting processes. The content changes of major elements and interstitial elements were evaluated based on the chemical analysis at the top and bottom of the ingots and castings. Results show that the contents of C, N, H, Fe and Si have almost no change in the ingots and castings, suggesting that the chemical analysis on these elements can be based on the batch analysis. The O content keeps almost the same in different ingots, but exhibits relatively large differences in castings, which was probably influenced by the reaction between the shell mold and the molten alloy, and the spalling of face coat of the shell mold during casting. For the major elements of Al, Nb and Cr, the composition difference between the top and the bottom of the ingots is less than that of the castings. But for the O element, the trend is different, especially for the castings, suggesting that the investment casting is a homogenization process for Cr and Nb, but a differentiation process for O. The contents of major elements in castings fluctuate mainly in the same range as that in the ingots, indicating that the contents of the major elements are controllable during investment casting.

Martensitic microstructure of AISI 4340 steel can be heat treated to achieve the desired mechanical properties. However, mechanical properties degrade owing to the impurities and cleanliness during the steel production. In this work, AISI 4340 steel was produced through three different routes, such as vacuum degassing (VD), electro slag remelting (ESR), and vacuum arc remelting (VAR), followed by austenizing, hardening, and tempering. Further, mechanical characterization such as tensile, hardness, and toughness were carried out in a wide range of tempering temperatures (171-649 °C). A variation in mechanical properties was observed due to the evolution of precipitated carbide with the tempering temperature in all three routes. A thicker carbide layer along the martensitic lath boundary led to higher embrittlement in VD and VAR for tempering regime 171-427 °C. The absence or lesser embrittlement in ESR attributes to the homogeneously distributed fragmented carbides. Martensitic lath coarsening, ferritic phase formation along with the precipitated carbide distribution, significantly enhances the fracture toughness over the impact toughness at higher tempering temperature (> 316 °C). The difference in the mechanical properties in all the three routes is found to be sensitive toward the chemical composition causing a marked difference in the carbide precipitation and its distribution along the martensitic lath boundaries.

Titanium alloys are excellent candidates for structural components submitted to high temperature owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability. Due to the complex service conditions of spacecraft, the creep property of titanium alloy has been recognized. The microstructural evolution, mechanical properties of Ti-6Al-4V-xSi-ySc alloys have been investigated. Alloys were prepared by three times vacuum arc remelting followed forging, rolling and heat treatment at 950 °C/0.5 h/AC and 510 °C/5 h/AC. Then specimens were subjected to uniaxial tensile and creep test. The strengthening and creep resistance mechanism of the alloys were analyzed. The results shown that the grain sizes of alloys were refined significantly by Sc and Si addition. The Si and Sc plays a role in grain refinement and solid solution strengthening. At the same time, the alloy matrix was purified due to the formation of Sc2O3 particles. The Si and Sc addition improve the creep resistance comparing the base alloy. This can be attributed to the strengthening of solid solution of Si and the silicide also have the inhibiting effect on the dislocation movement during creep. Si promote the diffusion of V and suppress the formation of α2 phase. Sc in titanium alloy has three forms, some of which are solid-dissolved, some of which form Sc2O3, and some of which form horseshoe-shaped Al3Sc. The formation of Al3Sc particles is helpful to improve the creep properties of titanium alloy. Sc can inhibit the precipitation of silicide and promote the formation of α2 phase, which are helpful to improve the creep resistance of titanium alloy.

International audience; The Electron Beam Melting (EBM) process has emerged as either an alternative or a complement to vacuum arc remelting of titanium alloys, since it is capable of enhancing the removal of exogenous inclusions by dissolution or sedimentation. The melting of the primary material is a first step of this continuous process, which has not been studied so far and is investigated experimentally and numerically in the present study. Experiments have been set up in a 100 kW laboratory furnace with the aim of analyzing the effect of melting rate on surface temperature of Ti-64 bars. It was found that melting rate is nearly proportional to the EB power while the overheating temperature remains roughly independent of the melting rate and equal to about 100 °C. The emissivity of molten Ti-64 was found to be 0.22 at an average temperature of about 1760 °C at the tip of the bar. In parallel, a mathematical model of the thermal behavior of the material during melting has been developed. The simulations revealed valuable results about the melting rate, global heat balance and thermal gradient throughout the bar, which agreed with the experimental values to a good extent. The modeling confirms that the overheating temperature of the tip of the material is nearly independent of the melting rate.

Digital image analysis techniques were developed to autonomously characterize dendritic solidification features in microstructures of a nickel alloy 718 ingot produced by vacuum arc remelting (VAR). Automated macrophotography was implemented to image microstructures and produce large image montages of etched ingot cross sections. Two image analysis techniques, particle identification and two-point correlation, were applied to autonomously measure primary dendrite arm orientation and secondary dendrite arm spacing from the image montages. Particle identification measured individual dendritic features. The two-point correlation technique measured averaged feature values over defined image areas. These methods are described and compared. Melt pool profile and solidification time histories were reconstructed from primary dendrite arm orientation and secondary dendrite arm spacing measurements, respectively. These characterization techniques provide two new methods of reconstructing melt pool profiles and solidification times in cast ingots. The information produced is expected to be useful in the validation of computational models for solidification during VAR, similar remelting processes, and general casting processes that produce dendritic solidification features.

Cr-Al alloys are attracting attention as oxidation resistant coating materials for high temperature metallic materials due to their excellent high temperature stability. However, the mechanical properties and oxidation resistance of Cr-Al alloys can be further enhanced, and such attempts are made in this study. To improve the properties of Cr-Al alloys, Si is added up to 5 wt%. Casting specimens with different amounts of Si content are prepared by a vacuum arc remelting method and isothermally heated under steam conditions at 1,100oC for 1 hour. The as-cast microstructure of low Si alloys is mainly composed of only a Cr phase, while Al8Cr5 and Cr3Si phases are also observed in the 5% Si alloy. In the high Si alloy, only Cr and Cr3Si phases remain after the isothermal heating at 1,100oC. It is found that Si additions slightly decrease the oxidation resistance of the Cr-Al alloy. However, the microhardness of the Cr-Al alloy is observed to increase with an increasing Si content.

Plenty of papers with regard to the processing of TiAl alloys via investment casting, forging, rolling, extrusion pressing as well as mechanical machining have been published, whereas the manufacturing of gamma-TiAl based alloys and corresponding semi-finished products has not been entirely described so far. The aim of this paper is to review and evaluate the present technologies of TiAl alloy production on an industrial scale. Metallurgical alloying techniques such as vacuum arc remelting (VAR), plasma arc melting (PAM) and electron beam melting (EBM) are being shortly described and evaluated with regard to their advantages and disadvantages from both technical and economical point of view. Particular focus is set on some specifics in metallurgical processing of TiAl alloys compared to Ti and Ti alloys. Outstanding requests on the accuracy of chemical composition, microstructural homogeneity, acceptable local deviations of alloying elements, small sizes of the products, and, additionally, the very limited wrought processing capability of TiAl alloys require a set of adjusted metallurgical technologies for the manufacturing of semi-finished products. With this regard, the production of small sized semi-finished parts via skull melting technologies and subsequent centrifugal casting in permanent moulds have been successfully developed and industrialized. Both, VAR skull melting (VAR SM) for ingot conversion and induction skull melting (ISM) for the conversion of valuable revert materials result in technically indistinguishable products due to the application of a consistent centrifugal casting technology. Both procedures offer the highest flexibility on product shapes and dimensions for minimizing the specific materials usage, which has a direct positive influence on final component costs. Resulting materials properties of the semi-finished products meet entirely the different (customer related) specification requirements. There are basically no technical limitations with regard to TiAl alloy compositions as it is the case for TiAl alloy manufacturing via other technologies.

International audience; During the processing of maraging steels, Titanium easily combines with Nitrogen to form nitride inclusions, known to be deleterious for fatigue properties of the alloy. According to thermodynamic calculations, the precipitation occurs during solidification of the vacuum arc remelted (VAR) ingot. A coupled model of titanium nitride (TiN) inclusion precipitation and vacuum remelting has been setup to study the inclusion cleanliness of the ingot. The nitrogen content, nuclei numeral density and solidification time appear as the key factors which control the inclusion size.

Main modeling challenges for vacuum arc remelting (VAR) are briefly highlighted concerning various involving phenomena during the process such as formation and movement of cathode spots on the surface of electrode, the vacuum plasma, side-arcing, the thermal radiation in the vacuum region, magnetohydrodynamics (MHD) in the molten pool, melting of the electrode, and solidification of the ingot. A numerical model is proposed to investigate the influence of several decisive parameters such as arc mode (diffusive or constricted), amount of side-arcing, and gas cooling of shrinkage gap at mold–ingot interface on the solidification behavior of a Titanium-based (Ti-6Al-4V) VAR ingot. The electromagnetic and thermal fields are solved in the entire system including the electrode, vacuum plasma, ingot, and mold. The flow field in the molten pool and the solidification pool profile are computed. The depth of molten pool decreases as the radius of arc increases. With the decreasing amount of side-arcing, the depth of the molten pool increases. Furthermore, gas cooling fairly improves the internal quality of ingot (shallow pool depth) without affecting hydrodynamics in the molten pool. Modeling results are validated against an experiment.

Кондрашов Евгений Николаевич, канд. физ.-мат. наук, ведущий специалист НТЦ, ПАО «Корпорация ВСМПО-АВИСМА», г. Верхняя Салда; kondrashov@vsmpo.ru. Русаков Кирилл Андреевич, инженер по электронной микроскопии первой категории, ПАО «Корпорация ВСМПО-АВИСМА», г. Верхняя Салда; rusakov_ka@vsmpo.ru. Ледер Михаил Оттович, директор по науке и технологии, ПАО «Корпорация ВСМПО- АВИСМА», г. Верхняя Салда; moleder@vsmpo.ru. Куликов Дмитрий Сергеевич, инженер-исследователь НТЦ, ПАО «Корпорация ВСМПО- АВИСМА», г. Верхняя Салда; salda87@mail.ru. E.N. Kondrashov, kondrashov@vsmpo.ru, K.A. Rusakov, rusakov_ka@vsmpo.ru, M.O. Leder, moleder@vsmpo.ru, D.S. Kulikov, salda87@mail.ru VSMPO-AVISMA Corporation, Verkhnyaya Salda, Russian Federation Для проведения математического моделирования затвердевания слитков необходимо знание температурных зависимостей теплофизических свойств затвердевающего сплава и параметров граничных условий, включенных в математическую модель. В настоящей работе были выплавлены два слитка сплава Ti–10V–2Fe–3Al и проведено исследование их макроструктуры. Измерены координаты профилей изотерм затвердевания, и с помощью решения обратной задачи теплопроводности, определены некоторые теплофизические характеристики жидкой фазы и параметры граничных условий для вакуумного дугового переплава (ВДП), прямое экспериментальное измерение которых сопряжено с большими трудностями. Для определения неизвестных параметров математической модели методом решения обратной задачи теплопроводности используется итерационный Maximux A Posteriori (MAP) алгоритм, ранее апробированный для других сплавов на основе титана. Искомыми (т. е. изначально неизвестными) параметрами для математической модели процесса ВДП являлись: теплопроводность и теплоемкость при температурах солидуса и ликвидуса; коэффициент теплоотдачи от слитка к изложнице и коэффициенты относительного вклада теплоотвода излучением для поддона и изложницы. В качестве начального приближения для неизвестных параметров были взяты соответствующие величины для сплава BT3–1. В качестве заданных параметров были использованы значения коэффициента теплопроводности и удельной теплоемкости в интервале температур 20‒1300 °C из базы данных программы JMatPro, рассчитанные для заданного химического состава. Плотность, теплота фазового превращения, динамическая вязкость и электропроводность были взяты из литературных источников по сплаву Ti–10V–2Fe–3Al. Так как на сегодня нет данных по равновесной фазовой диаграмме сплава Ti–10V–2Fe–3Al, поэтому для вычисления температур равновесного ликвидуса и солидуса используется модель независимых компонент (линейная модель) многокомпонентного сплава. Найденные значения параметров позволяют удовлетворительно описать изменение профиля жидкой ванны при наплавлении слитка во время ВДП для различных условий процесса (диаметр изложницы и сила тока дуги). Результаты, полученные в работе, могут быть использованы для проведения математического моделирования процесса затвердевания слитков из сплава Ti–10V–2Fe–3Al при вакуумном дуговом переплаве с другими диаметрами изложницы и силой тока дуги. To carry out mathematical modeling of solidification of ingots, it is necessary to know the temperature dependences of the thermophysical properties of the solidified alloy and the parameters of the boundary conditions included in the mathematical model. In the present work, two ingots of Ti– 10V–2Fe–3Al alloy are smelted and their macrostructure was investigated. The coordinates of the solidification isotherm profiles were measured and, using the solution of the inverse heat conduction problem, some thermophysical characteristics of the liquid phase and the boundary conditions for vacuum arc remelting (VAR) were determined, the direct experimental measurement of which is very difficult. An iterative Maximux A Posteriori (MAP) algorithm, previously tested for other titanium- based alloys, is used to determine the unknown parameters of the mathematical model by solving the inverse heat conduction problem. The required (i.e. initially unknown) parameters for the mathematical model of the VAR process were: thermal conductivity and heat capacity at solidus and liquidus temperatures; сoefficient of heat transfer from ingot to mold and coefficients of relative contribution of heat removal by radiation for tray and mold. As the set parameters, the values of the thermal conductivity coefficient and specific heat capacity in the temperature range 20‒1300 °C from the JMatPro database were used, calculated for the specified chemical composition. The density, heat of phase transformation, dynamic viscosity, and electrical conductivity were taken from the literature on the Ti–10V–2Fe–3Al alloy. The found parameter values allow us to describe satisfactorily the change in the profile of the liquid bath when the ingot is fusing in the VAR for different process conditions (the diameter of the mold and the arc current). The results obtained in this work can be used for mathematical modeling of the process of solidification of ingots made of Ti–10V–2Fe–3Al alloy during vacuum arc remelting with other mold diameters and arc current.

In the current work, the microstructure, mechanical properties and machinability of Ti15SnxCu alloys (x = 0 to 2 wt. %) were investigated. The alloy was prepared by the vacuum arc remelting and casting route and then thermally processed by solutionizing at 1000 °C for 2 hours, followed by water quenching. By controlling the heat-treated condition and Cu content, the highest bending strength and modulus were obtained from three-point bending testing. The increases were mainly caused by the strengthening effects of the formation of crystallites with fine grain size and nano-Ti2Cu precipitate phase. In addition, nano-Ti2Cu precipitation was caused by crack initiation and propagation, which reduced the ductility and improved the machinability of Ti15Sn2Cu alloy.

The high Nb containing TiAl alloy with a nominal composition of Ti–44Al–8Nb–0.2W–0.2B–0.1Y was fabricated by a Vacuum Arc Remelting furnace. The microstructure and mechanical properties of specimens located in different sites of the ingot were investigated. Owing to the influence of melting process and electrode fabricating method, the morphologies and phase containing of this near lamellar structure in the top, middle, and bottom parts of ingot were different. The subtle difference in microstructure strongly influenced the room and high-temperature tensile properties in turn. However, the dominant influence factor of the mechanical properties was the defects at the bottom of this large-size ingot, though the bottom had the finest grain size.

The research was mainly focused on the phase transformation of Ti-42Al-5Mn (at%) alloy produced by vacuum induction melting (VIM) and vacuum arc remelting (VAR) followed by wrought process. The phase transformation kinetics of the alloy during continuous cooling under the cooling rates of 0.1 °C/s, 0.5 °C/s, 2 °C/s, 10 °C/s, 50 °C/s, and 200 °C/s were identified by the Gleeble-3800 system, which is finally used to construct a schematic continuous cooling transformation (CCT) diagram of this alloy. The related phase composition, microstructure and property of the alloy were studied using X-ray diffraction (XRD), electron probe micro analyzer (EPMA), transmission electron microscope (TEM) and Vickers hardness (HV). It shows that six kinds of phase transformation are existed during continuous cooling from 1300 °C with the cooling rates of 0.1 °C/s, 0.5 °C/s, 2 °C/s, 10 °C/s, 50 °C/s, 200 °C/s and WQ, including β→α2′, β→α, β→γ, β→βo/α→α2, α2→α2/γ and α2/γ→βo,sec. It reveals that partial transformations would be inhibited when the cooling rate is relatively high. The martensitic structures (α2′) obtained by β→α2′ were formed under the WQ condition after holding at 1300 °C for 5min, and it will be completely restrained below the cooling rate of WQ. For the β→γ, it is restrained if the cooling rates are higher than 50 °C/s. The α2→α2/γ could be also suppressed when cooling with 200 °C/s, and the γ lath within the supersaturated α2-grains would be formed at lower cooling rate below 50 °C/s. For 0.5 °C/s and 0.1 °C/s, a small amount of dotted βo (βo,sec) phases can be formed in the lamellar interfaces, which is proved the reaction products of α2/γ→βo,sec. Furthermore, the effect of cooling rates on the microstructure, including interlamellar spacing (λ) and γ grains are also identified and discussed.

Sn-0.7Cu-0.075Al solder alloy adding with Ce and La had been successfully prepared by applying ball-milling and vacuum arc remelting. The influence of Ce and La on microstructure and corrosion behavior of Sn-0.7Cu-0.075Al solder alloy was investigated. The results showed that Ce (La)-containing solders had refined grains and obvious directional tendency due to the dispersive refiner (CeO2 and La2O3). Electrochemical potentiodynamic curves revealed three different stages of the reaction, including anodic and cathodic processes, prepassivation section, and stable passivation stages. The self-corrosion potential (Ecorr) of alloys with Ce and La addition were a little bit more negative, hardly making a difference on corrosion occurrence. However, the corrosion current density (Icorr) and passivation current density (Ip) decreased by two-thirds and one-half respectively, which indicated a better corrosion resistant after adding rare earths. The recorded micrographs of corroded surface at different polarized points witnessed the formation of corrosion product film both on prepassivation and passivation stage. Moreover, the cross section of corrosion product film showed the coarse, loose film in Sn-0.7Cu-0.075Al solder and adherent, compact film in Ce (La)-containing solders, which further indicated an excellent anti-corrosion property.

In this paper, the effects of Ta substitution for Nb, on the microstructure and corrosion fatigue behavior of metastable Ti-18Nb-14Zr biomedical alloy are investigated for the first time. For this purpose, besides previously studied ternary Ti-18Zr-14Nb alloy, new quaternary Ti-18Zr-13Nb-1Ta (at.%) biomedical alloy was also synthesized by vacuum arc remelting method and subjected to thermomechanical treatment processes. The in situ electrochemical behavior and subsequent functional fatigue life of both alloys showed a strong dependence on the composition and microstructure. The electrochemical results from the test bench demonstrated that during monotonic cycling the fatigue life of Ta-added alloy was significantly longer than that of the Ti-18Zr-14Nb alloy. Thus, the addition of Ta to the ternary Ti-18Zr-14Nb alloy was found to be very effective in increasing the resistance to fatigue degradation mainly by exhibiting excellent protective passivation tendency. Based on the electrochemical evaluation and fractrographic characteristics, it is concluded that the combined effect of the stable passive film formation and higher development of a nanosubgrained structure in β phase results in the prolonged fatigue life of Ta-added alloy.

Compositional tuned non-equiatomic refractory high-entropy alloys are coveted materials as they achieve considerable plasticity through transformation-induced plasticity (TRIP) behavior. In this study, a novel Ti-rich Ti60Mo10V10Cr10Zr10 refractory medium-entropy alloy (RMEA) was designed using FactSage. The plastic deformation of the alloy produced using vacuum arc remelting was investigated through a room-temperature compression test at different strain rates. A high strain-hardening rate and an m-value of 0.031 were observed in the Ti-rich Ti60Mo10V10Cr10Zr10 RMEA. The dimple structures formed in BCC phases and TRIP-assisted deformation attribute to the strength and ductility trade-off in Ti-rich Ti60Mo10V10Cr10Zr10 RMEA.

An amorphous Ti-37.5Zr-15Cu-15Ni (wt.%) ribbon fabricated by vacuum arc remelting and rapid solidification was used as filler metal to vacuum braze TiAl alloy (Ti-45Al-2Mn-2Nb-1B (at.%)). The effects of brazing temperature and time on the microstructure and strength of the joints were investigated in details. The typical brazed joint major consisted of three zones and the brazed joints mainly consisted of α 2- Ti 3 Al phase, α-Ti phase and (Ti, Zr) 2 (Cu, Ni) phase. When the brazing temperature varied from 910 °C to 1010 °C for 30 min, the tensile strength of the joint first increased and then decreased. With increasing the brazing time, the tensile strength of the joint increased. The maximum room temperature tensile strength was 468 MPa when the specimen was brazed at 930 °C for 60 min. All the fracture surfaces assumed typical brittle cleavage fracture characteristic. The fracture path varied with the brazing parameter and cracks preferred to initiate at (Ti, Zr) 2 (Cu, Ni) phase and propagation path were mainly determined by the content and distribution of α-Ti phase and (Ti, Zr) 2 (Cu, Ni) phase.

This study investigated the thermodynamic parameters, microstructures and electrochemical properties of TiMoVWCr and TiMoVNbZr bio-refractory high-entropy alloys (bio-RHEAs) prepared using the vacuum arc remelting process. The alloys were characterized using field emission scanning electron microscopy, field emission electron probe microanalyzer, X-ray diffraction analysis, and potentiodynamic polarization tests. The determined thermodynamic values of Ω-parameter, atomic size difference and valence electron concentration for the TiMoVWCr and TiMoVNbZr bio-RHEAs were within the range of solid solution formation. A high-temperature stable single BCC1 phase was obtained using the thermodynamic equilibrium calculations for the TiMoVWCr and TiMoVNbZr systems. The TiMoVWCr alloy microstructure comprised a dendrite, an inter-dendrite, and a second phase, while TiMoVNbZr alloy comprised a dendrite and an inter-dendrite. The TiMoVWCr alloy forming the stable single body-centered cubic solid solution demonstrated homogeneous microstructure and high phase stability. Moreover, pitting resistances of TiMoVWCr and TiMoVNbZr bio-RHEAs were remarkably superior to that of ASTM F75 alloy.

Ti–22Fe–23Mn(at.%) eutectic brazing alloy ribbon fabricated by vacuum arc remelting and rapid solidification as filler metal used to vacuum braze Ti–45Al–2Mn–2Nb–1B(at.%) alloy. The effects of brazing temperature and time on the interfacial microstructure and joining properties were investigated in detail. The microstructure of the Ti–20Fe–21Mn brazing alloy presented excellent diffusion ability, and the brazed joints mainly consisted of α2/γ lamellar phase, single α2 phase, B2 phase, and boride. The brazed joint's tensile strength first increased and then decreased with the brazing temperature in the range of 1170 °C–1250 °C, and the holding time varied from 5 min to 60 min. The highest tensile strength at room temperature was 540 MPa when the joint brazed at 1230 °C for 45 min. The high-temperature tensile strength first increased and then decreased with the testing temperature. The high-temperature tensile strength of Ti–22Fe–23Mn(at.%) alloy was superior to Ti–Zr–Cu–Ni (at.%) alloy. The high-temperature tensile strength was lower than 45XD alloy below 850 °C. However, the tensile strength was closer to 45XD alloy when the testing temperature varied from 900 °C to 1000 °C. All the cracks nucleated and propagated in the poor boride zone, and the fracture surfaces presented typical brittle cleavage fracture characteristics.

Experimental results have shown that high-strength steels can fail in the Very-High-Cycle Fatigue (VHCF) regime with cracks originating from internal defects. Material cleanliness thus plays a major role in the VHCF response of high-strength steels and refinement processes (eg, electroslag remelting [ESR] and vacuum arc remelting) could significantly enhance their performance. The present paper aims at investigating the effect of the ESR process on the VHCF behavior of an AISI H13 steel by carrying out fully reversed ultrasonic tension-compression tests on hourglass specimens manufactured with and without the ESR process. Size effect is also taken into account in the paper: the effectiveness in the prediction of the VHCF response of specimens with large risk-volumes from experimental data on specimens with small risk-volumes is discussed and experimentally validated.

Understanding the arc dynamics during VAR is important for controlling the final quality of the ingot, as the spatial and temporal distribution of the arc dictates the electric current and energy inputs at the ingot top, which in turn affect the hydrodynamics of the metal in the molten pool and the solidification conditions of the ingot. The arc dynamics during vacuum arc remelting was quantitatively investigated based on the analysis of the light emitted by the arc and reflected by the molten pool using photodiodes placed inside a full-scale furnace. The measurements allowed us to determine the location of the arc luminosity centroid and to follow its displacement as a function of time. They were made during the melt of a Ti64 alloy with an imposed alternated electromagnetic stirring of high intensity. The arc dynamics was found to be most of the time periodic, asymmetrical, and strongly correlated to the evolution of the stirring magnetic field. The arc centroid exhibited three regular displacement patterns throughout the melt. A common characteristic to all three patterns was the relative stability of the centroid during stirring plateaus and its rapid motion during stirring ramps. An evolution towards a much more centered distribution of the centroid was observed with the arc power decrease during the hot-topping phase. Possible implications of the observed arc dynamics on the final quality of the VAR ingot are discussed.