Tungsten Copper Contact HIP Process

Tungsten copper contact has excellent electrical, thermal conductivity and chemical stability, but the problem in densification is always a barrier in its developing way. And this incomplete densification will have an bad influence on the hardness, the strength, wear resistance and arc ablation resistance conversely. So the relevant researchers propose that pressure sintering, a total reduction of chemical and explosive compaction method special process to improve the density of tungsten copper contact material. However, there are some defects in these processes, such as high operation and maintenance costs, be suitable for the parts with small size and so on.

In order to improve the properties of tungsten copper contacts, we combine tungsten copper contact used in high voltage circuit breakers to study HIP process for tungsten copper material impact, and its elimination of the porosity, densification mechanism and related factors. HIP (Hot Isostatic Pressing), it places the product into a closed container, which is applied to each peer pressure while applying heat, under the action of high temperature and pressure, the product can be sintered and densified. HIP has many advantages, such as combines the advantages of hot pressing with isostatic pressing, lower molding temperature, excellent densification and performance, which is essential for high-performance material manufacturing; now, in the United States, Japan and Europe to achieve the industrial, marine, aviation, aerospace, automotive and other fields have been widely used.

Before HIP process, tungsten powder mixed with a certain amount of copper, cold isostatic pressing, low temperature pre-sintered to give semi-finished copper by infiltration. It uses argon (Ar) as pressure transmission medium, temperature control (tungsten-rhenium thermocouple measurement), pressure, dwell time and other relevant parameters, before and after the HIP process copper tungsten contact material hardness, density, bending strength and conductivity of comparative measurements. The density uses conventional Archimedes drainage method; the hardness uses Rockwell hardness HRB and refers to Brinell hardness HB; flexural strength is measured by GB electrical contact material basic performance; electrical conductivity is measured by eddy current conductivity tester.

The experimental result shows that HIP densification mechanism of tungsten copper contacts is similar to the cast alloy, which removes internal defects by deformation - closed - diffusion under high temperature and high pressure and achieves completely densification. Therefore, it requires after-infiltrated material should have good closure, all internal defects, osteoporosis and so can not in communication with the outer surface. If all the defects can not be guaranteed enclosed inside the blank in the process of infiltration, the density after HIP process changes little, even no change. In addition, HIP treatment effect is also related to the content of copper. When the HIP temperature reaches a temperature close to the melting point of copper, its surface will be leaking copper beads phenomenon. Overall, HIP process can promote tungsten copper contact completely densification, which remarkably improves the mechanical and physical properties, and effectively solves dispersion and reliability.

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Fiber-structure Tungsten Copper Contact

Tungsten copper is a psudoalloy, which is composed of two kinds of immiscible and has a great difference in physical and chemical properties metals. Since it has both advantages of W and Cu (high hardness, high strength, excellent corrosion resistance of W, excellent electrical and thermal conductivity of Cu) so that it has a broad application prospect in high-pressure, high-load vacuum circuit breaker and microelectronics fields. Due to the special nature of tungsten copper material itself, it is basically prepared by PM (Powder Metallurgy) process, but also for this reason that makes the structure and properties of tungsten copper alloy products subject to certain restrictions.

In order to make the organizational structure of tungsten copper contact more reasonable, the relevant researchers made many attempts in recent years, such as PIM (Powder Injection Molding), functionally graded materials, nano-structure and W-Cu tungsten fiber reinforced composite structure. Here we focused on the preparation of the fibrous structure of tungsten copper contacts and analyze the factors that affect performance and ablative infiltrated. The use of vacuum infiltration process, and select netting lamination to tungsten as weft, warp knit copper-dimensional net. Under vacuum condition, liquid copper has better liquidity and there is no air in the pores, which is more conducive to liquid copper fill-in. Tungsten braided copper mesh (copper as the infiltration time of induction of copper) and copper billets, and then the two stacked together in a vacuum sintering furnace infiltration, and sintered copper above the melting point (about 1300 ℃).

Copper in the molten state infiltrated in pores of tungsten skeleton by capillary forces, thereby connected to each other and form a dense material integrally. The advantage of using this method is that tungsten wire can distribute uniformly and copper wire can effectively induce. Since the most difficult to achieve tungsten copper contact with fiber-structure is how to make the fibers uniformly distribute in the matrix, whose distribution will affect the final properties directly. The weaving process can control tungsten wire to adjust the spacing between fibers. In addition, the distribution of copper wire at a high temperature infiltration, which presents the liquid copper supplement, under the action of surface tension, integration can reduce the surface area, prompting tungsten copper contact materials densification.

Tungsten wire diameter, infiltrated temperature and time all have an effect on the process. It uses tungsten fiber to take place of tungsten powder of conventional PM. Too large granularity of tungsten powder will have segregation and appear large area Cu-rich region, the binding force between the tungsten particles is also poor; too small granularity will prone to accumulate, leading to difficult to form a passage between the capillary and even hinder the formation of closed-cell infiltration were, so that the anti-arc erosion capacity decreases dramatically.

Fiber-structure has straight route so its density is higher after infiltration. But with the decreasing fiber diameter, it easily to form when copper was infiltrated pointed or wedge-shaped space, and solidification resistance is also large so that the defect forms. In addition, infiltration temperature has an optimum range, below the temperature which the sintered skeleton strength decreases, and the extension of sintering time, decrease the efficiency and increase energy consumption; the high temperature which the copper was in favor of lowering the viscosity of infiltration, but on the other hand the surface tension of liquid copper is reduced, and has an adverse effect on infiltration.

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 Contact Microwave Sintering

Except conventional sintering process, microwave sintering as a new sintering process is also gradually began to apply in the tungsten copper material. It uses special microwave band has the fine structure coupled with a basic material to generate heat, and material dielectric loss in the electromagnetic field of the material as a whole it is heated to the sintering temperature to achieve densification. Microwave sintering has many advantages, such as volumetric heating, heat conduction from the inside out and stepwise temperature distribution within the high outside low, which are beneficial for heating rate, sintering time and energy efficiency. For powder metallurgy industry, it is essential that lower cost of production and lower energy consumption, so microwave sintering has a broad prospect in tungsten copper contact.

Tungsten copper (W-Cu) contact is a kind of psudoalloy that consist of W and Cu immiscible and with a great difference in the melting point, which means it is difficult to achieve higher density by conventional sintering method and it has a bad influence on the electrical and thermal conductivity, hermeticity and other mechanical properties. Compared with conventional sintering process, microwave sintering can effectively improve the density of tungsten copper contact materials to improve the microstructure and increase other comprehensive performance.

From microwave sintering temperature and holding time point of view, the sintering temperature rises to a certain temperature, density tungsten copper contact materials increases, the relative density of up to 99.8%, close to fully densification. This is due to the temperature rise reduces the wetting angle, improved copper solution on a solid phase wettability of tungsten, reducing the resistance of the particle rearrangement process, the particles rearrangement sufficiently improve the densification rate. Meanwhile, temperature increases can also reduce the viscosity of liquid copper and increase in liquid copper capillary force mobility, which will be conducive to densification. But thereafter the temperature increased, lower relative density decreased, which is due to the reduced coefficient of viscosity, the effect of gravity copper deposited on the bottom of the fluid will gradually lead to the formation of a new gas into the pores, thereby reducing the density.

The sintering additive also has a great impact on the tungsten copper contacts sintering densification. The experiments show that adding a small amount of Co, Ni can significantly improve the solubility of W, and help to improve the ability of densification. In the liquid phase sintering process, W in solid solution reacted with sintering aid or intermediate phase. And the product will form a continuous layer of wrapping on W grains surface, which can significantly reduce the surface tension between the liquid and the copper particles W and improve wettability of the two phases.

In addition, copper liquid under the action of capillary force, the gap between the W particle flow and cause a rearrangement of W particles, thereby significantly promoting compact shrink compact. However, copper liquid flow too often will lead to the emergence of copper accumulation pool, even reduce the uniformity of the sample. Overall, by analyzing the experimental data, in the manufacture of tungsten copper alloy contact process, the microwave sintering technology compared to conventional sintering has a significant advantage in heating rate and sintering cycle; sintering additive selection can promote the densification of tungsten copper contacts；samples of microwave sintering has more uniform microstructure and better mechanical properties.

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 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. There is a comparison between tungsten copper contact tip and brass contact tip:

From the table we can see that the contact tip compared to tungsten copper contact tip brass longer life, better welding performance, which can effectively improve the overall efficiency. 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.

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.

Tungsten Copper with Gradient Structure

Tungsten copper (W-Cu) and molybdenum copper (Mo-Cu) are composed of respectively tungsten and molybdenum with copper, which called two-phase composites and has many advantages when it used in some devices with high power, such as high hardness, high strength, high melting point, excellent chemical stability, excellent thermal and electrical conductivity and lower coefficient of thermal expansion. As a kind of electronic packaging heat sink material takes place of conventional materials gradually, the related researchers make an intensive study on tungsten copper, which includes add active agents, change powder properties to improve the sintering density of tungsten copper materials.

However, the conditions of some industries today have become more and more strict (including temperature, pressure, power, etc.), which requires tungsten copper has better properties. Inspired by tungsten carbide with gradient structure, the Japanese researcher propose new concept of functional materials with gradient structure and from the preparation process structure, computer simulation and forecasting has done sufficient research, have also made substantial progress, so that it plays an important role in some high-power devices. Tungsten copper composite material is kind of two-phase psudoalloy, which composed of two metals tungsten and copper with a great difference in physicochemical properties.

Its properties will change with the structure. Viewed from the aspect of gradient structure, it can has one end with a high hardness, high melting point, tungsten or copper content is low high-density tungsten copper, while the other end is a good electrical and thermal conductivity and high plasticity of copper or copper content of tungsten, copper, in this way the formation of gradient structure having a tungsten-copper composite materials have a good specificity and a broader application prospect.

For the manufacturing process of the gradient structure tungsten-copper composite materials, researchers and scholars in related fields, and also made a variety of attempts to conceive. Here is a brief introduction to several related new technologies, such as conventional dry lamination method, hierarchical load a different size of tungsten powder, cold pressed, sintered, after copper infiltration preparing different graded material consisting of tungsten-copper ( good sintered porous tungsten skeleton electrochemical corrosion formed along the direction of tungsten skeleton having a gradient porosity by infiltration of copper can be obtained having a continuous change in the composition of tungsten copper gradient material); the other one uses hot isostatic pressing diffusion bonding to form tungsten copper with gradient structure by different contents.

In addition, another type is prepared by continuous gradient layer, such as slip casting, sedimentation molding, centrifugal molding, etc. Plasma spraying is a kind of new method that are compacting and sintering tungsten copper powder with different content. There are two methods which have already patented process, one is the use of powder metallurgy - infiltration process. Preparation of powder metallurgy method which utilizes two components completely different copper tungsten compact, then where the thermal conductivity of tungsten copper larger compact embedded in another compact, due to the embedding of relatively high copper content briquette making its thermal conductivity is relatively high, and has a lower peripheral compact copper content, thus ensuring the overall coefficient of thermal expansion gradient material decreases. Another one is that combines tungsten copper (W-Cu) with ceramic based on aluminum nitride-aluminum (AlN-Al), ceramic has a gradient structure with a metal having a thermal expansion coefficient due to the match, so the lower internal stress, and as part of a combination of metal and ceramic high thermal conductivity such that heat will not affect the heat concentrated in the buffer layer and the heat radiating effect of the heat sink materials.

Tungsten Copper Electrode Description

Tungsten copper electrode is kind of composite metal material and is composed of high purity tungsten powder and good conductivity Cu powder through isostatic pressing and high temperature sintering. Therefore, tungsten copper electrode not only has high melting point(3410℃) and high density (19.34 g/cm3) of W, but also has good conductivity and other advantages of Cu.

In addition, tungsten copper has good thermal resistance, high thermal conductivity and low expansion, which can be partly used in resistance welding or electrical contacts. EDM and EDM is the most widely used tungsten copper as electrodes. 

According to applications, tungsten copper electrode can be specifically divided into resistance welding electrode, EDM electrode and the electrode of high pressure discharge tube, etc.

 1 .Resistance Welding Electrode

Resistance welding electrode is using thermal resistance for welding, which is produced by the pressure of electrode and current run through contact area or close area. It takes advantage of the thermal resistance to melt or model the work-piece and combined it with metal. Resistance welding can be also divided into four types, such as spot weld, caulk weld, beading weld and butt weld. The material of electrode plays a significant role in resistance welding, which can press the welding parts, supply great amount of current and promote the welding area cool down and so on.

It requires that electrode materials should have good mechanical strength (not be out of shape after stamping), good thermostability (not be out of shape after welding), excellent thermal conductivity (not be easily heat by current) and can not be combined with the welded material (simply not be stick with the welded material). Therefore, tungsten copper could meet a criterion above. In addition, there are some description and rules in the standard of Japanese copper alloy electrode (JIS Z 3234-1999).

2. EDM Electrode

EDM (Electrical Discharge Machining) is also called as discharge machining or electric corrosion machining, which uses pulse discharging between electrodes. The principle is that the electrode and the work-piece used as two poles and put the liquid in the gap of discharge, the pulse voltage will puncture the liquid when the distance decreasing