Since the high strength, excellent thermal and electrical conductivity and arc erosion resistance, tungsten copper has been becoming the one of the important materials for electrode application. There are many influencing factors of tungsten copper electrode materials, but the vast majority of literature can consult to affect mostly concentrated in the preparation process (tungsten skeleton, density, hardness, uniformity) of tungsten copper electrode material. We introduce the effect of tungsten powder granularity on tungsten copper electrode. Viewed from the distribution and structure, tungsten copper with the same composition, the finer particle size of tungsten will distribute more uniformly. But the possibility of closed-pore and defects appearing is also increasing, Cu enrichment increasing and the overall uniformity decreasing.

For the aspect of the hardness and the density, with the increasing of powder granularity, the pressing density and degreasing density of the tungsten skeleton fabricated by different granularity of tungsten powder is basically the same, and the overall density of tungsten copper also decreased after the infiltration. Take tungsten copper W-30Cu as example, When the tungsten powder particle size of 2.65μm, the highest hardness, Brinell hardness up to 222HB. With the powder size increases, the hardness decreases when the tungsten powder particle size of 8μm minimum hardness, Brinell hardness is 190HB. This is due to the higher density brings the greater brittleness. The powder granularity decreases, the specific surface area increases, the higher surface energy, the greater sintering activity and the more obvious volume shrinkage after sintering, which increases the content of W, improves the overall density and hardness. In the electrical conductivity, tungsten powder particle size of the smaller and more easily when pressed cause tissue inhomogeneity of skeleton sintered in the passage is closed and prone to clogging, thus resulting in voids or defects in copper-rich material and cause copper deficiency or liquid infiltration feeding can not effectively reduce the integrity of the copper network grid after infiltration, so that the electrical conductivity decreased.

EDM (Electrical Discharge Machining), which the properties of the using electrode material have a direct effect on the overall performance (such as the instrument consumption, the removal rate of material, the surface quality and so on). Therefore, in the process of EDM, the choice of the electrode materials is the key factor in the manufacturing process. Electrode materials not only need the good performance in thermal and electrical conductivity, but also need the low coefficient of thermal expansion and other mechanical properties requirements so that the excellent heat resistance, deformation resistance and low consumption can be ensured. With the popularization and developments of EDM technology, the related electrode materials have been reforming gradually. At present, already in production and are being developed in the electrode materials include graphite (C), tungsten (W), copper (Cu) and other elemental metal or nonmetallic substance, steel, cast iron, copper-based or tungsten-based alloy composite material, polymer composites, diamond, etc.

The graphite can be used in EDM with large discharge current, which has low consumption in roughing process and has high consumption in finishing process and it is difficult to meet the surface roughness required. In addition, the proportion of graphite electrodes is relatively light, brittle, difficult to use in general machining thin or fine hair processed into a shape, which in some fine or complex shapes EDM application has been subject to certain restrictions. By comparison, tungsten copper material is a kind of new high-performance electrode material that has high strength, low coefficient of thermal expansion and excellent spark erosion resistance, which has been widely used in machining tool steel and tungsten carbide workpiece. However, as the price of tungsten copper electrode is relatively higher than ordinary graphite electrodes or copper electrode material prices, which is also the one of barrier to popularize tungsten copper electrode material.

The process of vacuum coating is used to modify a surface by evaporating a coating material with tungsten heater under vacuum and condensing it on the surface. It is normally carried out under high vacuum conditions. The material to be evaporated is heated until its vapor pressure appreciably exceeds the residual pressure within the vacuum system. Notices vacuum coating machine are as follows:

1. The equipment should always be kept clean, especially the parts inside the bell, it should be regularly cleaned with NaOH solution and without any dust and impurities and oil.
2. Operators who have not been training cannot be allowed operate the equipment alone. Coating machine operator must be strictly enforced operating procedures. Operators should understand that if there is an error of operation sequence, it may result in damage to equipment parts.
3. Machine must be cooled with water before opening the diffusion pump. Cooling water better use treated demineralized water to prevent fouling of circulating water pipeline, influencing the water cooling effect.
4. PVDF film gilded metal electrode can be made without baking program. Do not buy this section when ordering coater.
5. When turning the regulator hand wheel, the action should be slow, it is not allowed to use the quick movement operating mode, because the mobile brushes is easy to break.
6. When bell lift, operators should pay attention to the safety, they are not allowed to use hammers to hit faying face of the bell, in order to prevent scratches and impact marks, thereby affecting the combination effect between bell and faying face.
7. Pay attention to check the amount of lubricating oil pump regularly, timely make up the oil. Diffusion pump should be fuel filling.
8. The overhaul of pump should be operate by experienced maintenance fitter, and it is not allowed to knock the parts by hammer when disassemble them. And lubricating oil must be filtered before injected into the pump body.

Except playing an important role in cutting field, tungsten carbide has been widely used in mining and drilling industry. The major product of tungsten carbide mining tool is tungsten carbide button, which can be assembled on the tool and use the impact load produced by own bit pressure and rotation to crush the rocks. In the process of rock drilling, the bit not only should endure the high-frequency impact, but also need to endure twisting, bending, stretching and compression and other complex and the role of stress in the high-speed rotary collision environment subject to wear and corrosion of rock, mineral water and other working medium. So tungsten carbide mining tools have higher requirements in wear resistance and toughness.

At present, the major trends of tungsten carbide mining tools include double-crystal structure, double binder phase structure honeycomb structure and low-Co coarse grain tungsten carbide. Double-crystal structure carbide is also called non-uniform grain carbide. And due to there are two peak value on the WC grain distribution curve, so it also called double peak structure carbide. Wherein the coarse grain WC structure provides good ductility and toughness, a certain proportion of fine grained WC provides high wear resistance; double binder phase structure carbide has a greater degree of freedom (including the size, the hardness, the toughness, the volume ratio of the hard phase and the strength and toughness of the base) in micro structure design than common tungsten carbide. It can match the performance required by individually controlling micro-structure and properties; honeycomb structure carbide through component structure and property design to form low-Co fine grain distribution and high-Co coarse grain distribution and show the honeycomb structure; Structural design principle of low cobalt carbide coarse grain is: WC coarse grains, smaller than the surface area of the alloy in the Co layer thickness, thereby increasing the impact toughness of the alloy; alloys increase and decrease the content of Co content in WC so that the wear resistance of the alloy.

With more and more materials difficult to manufacture and the popularity and development of CNC (Computer Numerical Control) machine tools, the requirements of cutting tool is higher and higher correspondly, especially in cutting accuracy, cutting efficiency, reliability and customization. Conventional cutting tool materials are difficult to meet the requirements of high efficiency and low production cost of modern manufacturing industry, so tungsten carbide has played an important role in cutting fields gradually because of it excellent performance. Tungsten carbide materials mainly composed of a hard phase WC and Co binder phase, WC phase is mainly responsible for the contribution of abrasion resistance, and Co phase is to assume the role of enhanced toughness. However, the wear resistance and toughness is always a contradiction difficult to be reconciled, the wear resistance enhanced and the toughness weakened correspondly, and vice versa. In order to reconcile the contradiction, the relevant researchers have studied further and through strengthening the binder phase, heat treatment, surface coatings and functionally graded structure to prepare a variety of new alloy, which has both high toughness and high wear resistance.

At present, the major trends of tungsten carbide cutting tools include functional gradient structure, high Co content and fine grain structure and coated tungsten carbide. Functional gradient structure carbide is based on the principle of FGM (Functionally graded materials) and change the micro-structure distribution of conventional tungsten carbide to form gradient structure in one-dimensional, two-dimensional space and even three-dimensional space. It can remarkably improve the cutting efficiency and extend the service life of the cutting tools; high Co content and fine grain carbide, the density, hardness and strength of the fine grain cemented carbide were significantly higher than normal grain carbide, then increases Co content appropriately, which not only can meet modern industry and special applications of new materials processing needs, especially for the manufacture of high load, high stress and wear sharp precision molds and tools; coated tungsten carbide deposits a thin wear resistance layer to improve the wear resistance on the base. Furthermore, the coating layer can combine different elements to achieve single or multilayer according to different requirements.

Vacuum deposition is a family of processes used to deposit layers of material atom-by-atom or molecule-by-molecule on a solid surface. The deposited layers can range from a thickness of one atom up to millimeters, forming freestanding structures.  It is widely used in metallic films, transparent conductive oxides (TCO), superconducting films & coatings. Multiple layers of different materials can be used, for example to form optical coatings. When the vapor source is a liquid or solid the process is called physical vapor deposition (PVD). Vacuum metallization is a process that creates a unique quality finish used in the manufacture of products worldwide When the source is a chemical vapor precursor the process is called chemical vapor deposition (CVD). Often a combination of PVD and CVD processes are used in the same or connected processing chambers.

The points of operation of shelve-on and shelve-off:

1. Check up the base oil quality before the shelve-on, if it is unqualified, it should be cleaned and hen re-oiling.
2. Clamp must be stable to ensure that injection mold parts do not fall when rotating vacuum chamber.
3. Loading and hanging position of injection mold parts would have marks after plating. In addition, if the clamping force is too large injection mold parts may be deformed, so operators can the inlet / runner as loading and hanging position, and then remove it after the plating.
4. In the process of shelve-on, operators should not touch the valid trial of injection mold parts, avoid leaving fingerprints smudges to impact plating effect.  
5. Cage should keep clean, and it needs a good scrub regularly.
6. Operators should carefully remove the injection mold part, and it should not be scratched.
7. Interlayer should be padded with a clean paper.
8. Plastic pots should be covered well to avoid dust.

In TIG welding (tungsten inert gas welding), tungsten electrode under heavy current and poor argon protective is prone to form rim on the surface of the electrode tip. The rim will hinder the argon to flow and rare earth oxide on the electrode surface to migrate, exacerbating burning, and destabilizing electrode’s performance.

Under the same conditions, W-CeO2 is the earliest to form rim, followed by the W-Y2O3, and finally the W-La2O3. In addition, the argon gas flow, the arc length will have some influence on the rim forming.

Effect of argon gas flow rate: In the test electrode arc length is 3mm and electric current is 160A. Arcing voltage is 76V. By changed the flow rate of argon found that the smaller argon gas flow rate, the shorter the rim appears.

Effect of arc length: In the tests, argon gas flow rate is 3L / min and electric current is 160A. Arc voltage is 76V. By changing the length of the arc found, the longer arc length, the shorter the rim appears.

Observed electrode SEM photograph after welding found the electrode tip is divided into three areas. A area and C area is rough. B area is smooth. Besides, the rim usually appears between C area and B area. And this area is dendrite structure described rim growth method is based on dendritic.

In the arc burning process, under the joint action of the arc and the heat resistance, on one hand, the tungsten on the electrode surface will melt and evaporation. On the one hand, it will show recrystallization. In C area, tungsten recrystallization rate is greater than melting and evaporation rate, so there will form rim. In addition, during welding process although electrode has argon gas protection, but there is still a small part of the oxidizing gas impurities involved. Further, intruded by oxygen molecules in the air, the tungsten on the electrode surface will oxidize at a lower temperature C area to generate tungsten oxide. These oxides will decompose at high temperatures, deposited at recrystallization dendrite, forming the rim.

With the development of science and technology and the improvement of human environmental awareness in recent years, people develop a variety of new electrode materials to replace thoriated tungsten electrodes. In the 1960s, the Soviet Union started to develop new materials. China in 1973 developed the W-CeO2 electrode. The late 1980s, Japan launched a series of rare earth tungsten electrode including a W-Y2O3, W-CeO2 and W-La2O3 and so on. The composite rare earth tungsten electrode is introduced in the 90s by adding a variety of rare earth oxide to obtain, which has excellent welding performance.

The component of HWCYL20 tungsten electrode includes 0.4wt% La2O3,0.4wt% CeO2 and 1.2wtY2O3 and tungsten oxide. Mixed these three kinds of rare earth nitrate solution with blue tungsten oxide, after dried and reduction, can obtain the ternary rare earth tungsten powder. Through the pressing, sintering, forging, annealing, drawing and grinding can finally obtain HWCYL20 electrodes with different diameters.

Analyzed SEM photograph of ternary rare earth tungsten powder found the Fisher particle size of powder is about 1.7um, having smaller particle size. And this is mainly because rare earth elements beneficial to inhibit tungsten grain growth. Tungsten electrode after sintering, rare earth oxide particles as the second phase uniformly distributes in the tungsten matrix. Rare earth oxide particle size is about 1 ~ 2um. After welding rare earth oxide particle size has no significant change.

Compare Ø1.6mm HWCYL20 electrode and thorium tungsten electrode welding performance found, HWCYL20 after welding there is dendrites projecting showed on the surface of the electrode tip, which great damage arcing and welding performance of electrode. Found at high powder lens there was sunken on the surface of electrode tip. And after welding thorium tungsten electrode tip was blunt, which seriously affects the arc performance of the electrodes, having severe burning. In addition, the electronic work function of HWCYL20 electrode is 2.76eV and burning rate is small than thorium tungsten electrode. It can be seen, HWCYL20 electrode having good welding performance.

Except HIP (Hot Isostatic Pressing), there is a kind of CIP (Cold Isostatic Pressing) correspondly. It generally to press the sealed materials in plastic mold from each direction at room temperature simultaneously, which used more for powdered metal or non-metallic materials, molding, providing a pre-sintered compacts for following sintering. Tungsten copper alloy is composed of two mutually soluble Cu and W, which has a great difference in physical and chemical properties, called pseudo alloy. So it is difficult to manufactured by conventional method, must be fabricated by powder metallurgy (PM). According to different pressure transmission fluid, including cold isostatic wet bag method and the dry bag method isostatic pressing and soft mode. Since the conventional molding method between the powder and the powder, powder and punch and die wall there is a certain friction, so that during the pressing force distribution and transmission of certain changes occur, and also resulted in various parts of the compact density and intensity uneven distribution; by comparison, CIP has more uniform molding pressure, which can ensure the compacts have uniform density and net shape, low consumption of mold and high molding efficiency under low molding pressure.

In addition, it is important that the controlling of pressing rate in CIP process, and can directly affect the density of the density of compact. It not only has an effect on state friction and work hardening of powder particles, but also has an effect on gas escaping. If the compression speed is too fast, not easy to escape the gas, the gas left in the blanks in the relatively more in the subsequent sintering process are correspondingly difficult to eliminate left voids or pores. What’s more, pressing too fast will make the inside of the powder aggregate greater stress, resulting in relief after the compacts elastic aftereffect. Therefore, reduce the speed of pressing pressure and extend the dwell time appropriately can delivery the pressure completely and have sufficient time for air escaping, which is also beneficial for density distribution and avoiding the elastic after-effect.

Tungsten copper material is composed of tungsten and copper, which contains all advantages of this two metals, such as high strength, high hardness, excellent wear and corrosion resistance, good resistance to arc erosion, welding resistance, excellent electrical and thermal conductivity, which can be widely used in high-voltage switch, vacuum switch, electrical contacts, EDM electrodes, welding electrode and plasma plating electrodes fields. In addition, in the field of microelectronics, such as LSI (Large Scale Integrated Circuit) and high-power microwave devices used as the substrate, embedded blocks, connectors and cooling elements. Tungsten copper can effectively reduce the stress by the difference of coefficient of linear expansion and insufficient heat radiation, and extend the service life of electronics.

Since tungsten and copper are immiscible, it can only be fabricated by (PM) powder metallurgy. Based on this process, it develops many new processes, such as MA (Mechanical Alloying), oxide reduction, hot gradient method, thermo-chemical method, injection molding, activated liquid phase sintering, fiber reinforced, HIP (Hot Isostatic Pressing), composite powder reduction and so on. But those methods have some defects to some extend. Hot hydrostatic extrusion is working on a four-post hydraulic machine, mold using three sets of combination of pre-stressed die, while using the outer heating coil and ceramic heating tube mold preheated. With the increasing sintering temperature, the relative density of sintered compact increases, trace activator Ni added help to improve the relative density of sintered compact. Temperature increase can improve the wettability of copper solution to solid tungsten, and it is beneficial for Cu solution spreading on the surface of W grain, reducing the resistance of rearrangement process and improves the densification rate. Furthermore, with the increasing temperature, the viscosity of copper solution decrease, this is beneficial for improving the flowing rate by the capillary force and contributing the densification process.