High-melting Materials Research Articles

Processing of W and W - Ta alloys via laser powder feed directed energy deposition

The microstructure, porosity and Vickers hardness of pure W, W - 15% Ta and W - 21% Ta fabricated by Laser Powder Feed Directed Energy Deposition (LPF-DED) in ambient air and inert build environments were studied in this work. Severe microcracking and porosity were observed in all samples when building in ambient air and Ta was selectively oxidized. Under inert atmospheres, pure W was manufactured with no bulk microcracking and 1.7% porosity. Increased Ta content led to decreased porosity and increased hardness with again no microcracking observed. The lack of cracking in the inert was attributed to the increase in build temperature and reduced oxidation.The decrease in porosity, increase in hardness with W - Ta was attributed to the decrease in liquidus temperature with increasing Ta. Micrographs also show grains refinement with increasing Ta content and a cell structure was reported for W - Ta alloys. This work provides relevent information about manufacturing of high temperature melting materials via LPF-DED.

Spark Plasma Sintering of Complex Metal and Ceramic Structures Produced by Material Extrusion.

Alternative approaches to laser fusion for the additive manufacturing (AM) of metals are often hampered by the need for long sintering cycles. Typical sintering cycles require heating at temperatures above 80% of the melting point for several hours. The process is time- and energy-consuming, particularly when high-melting materials are involved. Applying pressure can drastically reduce the time and temperature required for densification. Recently, a particular kind of pressure-assisted sintering process known as spark plasma sintering (SPS) or field-assisted sintering (FAST) received considerable attention in academia and industry due to its ability to enhance densification. However, conventional SPS/FAST techniques cannot be directly applied to the densification of objects presenting a complex geometry. This work shows how a modified SPS/FAST setup, operating in a pseudoisostatic mode, can be used for debinding and sinter objects produced by material extrusion. This approach can be applied to metals and metal-based and ceramic-based composites when their geometry does not include closed cavities. Depending on the characteristics of the pressure-transfer medium, some level of anisotropy in the volume reduction associated with the densification can be observed. Still, it can easily be corrected by appropriately compensating sintering deformation during printing. Using this approach, the time required for the debinding and sintering can be reduced considerably. It represents an alternative approach to the AM of a wide range of inorganic materials characterized by a relatively low-cost, high material flexibility, and low environmental impact.

Laser Floating Zone Growth: Overview, Singular Materials, Broad Applications, and Future Perspectives

The Laser Floating Zone (LFZ) technique, also known as Laser-Heated Pedestal Growth (LHPG), has been developed throughout the last several decades as a simple, fast, and crucible-free method for growing high-crystalline-quality materials, particularly when compared to the more conventional Verneuil, Bridgman–Stockbarger, and Czochralski methods. Multiple worldwide efforts have, over the years, enabled the growth of highly oriented polycrystalline and single-crystal high-melting materials. This work attempted to critically review the most representative advancements in LFZ apparatus and experimental parameters that enable the growth of high-quality polycrystalline materials and single crystals, along with the most commonly produced materials and their relevant physical properties. Emphasis will be given to materials for photonics and optics, as well as for electrical applications, particularly superconducting and thermoelectric materials, and to the growth of metastable phases. Concomitantly, an analysis was carried out on how LFZ may contribute to further understanding equilibrium vs. non-equilibrium phase selectivity, as well as its potential to achieve or contribute to future developments in the growth of crystals for emerging applications.

Modeling of Structure Formation in Mixtures Using the Method of Self-Propagating High-Temperature Synthesis

An investigation is made of the specific features of compaction of thin layers consisting of monodisperse calibrated solid balls that model a bidisperse powder mixture of large metallic and fine nonmetallic particles used for fabricating layer-by-layer compressed long-measuring blanks intended for the production of high-melting materials by the method of self-propagating high-temperature synthesis. Consideration is given to the case of one-sided axial compression of thin layers of balls in a matrix of hexagonal cross section at the ratio of the cross-sectional dimension of the matrix to the ball diameter equal to L/d ≈ 15.

Sintered Copper-Based Powder Friction Material Filled with Fullerene-Like Glass Carbon

Existing compositions of sintered copper-based powder friction materials have been analyzed. It has been indicated that these materials, which operate under lubricating conditions, usually contain fine pencil-type or coarse casting graphite as an antiseize additive. As a friction additive, oxide and carbide powders and other high-melting materials are used. In this work, the results of investigations of tribotechnical properties of the sintered powder friction material based on copper filled with glass carbon are given. It is shown that its use provides an increase in the friction coefficient of the material with a decrease in wear over the period of its operation.

SAFETY WORK BY MANUFACTURE POWDERED ZIRCONIUM

Paper it is devoted working out of provisions on safety work of workers on sections manufacture of powdered zirconium. The thin chip and zirconium rasping’s easily light up. At presence in air of certain concentration of a dust from zirconium and a heating source there can be an ignition and explosion. Therefore it is widely used in fireworks at manufacturing of lamps for flashlights, caps-detonators, and a nitro powder and for fireworks. By working out of processes manufacture of a powder from zirconium, at designing of industrial installations and their maintenance it is necessary to consider, as it is told above, tall explosive and fire danger of this product. Therefore production processes a powder of zirconium should be mechanized and automated. All works (restoration, flushing out, treatment, crushing, screening and another) should be carried out in the separate premises rigged with system of plenum-exhaust ventilation. The metal powder in the form of a mix with water is stored in an incombustible room with constant temperature a little above a freezing point. The powder relative humidity should be in limits of 15-20 %. Separately packed portions of a powder are recommended to be kept separately for decrease quantity of zirconium which can be annihilated fire in case of a fire. Burning rather zirconium small amounts can be stopped a considerable quantity of the lather, applied so that not to call powder inflating. In these cases it is possible to apply dry sand and feldspar also. If in circulation there is a small amount of zirconium in the form separate portions properly packed in case an ignition one of them it is better to give the chance to burn down easy to it up to the end. Workers in production areas and premises storing of a powder should be in special shoe without metal nails and in overalls from a fire-resistant material, for protection against fire to wear goggles or the shield for the person from a high-melting material.

Precipitation behaviour of TiN in Nb-Ti containing alloyed steel during the solidification process

ABSTRACTA transverse crack on the slab corner became a severe defect for Nb-containing steel due to precipitation of NbN particles along the prior austenite grain boundary. By adding Ti, the TiN particles were in priority precipitation than NbN which kept more Nb as solution condition in steel. In the present research, the formation mechanism of TiN was investigated by thermodynamics calculation and experiments. It came to the following conclusions. With an increase in the cooling rate of molten steel, the precipitation location of TiN particles moves from the γ grains boundary into the matrix. Based on the Ohnaka micro-segregation model, the precipitation behaviour of [Ti] and [N] was investigated under various solid fractions during the solidification process. As the solid fraction is larger than 0.95, the [Ti][N] value was higher than equilibrium value. Furthermore, inclusion of a high melting material such as Al2O3 played an important role in decreasing the nucleation potential barrier of TiN, which enhanced the formation of TiN particles in the molten steel. For micro-segregation models, according to the segregation degree at the solidification front, they can be sorted in the following sequence, Scheil > Ohnaka(2α) > B–F > C–K > Ohnaka(4α) > V–B > Lever.

Coevaporation and structuring of titanium–aluminum alloy thin films

Intermetallic phases of binary material systems, such as TiAl, Ti3Al, RuAl, and Ni3Al have special physical properties such as a high oxidation resistance and low creep at high temperatures and a mechanical stability over wide temperature ranges. Due to new fields of application, such phases became increasingly important in the last two decades. In general, alloys can be sputtered very easily and reproducible. In surface acoustic wave (SAW) technology and microelectronics, the lift-off structuring technique is a fundamental process in the production of structured thin (<500 nm) metallic electrodes especially for low-cost fabrication of interdigital transducers (IDT). However, the structuring by standard lift-off technology only results in high quality IDTs for evaporated and not for sputtered layers. In order to investigate the intermetallic phases of the binary Ti-Al material system for IDT fabrication for SAW technology, a modified evaporator system for the simultaneous deposition of the low (Al) and the high (Ti) melting materials is presented.

Luminescence properties of the Mg co–doped Ce:SrHfO3 ceramics prepared by the Spark Plasma Sintering Method

1300 or 1400 °C pre–sintered Al/Ce/Mg:SrHfO3 and Al/Ce:SrHfO3 ceramics were prepared by the Spark Plasma Sintering (SPS) in order to search for a new scintillation material with a high–effective atomic number(Zeff) and good light output. The SrHfO3 has a high Zeff of 60, and high gamma–ray detection efficiency is expected. Meanwhile it has a high melting point of over 2500 °C, and single crystal is hard to be grown. On the other hand, high melting materials can be prepared as ceramics, and the SPS method is a simple process to fabricate the ceramics within a few hours. Thus, we prepared the samples using the SPS method, and their optical and scintillation properties were investigated. We found that Al/Ce/Mg:SrHfO3 and Al/Ce:SrHfO3 ceramics had an emission wavelength at around 400 nm originating from 5d–4f transition of Ce3+. Moreover, Al/Ce/Mg:SrHfO3 pre-sintered at a temperature of 1400 °C had a light output of approximately 5,000 ph/MeV. In this paper, the light output of Mg-co-doped samples was improved compared with the Mg-free ones. The light output also depends on the pre-sintering temperature.

Friction assisted solid state lap seam welding and additive manufacturing method

Abstract This paper describes results of seam welding of relatively high temperature melting materials, AISI 304, C-Mn steels, Ni-based alloys, CP Cu, CP Ni, Ti6Al4V and relatively low temperature melting material, AA6061. It describes the seam welding of multi-layered similar and dissimilar metallic sheets. The method described and involved advancing a rotating non-consumable rod (CP Mo or AISI 304) toward the upper sheet of a metallic stack clamped under pressure. As soon as the distal end of the rod touched the top portion of the upper metallic sheet, an axial force was applied. After an initial dwell time, the metallic stack moved horizontally relative to the stationery non-consumable rod by a desired length, thereby forming a metallurgical bond between the metallic sheets. Multi-track and multi-metal seam welds of high temperature metallic sheets, AISI 304, C-Mn steel, Nickel-based alloys, Cp Cu, Ti6Al4V and low temperature metallic sheets, AA6061 were obtained. Optical and scanning electron microscopy examination and 180 degree U-bend test indicated that defect free seam welds could be obtained with this method. Tensile- shear testing showed that the seam welds of AISI 304, C-Mn steel, Nickel-based alloy were stronger than the starting base metal counterparts while AA6061 was weaker due to softening. The metallurgical bonding at the interface between the metallic sheets was attributed to localized stick and slip at the interface, dynamic recrystallization and diffusion. The method developed can be used as a means of welding, cladding and additive manufacturing.

Mechanical Behaviour of Friction Stir Welding Joints of Aluminium alloy of AA6351 with AA6351 and AA6351 with AA5083

Modern structural application demands reduction in both the weight and as well as cost of the fabrication and production of materials. Aluminium alloys are the best choice for the reduction of weight, cost and replacing steels in many applications and Friction Stir Welding (FSW) process efficient and cost effective process. FSW is solid state welding process in which material is not melted during welding process so it overcomes many welding defects compared to conventional fusion welding process which is initially used for low melting materials. This process is initially developed for low melting materials like Aluminium, Magnesium, Zinc but now process is useful for high melting materials like steel and also for composites materials. The present study describes the effect of FSW process involving butt joining of similar Aluminium alloy combinations of AA6351 with AA6351 and dissimilar Aluminium ally combinations of AA6351 with AA5083 on the tensile, hardness and impact behaviour.

Friction stir welding in stainless steel sheet of type 430 using Ni-based dual two-phase intermetallic alloy tool

Ferritic stainless steel SUS430 sheets were friction stir welded by using a Ni-base dual two-phase intermetallic alloy tool. After friction stir welding (FSW), the SUS430 work and the tools were evaluated in terms of microstructure and mechanical properties. The tensile specimens cut from the welded joints fractured in the base metal portion and their fracture strength was equal to that of the base metal. The stir zone comprised of recrystallized fine microstructure was observed, and also the thermo-mechanically affected zone was observed in an advanced side. Hardness in the upper one-third layer of the welded cross section was higher than the base metal. The admixture matter from work to tool surface occurred whereas that from tool to work surface did not take place in the scanning electron microscopy-EPMA resolution level. The amount of wear of tool was negligibly small, suggesting that the Ni-base dual two-phase intermetallic alloy is promising as a new type of FSW tool used for high melting materials such as steel.

Review of the Effects of Friction Stir Welding Speed on Stainless Steel Type 304L

Friction Stir Welding (FSW) is a solid state welding method and is common for aluminum alloys. There have been many studies to apply this process for high melting materials such as steels and titanium. To make it applicable, there are many variables that must be considered, which one of them is FSW speed. Welding on high melting materials such as steels and titanium with traditional methods needs too high energy, many welders, electrodes, and generally is time consuming. By using friction stir welding, cost would be reduced on consumable materials, welders and energy. However, considerations of feasibility and different conditions for optimizing the method are so important. In this review paper, the main discussion was about stainless steel 304L and investigated the effects of friction stir welding speeds. Finally, a brief discussion was presented to summarize the effects of speed on friction stir welding.

Study on the microstructures, electrical resistance and mechanical properties of sputtering chromium target by HP, HIP and canning–HIP processes

In recent years, pure chromium (Cr) targets have been commonly used in metal surface coating treatment and flat-panel displays. In the traditional production of a pure Cr-target, there is a greater use of casting methods; however, the metal ingot frequently suffers from ingredient segregation, porosity and non-uniform microstructure defects. Powder metallurgy (PM) is a good method for fabricating high melting materials with better microstructure and properties. This study produced Cr targets using hot pressing (HP), hot isostatic pressing (HIP) and canning–HIP of PM technology. The experimental results showed that the Cr targets made by HP–HIP can further improve the density and mechanical properties. The relative density increases from 98.8% to 99.3%. Canning–HIP of the Cr target, in particular, can provide smaller grain size (50μm), lower porosity about 0.3%, and increased relative density to 99.7%, with a TRS of up to 58MPa. The canning–HIP process also shows the optimal electrical resistivity (8.003×10−5Ω-cm), which suits for applications in the sputtering process.

Use of overdriven detonation in coating application

Overdriven detonation waves allow one to produce coatings of high-melting powder materials and improve the quality of coatings sprayed from lower-melting-point materials. The kinetic and thermal energies of detonation products behind the front of overdriven detonation waves are much higher than those behind the front of self-sustained Chapman-Jouguet detonation waves traditionally used in spray processes. This paves the way toward the design of small-size spraying guns including those for applying coatings on the inner surfaces of parts.

Atmospheric Plasma Spraying of High Melting Temperature Complex Perovskites for TBC Application

High melting materials have always been very attractive candidates for materials development in thermal barrier coating (TBC) applications. Among these materials, complex perovskites with Ba(Mg1/3Ta2/3)O3 and La(Al1/4Mg1/2T1/4)O3 compositions have been developed and deposited in TBC systems by atmospheric plasma spraying. Spray parameters were optimized and in-flight particle temperatures were recorded using Accuraspray-g3 and DPV 2000. Plasma sprayed coatings were found to undergo non-stoichiometric decomposition of components which could have contributed to early failure of the coatings. Particle temperature diagnostics suggest that gun power of ~15 kW or lower where majority of the particles have already solidified upon impact to the substrate could probably prevent the decomposition of phases. Additionally, it has been found that the morphology of the powder feedstock plays a critical role during atmospheric plasma spraying of complex perovskites.

Effects of HIP Treatment on the Microstructure and Properties of Cr35-Si65 Target

Hot Isostatic Pressing (HIP) can be used for upgrading castings, densifying pre-sintered components, consolidating powders, and interfacial bonding. Hot pressing is a good method for fabricating on high melting materials with better mechanical properties. Commercial as-hp treated Cr35-Si65 targets are used throughout this study. The aim of this paper is to discuss the methods and to find a suitable HIP treatment for the as-hp treated Cr35-Si65 target. Meanwhile, we also to evaluate the effects of HIP treatment on the microstructure and properties of Cr35-Si65 target. The experiment results show that HIP treatment at 1100°C under 175 MPa for 2 hours of Cr35-Si65 target is the most suitable condition. It can reduce the open pore porosity by 20% and close pore porosity by 30%. The density could be increased to 3.64×10−3 kg/m3.

High-temperature thermodynamics by laser-vaporization mass spectrometry: An approach based on statistical mechanics

The problem of correlation between the temperature of the target surface and the mass-spectrometer signal in laser-vaporization mass spectrometry has been analyzed theoretically. An approach based on statistical mechanics has been applied in order to describe the transient vaporization into vacuum of molecules effused from the area of the target surface struck by a laser pulse of moderate power density and time duration of some tens of ms (Langmuir vaporization). In particular, an expression for the intensity of the output signal of the mass spectrometer, I( l,t), has been derived as a function of the detection time, t, and of the distance, l, of the ionizing chamber of the spectrometer from the target. A simple numerical method for the calculation of I( l, t) according to the time profile of the target temperature is also provided. By fitting experimental I( t) values with the theoretical expression one can retrieve thermodynamic quantities involved in the sublimation/evaporation process of the molecular species analyzed, such as enthalpy and equilibrium vapor pressure (or, alternatively, vaporization coefficient). As an illustration, this fitting was performed on experimental measurements of pyrolytic graphite sublimation in the temperature range 3200–3700 K. The analysis developed will be useful for the interpretation of experimental datasets in order to retrieve high-temperature thermodynamic data, especially on high-melting materials. Research in this domain is being launched for nuclear materials, particularly for Generation IV advanced fuels.

Preparation of Ta(C)N films by pulsed high energy density plasma

The pulsed high energy density plasma (PHEDP) is generated in the working gas due to a high-voltage high-current discharge, within a coaxial gun. In PHEDP surface modification, discharge is applied for preparing the amorphous and nanostructured high-melting materials as thin films deposited on various substrates. In this investigation, Ta(C)N films were deposited using PHEDP on stainless steel. Pure tantalum and graphite were used as the inner and outer electrodes of the PHEDP coaxial gun, respectively. Nitrogen was used as the working gas and also one of the reactants. Preliminary study on the films prepared under different conditions shows that the formation of Ta(C)N is drastically voltage dependent. At lower gun voltage, no Ta(C)N was detected in the films; when the gun voltage reaches or exceeds 3.0 kV, Ta(C)N occurred. The films are composed of densely stacked nanocrystallines with diameter less than 30 nm, and some grains are within 10 nm in diameter.

Concept, techniques, deposition mechanism of impulse plasma deposition — A short review

At the beginning of 80s last century, our research group gathered around Professors Mieczyslaw and Aleksandra Sokolowski recognized that the application of non-equilibrium plasma is necessary in synthesis of monotropic phases of high melting materials. It was evident for us that impulse plasma ensures both the highest level of non-equilibrity and highest level of vapour ionisation. These conditions seemed to be especially suitable for synthetizing the phases with high energetic barrier of nucleation process. The method of deposition of high melting materials layers by the use of impulse plasma was called the Impulse Plasma Deposition (IPD). The IPD device consists of the condenser battery charged to the voltage of order of kVs, plasma coaxial accelerator, ignitron setup, vacuum chamber and substrate holder. Plasma is generated with the frequency of 10 − 1 –10 Hz. The life time of plasma in each impulse is of order of 10 − 4 s. During the discharge of condensers individual plasmoids are being accelerated in the coaxial generator by the Ampere force to the speed of the order of 10 4 m s − 1 and directed to the substrate. The substrate is nonheated from any external heat source prior, during and after the plasma process. Experiments showed that the nucleation of phases takes place on ions of plasma and layer is constituted by the limited coalescence of the subnano- or nano particles on the substrate surface. Layers of DLC, c-BN, oxides, interstitial phases and complex metallic alloys with nano- or amorphous/nano-crystalline structure are produced with the use of IPD. In 1989 the IPD method was implemented to the industry for deposition of TiN layers on cutting tools.