Search

Hot deformation studies of a newly designed γ + α2 based TiAl alloy of composition Ti–42Al–6Nb–3Cr–0.1B at.% (nominal) realized through ingot metallurgy route using double vacuum arc remelting were carried out. Hot isothermal compression testing was performed in Gleeble™ 3500 at different temperatures ranging from 1123 to 1373 K at 50 K intervals and strain rates of 0.001–1 s−1. Processing maps were developed using an approach of dynamic material modeling of the flow curves to establish the safe hot working regime. Strain rate sensitivity and Zener–Holloman parameters were calculated and constitutive equation was derived. Microstructural investigation revealed dynamic recrystallization and activation of multiple twin systems as the main softening mechanisms operating at optimum hot working conditions. Safe hot working temperature and strain rate regime for the alloy was found to be in the temperature range of 1323–1373 K and strain rate range of 0.001–0.01 s−1.

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 results of original research into the structure and statistical distribution of elements alloyed into ingots from a new Russian intermetallic TiAl alloy having two variable compositions (Ti–44.5Al–2V–1Nb–1.5Zr/2.5Cr–0.1Gd, at.%) are presented. The experimental ingots having a nominal weight of 3–30 kg were obtained according to two technological schemes: 1 — triple vacuum arc remelting (VAR + VAR + VAR) with a consumable compacted electrode; 2 — VAR → VAR → single vacuum induction melting (VAR + VAR + VIM) in a cold crucible furnace. The statistical processing of the chemical analysis results was carried out using Shewhart charts. The results indicate a minimum degree of volumetric macrosegregation in the ingots and the almost complete absence of segregation inhomogeneity in Zr- and Cr-containing compositions: the maximum range of Al content over the cross section of triple-remelted ingots was no more than 0.84 at.% (0.42 wt.%), while along the height of the ingots, Al content was no more than 1.87 at.% (0.55 wt.%).

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.

Our recent works are devoted to simple thermal model concerning the ingot solidification during vacuum arc remelting (VAR). The nonlinear PDE solving algorithm of model implementation has been tested by analytical solutions within constrained systems. To obtain these solutions a special linearization method of the heat equation is first proposed. The obtained solutions can be specifically applied to hypothetical alloys with peculiar thermo-physical properties, meeting the rigid linearization requirements. The VAR model of the kind has been verified. In order to validate the model, a mixed experimental and theoretical technique has been applied to determine certain thermo-physical properties of Ti-10V-2Fe-3Al alloy, required for the model calculations. The technique is based on the liquid pool profiles analyzing in fully solidified VAR ingots. The experimental part of the technique enables easy estimate of liquid pool contours. The theoretical part is based on solving the inverse heat conduction problem for a solidifying ingot by means of represented VAR model. The results have been applied to calculate pool profiles for Ti-10V-2Fe-3Al titanium alloy. The results of the model calculations prove to be in sufficient agreement with the experimental data.

To investigate the microstructure, segregation, and suitable homogenization process of as-cast GH4169D alloy, the microstructure, elements segregation, and precipitates of cast GH4169D ingots prepared by vacuum induction melting (VIM) and vacuum arc remelting (VAR) were observed by optical microscopy (OM), scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDS). According to the residual segregation model and simulation results of DICTRA thermodynamic software, the homogenization temperature and time range were set as 1120–1170°C and 5–20 h, respectively. The experimental results showed that microscopic dendrite and element segregation occurred in the interior of ingots and the main segregation elements were Nb and Ti. In addition, the precipitates were mainly distributed in interdendritic regions and were composed of NbC, Laves, γ′, and δ phases. The homogenization process suggested that the interdendritic detrimental precipitated Laves phase can be eliminated or redissolved after homogenization at 1150°C for 20 h, suggesting it was the most suitable homogenization treatment. Thermal compression test results showed that the GH4169D alloys after homogenization treatment had no cracks and dynamic recrystallization occurred, with recrystallization volume fraction increasing with temperature, indicating a good working plasticity at temperatures from 1050 to 1200°C.

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.

A thermal model is developed for the ingot solidification during vacuum arc remelting (VAR) and is applied to calculate pool profiles for a VT3-1 alloy. The pool profiles are calculated for two remelting schedules, and the calculation results are compared with radiography data. The model calculation results are shown to agree satisfactorily with experimental data. The model is used in practice to develop conditions for the final remelting of a VT3-1 alloy to exclude the formation of segregation defects, namely, β flakes and macrosegregation. The developed model can be used for technological calculations and can give important information on the dynamics of VAR ingot solidification.

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.

In this paper, a novel biocompatible alloy defined as FeMoTaTiZr was obtained and functionalized by hydroxyapatite-based coatings (HAP) in order to increase their biocompatibility, bioactivity, and resistance to corrosion for to be used as bone implants. To obtain the surface with antibacterial properties, the HAP coatings were doped with small amount of Zn. The alloy was prepared using the VAR (Vacuum Arc Remelting) equipment, while the coatings by RF magnetron sputtering method. The EDS analysis confirmed the presence of Ca and P in the case of all developed coatings, having Ca/P ratio ranged from 1.69 (undoped HAP) to 1.96 (Zn doped HAP). The (Ca+Zn)/P ration was of about 2.15 for the Zn doped HAP coatings. The XRD and ATR-FTIR investigations confirmed the presence of calcium phosphate phases. After coating with HAP, the roughness of uncoated substrates increased with 1.4 times, and it was considerably increased by the Zn addition with 2.4 times. The electrochemical tests showed that the un-doped HAP exhibited good corrosion behavior, while Zn doped HAP coatings have a high dissolution rate in fetal bovine serum, being more proper as a biodegradable material.

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.

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.

In this paper, the role of Ti on the in-situ formation of carbides and its effect on the microstructure of Fe-7Al-0.35C alloy have been investigated. Initially, Thermo-Calc software was used to predict the phases present in the alloys which were validated by experimental work. Vacuum arc remelting process was used to make an alloy pancake of 10-mm thickness, which was hot-rolled to 2-mm thickness. The alloys were characterised by X-ray diffraction, optical, scanning electron microscope and electron probe micro-analysis. The results show that all the alloys exhibit two types of TiC precipitates, which are dark cuboidal as primary and dark acicular type as secondary precipitates along with grey-coloured needle-shaped κ-carbide precipitate in α(Fe–Al) matrix. The carbon present in the alloy is partitioned between TiC and κ-carbide precipitates. Addition of Ti has also resulted in grain refinement of all the alloys.

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.

NiTi-based shape memory alloys are successful owing to its capacity to cover specific applications unreachable by binary NiTi. The additions of ternary, and even quaternary, elements are intended to change specific properties. Known for its antibacterial activity, Ag became an alloying element in a search for a functional biomaterial; however, the melting appears to hampering the system exploration. A special melting procedure by vacuum arc remelting was developed based on chemical and thermal analysis, via EDS, XRF, and DSC, assessing the element loss and ingot homogeneity, respectively. By alloy design, different Ag content NiTiAg SMA were produced and analyzed on as-cast condition. The melting procedure developed involves specific feedstock cares and preparation, melting, and some remelting steps. The measured chemical composition slightly differs from the nominal due to alloying element loss and the melting reaction thermodynamics. Being the lower the possible, the remelting steps were optimized to maintain the compromise between chemical composition and compositional homogeneity through the ingot, since the Ag content stabilizes along them, also indicating a limited content possible to be alloyed. Ag-yields are content-dependent, while the Ni:Ti relation is stable, being therefore the melting of NiTiAg SMA better performed by VAR than other melting routes under high vacuum conditions.

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.

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.

The possibility of hydrogenating a high alloyed intermetallic alloy based on Ti2AlNb compound with high hydrogen concentration at low pressure of about 0.1 MPa with hydride formation has been studied for the first time. The study is carried out using alloys fabricated by vacuum arc remelting (cast alloy) and pendent drop melt extraction (the rapidly solidified alloy). It is found that rapidly solidified alloy with β-phase can absorb more than 2.0 wt % H. The high absorbing ability of the rapidly solidified alloy (fiber) is associated with a fine-dispersed microstructure and a high specific surface area. The cast alloy of a similar chemical composition with a coarse-grained microstructure and low specific surface area has low absorption ability in various phase compositions with maximum hydrogen absorption degree of 0.44 wt % H in quenched β-phase state.

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.

Ti-18Zr-14Nb, Ti-18Zr-13Nb-1Ta, Ti-18Zr-12Nb-2Ta and Ti-18Zr-11Nb-3Ta (at%) shape memory alloys were obtained by vacuum arc remelting and subjected to different thermomechanical treatment (TMT) schedules. The transmission electron microscopy analysis revealed that a TMT, which consisted of cold rolling with a true logarithmic strain of e = 0.3 and post-deformation annealing at 600 °C (30 min), led to a subgrained structure formation with a size of structural elements of 200–300 nm and to a room temperature superelastic behavior. The X-Ray diffraction (XRD) analysis showed that a gradual replacement of Nb content by its Ta equivalent decreases the impact of alloying elements on the β-phase stabilization phenomenon and suppresses the ω-phase formation: at room temperature, Ti-18Zr-14Nb and Ti-18Zr-13Nb-1Ta alloys contain mainly parent β-phase, while Ti-18Zr-12Nb-2Ta and Ti-18Zr-11Nb-3Ta alloys contain considerable amount of α”-martensite. The crystallographic resource of recovery strain for all the alloys exceeds 5% and reaches 6%, for the Ti-18Zr-11Nb-3Ta alloy. The fatigue life of the Ti-18Zr-13Nb-1Ta alloy is almost twice as high as that of the Ti-18Zr-14Nb alloy. During multi-cycle mechanical testing, the following regularity appeared for all the alloys tested: during 10–15 first loading-unloading cycles, the mechanisms of plastic deformation and stress-induced martensite formation and stabilization prevail, while after that, the β⇄α” martensitic transformation mechanisms become dominant, and the alloys’ behavior turns from elasto-plastic into superelastic.

The effect of structural defects of wrought semifinished products of vacuum-induction melted alloy KhN55MVTs-VI on service properties is studied. As a result of analyzing the structure using electron microscopy, microdefects have been detected that have an unfavorable effect on alloy ductility. It is established that defects are metallurgical in nature and of casting origin, and they form on aluminum oxide particles distributed through the whole volume of a workpiece. It is demonstrated that vacuum-arc remelting after vacuum-induction melting provides the absence of microdefects of this nature.

The columnar-to-equiaxed transition in the solidification of a Ti–10V–2Fe–3Al alloy is considered during vacuum arc remelting. A GV curve is plotted using a linear model of a multicomponent alloy along with modified Hunt (to determine temperature gradient G as a function of supercooling ΔT) and Ivantsov (to determine the concentrations at the dendrite tip versus liquidus isotherm velocity V) models. The unknown parameters of the models are determined by comparing the results of model calculations with experimental data, which are also obtained in this work. The plotted GV curve is compared with the GV curve of a VT3-1 alloy.

The paper presents the microstructure and corrosion behavior of an AlTiNiCuAgSn new equiatomic multicomponent alloy. The alloy was obtained using the vacuum arc remelting (VAR) technique in MRF-ABJ900 equipment. The microstructural analysis was performed by optical and scanning electron microscopy (SEM microscope, SEM-EDS) and the phase transformations were highlighted by dilatometric analysis and differential thermal analysis (DTA). The results show that the as-cast alloy microstructure is three-phase, with an average microhardness of 487 HV0.1/15. The obtained alloy could be included in the group of compositionally complex alloys (CCA). The corrosion resistance was studied using the potentiodynamic method in saline solution with 3.5% NaCl. Considering the high corrosion resistance, the obtained alloy can be used for surface coating applications.

Influence of hydrogen pressure and internal hydrogen contents on short-term strength, plasticity, and plane-stress fracture toughness of 05Cr19Ni55 alloys at pressure up to 30 MPa was investigated. It was established that the crack resistance parameters Kc of alloys decrease with displacement rates decreasing similar to elongation (δ) and reduction of area (ψ) of smooth specimens. The maximum hydrogen influence is achieved at strain rate speeds less than 0.1 mm/min and hydrogen pressures above 15 MPa when δ and Kc of prehydrogenated samples are reduced by 3 times. The plane-strain conditions required for the evaluation of KІc were fulfilled on compact tension 05Cr19Ni55 alloy specimens with thickness above 20 mm under hydrogen pressure 30 MPa and preliminary dissolved hydrogen concentration above 20 wppm. Regardless of the test conditions, the value of the characteristics of plasticity (δ, ψ) and fracture toughness (Kс) of alloy (TO1) specimens oriented in the transverse direction (orientation TV) is significantly lower than that of specimens oriented in the longitudinal direction (LT). Alloy cleaning by vacuum arc remelting and optimization of heat treatment regime increase their hydrogen resistance.

Ni-Mn based Heusler shape memory alloys are type of smart materials which possesses both ferromagnetic and shape memory properties. Due to multifunctional properties these materials have increased significant interest for the applications in actuators, sensing devices and magnetic refrigeration. The aim of this work was to synthesize and structural study of Ni-Mn-Sn and Ni-Mn-Al alloys which have recently emerged as Gallium-free shape memory alloys. Two alloys Ni48Mn26Sn26 and Ni51Mn26Al23 (at %) were synthesized using vacuum arc remelting technique under an argon gas atmosphere to improve homogeneity of the alloys. The structural studies of the prepared alloys were conducted and compared using X-ray Diffraction (XRD) and scanning electron microscope (SEM) coupled with Energy -dispersive X-ray spectroscopy (EDX). The results revealed that an average crystallite size of Ni-Mn-Al was smaller than Ni-Mn-Sn alloy. The morphology showed an average particle size of 5-6 µm and 0.6-0.7 µm for Ni-Mn-Sn and Ni-Mn-Al alloys respectively. Magnetic behavior studied by Vibrating sample magnetometer (VSM) showed soft magnetic behavior of the alloys. The synthesized alloys have exhibited and confirmed closely matching stoichiometric composition of Heusler shape memory alloys (X2YZ) with no contamination.

A commercial Niobium–Hafnium–Titanium (Nb-Hf-Ti) alloy (C-103), produced by vacuum arc remelting (VAR), showed clear signatures of internal oxidation viz. presence of monoclinic-HfO2 at all the grain boundaries. Minor cold rolling, to ∼10% reduction in thickness, initiated cold cracking. This was observed at some, but not all, of the high angle Nb–Nb grain boundaries containing coarse HfO2 2nd phase oxide precipitates. Closer microscopic examination revealed cold cracking at selective Nb-HfO2 interfaces. There appeared no clear mesoscopic experimental rationale behind this selective interfacial cold cracking. In order to understand this, density functional theory (DFT) calculations were performed on the metal-oxide interface models. They showed significant separation or decohesion energy difference (∼76%) with different atomistic bonding at the terminating layer of the Nb-HfO2 interface. In particular, the interface with one atomic layer of Nb bonded with oxygen of HfO2 had very low work of separation, which was about ∼8% lower than the Nb–Nb interface of the bulk Nb. In brief, the DFT simulations brought out the defining role of metal-oxide interface’s terminating layer on the interface decohesion. This is in agreement with the past theoretical research performed on several metal||non-metal interfaces. The present study extends this hypothesis to a practical example of selective cold cracking of a commercial Nb-Hf-Ti alloy.

The novel superelastic Ti-44Zr-10Nb (at.%) alloy was obtained by the vacuum arc remelting method and subjected to homogenization (950 °C, 60 min) and thermomechanical treatment (TMT), which consisted of cold rolling (CR) with a 25% thickness reduction rate and consequent post-deformation annealing (PDA) at 550 °C for 30 min. The analysis of the chemical composition was conducted by the EDS method. It was demonstrated that the obtained chemical composition of the alloy was in good correspondence with the nominal chemical composition. The phase composition of the alloy after TMT was investigated by the XRD technique. The lattice parameters of β and α” phases were measured using XRD data to calculate the crystallographic recovery strain limit. The maximum transformation strain of 7.3% was obtained in the [011]β direction.

Results are presented from studies performed to develop a technology for obtaining ingots of sparingly alloyed titanium foundry alloy VT40L by vacuum-arc remelting in a VD5M furnace. The structure and phase composition of the alloy and the degree of segregation of the main alloying elements over the volume of the ingot are studied. The research results are used to give recommendations on a refining regime that ensures the production of chemically and structurally homogeneous ingots.

Limited by the composition, the service temperature of high-temperature titanium alloys have been restricted to 600 °C for many years. In this study, a self-designed Ti–6Al–3Sn–10Zr-(Mo, Nb, W, Si) near-α titanium alloy that can be used at 650–700 °C was fabricated by vacuum arc remelting (name as DsTi700). Isothermal compression tests were performed at 975–1100 °C and in the strain rate range of 0.01–1 s−1. The results indicate that the flow behaviors of DsTi700 alloy under high strain rate are different from that of some traditional near-α titanium alloys and the peak stress values are generally higher than those of some common near-α titanium alloys at the same/similar deformation conditions. The deformation activation energy Q in β phase field is 240.2 kJ/mol. Moreover, the processing map were developed to determine the optimal processing window. Finally, DsTi700 alloy pancake with basket-weave microstructure was successfully prepared by multi-pass hot-forging. Tensile tests exhibit that the elongation of DsTi700 alloy at room temperature is nearly 13%, the UTS exceeds 600 MPa at 650 °C, which is almost equal to the UTS of some traditional near-α titanium alloys at 600 °C. Moreover, the UTS and elongation of DsTi700 pancake are 511 MPa and 24.1% at 700 °C.

Utilizing Pro-cast software, the whole vacuum arc remelting process of high-alloy bearing steel ingot (the diameter was 160 mm and the high was 600 mm) was simulated. And moving face quality and moving boundary conditions were added to the simulation. Purposes of the simulation were to explore the influence of smelting powers on the temperature field, pool shape and solidification microstructure in vacuum arc remelting process. The depth of molten bath gradually increased and stabilized finally and the pool shape transferred from flat to funnel. When smelting power increased, the depth of molten pool became deeper and the width of mushy zone slightly reduced; the size of primary dendrite and secondary dendrite spacing increased significantly; the percentage and size of columnar crystals also increased. A reasonable power-time cure was given to guide industrial melting after simulation, the size of molten pool morphology and microstructure were controlled in an ideal range under the reasonable cure. The simulated grain morphology agreed well with the experimental pickling result.

The effect of combined addition of carbon and titanium on structure and properties of Fe–7 wt%Al alloys has been studied. Pancakes of four alloys with nominal compositions, Fe–7Al–0.05C–0.2Ti (alloy-1), Fe–7Al–0.5C–2.0Ti (alloy-2), Fe–7Al–1.0C–4.0Ti (alloy-3) and Fe–7Al–2.0C–8.0Ti (alloy-4) were prepared by non-consumable arc melting. The arc melted pancakes were examined using scanning electron microscopy, electron probe microanalysis, and X-ray diffraction to understand the microstructure of these alloys. The dendritic solidification structure was observed in alloys 2–4. The microstructure of these alloys also revealed the presence of TiC precipitates, whereas no such phase was observed in alloy 1. The size and volume fraction of these precipitates increased with increase in the concentration of Ti and C. The yield strength of Fe–7 wt%Al alloy at both room temperature and at 873 K increases with increasing carbon and titanium.This may be due to the composite strengthening arising out of increased precipitations of hard TiC precipitates.

To improve the hydrogen desorption properties of magnesium hydride, the composite material with composition of MgH2-5 at% TiCrMn0.4Fe0.4V0.2 alloy has been prepared by co-milling of MgH2 powder with alloy prepared by vacuum arc remelting method. The effect of additive on MgH2 structure, i.e. crystallite size (D), lattice strain (ɛ), particle size (d), and also hydrogen desorption temperature (T) of obtained composite was evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) methods. It has been shown that the addition of TiCrMn0.4Fe0.4V0.2 alloy to magnesium hydride can yield a finer particle size after mechanical alloying. As a result it leads to a decrease in the temperature of MgH2 hydrogen desorption. The lowest achieved temperature of hydrogen desorption is related to the sample which is mechanically milled for 5 hours, whose temperature is 378° C.

Effect of heat treatment on mechanical properties and ballistic performance of a new α+β titanium alloy Ti–4Al–2.3V-1.9Fe against 7.62 mm ball projectiles was studied. A 20 kg ingot of Ti-4Al-2.3V-1.9Fe was produced by vacuum arc remelting and thermo-mechanically processed to 15 mm thick plates. These plates were subjected to different heat treatments and their mechanical properties and ballistic performances were evaluated. Plates that were solution treated below the β-transus temperature followed by aging exhibited good combination of strength and ductility and better ballistic performance.

Titanium alloy Ti5Al3Mo1.5V is used in the fabrication of critical engine and pyro components for space applications. The alloy processed through double vacuum arc remelting and finish forged in α−β regime has been studied for its response to various heat treatments. Solution treatment and aging cycles have been varied to study their effect on tensile properties of the alloy. Response to solution treatment and aging is found to be significant in improving the mechanical properties. Specimens subjected to higher solution treatment temperatures (900 °C) i.e., Tβ-50 °C and higher aging temperature and time showed the highest strength with moderate ductility. It can be attributed to the presence of α’-phase and precipitation of fine secondary α. The presence of large amount of β-phase is noted through EBSD in the sample heat treated at higher temperature, which may also have precipitation of fine secondary α during aging at higher temperature and or for longer aging time.

Some perspective materials are characterized by shape memory effect and NiTi alloy belongs to their main representatives. NiTi is an approximately equiatomic alloy of nickel and titanium and it possesses interesting properties, such as superelasticity, pseudoplasticity and good corrosion resistance. Hence, it is used in different branches of industry (aerospace, medicine, engineering etc.). Common manufacturing melting methods of this alloy are vacuum arc remelting (VAR) and vacuum induction melting (VIM) methods. However, these methods have some disadvantages. The VAR process must be repeated several times to achieve sufficient homogeneity of manufactured ingots. During the VIM process the melt can be contaminated by carbon originated from graphite crucible. Therefore, powder metallurgical methods have been extensively investigated in last years as an alternative to the common processes. In this work, NiTi samples were prepared by the thermale xplosion mode of self-propagating high-temperature synthesis (TE-SHS). Chemical and phase composition, as well as microstructure and hardness of the prepared samples were studied. Afterwards, the samples were heat treated and the influence of the annealing on the studied characteristics was investigated.

Studies were carried out to evaluate the effect of lanthanide elements which are generated during the fission process on the interaction between metal fuel and cladding material. Quartenary lanthanide alloy as Nd-Ce-Pr-La and Sm-contained quintenary alloy were manufactured by vacuum arc remelting and a diffusion couple test with HT9 (12Cr1MoWV) alloy was carried out at 660 and 700 °C for up to 231 h followed by microstructural analysis. The results showed that interdiffusion between lanthanide element (Nd, Ce) and Fe took place as the diffusion couple test proceeds to form intermetallic compounds as an RE2(Fe,Cr)17 (RE=Nd, Ce, Pr, La) type. As the number of alloying elements increased, the reaction layer thickness increased, but a deviation of the theoretical non-linear relationship as well as an increase in the rate exponent occurred. Instantaneous diffusion of Fe into a lanthanide side and its associated Fe depletion beneath the interface acted as the major driving force in forming the reaction layer. The addition of Ce enhanced the Nd diffusion and increased the layer growth when compared to pure Nd alone.

In 2006, J. Sato et al. discovered the L12 gamma-prime phase in the Co-Al-W alloy system. Since that time there has been a significant academic effort to characterize and understand the thermodynamics, the structure, and properties of alloys in this system. That work has shown that such alloys have promise as next generation high temperature materials due to the ability to engineer a high gamma-prime content alloy with a higher gamma prime solvus and higher melting point than many Ni-base gamma-prime strengthened alloys. Furthermore, a relatively narrow range of solidification temperature and large range of temperature between the gamma-prime solvus and the solidus are two characteristics that suggest cast and wrought versions of the alloys should be able to be manufactured routinely. However, to date all published research has been on small, laboratory scale samples typically less than about 2 kg, cast and hot rolled or cast as single crystals. This paper describes ATI’s experience in assessing the feasibility of manufacturing a cast and wrought billet product in the Co-Al-W-X alloy system. Three 22 kg heats were produced to examine a small range of alloy compositions of potential commercial interest: Co-9Al-9W, Co-9Al-9W-2Ti, and Co-9Al-9W-2Ti-0.02B, respectively. Each heat was vacuum induction melted and vacuum arc remelted. The as-cast microstructure will be presented. Ingots were homogenized and hot worked. The microstructure at various stages of production are shown and hot working behavior is described.

Some research results are introduced briefly in this paper. A new kind of titanium alloy was designed based on nine elements system, which belongs to (a+b) type. Bars with diameter of 14 mm were produced via Vacuum Arc Remelting (VAR) melting and conventional forging and rolling facilities. Influence of alloy elements contents and heat treatments on microstructure and mechanical properties of the new alloy were studied. The results show that Ultimate Tensile Strength (UTS) is about 1200~1700MPa and Elongation (EL) is normally less than 5% at R.T., though Electron Beam (EB) welding can be proceeded, but the toughness of the alloy is poor at R.T.High temperature (HT) short-term strength of the alloy is also acceptable up to 600. Based on the above performances, the new material can be applied in the corresponding circumstances.

This paper describes the development and validation of a comprehensive multiscale modeling approach capable of predicting at the mesoscopic scale level the ingot solidification structure and solidification-related defects commonly occurring during the vacuum arc remelting (VAR) process. The approach consists of a coupling between a fully transient macroscopic code and a mesoscopic solidification structure code. The predictions from the multiscale model, including grain morphology and size and columnar-to-equiaxed transition, were validated against experimental measurements for a 20-inch (508 mm) diameter VAR alloy 718 ingots. The validated model was then used to investigate the effects of melting rate and ingot diameter on the solidification structure of VAR processed 718 ingots.

Ti-3Al-2.5V ingot was produced, processed into a titanium alloy wire of 9mm diameter, and the characteristics were studied in comparison with imported material. The ingot satisfied ASTM Grade 9 standard showing oxygen content of 0.11wt% and iron content of 0.085wt%. The hardness of the 9mm diameter titanium alloy was similar to that of the imported material showing values between 225 and 250Hv, and the tensile strength of the imported material was 804MPa while that of the domestic development was 734MPa. The elongation of the imported material was 12% while that of the domestic development was 22%. A new process of manufacturing 9.0mm diameter titanium alloy wire through forging and multi-step hot rolling process out of 400mm diameter ingot was developed. Key Words : Titanium;eyerim;Gr.9;Ti-3Al-2.5V;Titanium Alloy;vacuum arc remelting 본 연구를 위해 후원해준 대구광역시와 지역 안경업계, (재)한국안경산업지원센터, (주)KPC 및 대구보건대학 관계자 여러분께 감사드린다. * 교신저자 : 김상연(sykim@dhc.ac.kr)접수일 11년 11월 21일 수정일 (1차 11년 12월 29일, 2차 12년 01월 04일) 게재확정일 12년 01월 05일

A Ti–43Al–9V–0.2Y (at.%) alloy ingot with the size of Ф 160 × 400 mm was prepared by vacuum arc remelting (VAR). The microstructure of the as-cast Ti–43Al–9V–0.2Y alloy was composed of B2/α 2 /γ lamellar colonies and massive B2 and γ phases which were distributed along the boundaries of these lamellar colonies in the form of equiaxed grains. Based on the grain size variation along the radius direction of the ingot, the ingot could be divided into four ring regions from brim to centre. It has been understood that the grain size variation between these four regions was due to the interplay of the effects of the cooling rate and the yttrium content on solidified microstructures in these regions. Mechanical testing of the samples cut from these four regions showed that there existed a clear correlation between the yield strength and the average grain sizes of the four ring regions, which approximately conformed to a Hall–Petch relationship.

Maraging steels are a group of materials with high strength and toughness. Titanium is the most widely used element in the above group, which helps to improve the mechanical properties by the formation of coherent Ni3Ti precipitates during the aging process. However, due to the high affinity of Ti to elements such as C, N, S and O, harmful inclusions of these elements may form in the steels if due care is not exercised during the processing. The present research explores the effects of titanium, within the range of 1–2 weight percent, on the mechanical properties of C300-grade maraging steels produced by vacuum arc remelting (VAR) technique. Then there is a discussion of the formation of deleterious titanium-rich inclusions and their effect on the mechanical properties of steel.

High-entropy alloys have been found to have novel microstructures and unique properties. The main method of manufacturing is vacuum arc remelting. As in situ cladding laser cladding has capability of achieving a controllable dilution ratio, fabricating highentropy alloy by laser cladding is of great significance and potential for extensive use. In this study, a novel AlxFeCoNiCuCr high-entropy alloy system was manufactured as the thin layer of the substrate by laser cladding; also high temperature hardness, abrasion performance, corrosion nature of the AlxFeCoNiCuCr high-entropy alloy were tested under the different ratio of aluminum. This study shows higher aluminum clad exhibit higher hardness, better abrasion resistance and corrosion resistance.

A novel (TiB + La2O3)/Ti-alloy composite was In situ synthesized through homogeneously melting in a non-consumable vacuum arc remelting furnace. Ti–35Nb–2Ta–3Zr β titanium alloy was chosen as the matrix Ti-alloy and different mass fractions of LaB6 were chosen as additions. Microstructure observations were examined by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The phase analysis was identified by X-ray diffraction (XRD). Largest ultimate tensile strength around 580 MPa and highest elongation around 30% is obtained in 0.1% LaB6-additioned specimen. The appearance of too many La2O3 particles and the reduction of oxygen in the matrix alloy also attribute much to the strength and plasticity of (TiB + La2O3)/Ti composites. Lower ultimate tensile strength around 526 MPa is obtained in 0.5% LaB6-additioned specimen.

Two process methods, mechanical alloying and vacuum arc melting, were used to prepare Ti0.37V0.38Mn0.25 alloy powders for studying their differences in hydrogen storage capacities. Ti0.37V0.38Mn0.25 samples produced by mechanical alloying showed an amorphous structure and a maximum hydrogen absorption of 1.76 wt%, but those prepared by vacuum arc melting exhibited a single phase BCC structure with no Laves phase, as well as a maximum hydrogen absorption of 3.62 wt%. The hydride in Ti0.37V0.38Mn0.25 alloy after hydrogen absorption was VH2, whose low reaction temperature allows for large amount of hydrogen absorption at ambient temperature. The hydride was, however, unstable and decomposed completely at relatively low hydrogen desorption temperature of 200 °C. After absorption–desorption cycling for 100 times, the mechanically alloyed powders, which did not pulverize as much as those of the arc-melting derived powders, showed smaller decline in hydrogen-absorption capability.