High Melting Point Materials Research Articles

Effect of Building Height on Microstructure and Mechanical Properties of Big-Sized Ti-6Al-4V Plate Fabricated by Electron Beam Melting

Electron beam melting (EBM) is a layer by layer additive manufacturing technology, which has the capability of producing near-net shaped parts with complex geometries. It is also suitable for handling high melting point and reactive metallic materials, such as Ti alloy, which is widely used in the aerospace and biomedical applications. The present study focused on the relationship between the microstructure and mechanical properties of big-sized Ti-6Al-4V parts. A plate (6mm×180mm×372mm) was additively manufactured by EBM. The microstructure evolution and variation of mechanical properties were investigated by using the x-ray diffraction, optical microscope, scanning electron microscope and tensile test. The results revealed that with an increasing in the build height, there was a variation in the microstructure and the mechanical properties of the build plate. Although only α phase and a relatively small fraction of β phase were detected in both the bottom and top specimens of the build plate, yield strength and ultimate tensile strength decreased with an increase of build height. This was attributed to the increase of α lath width which was caused by the different thermal histories along the build height of the plate.

Laser Ablation Resistance Behavior of Organosilicone Composite Coating on Various Substrates

In modern combat, laser weapons are widely used due to their high precision, velocity and heat detriment. Hence, it is of great importance to fabricate protective coating on the surface of core components, i.e. gasoline tank and aerofoil. In this study, an organosilicone composite coating was prepared on steel and aluminum substrates through a simple spray process to resist laser ablation destroy. This composite coating consists of organic resin base and inorganic functional fillings, which were made up of glass powder with high melting point materials such as SiO2, BN and ZrO2etc. Laser ablation resistance behavior was studied by means of oxyacetylene torch and laser irradiation. Results demonstrate that the coating presents excellent heat resistant behavior under 3000°C. Moreover, after impulse laser attack up to 105W/cm2, both substrates remain unhurt. As a result, this organosilicone composite coating can be used for anti-laser application in various fields.

Silicon carbide multilayer protective coating on carbon obtained by thermionic vacuum arc method

Thermionic vacuum arc (TVA) method is currently developing, in particular, to work easily with heavy fusible material for the advantage presented by control of directing energy for the elements forming a plasma. The category of heavy fusible material can recall C and W (high-melting point materials), and are difficult to obtain or to control by other means. Carbon is now used in many areas of special mechanical, thermal, and electrical properties. We refer in particular to high-temperature applications where unwanted effects may occur due to oxidation. Changed properties may lead to improper functioning of the item or device. For example, increasing the coefficient of friction may induce additional heat on moving items. One solution is to protect the item in question by coating with proper materials. Silicon carbide (SiC) was chosen mainly due to compatibility with coated carbon substrate. Recently, SiC has been used as conductive transparent window for optical devices, particularly in thin film solar cells. Using the TVA method, SiC coatings were obtained as thin films (multilayer structures), finishing with a thermal treatment up to 1000°C. Structural properties and oxidation behavior of the multilayer films were investigated, and the measurements showed that the third layer acts as a stopping layer for oxygen. Also, the friction coefficient of the protected films is lower relative to unprotected carbon films.

The Migration Characteristics of Sodium during Biomass Combustion

During biomass combustion, alkali metals are partly released to the gas phase and form low melting point compound, which may enrich to the heat exchangers and cause heavy sinters in the incinerator. The aim of this study is to obtain quantitative data on the migration of sodium by measuring the content of sodium remained in the combustion products using AAS. Three groups of biomass ashes were produced respectively to investigate the influence of combustion temperature, fuel thickness and kaolin addition. The results indicate that, rising temperature enhances Na release from the biomass to the gas phase, while increasing the fuel thickness does the opposite. The reaction of kaolin and Na to generate a high melting point material inhibits the migration of Na, which reduces the biomass sintering in the incinerator.

The Sintering Characteristics of Industrial Solid Waste Incinerator

Burning the industrial solid waste can form low melting point alkali salts to cause heavy sinters in the incinerator. The utilization of additives is proved to be effective to reduce the sintering in this work. Three additives (lime, kaolin and coal ash of an electric power plant) were mixed in different proportions with the industrial solid waste, and then an ash fusibility test was performed on the solid waste and the mixtures. The results show that, the solid waste exhibits a low melting point and the chemical additives can increase it efficiently. Furthermore, the anti-sintering mechanisms may conclude that the additives react with the alkali salts in the solid waste to form the high melting point materials.

Measurements of liquid and glass structures using aerodynamic levitation and in-situ high energy x-ray and neutron scattering

Investigation of high temperature molten materials and their evolution to the amorphous state is often hampered by unwanted reactions with container surfaces. This work used aerodynamic levitation in combination with laser beam heating to study high melting point materials that can form supercooled liquids or glasses. Details of the instruments that are being used at the Advanced Photon Source and the Spallation Neutron Source to study molten oxides with high energy x-ray scattering and neutron diffraction with isotope substitution are presented. Examples of measurements are used to illustrate the use of the instruments. Plans for further development and application of the capabilities are presented.

Anisotropic Nano-Column Arrays of Bismuth and Its Conductivity

Anisotropic nanostructures are becoming more and more attractive due to their unique properties different from isotropic nanostructures. However, previous most of studies are limited to high melting point materials with poor crystalline, which has confined their extended applications. In this work, we successfully prepared the anisotropic nano-column arrays of bismuth (melting point: 271.3 degrees C) with improved crystallinity by glancing angle deposition. The anisotropic conductivity of the products is investigated, and its origin is ascribed to the anisotropic scattering of the carriers in the boundary layer. Our work is not only helpful to understand the anisotropic nanostructures fabricated by glancing angle deposition on both their growth and properties, as well as provides an approachable route for constructing functional devices based on Bi and its anisotropic nanostructures.

Application and Research on Reducing Reaction of Boron Slag in the Steelmaking Engineering

Analyzed the reaction between slag and liquid iron and done a lot of experiments in the Lab to find the effect of many factors. It shown that putting into CaO to low the reaction activity with small amount of calcium oxide added, it can make the expansion in reaction to be inhibited, and improve the content of CaO in further. Silicate is high melting point material in the reaction product. After the reaction it reduce the slag fluidity to the slag with addition of CaF2, which can further improve the effect of reduction reaction.

Microstructural Evolution and Thermal Stability Characterization of a High Temperature Die Attach Lead-Free System

There is a need for electromechanical devices capable of operating in high temperature environments (>200°C) for a wide variety of applications. Today's wide-bandgap (WBG) semiconductor based power electronics have demonstrated a potential of operating above 400°C, however they are still limited by packaging. Among the most promising alternative is the Au-Sn eutectic solder, which have been widely used due to its excellent mechanical and thermal properties. However, the operating temperature of this metallurgical system is still limited to ∼250°C owing to its melting temperature of 280°C. Therefore, a higher temperature resistant system is much needed, but without affecting the current processing temperature of ∼325°C typically exhibited in most high temperature Pb-Free solders. This paper presents the development and characterization of a fluxless die attach soldering process based on gold enriched solid liquid inter-diffusion (SLID). A low melting point material (eutectic Au-Sn) was deposited in the face of a substrate, whereas a high melting point material, gold in this instance, was deposited in its mating substrate. Deposition of all materials was performed using a jet vapor deposition (JVD) equipment where thicknesses were controlled to achieve specific compositions in the mixture. Sandwiched coupons where isothermally processed in a vacuum reflow furnace. SEM and EDS were employed to reveal the microstructural evolution of the samples in order to study the interfacial reactions of this fluxless bonding process. Mechanical characterization of the each individual intermetallic phase was achieved by nanoindentation. Differential scanning calorimetry demonstrated the progression of the SLID process by quantifying the remaining low melting point constituent as a function of time and temperature. Post-processed samples confirmed the inter-diffusion mechanism as evidenced by the formation of sound joints that proved to be thermally stable up to ∼490°C after the completion of the SLID process.

摩擦攪拌接合技術の現状と展望

Over twenty years has passed since the friction stir welding was developed. During this period, various improvements and developments have been made, and this method has been put to practical use in a very wide range of industry. Because, in this method, the welding is performed in a solid state, and a refined microstructure is formed due to severe plastic deformation by the rotation tool, a variety of excellent joint properties is obtained, and in some cases, the joint strength exceeds that of the base material. However, at present, this method is put to practical use only for light metals such as Al alloys. Accordingly, the friction stir welding technology of high melting point materials such as steel has been strongly desired. Based on the current status, in this paper, prospects of the friction stir welding technology are discussed.

Mechanical Properties and Microstructure of SS400 Friction Stir Welds Pursuant to Welding Distance

FSW have advantage as defect such as porosity, metallic compounds decrease than other welding process. So, FSW was researched about low melting point materials. However, welding of high melting point and high strength materials attract attention because of high mechanical properties was needed due to industrial development. In this study, FSW is enforced using the kind of high melting point materials as SS400(SPHC). However, the tool must have super heat-resisting and abrasion resistance. So, WC-X%Co tool was manufactured by SPS method. The result, welding is successfully practice using WC-X%Co tool to 50m without fracture of tool.

The Application of the Wettability of Liquid-Solid in the Manufacture of High and Low Voltage Contacts

High or low voltage electrical contact is a kind of pseudo alloy which is mostly composed of a high melting point material and a low one. Liquid-solid wettability is widely used in the manufacture of contact materials and its subsequent processing. This article focuses on several solutions to the difficulties encountered during the process by liquid-solid wettability.

Hot spot in GdBa2Cu3O7−δ-based composite ceramics rods and their applications for oxygen sensors

A hot spot, which is a local area glowing orange, appears in a LnBa2Cu3O7−δ (Ln: rare earth element) ceramic rod when a voltage exceeding a certain value is applied to the rod at room temperature. After the appearance of the hot spot, the current changes according to the oxygen partial pressure in ambient atmosphere, which acts as an oxygen sensor without the need for any heating system. The GdBa2Cu3O7−δ rod tended to be melted and broken by a sustained presence of the hot spot in a high oxygen partial pressure Po2 (∼100 kPa). The composite rod containing high melting point materials, such as BaAl2O4, BaZrO3 and Gd2BaCuO5, showed a remarkable high durability in O2 atmosphere. In a low Po2 (< 0.02 kPa), the current through the GdBa2Cu3O7−δ rod decreases to almost zero and the hot spot disappeared, resulting in an insensitive rod to oxygen. The composite rod containing CuO detected oxygen even in Po2 < 0.002 kPa.

Mechanical properties of thixo-formed austempered ductile iron

Semi-solid processing of metallic materials has been investigated for some time; however, this innovative production process has not fully established for ferrous alloys like ductile cast iron in the industry yet. Ferrous alloys-specially ductile cast iron-because of increasing complexity due to high temperature processing and some other limitations have been allocated a small share of this useful forming process to themselves. However, this work describes that thixo-forming of ductile iron despite all of the limitations is possible even for thin sections (less than 1 mm). Die temperature and injection velocity are the most effective parameters to thixo-forming particularly for high melting point materials such as ductile cast iron. Filling behavior, shape factor of graphites and fluidity of thixo-formed specimens were characterized. In addition, defects as well as shrinkage and cold laps were examined to achieve sound specimen. Subsequence to successful thixo-forming, two step austempering was performed to accomplish a uniform structure with minimum untransformed austenite volume (UAV). Following austempering, tensile test was carried out and the results show good combination of tensile strength and elongation for treated specimens (1 137 MPa strength and 12% elongation in best situation).

Synthesis of Mullite by Means of Transferred and Nontransferred Arc Plasma Melting

Arc plasma melting technique is a simple method for the synthesis of high melting point materials. In this article, mullite was synthesized by transferred arc plasma (TAP) and nontransferred arc plasma (non-TAP) melting processes, and the results were compared. The mixes of alumina and silica powders (3:2 mole ratios) were ball milled for four hours and then melted in an arc plasma torch, used in transferred and nontransferred mode, at 5 kW input power and two minutes of processing time. Argon gas was used as a plasma-forming gas. The crystalline phases and the microstructural features of the melted samples were determined by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. A complete crystallization of mullite, with dense, thick whiskers-shaped crystals, was achieved in TAP processing of the alumina/silica system. On the other hand, the non-TAP process produced porous mullite along with a small amount of residual alumina phase. Differential thermal analysis (DTA) curves of the synthesized mullite samples allowed a deeper understanding of the mechanisms of mullite formation during the two different processes.

Co-Re-based alloys for high temperature applications: Design considerations and strengthening mechanisms

Cobalt-Rhenium base alloys are being developed for applications at temperatures beyond Ni-base superalloys. The high melting refractory element Re readily dissolves in Co and thereby changes the character of a Co-based alloy to a high melting point material. So far Co-Re system has not been investigated from the point of view of strengthening and oxidation and therefore different possibilities of strengthening mechanisms have been explored for our alloy development. Cr, a common element for oxidation resistance in many systems, is added along with Si in Co-Re alloys to improve oxidation behaviour at high temperatures.

Mechanical characterization of aluminium nanofilms

The mechanical properties (Young’s modulus, hardness, wear resistance) of aluminium nanofilms on silicon substrate are studied. Size effect on these mechanical properties are exhibited. Young’s modulus, hardness and wear resistance increases when the thickness is reduced. Experimental investigations have been led by atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nanoindentation. Compared to the bulk values, hardness and wear resistance of one aluminium nanofilm (thickness = 100 nm) have increased by a factor ∼7 whereas the Young’s modulus only increased by a term ∼15%. By comparing mechanical properties between high and low melting point materials, we conclude that high melting point materials have a decreasing behaviour of the Young’s modulus with size whereas low melting point materials have an increasing one.

Study of the Key Issues of Friction Stir Welding of Titanium Alloy

As a new solid-state welding process, friction stir welding (FSW) has been successfully used for joining low melting point materials such as aluminum and magnesium alloys, but the FSW of high melting point materials such as steels and titanium alloys is still difficult to carry out because of their strict requirements for the FSW tool. Especially for the FSW of titanium alloys, some key technological issues need to solve further. In order to accomplish the FSW of titanium alloys, a specially designed tool system was made. The system was composed of W-Re pin tool, liquid cooling holder and shielding gas shroud. Prior to FSW, the Ti-6Al-4V alloy plates were thermo-hydrogen processed to reduce the deformation resistance and tool wear during the FSW. Based on this, the thermo-hydrogen processed Ti-6Al-4V alloy with different hydrogen content was friction stir welded, and the microstructural characterizations and mechanical properties of the joints were studied. Experimental results showed that the designed tool system can fulfill the requirements of the FSW of titanium alloys, and excellent weld formation and high-strength joint have been obtained from the titanium alloy plates.

Performance analysis of EDM electrode fabricated by localized electrochemical deposition for micro-machining of stainless steel

Electrical discharge machining (EDM) is an important and widely used process for the fabrication of complex three-dimensional structure of micro-tools, micro-components, and parts with micro-feature. It allows high precision, low setup cost, large freedom of design, and good surface quality. However, in order to produce different varieties of high-accuracy structures on machine, microelectrode fabrication is necessary so as to reduce the clamping error which is one of the biggest challenges in the field of micro-EDM. In this study, it has been shown that localized electrochemical deposition (LECD) is one of the simplest, inexpensive, and damage-free ways to fabricate complex-shaped electrodes for micro-EDM compared to other conventional electrode fabrication processes. In this study, electrode was fabricated with the help of a non-conductive mask which was placed between the anode and the cathode where the cathode was placed above the anode and mask and the system was immersed in a plating solution of acidified copper sulfate. The micro-EDM was carried out by the deposited electrode without changing or removing its orientation. The performance of LECD electrode was evaluated in this study by micro-holes fabrication on high melting point material such as stainless steel in terms of the material removal rate, tool relative wear ratio, and dimensional accuracy. Finally, the performance of the LECD electrode was also evaluated by a comparative study with a circular EDM electrode for fabrication of complex three-dimensional structure.

Microstructure characterization of nanocrystalline Ni 3C synthesized by high-energy ball milling

Preparation of a metal carbide by a conventional route requires a huge instrumentation regarding melting the metal and graphite under vacuum at a very high temperature. However, mechanical alloying process is a very useful method for the fabrication of high melting point materials like metal carbides, which additionally produce nanocrystalline structure with improved properties. This article reports the microstructure characterization of nanocrystalline Ni 3C synthesized at room temperature by mechanical milling of Ni and graphite powders under inert atmosphere. The stoichiometric Ni 3C phase is formed after 5 h of milling. Microstructure of the prepared materials is characterized in terms of lattice imperfections, primarily by analyzing the X-ray powder diffraction data, employing both Warren–Averbach's method of line profile analysis and Rietveld's structure refinement method. The phase transformation kinetics studied by the Rietveld method reveals that the graphite powder becomes amorphous at the early stage of milling and then diffuses into Ni matrix and a Ni–C solid solution is formed within 1 h of milling. The high-resolution electron microscopy reveals that the Ni 3C phase is initiated as a thin shell on Ni–C core within 2 h of milling and becomes stoichiometric in composition within 5 h of milling. Electron microscopy observations agree well with the X-ray measurement of particle size (∼9 nm) of Ni 3C phase in 5 h milled sample and Ni–Ni 3C core shell structure in 3 h milled sample.