Infiltration Time Effect on Tungsten Copper Electrode Properties

Take W-Cu tungsten copper electrode as an example, with increasing infiltration time, the density of tungsten copper electrode increases. And after that the infiltration density reaches the maximum, the density of tungsten copper electrode decreases by the time. The density and hardness of tungsten copper W-25Cu in different infiltration time as follow:

In the process of infiltration, copper solution completely infiltrated tungsten skeleton will take some time, with the increasing infiltration time, tungsten skeleton has infiltrated more fully, the corresponding density of tungsten copper electrode was improved. However, when tungsten skeleton was completely infiltrated by copper solution, if the temperature continues to increase the infiltration density changed a little longer this time but likely to cause the liquid copper tungsten particle erosion, some places inside may appear copper pool, which decrease the density of tungsten copper electrode.In addition, due to the diffusion of crystal grains, the odds of the liquid copper into the tungsten particles increases, the lattice stress decreases, and the tungsten particles are rearranged so that the partial so that the construction is more uniform. Viewed from the cost, it is useless to increase infiltration time.

In the early of infiltration, tungsten skeleton was not completely infiltrated by copper solution, which lack of density and hardness. However, the infiltration has become more and more fully as time goes by so that the density and hardness of tungsten copper electrode will rise. But when infiltration is completely and time continue to increase, it may lead tungsten particle to grow up and evaporated tungsten particles in liquid copper, which makes tissue distribution is uneven, the hardness decreased accordingly. Except that the density and hardness of tungsten copper electrode, the electrical conductivity is also an crucial property when it used as electrode in EDM or ECM.

Tungsten Copper Liner Warm Flow Compaction

Tungsten copper liner is a kind of psudoalloy that composed of W and Cu, which is immiscible and forming compound with each other. So it is difficult to fabricate by common pressing-sintering process, the most widely used in tungsten copper products is powder metallurgy (PM), which includes infiltration and activated liquid-phase sintering. Infiltration presses tungsten powder into a compact, at a certain temperature pre-sinter the porous tungsten skeleton with density and strength. And then the low melting point of the molten liquid copper is infiltrated tungsten skeleton in order to obtain tungsten copper alloy with fully densified. The main mechanism is the liquid metal wetting porous matrix metal, under the effect of capillary forces along the inter-particle pore liquid copper flows and fills pores of the porous tungsten skeleton.

According to the sintering temperature, infiltration process can be specifically divided into sinter tungsten skeleton at high temperature + Cu infiltrated and sinter composite powder at low temperature + Cu infiltrated. Sinter tungsten skeleton at high temperature + Cu infiltrated presses tungsten powder into a compact before sinter and infiltrated Cu at 1800-2200℃. Since the tungsten powder at a high temperature to fully restore the remaining low-melting impurities and sub-oxides can be restored by evaporation gasification and thermal decomposition was removed, thus prepared tungsten copper shaped relative density of 99.2% comprehensive and excellent performance.

However, it also has some disadvantages, such as long production cycle, the control parameters are many and complex and high production cost. While sinter composite powder at low temperature + Cu infiltrated is mixed with a small amount of induced copper before sintering and infiltration. Generally, induced copper content of about 2.5% -3.5% and the granularity is similar to tungsten powder, which can effectively improve the compacting performance and the flowability of liquid Cu. But too much of the added amount of copper will result in enrichment-induced infiltration of copper, so that the overall the density of tungsten copper liner decreases.

Overall, compared with the injection molding suitable for the smaller components, warm flow compaction is more suitable for the larger components with complex structure and shape. It has higher requirements on the granularity of raw material and is sensitive to the temperature changes and the amounts of binder. Low temperature may cause mixing powder flow properties deteriorated, so that the tungsten copper shaped charge density distribution can not be molded or uneven. High temperature may obviously separate the two phase (the mixed powder and the binder). The excessive amount of adhesive may cause infiltrated tungsten skeleton pore through the large, so that the density decreases and easily deformed. In addition, warm flow compaction combines the advantages of injection molding and warm compacting process, and it can effectively improve the density, the penetration depth and armor capability of tungsten copper liner, which is the ideal choice for tungsten copper liner manufacturing in the future.

Nano Tungsten Copper Electrode Research

The granularity and uniformity of tungsten and copper powder has an effect on tungsten copper electrode sintering, and the decreasing granularity will improve the comprehensive properties of materials, such as the density, the hardness, the electric and thermal conductivity. Theoretically, powder metallurgy (PM) uses metal powder (or metallic oxide powder) as raw materials, after compacting and sintering, the granularity of powder is coarser. Compared with PM, nano tungsten copper has higher surface energy, which atoms move by higher interfacial energy, shrink the small pores in sintering process and in case of the diffusion of pores. Therefore, nano tungsten copper research is beneficial for the densification at lower temperature.

Although the process of nano tungsten copper is similar to the traditional PM, which can be divided into preparation, compacting and sintering, due to the characteristic of nano particle, there are some differences between them. Overall, the most widely used process of nano tungsten copper main are Sol-Gel method, Metal Alloying (MA), Mechano-Thermo-chemical Process, spray drying and so on.

Metal Alloying (MA), uses high energy ball milling for tungsten copper mixed powder grinding, achieves the nano powder (the granularity is about 20nm-30nm). Then compacts the blank by the nano powder and sintering in hydrogen atmosphere at 1000℃, nano tungsten copper with high related density can be achieved.

The so-called sol - gel (Sol-Gel) is the use of compounds with high chemical composition as the precursor in the liquid phase under these uniformly mixed materials, hydrolysis and condensation reactions to form a stable transparent sol in solution sol particles by aging between slow polymerization to form a three-dimensional network structure of the gel, the gel network between full solvent loses fluidity to form a gel. After drying, sintering and solidifying, sol can be produced with molecular or nano substructure. At the academic front, some researchers succeed in preparing MoW and CuW high-performance powder. However, this kind of process has some shortcomings, such as the content of water vapor and impurities is difficult to control in the process of hydrogen reduction, which these problems will influence the later sintering process.

Mechano-Thermo-Chemical process, uses ammonium paratungstate and copper nitrate as raw materials to prepare a mixed solution, and then spray drying the mixed solution to obtain a metal powder mixture through a rotary atomizer and the subsequent drying process of the precursor, the precursor of combustion, the formation of tungsten copper W-Cu composite oxide powder, then milled oxide powder and two-step hydrogen reduction, thereby preparing nano-tungsten-copper composite powder.

Tungsten Copper Electrode — Chemical Co-precipitation

Tungsten copper is a kind of psudoalloy, which is composed of W with body-centered cubic structure (bcc) and Cu with face-centered cubic (fcc) structure and they are immiscible or not forming intermetallic compound. It not only has high hardness, high strength, low coefficient of thermal expansion and excellent wear resistance and corrosion resistance of W, but also has excellent electrical conductivity, thermal conductivity and plasticity, which can be widely used in some electrical contact materials or electrode materials. Generally, the basic process is: mixing → forming → infiltration, sintering → post-processing.

But tungsten copper electrode fabricated by conventional process, regardless of liquid-phase sintering or solid-phase sintering, the relative density of tungsten copper products produced will lower than 98% because of the wetting angle and the insoluble W in liquid Cu. Although the heating process and re-pressing or re-sintering can remarkably improve this situation, the cost is increasing and the overall efficiency is decreasing. Furthermore, in the sintering process will happen inevitably growth of tungsten grains, which would make it difficult to meet the performance of the market demands tungsten copper electrode material now.

In order to improve the sintering density of tungsten copper electrode and other tungsten copper composite materials, relevant researchers use activated sintering by adding additives. However, the activator can significantly improve the density of tungsten-copper alloy, it will also have some effects on the electrical and thermal conductivity, which is not suitable for the occasions has high demands on electrical and thermal conductivity. So chemical co-precipitation of copper tungsten nano composite powder prepared by reduction combined with hydrogen, by pressing and sintering process to obtain a high-performance compact tungsten copper alloy electrodes become a new hotspot.

The definition of chemical co-precipitation is that in solution mixing materials with different chemical compositions were prepared precursor precipitate mixture added a suitable precipitating agent, then the precipitate is dried or calcined, to thereby obtain the corresponding powder particles. It has two advantages, one is a nano-powder materials can be obtained directly by chemical composition homogeneous solution in a variety of chemical reactions, and the other is easy to prepare small particle size and distribution of nano-powder materials.

The experiment use ammonium tungstate, copper sulfate pentahydrate and concentrated nitric acid as raw materials. The specific operation of concentrated nitric acid in a copper nitrate solution was added with stirring, and then the mixed solution was added a solution of ammonium tungstate, a magnetic stirrer in the chemical co-precipitation reaction; After 1h the reaction solution was removed and the precipitate was placed in a muffle furnace firing 2h, to obtain tungsten copper composite oxide powder; after reduction by hydrogen obtained tungsten copper composite powder; then the tungsten-copper composite powder is extruded to form a green with a certain density and strength, ultra-fine grain was finally sintered tungsten copper alloy products.

Tungsten copper powder is polygon and the granularity is between 30nm – 50nm. Cu into a network-like structure of the W particles are bonded together in an approximation polygon and evenly distributed. This is because the raw material for preparing tungsten-copper composite powders of tungsten and copper salt solution, the distribution of the particles in the solution itself more evenly in the strong magnetic stirring effect, will make the precursor powder to retain the basic solution mixed state molecular level. And calcination and hydrogen reduction process in low temperature effectively inhibited the growth W grains. In addition, the initial structure of the powder is the oxides of tungsten and copper, their mutual isolation is not conductive to the growth of tungsten oxide particles, but is beneficial for evenly dispersed tungsten copper composite powder. From the fracture morphology, W grain evenly distributed in the Cu phase, forming larger dimples around, Cu phase has continuous web-like distribution along with the W grains. From the structure, with the increase in the sintering temperature, tissue distribution is more uniform, the porosity is also decreased. From the properties of alloy, Tungsten-copper composite compacts during sintering two-phase distribution, effective at power-conduction electron-average running speed increases, the conductivity also increases; complete copper network-like structure decrease the contact area of coarse W grains, which is difficult to form necking and beneficial for thermal conduction.

Tungsten Copper Contact Tip

Tungsten copper contact tip is a kind of welding consumables and it is generally located in the end of welding torch, which play a role in delivering welding wire. According to the hole shape, it can be divided into round, square, ellipse, triangle and so on. Common used materials for contact tips include pure copper, brass, beryllium copper, chromium zirconium copper, beryllium cobalt copper, etc.

In the resistance welding process, not only requires the contact tip has good electrical conductivity, but also required at high temperatures still has high strength, wear resistance and corrosion resistance to electrical properties. In practical, the contact tips use pure copper and beryllium copper, which have poor wear resistance and during welding process will easily spatter adhesion. It cause clogging of the tip or the wire and the contact tip bonding, which make the contact tip failure. Furthermore, replacing contact tip frequently will affect the welding performance and decrease the overall efficiency. Compared with pure copper, chromium zirconium copper and beryllium cobalt copper has higher hardness and better wear resistance at room temperature. But it has fewer sources, relatively complex process and higher cost.

Tungsten copper has both advantages of W and Cu, which not only has higher hardness, but also has excellent wear resistance, galvanic corrosion and higher softening temperature. Whether as the electrical resistance welding electrode with special requirements for the stress or as the contact tip used in arc welding, tungsten copper material has a great advantage, which is an important role of the electrical processing and welding occasion. Tungsten copper contact tip is sintered by tungsten and copper composite powder and the tungsten skeleton uniformly distributed in the copper matrix. When the temperature exceeds the melting point of copper, tungsten skeleton liquid copper can stick as a huddle and constitute a good conductor of heat passage, so tungsten skeleton area overheating does not occur in the process.

Theoretically, the room temperature strength of metal depends on two basic factors: one is binding force of metal atom, the other one is the resistance to dislocation motion. Common by increasing resistance to dislocation movement to improve the strength and work hardening methods are split out strengthened. However, these methods the effect of increasing temperature decreases until it disappears, and some rely precipitates precipitation hardening copper alloy, when raised to a certain temperature, the precipitate into the matrix meet again, so that a sharp decline in the strength of the material. By comparison, tungsten copper material does not has phase change, recrystallization phenomena at high temperature and the physical and chemical properties are stable.

The experiments show that 70W-Cu has higher hardness and better electrical conductivity than beryllium cobalt copper, and its softening temperature is twice more than beryllium cobalt copper, so as for flash butt welding electrode wear or require a higher arc welding contact tip applies quite well. In addition, in the process of vertical welding, when the thickness of the weldment 22-28mm, wire diameter φ2.4mm, 2.8mm the pore size of the contact tip, tungsten copper contact tip and chromium copper contact tip after welding has a great difference in wear. Tungsten copper welding contact tip at 20m, the circular aperture can remain unchanged, ensure the continue welding; The chromium copper welding contact tip about 2m, circular conductive mouth to occur due to poor abrasion resistance unilateral eccentric, expand the aperture and are unable to continue welding. Overall, tungsten copper contact tip has higher hardness, better thermosetting, wear resistance, excellent arc ablation resistance, anti-adhesion, which is a kind of contact tip materials with a broad application prospect.

Elkonite Tungsten Copper

Elkonite tungsten copper is a kind of alloy that has high density, high hardness, high strength and good corrosion resistance. Tungsten copper is suitable for embedded block, contacts, galvanic corrosion electrode and so on.

Grade	Class	Content(%wt)	Hardness	Conductivity(%IACS)
Elkonite10055	1W3	55W, 45Cu	70HRB	49
Elkonite10068	3W3	68W, 32Cu	83HRB	42
Elkonite10070	5W3	70W, 30Cu	88HRB	42
Elkonite10075	10W3	75W, 25Cu	92HRB	38
Elkonite10080	30W3	80W, 20Cu	98HRB	34
Elkonite10250	TC5	50WC, 50Cu	94HRB	45
Elkonite10256	TC10	56WC, 44Cu	100HRB	42
Elkonite10270	TC20	70WC, 30Cu	37HRC	30

1W3, 3W3 generally used as embedded block for flash welding and butt welding, which has higher requirement of conductivity and malleability. These materials can also be used for welding (as a spherical electrode) for low-conductivity ferrous metals such as stainless steel;

5W3, TC5 is suitable for light projection welding and other low-pressure welding;

10W3 is suitable for most of flash welding, light electric upsetting, electric forging die, and seam welding inserts;

TC10 used for mass production of solder bumps where the weld pressure is set relatively high. Non-ferrous metal processing and low carbon steel electric forging rough This material is commonly used as a stamped surface, cross-welding large diameter wire and bar;

TC20 is extremely hard and hard to be machining, which has been widely used in electric upsetting and electroforming.

Tungsten Copper Heat Sink Application

Tungsten copper heat sink has high hardness, excellent conductivity, low CTE and good hermeticity, which plays an important role in mechanical support, radiating passage, signal transmission, chip protection and so on. So tungsten copper heat sink has many applications, such as plate heat exchanger, electronic radiator, integrated circuit, microwave component and CPU the occasions with high requirement to hermeticity and radiating.

Used for plate heat exchanger

Tungsten copper heat sink for plate heat exchanger forms high-voltage circulating structure by vacuum welding of contact points. And the circulation structure makes the hot and cold fluid in the plate heat exchanger produce strong turbulence and achieves high heat transfer effect.

Used for electronic radiator 

Tungsten copper heat sink used for electronic radiator is also called as tungsten copper radiator, which can take heat away and cool down without external power supply.

Used for microwave component 

Working in the microwave band (frequency 300 ~ 300000 MHz) of the device, known as microwave components. Microwave devices can be divided into microwave oscillators (microwave sources), power amplifiers, mixers, detectors, microwave antennas, microwave transmission lines according to their functions. Tungsten copper heat sink used for microwave component plays an important role in mechanical support and heat conductivity, which is one of the important parts of microwave system.

Used for CPU

CPU will produce a lot of heat when it is working, if not timely disseminate the heat out, it is easy to lead to poor computer operation, or even burn the CPU. Tungsten copper heat sink used for CPU can cool it down and keep working stability.

Used for integrated circuit 

Tungsten copper heat sink for integrated circuit connects the required transistors, resistors, capacitors and inductors and other components and wiring, made in a small or a few small pieces of semiconductor chips or dielectric substrate, and then packaged in a tube, the circuit has become the desired micro-structure; it combines all components as a whole in structure and promote the development towards miniaturization, low power consumption.