Tungsten Copper Electrode and Other Materials Comparison — Part I

The using of electrode material has a huge effect on electrical discharge machining (EDM), such as the wastage of tool, MRR (Material Removal Rate), the surface quality of work-piece and so on. Therefore, the choice of electrode material should not be ignored in EDM and it depends on the situation.

First of all, the electrode should have high melting point, good conductivity, low coefficient of expansion and some excellent mechanical properties so that it can be thermal resistance, not easy to deformation and has low wastage in EDM. Theoretically, the micro crystal structure of electrode is beneficial for decreasing the wastage of electrode and properly reduce the size of grain will be better. In addition, the material of electrode should pledge stability, good quality of surface, reasonable price and easily for machining to EDM.

With the development of EDM, the material of electrode and the related manufacture makes a great progress. At present, there are so much electrode materials, such as graphite, tungsten (W), copper (Cu) and some other metal or non-metal elementary substances. In addition, steel, cast steel, Cu-based and W-based composite materials or diamond can be also used as EDM electrode.

1. Graphite

As for the aspect of chemical, graphite is an allotrope of carbon element, which covalently bound covalent molecular bonds. Its has high boiling point and melting point, the melting point up to 3652 ℃, the boiling point of 4827 ℃, insoluble in water. And it also has excellent electrical and thermal conductivity, chemical stability and workability so that it is widely used as EDM electrodes. In addition, graphite also has different kinds, which can be specifically divided by graphite particle density, the size and mechanical and electrical properties.

Fine graphite has small grain, porosity and good mechanical strength, which has low wastage of electrode in EDM. But its MRR (Material Removal Rate) is undesirable. At present, the most of graphite grain size is below 10μm, which depends on the conditions electrode works (finishing, semi-finished or roughing) and its shape when we make a choice. In addition, the roughness of work-piece surface is related with the size of graphite grains, the average particle size below 1 μm is specialized for finishing.

Compared with other materials of electrode, graphite can be used in EDM with large discharge current, which remarkably increasing the efficiency. Although graphite has low proportion and price, it is too fragile to machining into the shape of thin. Therefore, it is limited in EDM and researchers find that high speed milling can be improved to some extent.

Some researchers put graphite electrode into molten metal (such as Cu or Al) in order to improve the properties of graphite electrode in EDM. At the same time, pressing the liquid metal and make Cu or Al fill in the pore of graphite electrode for improving the strength and thermal conductivity of the electrode.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.com or by telephone:86 592 5129696, we are at your service.

Effect of TiC in Copper-tungsten Electrodes

Due to the high thermal conductivity of Cu, and the better spark erosion resistance, low thermal expansion coefficient and high melting temperature of W, copper-tungsten electrodes have been widely used for machining die steel and tungsten carbide work-piece. The materials normally used in EDM electrodes are various types of copper, graphite, tungsten, brass and silver. But copper-tungsten has better properties. The low melting point of Cu reduces the resistance to electrode wear.

At high tungsten content, there is porosity in the liquid phase sintered electrode due to the insolubility between the Cu and W. This greatly impedes densification during the solution-reprecipitation stage of liquid phase sintering. Hence, this makes it necessary to introduce another material with high melting point. Materials having good electrical and thermal conductivity with a high melting point are used preferably in copper-based electrodes to resist electrode shape-loss.

Titanium carbide (TiC) is an extremely hard refractory material with high melting temperature, and high thermal shock and abrasion resistance. It is used mainly for powder metallurgical parts including cutting tool tips, dies, wear parts and resistant coating. In industry, the manufacturing of Cu-W composites is usually done through infiltration of Cu into a porous, pre-sintered tungsten compact, or through the liquid phase sintering of compacts pressed from mixed powder.

In some researches, Cu-W/TiC was investigated and fabricated through liquid phase sintering. In is reported that the additive metals (iron, cobalt and nickel) can enhance densification in the liquid phase sintering of Cu-W. In order to increase the densification of the Cu-W matrix, nickel (Ni) was introduced. In addition, the densification of Cu-W/TiC sintered electrodes can be improved by the addition of Ni. However, due to the insolubility of Cu, W and Tic, and the amount of Cu apparently reduced by the cold welding in ball milling, porosity cannot be avoided. Nevertheless, with increasing TiC, the distribution of the particle size becomes narrow.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.com or by telephone:86 592 5129696, we are at your service.

LED Tungsten Copper Heat Base for Heat Dissipation

With the world's attention of environmental awareness, energy saving has been an irresistible trend of the moment. The LED industry is one of the fastest growing industries; LED products not only have a great advantage in terms of energy saving, but also have high efficiency, fast response time, long life cycle and do not contain toxic substances, which is outstanding in similar products. In general, the input power of LED high power products has about 15% of electrical energy into light energy, and another 85% of the electrical energy is dissipated into heat. So if the LED light emitting heat generated not been able to export, it will make the temperature of the LED screen is too high, thus affecting its luminous efficiency, stability and product life cycle. In order to improve the luminous efficiency, thermal dispersion management and design LED system become an important research topic.

The ways of heat dissipation mainly includes: air heat dissipation, heat the substrate to export, export gold wire cooling, through-hole heat dissipation and so on. Here we introduce the substrate cooling. In LED products typically requires multiple LED assembled on a circuit board. In addition to the circuit board is responsible for carrying LED module structure, on the other hand it also needs to play the role in heat dissipation. LED heat dissipation substrate mainly takes advantages of the excellent heat conductivity of its thermal substrate material to derived from the LED grain. Thus according to the ways of LED heat dissipation, can be divided into two types, LED grain board and the system circuit board. These two are multiplied by different heat dissipation board carrying the LED chip LED grain and the LED grain emits light generated by the circuit board to the system, and then absorbed by the atmosphere via the heat dissipating board LED die, to achieve the dissipation of the heat effect. Tungsten copper material has high strength, low coefficient of thermal expansion, excellent plasticity and thermal and electrical conductivity, which is the perfect choice for LED board. Compared with single metal, such as Al substance, it can avoid the thermal mismatch and have better stability and heat dissipation.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.comor by telephone:86 592 5129696, we are at your service.

Tungsten Copper Throat Insert

Solid rocket motor spray tube by controlling the expansion of the combustion chamber exhaust gas generated energy is efficiently converted to kinetic energy, so as to provide the required power for the aircraft. Throat insert located in the larynx of the spray tube, which plays an important role in restricting the throat area expansion by ablations and the decreases of the thrust. Throat insert usually need to be heated from room temperature to more than 2000℃  and produces a great temperature gradient and thermal stress when the engine working, which is also the main reason for the cracks and failure of throat insert materials. Furthermore, such high-performance engine for rocket often uses metal powders (such as Al) as propellants combustion at high temperature of about 3000 ℃ high burning rate entrained flow of solid particles or liquid droplets (Al2O3) and scoured the throat insert intensely. It is difficult to ensure a stable aerodynamic shape even the fragmentation occurred if the throat insert has severe ablation, so it will has an bad effect on the thrust and efficiency of the engine.

With the application of throat insert becoming wider and wider, such as rocket boosters, long-range missiles, solid rocket engine and so on, and the more and more types of the metal additives, the materials properties for throat insert has been confronted with the higher requirements, which is also a key to the solid rocket technology developments. In general, throat insert materials used for solid rocket engine include refractory metal, graphite, carbon and carbon-based composite material, reinforced plastics and ceramic-based composite materials, etc. Among them, tungsten copper is one of the very suitable materials for throat insert fabricating. In addition, throat insert heat conduction can be divided into three steps: 1.Engine ignition instant impact heating; 2. Ablation when working steady; 3. The cooling process of flameout; wherein the thermal shock of throat insert often occurs at the moment of the ignition.

Tungsten copper throat insert fabricated by the infiltration process, which not only has high hardness, high density, high strength, high melting point, low coefficient of thermal expansion and excellent wear and corrosion resistance of W, but also has excellent ductility, thermal and electrical conductivity of Cu. What’s more, since there is a great difference in the melting point between W and Cu, at high temperature higher than the melting point of Cu, Cu will evaporate and take away the most of heat and the hard phase W left. So it ensures the stability of throat insert works, and tungsten copper is also known as sweating heat sink material.

Through related experiments the researchers found that coarse grain has better performance in thermal shock resistance and poor in ablation resistance, conversely. Rocket spray tube entrained within particles or liquid phase stream high burning rate will continue to scour throat insert, and this two-phase flow weakly oxidizing, such throat insert constantly ablated, which is a complex physical and chemical process covered by heat conduction, mass conduction, transmission capacity and chemical reactions. According to different ablation principles, it can be specifically divided into thermal ablation, melted ablation and mechanical erosion. When the surface temperature of tungsten copper throat insert is higher, melted copper was deposited on the inner surface, which will cause thermal effect and prevent heat transfer to the inside of the material.

In addition, when the gas temperature below the melting point of tungsten, tungsten skeleton does not melt, ablation occurs at this time of the melting of copper and tungsten substrate by gas particles (such as Al2O3) erosion produced by mechanical erosion. Currently, copper tungsten throat insert prepared have been able to successfully applied to 3600 ℃, 6.88MPa under thermal environment at this temperature above the melting point of W, tungsten skeleton is also possible to melt ablation. From the view point of throat insert structure, improving the roughness and prolonging the length of the straight section can remarkably improve the ablation resistance of throat insert.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.comor by telephone:86 592 5129696, we are at your service.

Nano Tungsten Copper Composite Material

Nano tungsten copper composite material is also known as ultra-fine tungsten copper composite material, which compared with common grain tungsten copper, has better mechanical and chemical properties, such as high density, high hardness, high strength, excellent wear and corrosion resistance and perfect thermal and electrical conductivity, etc. Its granularity usually between 1nm -100nm and the nano grain has several characteristics is given as follow:

1. Small size effect: When the coherence length or penetration depth dimension and the wavelength of light particles, de Broglie wavelength and other physical characteristics of the superconducting state of a considerable size or less, crystal periodic boundary conditions will be destroyed, the density of atoms near the surface of the particle layer of amorphous nano-particles reduced, resulting in characteristic sound, light, electricity, magnetic, thermal, mechanical and other changes in the new physical properties;

2. Surface effect: With the decreasing grain size, the ratio of surface atoms and total atoms of nano tungsten copper grains is dramatically increasing and the binding energy of grain is correspondly increasing, which changes the properties of nano grains;

3. Quantum size effect: When copper tungsten particle size down to a certain size, the electron energy levels near the Fermi level from continuous to discrete energy and transformation. During the existence of discrete energy level occupied molecular orbital, at the same time there are also contrary to occupy the lowest molecular orbital, and the spacing between the high and low rail level with the smaller diameter of the nano particles increased;

4. Macroscopic quantum tunneling effect: Electrons have wave-particle duality and the ability to penetrate the barrier, known as the tunnel effect. Macroscopic quantum tunneling effect will be the basis for future microelectronics, optoelectronics, or it further establishes the limits of miniaturization existing microelectronic device;

5. Coulomb blockade and quantum tunneling: In nano scale dimensions, the charging and discharging process is not continuous, filled with an electron energy required is called the Coulomb energy blockage. In such a small system of single-electron transport behavior is known as Coulomb blockage effect, if the two quantum dots connected by a junction, a single quantum dot electrons through the energy barrier to another quantum dot is the quantum tunneling.

Nano tungsten copper composite material has better performance in thermal properties, magnetic properties, optical properties, the super-conducting properties, catalytic properties and so on. From the thermal properties, at extremely low temperatures, the thermal resistance of tungsten copper nano particle is almost zero; from magnetic properties, nano grain will enter super-paramagnetic state when it exceeds a certain threshold and shows high coercivity; from optical properties, nano particle quantum size effect is more significant, in the optical performance of the wideband receiver, the dispersion obtain some special optical properties; and the super-conducting transition temperature of nano tungsten copper grain increases as the decreasing granularity. In addition, from catalysis nature, as the particle size decreases the reactivity significantly increased under appropriate conditions capable of catalyzing the breakage H-H, C-H, C-C, C-O chemical bond and so on.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.comor by telephone:86 592 5129696, we are at your service.

Tungsten Copper Contacts Cryogenic Treatment

Cryogenic treatment refers to process the blank at -190℃-230℃, which has a broad application prospect, such as non-ferrous metal, ferrous metal, metal alloy, carbide, plastic, silicate and so on. The basic principle is that in the process of metal hardened to cooling by heat treatment, which produces alloy and carbon dissolved and combined with the formation of austenite(Austenitic is a lamellar microstructure, usually ɣ-Fe solid solution in a small amount of non-magnetic solid solution of carbon) and diffusion; in the cooling process, since the low temperature produce suppress the formation of martensite(The crystal structure of martensite is body-centered tetragonal (BCT). High carbon steel is usually accelerated cooling to obtain such organizations and high strength and hardness of steel is one of the main features of martensite.), the final transition point (Mf) is definitely low.

Austenite is very unstable and easily decomposes at low temperature, so the original defects (pores and internal stress concentration part) and becomes plastic flow structure refinement. Therefore, as long as put the metal at ultra-low temperature, the austenite is converted into martensite, which eliminates the internal stress. In addition, due to the contraction of the tissue volume at ultra-low temperature, Fe lattice constant decreases and the driving force to strengthen the precipitation of carbon atoms, so a lot of martensitic matrix deposited ultrafine carbides. The strength of these ultra-fine crystalline materials will improve and increase the wear resistance and rigidity. And Ultra-low temperature can also be transferred metal atom transport capacity, which makes the atoms can not be separated and become closer.

There are some experiments shows that high-pressure vessel after cryogenic treatment can meet the requirements of the strength of solid propellant rocket; some down-hole equipment for sour oil field after cryogenic treatment can improve the corrosion resistance and the welding cracks; some parts of the alloy cryogenic treatment, volume stability, dimensional stability and strength has been greatly improved.

At present, cryogenic treatment mainly applied in tool steel, non-ferrous metal applications under development step, here we discuss that the tungsten copper contacts cryogenic treatment process conditions affect its properties. Tungsten copper contact is a psudoalloy, which is composed of two kinds of immiscible and has a great difference in physical and chemical properties metals. There is no phase change in the reaction and it is brittle so that it is difficult to adapt conventional heat treatment hardening process to improve its relative performance. Cryogenic treatment is undoubtedly an ideal choice.

Viewed from the micro-structure, after cryogenic treatment, W matrix disperse a large number of Cu phase and the organization has significantly refined, which is due to precipitation of Cu solute in W after cryogenic treatment. In addition, it also can be found that with the increase in the copper content, the segregation phenomenon is also becoming increasing apparently. Copper particles dispersed precipitated tissue thinning, and atomic displacement volume shrinkage, tungsten copper contact density and overall strength has also improved.

While its hardness and strength has greatly improved after cryogenic treatment, and electrical conductivity with increasing tungsten content decreases. This is due to cryogenic treatment makes a lot of precipitated Cu and W form a solid solution, and is proportional to the electrical conductivity of tungsten copper contacts with the copper content. Overall, tungsten copper contacts after cryogenic treatment, may be little alternative to tungsten copper copper-tungsten less, not only improves performance, but also reduce costs.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.comor by telephone:86 592 5129696, we are at your service.

Tungsten Copper EFP Liner Manufacturing Process

Tungsten copper EFP liner, EFP is abbreviation of Explosively Formed Penetrator, which is “explosively formed piercing warhead” or “self forging fragmentation warhead”, some countries also known as P Charge (Projectile Charge), Misznay-Schardin Charge and mass shaped charge and so on. A typical EFP warhead consists of a metal liner, housing, as well as booster explosive components consisting of a series, there is usually a cover for drug and explosive type of pressure ring assembly is secured. It relies on the projectiles with high kinetic energy to armor, compared with conventional HEAT projectile with charge jet, in the high explosive detonation, the energy generated by the blast occurred folded by deforming Liner and get high speed, because the speed difference the presence of eventually forming a penetrator.

The explosively formed projectile EFP here we are introducing is also one of a kind shaped charge, it uses more than 120 ° cone angle hemispherical cap or hyperbolic Liner conduct charge. After the explosion, tungsten copper liner extruded by great load and after flip closed to form explosively formed projectile. And it has many advantages, such as less interferes to reactive armor, great penetration aftereffect and be insensitive to the height of burst. So the capacity of armor and penetrate highly depends on the materials of liner.

The conventional materials of liner include iron, copper, depleted uranium, tantalum and so on. Pure iron and pure copper has excellent plasticity, but their density is lower, which reduces the kinetic energy of projectile formed and the penetration force of the target material; the depleted uranium has a high density and plasticity, can greatly enhance the strength and armor-piercing Immunity range of thousands of degrees of high temperature burning effect, but the depleted uranium is still radioactive material, and it is harmful to human health; tantalum element is a kind of rare-earth element, it has the ability of penetration is much greater than copper and iron, but its high cost problems that have hindered the promotion of the use of the important factors.

By comparison, tungsten copper W-Cu system combines high hardness, high density, high strength and excellent chemical properties of W and excellent thermal conductivity of and plasticity of Cu. Since there is a big difference between W and Cu (W-3410℃，Cu-1083℃), After the explosion of copper is evaporated leaving a high hardness, high density hard phase tungsten, compared to copper Liner armor penetration depth can be increased by nearly 30%. Therefore, tungsten copper EFP liner has a broad application prospect in the future. Ordinary tungsten powder, copper powder and ultra-fine tungsten-copper composite powder prepared tungsten copper EFP Liner and its performance was compared. Wherein ultrafine tungsten copper composite powder is prepared by using spray pyrolysis, it uses a proportion of copper nitrate and ammonium metatungstate dissolved in distilled water into the mixed solution, and then the pressure centrifugal spray drier precursor powders, the precursor powder is then placed in roasting reduction furnace. Finally, wet ground and placed in a ball mill reduction in the reduction furnace, ultra-fine tungsten-copper composite powder particle size is formed between 100-300nm.

After the tungsten copper rod made of tungsten copper EFP started liner blank forging, which blank deformation has three steps: 1. upsetting the blank in the mold, in this process the blank upper and lower parts deformation occurs first, and upper and lower portions of the pores gradually become less under the influence of compressive stress, density increases, increasing the contact area with the punch, friction force increases, under the action of the metal tensile stress generated lateral flow; 2. metal flows hindered by the mold wall and it will flow along with the hole of the mold bottom, and in the process the pores reduces and the density increases; finally, when the metal flow to the ejector rod will enter the multi-pressure stage, mainly through its hydrostatic pressure to eliminate rough pores, so the effect is not significant.

In addition, in the process of tungsten copper EFP liner blank forging, there are two ways of deformation of the matrix material, one is only copper phase deformation, deformation does not occur with tungsten and tungsten particles along the direction of deformed copper matrix flow was streamlined distribution; the other one is both of Cu and W phase have deformation and form fibrous structure. In order to ensure that the final density, tensile strength and elongation to achieve the desired requirements, we should make a reasonable design for tungsten copper EFP liner shape and have sufficient deformation.

If you have any interest in our tungsten copper alloy products, please do not hesitated to contact us by Email:sales@chinatungsten.comor by telephone:86 592 5129696, we are at your service.