Protective Gas Research Articles

Design of ESR Slag for Remelting 9CrMoCoB Steel under Simple Protective Ar Gas

Thermodynamic calculations by using Factsage 7.3 and simple protective gas electroslag remelting (ESR) experiments were conducted to design the appropriate ESR slag for remelting the qualified 9CrMoCoB ingot. First, the proper basic slag was determined based on the phase diagram of CaF2–CaO–Al2O3–x%MgO calculated using Factsage 7.3. Second, equilibrium reactions between 9CrMoCoB and the basic slag containing varied SiO2, and B2O3 contents were calculated to study the effects of B2O3 and SiO2 on B, Si, and Al contents in steel. Then, equilibrium reaction experiments were conducted to validate the calculated results. Finally, the appropriate slags were attained and the simple protective Ar gas ESR experiments were conducted to make a verification. Results showed that the liquid phase region of the slag of CaF2–CaO–Al2O3–x%MgO at 1300–1400 °C increased first, then decreased with the MgO addition. With the B2O3 content increasing, the boron content increased, while the Si, Al contents decreased, and at a given B2O3 addition, the B and Al contents decreased with the SiO2 content increasing, whereas the Si content increased. The appropriate slags for simple protective gas ESR remelting 9CrMoCoB were 55%CaF2–20%CaO–3%MgO–22%Al2O3–2%SiO2–1.3%B2O3 and 55%CaF2–20%CaO–3%MgO–22%Al2O3–3%SiO2–1.7%B2O3.

Comparative Estimation of the Qualities of the Titanium Alloy Joints Made by Traditional Argon-Arc Welding and Innovative Arc Welding with Alternate-Pulsed Supply of Different Protective Gases

The welded joints of VT20 and OT4-1 titanium alloys formed by an innovative method (alternate-pulsed supply of argon and helium) are shown to have smaller grains and a wider melting zone in comparison with traditional argon-arc welding due to a more effective mechanical and thermal action of an arc in the weldpool. In addition, the innovative joints have a higher plasticity, a smaller scatter of the hardnesses over the cross section, and a higher welding speed.

ИМИТАЦИОННАЯ МОДЕЛЬ ЭЛЕКТРОДУГОВОГО ПОСЛОЙНОГО ВЫРАЩИВАНИЯ ВАЛИКА

The purpose of the work consists in the development of a simulation model of pad geometrical parameters and in definition of optimum modes for the method developed for the electric-arc direct layer growth of metal parts. The formation of a simulation model was carried out with the aid of CONSOL Multiphysics program complex. The result processing of experimental investigations was carried out by means of Compass-3D software support. For the definition of geometrical parameters of the pad grown there were welded samples with a consumable electrode in the environment of protective gases. Further there were microsections made of each sample in the transverse direction. The microsections cut out were ground, polished with the use of ASM 10/7 NVL diamond paste. For the definition of the microstructure the microsections were etched in 4% alcoholic solution of nitric acid. 
 The results obtained of the pad geometrical parameters are well correlated with experimental data. The error makes some 1…3%. On the basis of the model offered there is defined an optimum range for modes of electric-arc layer growth ensuring the required pad geometrical parameters. A pad height makes 3mm, a pad width – 3.5mm.

Experimental research on the behavior of EH 36 naval steel at the MAG-M mechanized butt welding

The paper presents the experimental research on the behaviour of EH 36 naval steel at the MAG-M mechanized butt welding in the naval field. Butt welded joint was performed in the four welding positions (PA/1G, PC/2G, PF/3G and PE/4G). In the welding process, two types of tubular wires and a mixture of active protective gases were used. The first part of the paper presents the effective welding of the four samples. The results of the non-destructive and destructive controls of the welded samples are presented below. The work is completed with the conclusions drawn from the experimental program. The good results thus obtained make it possible to apply the welding technologies of the EH 36 naval steel in the four analyzed positions.

Investigation into the Surface Layer Composition Formed on the Ml19 (Mg–Nd–Y–Zn–Zr) Magnesium Alloy during Melting under Protective Gas Atmospheres

The most currently widespread method of flux-free melting of magnesium alloys is melting under a protective gas atmosphere consisting of inert carrier gas with a small additive of active gas. The ML19 (Mg–Nd–Y–Zn–Zr) casting magnesium alloy contains yttrium and neodymium; these metals are rather active. The interaction of similar alloys with protective gas atmospheres is studied poorly and represents considerable practical interest. Sulfur hexafluoride (SF6) strongly affects global warming; therefore, the application of this gas is limited. In connection with this fact, HFC-R134a is used as active gas in several countries. The influence of protective gas mixtures consisting carrier gas (argon or nitrogen) and active gas (SF6 or HFC-R134a) on the composition of protective layer formed on the surface of the ML19 magnesium alloy melt is considered in this work. A special laboratory setup providing the contact of the protective gas mixture with metal during heating, melting, and solidification of the samples, which excluded the influence of surrounding atmosphere, was developed. The loss of alloying elements turned out to be insignificant, but the Y and Nd content in the alloy when applying nitrogen as carrier gas turned out to be lower than when using argon. The zirconium content was lower in alloys melted using SF6 as active gas. The composition and thickness of oxide films forming when using protective atmospheres SF6 and HFC-R134a are similar. The surface film consists mainly of magnesium fluoride (MgF2) with impurities of oxides, fluorides, and nitrides of zirconium, yttrium, and magnesium. The main distinction of the phase composition of the protective film when applying the HFC‑R134a is the presence of a considerable amount of carbon both in the form of compounds and in the free state. It is also established that a thorough dosage of HFC-R134a in protective atmospheres is required because an increase in its fraction in the gas mixture above 1 vol % leads to severe corrosion of the inner crucible surface during melting, which was not observed when using SF6.

Obtaining nano-disperse soot from orthoxylene by the high-voltage AC plasma torch

The article deals with the synthesis of fullerene-containing soot using high-voltage AC plasma torch. The plasma torch consists of three electric arc channels with three graphite rod electrodes. Orthoxylene vapors are fed into the arc zone of the plasma torch, and argon is used as a protective gas. In the plasma torch orthoxylene decomposes under the action of an electric arc. The prodused soot contains 5.4% C60 fullerene and 1.6% C70 fullerene.

A New Mechanism of Interaction between a Welding Arc Discharge of Reverse-Polarity Direct Current and an Aluminum Surface

The results of a study of aluminum welding by reverse-polarity direct current in a medium of protective gases (argon) at the stage of the binding and formation of the pool of melted metal are presented. It is shown that cathode spots in a current range of 5–50 A and action time of up to 1 s do not clean the cathode film from the aluminum surface but remelt the surface layer. The types of cathode spots that form on the aluminum surface are analyzed. It is shown that evaporation is the main mechanism for the removal of the oxide film. A new mechanism of the interaction between a welding arc discharge an aluminum surface is proposed: the main role in the formation of the welding pool is played by an immobile cathode spot, which, on the one hand, evaporates the oxide film and, on the other, intensely heats the surface layer of the aluminum to the phase transition due to high heat density. After the formation of the welding pool, the immobile cathode spot disappears, followed by the diffusion regime of welding arc burning. The regime is characterized by a uniform distribution of the electric field over the length of the discharge gap with a low potential decrease and occupies almost whole interelectrode gap.

Equipment and a Technique for Manufacturing Shaped Products from Refractory Metals Using the 3D-Printing Method

The original equipment has been developed and the feasibility has been shown of manufacturing shaped products from refractory metals by 3D printing using a high-pressure electric arc in a protective gas atmosphere. The proposed technique is performed using layer-by-layer metal deposition using local electric arc skull melting. In experiments aimed at manufacturing molybdenum crucibles, it has been shown that the speed of 3D printing is higher by 2–3 orders of magnitude than the speed of printing by selective laser sintering.

Influence of welding processes for underground pipeline repair on welder safety

The object of research is the welder safety during the repair and construction of underground pipelines. It is established that manual electric welding is characterized by significant influence on the human body, since the distance from the place of welding to the welder is 20–30 cm, the temperature in the pillar of the welding arc reaches 6500 K. It is contributes to the allocation in the surrounding space of a significant amount of metal vapor and fine particles (welding aerosol and toxic gases). Theoretical and experimental investigations of the initial part of the welding torch (at a height of 0.4–0.5 m) using manual, semi-automatic welding in the environment of protective gases and welding under a layer of flux have been carried out. Dependencies for determining axial temperatures and velocities are proposed. It is substantiated that the spreading of aerosols during welding of pipelines in the trench is determined by the physical processes of spreading the welding torch. The hygienic characteristics of the electrodes of the ANO type in the welding processes are investigated. It is established that the total amount of aerosol in the process of welding using ANO-4 electrodes with basic coating reaches 31 g/kg and toxic substances in aerosol up to 9 g/kg. The amount of gases in front of the welder shield during the welding of electrodes by ANO-8 reaches 20 mg/m 3 . Empirical equations for determination of aerosols concentration and gaseous concentration of harmful substances are obtained. In addition, an equation for determining the index of workplace pollution of welders, which made it possible to predict individual parameters of working conditions, is obtained. The mechanism of propagation of aerosols in the trench requires a special consideration, which can be carried out by the method of mathematical modeling, because such physical and chemical processes, as longitudinal and transverse dispersion, molecular diffusion play a role. The analysis of empirical formulas which can be recommended for determination of parameters in the initial section of a welding torch using flash welding of a pipeline in a trench is done.

Examination of the surface layer composition formed on ML19 magnesium alloy during melting at protective gas atmospheres

Currently the most common method of the magnesium alloys flux free melting is the melting under the gas protective atmosphere. This atmosphere consists of inert carrier gas with low addition of active gas. The ML19 casting magnesium alloy contains Y and Nd that enough active. The interaction of such alloys with gas protective atmospheres is poorly studied and has serious practical importance. Sulfur hexafluoride (SF6) has a great influence on the global warming and because of that its application is limited. As a result, the number of countries cross over to HFC-R134a as the active gas. This paper presents the investigation of the effect of gas protective mixtures consisting of carrier gas (argon of nitrogen) and active gas (SF6 or HFC-134a) on the composition of protective layer formed on the surface of ML19 magnesium alloy melt. It was developed a special laboratory setup providing the contact of the protective gas mixture with the alloy during heating, melting and solidification of the samples and preventing the influence of the surrounding atmosphere. The loss of the alloying elements was negligible but in the case of using nitrogen as a carrier gas the Y and Nd content in alloy was lower than if the argon is used. If SF6 is used as an active gas, the Zr content in alloys was lower. Composition and thickness of oxide film that formed in both SF6 and HFC-R134a protective atmospheres are mostly the same. The surface film is consist of magnesium fluoride (MgF2) with admixtures of oxides, fluorides and nitrides of zirconium, yttrium and magnesium. The key difference of protective layer phase composition if HFC-R134a used as an active gas is presence of the large amount carbon in the form of compounds and in a free state. Additionally, it was established that using of HFC-134a in protective atmosphere requires more careful dosage given the fact of its percentage in the gas mixture of more than 1 vol.% leads to severe corrosion of the crucible inner surface during the melting.

Determination of residual stress on TIG-treated surface via nanoindentation technique in Co-Cr-Mo-C alloy

The present study was undertaken to determine the amount of residual stress on the surface subjected to Tungsten Inert Gas (TIG) welding process in different protective gas environments (Ar-xN2, x = 20, 30 and 40 volume percent). It was shown that the increase of volume fraction of N2 gas in the welding environment led to more residual stress mainly due to the higher heat input. Nanoindentation technique was employed to obtain the variations of residual stress when Ar-40N2 protective gas was in use. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) method were used for microstructural study and phase identification. It was shown that applying higher heat input followed by quenching induced fully martensitic structure with very little amount of retained austenite. In addition, the magnitude of the residual stress in the TIG-treated area was measured to be ≈ 381 MPa using nanoindentation technique which was higher than the base metal. The type of residual stress was compressive which could be helpful for enhancing the surface properties and wear resistance of the alloy as a hip implant.

The relationship between convection mechanism and solidification structure of the iron-based molten pool in metal laser direct deposition

Metal Laser Direct Deposition (MLDD) is an additive manufacturing method involving multiple physical processes. Due to the existence of various complicated physical processes inside the molten pool, it is necessary to study the convection mode and solidification morphology in the molten pool. The convection of the molten pool generates heat and rapid solute transfer in the molten pool, which has an important influence on the solidification morphology of the deposited layer. In this study, the constructed MLDD numerical model was used to analyze the internal convection morphology of the molten pool. The convection form in the molten pool was revealed by setting different physical conditions. The results show that the Marangoni movement is the main factor in the formation of cladding layers. The impact force generated by the protective gas has an influence on the convective morphology, while the influence of gravity on the convection is limited. Through the numerical calculation, the relevant solidification parameters of the molten pool were obtained and verified by the MLDD experiment of the iron-based alloy powder. Numerical analysis and experimental results show that the Marangoni motion caused by the temperature gradient is the decisive factor leading to the solidification structure, and the phenomenon of columnar to equiaxed transition (CET) from the bottom to the top of the molten pool occurs.

Adsorptive Removal of Nerve Agent Gases by Carbon Nanotubes: A Density Functional Theory Study

Abstract Density functional theory (DFT) studies were performed to evaluate the adsorption behavior and electronic response of (4,4) carbon nanotubes (CNTs) to the organophosphorus nerve agents 3,3-dimethylbutan-2-yl methyl phosphono fluoridate (Soman), pinacolyl methyl phosphonate (SOS), diethyl fluorophosphates (SAS-F) and diethyl chlorophosphate (SAS-Cl). The calculations were performed using the triple numerical plus polarization (TNP) as the basis set with an orbital cutoff of 4.5 Å. The electronic exchange and correlation effects were analyzed by generalized gradient approximation (GGA) with the BLYP parameterization. The studied systems were fully optimized and adsorption energy (E ad), interaction distances, geometric and electronic structures were investigated. According to the obtained relatively high E ad, it was shown that Soman, SOS, SAS-Cl and SAS-F more likely to be absorbed on the CNTs surfaces, introducing an interesting candidate for chemisorption of the nerve agent gas molecules. As a result, the order of increasing of the E ad values of the studied systems were |E ad SAS-F/CNT| > |E ad SAS-Cl/CNT| > |E ad SOS/CNT| > |E ad Soman/CNT| systems. The calculated partial density of states (PDOS) of the adsorption systems confirmed the strong electrons interaction between the nerve agent molecules and the CNTs surfaces. The obtained results indicated the potential application of CNTs in the design and fabrication of protective low-cost gas filters against toxic odorless nerve agent gases.

Experimental Study of the Technology Parameters Affect in the Laser Welded Joints

The laser welding technology is improving immediately rapidly nowadays. It has many advantages again the traditional welding technologies. The heat affected zone in case of the laser welding is very thin and the penetration of the joint is depth. This high energy technology work by a focused high energy laser light accompanied by protective gases. For welding process well known the different laser devices (gas laser, solid-state laser, disc laser). The effect of the gases and the technological parameters are not well known yet. In this work, we wanted to find some relationship between the welding parameters and the joint mechanical properties. To find this relationship it was welded the joint by different technologies parameters and the samples experimented the joint mechanical properties with different parameters and controlled by the experimental way.

Structural and mechanical maintenance of quality of the rolled stock for cold upsetting of metal articles

A widely spread and most productive way to obtain finished metal articles with high structural and mechanical properties are methods of cold heading out of rolled metal, which must have a certain quality - the required plasticity, uniform structure and process parameters along the full length, as well as soundness. In conditions of fierce competition in order to improve the quality of the upset metal articles, the enterprises are forced to find reserves at all the points of the process chain for transformation of the original rolled metal. The greatest effect is achieved by the excluding of energy-consuming and labor-intensive annealing in protective gas furnaces and control of surface defects by etching or mechanical operations. This paper is presenting an economical and environment-friendly technology for structural and mechanical maintenance of high quality of rolled stock for upsetting of metal articles. The rolled steel prepared by this technology has a highly dispersed equally spaced structure without a decarburized layer with increased plasticity, which enables to reduce the number of transitions in the process of upsetting of metal articles and to increase the tools service life.

INFLUENCE OF POLYMERIC AND RUBBER MATERIALS ON HYDROCARBON-OXIDIZING BACTERIA

Polymeric materials are widely used in buildings and various industrial branches and consequently their persistence to microbial remediation draws scientist’s attention. Aim. To determin the influence of foamed polyethylene, ethylenevinylacetate and rubber on hydrogen-oxidizing bacteria: Pseudomonas pseudoalcaligenes 109, Rhodococcus erythropolis 102, Bacillus subtilis 138, isolated from damaged protective gas pipeline coatings. Methods. Bacterial quantity was determined by the serial dilution method; destruction index – gravimetrically for the weight loss; enzymatic activity – by the spectrophotometry on the KFK-3; changes in the chemical compound – by the IR Furrier spectroscopy on the TENSOR-37. Results. It was shown that in the presence of the studied materials as a sole carbon source catalase activity of P. pseudoalcaligenes 109, R. erythropolis 102 were decreased in 1.5–3.2 and 2.8–3.9, respectively, and in B. subtilis 138 were increased in 1.4–2.5 times than in control (Tauson media inoculated with bacteria and without material). Lipase activity of B. subtilis 138 and R. erythropolis 102 under the presence of studied materials were decreased in 1.2–3.8 times than in control. The study (by the IR-spectroscopy) of the polymeric and rubber materials components after the bacterial influence have shown that content of materials was not chemically changed. During 90 days of exposition the destruction coefficient of rubber was 0.4–0.6% (weight loss 10±0.9 and 16.6±2.6 mg depend on bacterial culture). For foamed polyethylene and ethylenevinylacetate destruction coefficient was not significant (weight loss up to 0.9±0.01 mg). Conclusions. Studied materials had been put in Tauson media as a sole carbon and energy source promoted the decrease of catalase activity in R. erythropolis 102 and P. pseudoalcaligenes 109, as well as lipolytic activity decreasing in R. erythropolis 102 and B. subtilis 138.

ТЕПЛОФИЗИКА ЩЕЛОЧНЫХ ЖИДКИХ МЕТАЛЛОВ. ЧАСТЬ 2: ФИЗХИМИЯ, ТЕХНОЛОГИЯ И ИННОВАЦИОННЫЕ ПРИЛОЖЕНИЯ (РЕТРОСПЕКТИВНО-ПЕРСПЕКТИВНЫЙ ВЗГЛЯД)

The article presents the results of experimental and analytical studies carried out at the SSC RF - IPPE in the field of physical chemistry, mass transfer, technology and innovative applications of alkaline liquid metal coolants. An integrated approach to the study of coolants as a complex multi component heterogeneous system, the state of which is determined by the interaction of coolant - impurities - structural (technological) materials - protective gas, was substantiated. Thermodynamic analysis and experimental studies of the coolants properties and the kinetics of their interaction with air, water, hydrogen, structural and technological materials determined the sources of impurities and their intensity. It is shown that for temperature parameters of modern NPPs, the required concentration of impurities in sodium and sodium-potassium alloy, can be provided by purification the coolants by cold traps. The deeper purification of ciilants required for use in high-temperature installations of niobium, tungsten, vanadium, tantalum is achieved by getters (hot traps). This method can also be applied when limiting the weight and size characteristics, for example, for a space NPP. A fundamentally new combined purification system from impurities was proposed and substantiated for a high-temperature NPP for the production of hydrogen with a sodium coolant temperature of ~900 °C. As a result of the development of alkaline liquid metal coolants, liquid metal technology has been proposed in various technical applications: sodium at nuclear power plants with fast neutron reactors, sodium and sodium potassium in the metallurgical and chemical industries; sodium-potassium, cesium, lithium - in space installations; lithium - in fusion reactors - thermonuclear reactors.

Contemporary Apparatus for Single Crystals Growth of Oxide Compounds and Metals by Optical Floating Zone (FZ)

A contemporary apparatus with radiation (light) heating for growth of single crystals of refractory oxides and metals is described. To reduce the dissociation or evaporation of the melt or crystal components, the growth process was carried out in oxygen or an alternative gas at pressures up to 100 bar. The annealing system applied directly in the growth process at 1650 °C under O2 pressure and at temperatures up to 2500 °C under protective gas flow, allows the obtaining of large and perfect single crystals. Many single crystals of oxide materials, including incongruently melting substances, such as Y3Fe5O12, Gd3Fe5O12, BaFe12O19, SrFe12O19, BaFe12-x AlxO19, and many others have been grown, and much more could be grown.

Microstructure and Mechanical Properties of Underwater Laser Welding of Titanium Alloy.

Underwater laser beam welding (ULBW) with filler wire was applied to Ti-6Al-4V alloy. Process parameters including the back shielding gas flow rate (BSGFR) (the amount of protective gas flowing over the back of the workpiece per unit time), focal position, and laser power were investigated to obtain a high-quality butt joint. The results showed that the increase of BSGFR could obtain the slighter oxidation level and refiner crystal grain in the welded metals. Whereas the back shielding gas at a flow rate of 35 L/min resulting in pores in the welded metals. With the increasing of the heat input, the welded metals went through three stages, i.e., not full penetration, crystal grain refinement, and coarseness. Crystal grain refinement could improve the mechanical properties, however, not full penetration and pores led to the decline in mechanical properties. Under optimal process parameters, the microstructure in the fusion zones of the underwater and in-air weld metals was acicular martensite. The near the fusion zone of the underwater and in-air weld metals consisted of the α + α′ phase, but almost without the α′ phase in the near base metal zone. The tensile strength and impact toughness of the underwater welded joints were 852.81 MPa and 39.07 J/cm2, respectively, which approached to those of the in-air welded joints (861.32 MPa and 38.99 J/cm2).

Investigation of the compressibility and sinterabilty of AZ91 powder production and particle production by gas atomisation method

Abstract This study intends to determine the pressability and sinterability of AZ91 powder production by gas atomisation method and that of the produced powder for partial production. Therefore, first, a gas atomisation unit has been designed and manufactured in the laboratories of the Karabuk University, Department of Manufacturing Engineering. Atomised powder production has been achieved at a temperature of 795 °C, with nozzle diameters of 2 and 4 mm and four different gas pressures (5, 15, 25, 35 bars). Argon gas has been used for atomisation and as a protective gas atmosphere. Scanning electron microscope (SEM) is used to determine the shape of the produced AZ91 powder, and a laser particle size analyzer is used to analyze the powder size. Additionally, a microhardness (HV0.025) measurement has been conducted to determine the hardness of the produced powders. To achieve a homogeneous distribution, the produced powders are mixed in a three-dimensional moving turbulator for 30 min. Mixed powders have been pressed at 300, 400, 500 and 600 MPa and have been sintered at 500 °C, 550 °C and 600 °C. Additionally, the density values have been determined before and after sintering of the materials. SEM images have been obtained from the fractured surfaces of the samples before and after sintering. XRD and EDX analyses have been performed to determine the chemical composition. Further, microhardness (HV0.5) is obtained from the pressure surfaces of the samples to determine the effects of the pressing pressure and the sintering temperature on the hardness. As a result of the experimental studies, it has been observed that the powder size decreases with the increase in gas pressure and that the powder shape generally changes from ligament and complex shape to droplet and spherical shape. From the XRD, XRF and EDX results, it has been determined that the structure comprises an α phase (Mg main matrix) and Mg17Al12 interphase, which is β phase, and very small amounts of MgO have been observed. The hardness of the produced powders increased based on the increase in gas pressure. The densities of the samples increased with both increasing pressing pressure and sintering temperature. It has been observed from the fractured surface SEM images that the number of pores formed in the samples decrease with an increase in the pressing pressure. It has been determined that the post-sintering structure exhibits a typical dendritic structure. In addition to the α-Mg matrix phase, β (Mg17Al12) intermetallic and α + β eutectic were formed in the structure. The microhardness values of the samples decreased depending on the sintering temperature; the highest hardness value was measured as 64,02 HV0.5 at a pressing pressure of 300 MPa and a sintering temperature of 500 °C, whereas the lowest hardness value was measured as 54,86 HV0.5 at a pressing pressure of 600 MPa and a sintering temperature of 600 °C.