Tungsten Copper Throat Insert

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

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

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

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

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

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Nano Tungsten Copper Composite Material

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

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

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

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

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

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

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

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Tungsten Copper Contacts Cryogenic Treatment

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

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

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

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

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

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

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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.

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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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