Tungsten Copper Military Nozzle

Tungsten copper military nozzle is kind of device accelerating air by changing the shape of inner wall, which has high hardness, high strength, high softening temperature, low coefficient of thermal expansion and excellent arc breaking performance. So it plays an important role in military high temperature and spiral accelerated pipeline. Tungsten copper military nozzle has many types, according to the specific performance of aircraft and engine, it can be specifically divided into fixed or adjustable convergent nozzle, convergent-diffused nozzle, eject nozzle and adjustable nozzle, etc.

Convergent nozzle: sectional area of the flow direction gradually reducing, in large mach flying, incomplete expansion will cause great loss of thrust;
Convergent-diffused nozzle: also known as Laval nozzle, is a kind of nozzle cross-sectional area diffuses after convergent, mainly used in supersonic fighter, the critical area and exit area are required to fly with the state regulation;
Eject nozzle: consists of adjustable convergent main nozzle and a fixed or adjustable ejector. It is light and has simple structure, can maintain good performance over a wide range of flight, it has been widely used in many high performance aircraft;
Adjustable nozzle: mainly used for high-speed flight after-burning turbojet aircraft or military after-burning turbofan engine. Easy to adjust nozzle area ratio, may vary with flight conditions, and often in a fully expanded state. Structure type balanced rod, folding, folding petal sleeve cone and so on.

In addition, tungsten copper military nozzle expansion accelerated as the airflow at a high speed jet and counter productive outward thrust. Most high-speed fighter uses adjustable nozzle and adjustable convergence-diffusion nozzle or ejector nozzle; common fixed convergent rocket engine-diffusion nozzle; vertical or short takeoff and landing aircraft using commutation nozzle. In addition, In the ASRM (Advanced Solid Rocket Motor) the front nozzle is also used tungsten copper material.

Tungsten Copper Throat Insert

Tungsten copper throat insert is lining material of solid rocket motor nozzle, and its high temperature performance and ablation resistance directly affects the thrust and efficiency of the engine. Solid rocket motor nozzle 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. The throat insert is located in the nozzle throat, and its main role is to limit the throat area due to erosion produced by increasing phenomenon, caused by the thrust decreases. When the engine is working, throat insert often require direct heating from room temperature to greater than 2000 ℃, resulting in significant temperature gradient and thermal stress, which is the main reason for failure of the crack and working throat lining material appears. In addition, for this type of high-performance rocket engines commonly used 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 severe erosion. If lining severe erosion is difficult to ensure a stable aerodynamic shape even fragmentation occurs, it will directly affect the thrust and efficiency of the engine.

Generally speaking, compared with other materials, tungsten copper has better performance in many aspects. Throat lining material for the solid rocket motor comprising refractory metal, graphite, carbon and carbon-based composite materials, reinforced plastics, ceramic matrix composite materials. Throat heat transfer can be divided into three stages: 1. engine ignition instant impact heating; 2. ablation steady when working; 3. flameout cooling. Tungsten copper material not only has high hardness, high density, high strength, high melting point, low thermal expansion coefficient and excellent wear and corrosion resistance, also has good ductility and electrical and thermal conductivity. And since the large difference of two kinds of metals, at higher than the melting point of copper, copper is evaporated away to leave most of the heat of the hard phase tungsten throat insert to ensure the stability of working.

Tungsten Copper Gas Vane

As a special wing in rocket jet, tungsten copper gas vane represents the thrust vector controlling technology. And it is indispensable in AAM active duty and in studying. Therefore, it has many strict design requirements as follow:
1. It should have a constant value close enough to lift the gradient to meet the maximum lift control requirements;
2. Differential gas vane should meet the requirements of rolling control;
3. Ensure small resistance to reduce the loss of engine thrust;
4. Rudder hinge moment and change the entire duration of the work to be relatively small in order to reduce the power requirements of the steering gear;
5. Gas vane small as far as possible, but should meet the strength and rigidity requirement. And reasonable location is convenient for attached parts designing and installation;
6. It can not produce mechanical interference when gas vane deflected to the maximum angle.

Based on the ablation mechanism, it can specifically divided into:
1. Effect of particle erosion: A large amount of high energy solid particles in gas stream impact the surface of gas vane intensely, which partial surface reach high temperatures in a short time and accelerate the material ablation. Besides, the surface roughness increases will lead to uneven distribution of the flow field to form a vortex, and lead to the accumulation of localized heat;
2. Mechanical erosion effects: the presence of a thermal expansion coefficient difference between the substrate materials caused by thermal stress generated when it exceeds the combined strength of the gas flow at supersonic peeling effect occurs.

Tungsten Copper Military Sheet

Tungsten copper military sheet is also called as heat sink plate, which has high thermal conductivity and excellent hermeticity. It has a broad prospect in RF, microwave, high power diode and other military fields. There are some common grades of tungsten copper military sheet used: 

Grade	Proportion（wt%）	Mass Density（g/cm3）	Relative Density（%T.D）	CTE （ppm/K）	Thermal Conductivity（W/m·K）
W90Cu	90±1	17.0	≥99	5.6-6.5	180-190
W85Cu	85±1	16.3	≥99	6.3-7.0	190-200
W80Cu	80±1	15.4	≥99	7.6-9.1	200-220

Except high-temperature liquid phase sintering, infiltration, activated liquid phase sintering, mechanical alloying and co-reduction, tungsten copper composite materials can be also manufactured by hot hydrostatic extrusion, electrolysis, plasma spraying, rapid directional solidification and sol-gel method.

Hot hydrostatic extrusion: On completion of four-post hydraulic machine, mold using three sets of combination of prestressed die, while using the outer heating coil and ceramic heating tube mold preheating;

Electrolysis: Electrolysis adopted in accordance with a certain proportion of NaCl, KCl, Na2WO4 and CuO4 mixed solution as graphite electrodes, continuous electrolysis 3h. The electrolysis products out into distilled water after boiling, by adding an appropriate amount of NaOH solution soak give the final product after filtration and drying;

Plasma Spraying: to strengthen the material surface and the new multi-purpose precision spraying surface modification technology in the field of tungsten copper electronic packaging material has broad application prospects;

Rapid directional solidification: produce specific temperature gradient between solidifying metal and non-metal solidification, and make alloys in a wide range of solubility solidification, high solid phase alloying elements to obtain content and grain refinement significantly fewer microscopic segregation;

Sol-gel method: metal alkoxides and their compounds as raw materials, under certain conditions hydrolysis medium and catalyst - the polycondensation reaction solution into a gel, and then by drying and heat treatment to obtain synthetic materials.

Tungsten Copper Sintering Technologies Comparison

There are many kinds of tungsten copper sintering technologies, such as conventional infiltration, mixed-pressing, pressure sintering and new SPS (Spark Plasma Sintering), etc, which have their own advantages and disadvantages. Next, we analyze these different sintering technologies by the principle and the applications. First of all, infiltration, which is called melt immersion, is the most widely used in tungsten copper products currently. It is obtained by adding a small amount of tungsten powder or copper powder compacts made of tungsten powder and tungsten and copper infiltrated compacts stacked together, and thereafter sintered at a temperature above the melting point of copper and under reducing atmosphere or vacuum.

In the process of sintering, copper in a molten state to rely on capillary action infiltrated tungsten skeleton, two sintering and infiltration step can also be performed separately. Infiltration has many advantages, such as high density, excellent sintering properties and electrical and thermal conductivity, good arc ablation resistance. But liquid copper barely rely on capillary forces infiltrated tungsten skeleton, this will lead to coarse and uneven distribution of copper particles sintered tungsten particles at high temperatures easily grew up together. In addition, after infiltration machined to remove excess copper and will increase costs and reduce the yield.

Mixed - pressing sintering process is one of the most conventional powder metallurgy, which basic process is preparation →ball milling → compacting →sintering. Sintering can be also divided into two parts, one is solid phase sintering (temperature lower than the melting point of Cu), the other is liquid phase sintering (temperature higher than the melting point of Cu). Since the solid solubility in the liquid phase W Cu is small, the material can not be conveyed by dissolution and precipitation particles rounded manner, and tungsten and copper infiltration is poor, it is difficult to achieve densification.

In order to improve mixed-pressing, relevant scholars uses activated agent (Ni, Pd and other activated elements) to increase the solubility of W in liquid phase, which is beneficial for the sintering process. However the additives have a bad influence on the electrical and thermal conductivity of tungsten copper products. Pressure sintering is a kind of secondary processing after sintering, especially for the conditions that one-step forming can not meet the requirements. Although hot pressing, repressing and re-sintering and HIP (Hot Isostatic Pressing) can remarkably improve the properties of tungsten copper composite material, they are limited by the costs and the efficiency. In addition, using hammering or cold rolling of tungsten-copper composite material for secondary processing can greatly increase the density and mechanical properties of the material. But when the content of W is higher, the ductility of tungsten copper will decrease and the difficulty of machining will increase.

Spark Plasma Sintering (SPS), which is also known as Plasma Activated Sintering (PAS) or Field Assisted Sintering Technology (FAST). According to different powder media, SPS can be divided into conductive and non-conductive, there is a big difference in mechanism between them. Generally, conductive SPS will produce a large amount of Joule heat generated by DC pulse current graphite mold; and the current through the powder will induce electric discharge between powder particles and arouse plasma. With the increasing density of plasma, High-speed reverse movement of the particle surface of the particles have a greater impact, so that the gas adsorption of escape or break an oxide film, so that the surface to be purified and activated, will be conducive to sintering. However, instantaneous high temperature generated by the discharge causes evaporation and melting of the grain surface, the grain at the point of contact to form sintered neck.

W-Cu Thermal and Electrical Conductivity Comparison of Different Process

Except test of hardness, density and micro-structure, for tungsten copper composite materials, which is widely used in EDM electrode, high-voltage discharge tube and heat sink, test of thermal properties (includes thermal conductivity and the coefficient of thermal expansion) and electrical conductivity are also essential. Combined with micro-structure of them, the researchers conclude some main reasons:

1. Although tungsten copper composite material has uniform distribution of W and Cu phase in the molding process, it still remains some porosity, which has a great impact on thermal conductivity of tungsten copper composite material;

2. Under the optimum Cu infiltration, there is no pore inside the sample, but Cu phase can not connect and form net structure. W and Cu phases distribute unevenly, in the process of heat conduction, part of thermal conductivity convey by W phase so that it is a critical factor of the lower thermal conductivity;

3. Relatively, injection molding process can effectively avoid the two defects, not only improve the density of tungsten copper products, but also W and Cu two-phase evenly distributed, thus it has a higher thermal conductivity.

Theoretically, thermal expansion of solid materials is due to the thermal vibrations of atoms as a center from its equilibrium position, which called crystal vibration non-harmonic effect. When the sintering temperature is increasing, atomic vibrations also stronger, the greater the energy of atomic vibrations, so that the microscopic atomic lattice parameters increase, the macro is manifested in the thermal expansion of solid materials. For single-phase material, the thermal expansion will increase as the temperature rises.

While for tungsten copper (W-Cu) two phases heat sink material, it has lower coefficient of thermal expansion, which thermal expansion behavior is much more complex than a single-phase material. The experiment shows that t lower temperatures, tungsten-copper composite material showed a negative thermal expansion, but only when the temperature exceeds a certain value showed positive expansion. Tungsten copper sample coefficient of thermal expansion of injection molding and compression molding process under more stable than copper infiltration sample, the magnitude of change is smaller.

This is due to the phase change, as well as the internal organization of the reasons magnetic stretch, thermal expansion of the material will show some special law. By increasing the degree of constraint W phase at elevated temperatures in the expansion phase of Cu, thereby reducing the thermal expansion coefficient of tungsten copper composite material. In addition, since the difference of the coefficient of thermal expansion of the materials, tungsten copper composite material will produce complex stress inside, whose distribution will restrain the thermal expansion behavior.

As for the electrical conductivity, it was detected by eddy current method. When an alternating current is cut coil (also called probes) near the surface of a conductive material, since the coil alternating magnetic field, it has an effect on the material surface and near surface induced swirling current, which called the vortex. Materials and eddy currents generate their own magnetic field coil reacts, which is related to the size of the surface conductivity near the surface. Non-ferromagnetic conductive material can be directly detected by eddy current sensor. After testing found that the sample injection molded tungsten copper has the highest conductivity, reaches 37.43%IACS, which is higher than molding sample (29.85%IACS) and infiltrated sample (33.18%IACS).

Tungsten Copper Properties Comparison of Different Process

The commonly used molding technologies are molding process, extrusion molding and injection molding, wherein the molding process and injection molding process widely used in tungsten copper materials. Molding process is also known as compression molding or press molding, it is a kind of processes that put first powdered, granular or fibrous plastic into the mold cavity at a molding temperature, and then close the mold to shape and solidify. Molding process has many advantages, such as less raw material wastage, low cost of equipments, one-step forming, suitable for plate with large size. But it has long lead time, low efficiency, not suitable for products with complex structure or shape, the size is limited by the compressor.

The injection molding process here refers specifically to metal powder injection molding (MIM), it is a kind of new near net shape powder metallurgy technology that introduce from modern plastic injection molding technology into the field of powder metallurgy. The basic process is that Firstly, the solid powder with an organic binder uniformly kneaded, granulated after heating under plasticized state (~ 150 ℃) with an injection molding machine into the mold cavity solidifying-forming, and then by chemical or thermal decomposition method of forming the blank the binder removal, the final densification to give the final product. While the advantages of MIM are high density, high product consistency, a wide range of applications and can be formed smaller in size and shape of the structure of complex products. However, it has high requirements for the injection, high cost of mold design and only suitable for small batch production.

Take W-Cu tungsten copper product as a example to compare molding process with injection molding of tungsten copper material properties. W-Cu theoretical density is 17.28g / cm3, the trend of relative density and relative density. As we can see from this graph above, With increasing sintering temperature, density of the obtained two processes copper tungsten composites are showing trend of increased first and then decreased. The difference is the temperature of the maximum density, the highest density  of molded samples at 1350 ℃, reaches 17.16g / cm3, while the sample injected at 1400 ℃ highest density is 17.17 g / cm3. After the further increase in temperature, both the density began to decrease. This is due to the sample over-burnt, Cu phase inside of tungsten copper exudates to surface and the pores and defects left in side. Under the optimum sintering temperature, the density of injected sample reaches 99.31%, molded samples reaches 99.78%. In addition, the hardness of tungsten-copper composite material (HRB) was positively correlated to its density, the greater the density, the hardness of the respective materials is also greater.

Besides, we also compare the micro-structure of tungsten copper with different processes. The specific procedure is that milled, polished tungsten copper composite sample after etching with FeCl3 salt solution for 2 minutes, with water to clean the surface of the etching solution, then wipe the surface with alcohol cotton, and then drying, Finally placed under microscope observation of the metallurgical microstructure. By comparing the SEM photomicrographs and photographs can be found that tungsten copper molded sample of W, Cu two-phase distribution is more uniform, uniform grain size, but segregation occurs at a constant temperature inside, causing a regional copper-rich, there are some porosity. While tungsten copper sample by injection molding, W and Cu distribute uniform and does not exist W-rich phase and Cu-rich phase of the phenomenon and Cu phase forms net structure around tungsten grains.