Tungsten Copper Liner and Terminal Sensitive Projectile

Recently, famous Chinese scientist Yang Shaoqing ammunition invited in the CCTV program for the audience of a presentation mysterious "Tank Terminator" – terminal sensitive projectile. Terminal sensitive projectile is also called as sensor detonated ammunition, which is a new kind of anti-armor weapon developed in 1970s. It can detect the presence of a target terminal ballistics, and can make warhead explosion direction towards the goal, mainly for autonomous attack armored vehicles top armor, it has long distance, high hit rate, good penetration effect in the 21st century information battlefield.

TSP is composed of major shells and propellant charge composition. Major missile includes elastomers, time fuze, projectile structure, end-sensitized bullets. And the end-sensitized bullet consists of save spin and steady deceleration scanning systems, sensor systems, central controller, advanced warhead, power, etc. Wherein the central controller is equivalent sensitivity projectile brain centers, its main role is to drive control, data acquisition, signal conversion and fire decision-making. But the final damage caused to the target is the EFP warhead. EFP-Explosively-Formed Projectile, heat liner formed by long thin jet of metal armor, except that after the EFP warhead explosion, shaped charge liner crushed deformed, forming a stout and dense penetrator pills, which speeds up about 2000 m/s, less than the shaped charge jet velocity (8000 m/s), the jet penetration is deeper.

TSP self-forging fragment warhead usually uses heavy metals to fabricate metal liner, which requires good ductility, high density and a reasonable price. From the properties, gold and rhenium is appropriate, but they cost a lot; although depleted uranium armor can meet the requirements, it still radioactive and many countries oppose to use. So copper used widely in liner in early days. Today, tantalum and tungsten copper liner is two main types of liner materials. Tungsten copper shaped charge jet of tungsten have a higher head speed at the time of penetrating armor can shorten the time through, thereby facilitating against reactive armor. But its crisp texture and poor powder adhesion, good ductility copper added contribute to its shape, so the stability of the jet improved and prevent from breaking.

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Tungsten Copper Heat Sink Material Hermeticity

Based on high density, high strength, excellent chemical stability and arc ablation resistance, tungsten copper material also has perfect thermal and electrical conductivity, which can be widely used in EDM electrodes, electrical contacts, military industry and heat sink materials. However, tungsten copper electrodes and contacts used for electrical machining has different requirements of properties with tungsten copper used in heat sink. As heat sink materials, tungsten copper not only be supposed to have excellent thermal conductivity, but also should have excellent hermeticity to ensure the equipment working stability. Since any porosity and leakage will lead to the operation failure of the microwave component.

In the early 1980s, tungsten copper has been chosen as heat sink materials, which due to it has the similar coefficient of thermal expansion to some ceramic, and both of them after brazing can not only guarantee the thermal matching, but also form a good thermal channel. Theoretically, W and Cu has big difference in physical and chemical properties, which the difference of melting point of them are as much as 2000℃. And they can not form a solid solution or a compound so that it is only suitable for using powder metallurgy process. And the best process is infiltration, tungsten powder is compacted to a certain density of blank, after sintering and shrinking at high temperature forms tungsten skeleton with a certain density and then at a temperature above the melting point of copper was infiltrated tungsten skeleton.

Since the high hardness and poor plasticity of tungsten powder, using a general manufacturing method infiltrated tungsten copper alloy will be some of the pores, the relative density can only reach about 60%. Densification at high temperatures also have some closing pores in copper infiltration process is not sufficiently filled with tungsten skeleton, reducing the product's tightness. In order to reduce the porosity of the relevant parameters need to be improved so that it can meet the requirement of hermeticity.
Merely rely on raising the temperature of the tungsten blanks shrink to increase the density, which is difficult to control precisely. Such as the deviation of heat matching, it is the major influencing factor of conventional infiltration hermeticity. Some researchers try to ultrafine tungsten powder added to certain activators, such as nickel (Ni), cobalt (Co), iron (Fe), etc., and then mixed with copper powder. After pressing and activated sintering, the relative density of tungsten copper can reach 98 % or more, which can be a good solution to tungsten copper heat sink material hermeticity issue. But it added activator of Ni, Co, Fe and other elements will be Cu and W-phase and phase mutually dissolved, and magnetic Fe, Cu content changes will directly affect the conductivity and the thermal conductivity of the material, so not suitable in the heat sink industry applications.

Therefore, on this basis, the researchers conducted a process optimization, the tungsten powder mixed with a small amount of copper powder, copper powder can effectively preserve this part of the green bodies connected pores, when carried out at high temperature and pressure infiltration of liquid copper can be fully effective filled tungsten skeleton. This section is also known as copper induction of copper, its main role lies in two main aspects, one is to enhance the strength of tungsten blanks, and the other is infiltration process hermeticity guarantee.

Tungsten powder has high hardness, poor plasticity, generally under pressure prone to "arch effect" between the powder. Once the pressure is too large, blank-arch bridge will make a release force is rupture and delaminated, and thus the relative density of tungsten powder can only reach about 60%. But copper powder has good plasticity, which can effectively destroy the "arch effect" between the tungsten powder and plastically deformed. Both of them can fill each other, engage with each other, thereby increasing the density and strength of tungsten copper green. On the other hand, since the initial tungsten skeleton have a uniform distribution of copper, the part of copper changed into liquid and complement with the copper liquid out side the skeleton at 1350℃.

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Tungsten Copper Wire

Tungsten copper alloy is a kind of psudoalloy, which consists of the hard phase W and the binder phase Cu two immiscible metals, so it only can be fabricated by PM (Powder Metallurgy). Tungsten copper material has both advantages of tungsten and copper, the high density, high melting point, excellent wear resistance and corrosion resistance of W; the excellent electrical and thermal conductivity, good plasticity of Cu; and at a temperature above the melting point of copper alloy of copper liquefied evaporated to absorb a lot of heat, reducing the surface temperature. So tungsten copper material is also known as heat sink materials.

According to the shapes and applications, tungsten copper products can be specifically divided into tungsten copper rod, tungsten copper block, tungsten copper plate, tungsten copper contact, tungsten copper tube, tungsten copper electrode, tungsten copper heat sink, tungsten copper wire and so on. In the early 1960s, tungsten copper wire and tungsten copper electrode has been used in EDM (Electrical Discharge Machining) and resistance welding because of its high density, high strength, excellent electrical and thermal conductivity and arc ablation resistance. So far, with the developments of relevant technologies and further study of researchers, tungsten copper begin to use in plasma electrode material processing, precision machining, spraying, LED and other electrode fields. But since the special PM structure of tungsten copper, it has been greatly limited used in wire. In order to improve the uniformity, mechanical properties and production cost, it needs to looking for new technologies and processes.

Used in EDM electrodes of tungsten copper wires are supposed to meet the following requirements:

1. On the basis of excellent electrical and thermal conductivity, it also has good resistance to spark erosion;

2. Good structure uniformity and density, in order to ensure the stability of the electrical processing and improve the utilization of electrode material;

3. It has lower machining consumption and dose not affects the quality and the overall efficiency;

4. Easy for molding, machining molds and products according to design requirements to provide a correspondingly shaped profile tungsten copper electrode bars or complex shapes.

The basic process of tungsten copper wires is : Mixing → molding or isostatic pressing → infiltration, sintering tungsten copper rod or tungsten copper block → machining. Except conventional infiltration process, there are some popular processes used more, such as high-temperature liquid phase sintering and activated liquid-phase sintering. The principle of infiltration is that porous tungsten skeleton wetted by copper liquid, under the capillary force the copper liquid flows along the W particle gap, filling the pores of porous tungsten skeleton. So tungsten copper materials have higher density, excellent sintering properties and electrical conductivity; High temperature liquid phase sintering since the sintering temperature is high, a long time, will make a lot of volatile copper phase, so that the sintered tungsten copper material density decrease, the performance will be subject to different degrees of impact, it is difficult to obtain a high density, high conductivity tungsten copper alloy material; activated liquid phase sintering improves the relative density, the hardness and tensile strength of tungsten copper by adding small amounts of trace elements (Ni, Fe, Pd, etc.). But on the contrary, the activated elements will dramatically decrease the electrical and thermal conductivity, which is not suitable for the occasions with high requirements of the conductivity.

The technologies to machine tungsten copper rod or block in wires include drawing processing, rolling processing, roller die drawing techniques and rotary forging technology. Drawing processing take advantage of metal plasticity, when working in the external force so that it is forced through the die, the metal cross-sectional area is compressed to obtain the desired cross-sectional shape and size of the processing method. Preparation of tungsten and copper wire by repeatedly hammering and drawing forming, drawing conducted at room temperature, metal products will produce obvious hardening.

But for tungsten copper with lower Cu content, it has poor plasticity, the drawing rate received extremely limited, which is difficult to draw molding; rolling process is to rely on the friction two rotating rollers and the rolling member rolling pulled into the roll gap, it is compressed to produce plastic deformation process. In addition, the rolling process can also refine the grain, improve the organization, can significantly improve the mechanical properties of the metal alloy, suitable for mass production; Roller die drawing process the billet is drawn in a non-grooved drive, freely rotating rollers consisting of, the sliding friction with the material of the die orifice was changed to rolling friction bearing, the stretching process is more effort not only suitable for drawing round wire, shaped wire may be stretched, but not suitable for low plastic material.

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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.

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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.

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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.