Tungsten Copper Used for Vacuum High-voltage Switch

Tungsten copper composite materials have widely used in electrical contacts, high voltage switches and breakers, especially in high voltage SF6, air / oil medium, large current circuit breaker. Recent years, with the rapid development of vacuum high-voltage switch, the contact materials have some innovation correspondly. Compared with other contacts, vacuum contact materials have higher requirements. Except the normal properties of switches, due to the surface of contact is particular clean, which will be easier welded in the air. So based on high resistance to weld, it also needs higher welding resistance, higher anti-electric erosion, low cut-off current and low content of gas. And tungsten copper excellent properties can perfectly meet the needs of high-voltage switch contacts.

From compression molding, for tungsten copper sheet contacts, CIP (Cold Isostatic Pressing) has good forming performance, but it has higher equipment investment and lower material utilization. The mechanical molding should be noted that the gap of molding tools and tungsten powder granularity. The smaller gap will cause the difficulties in stripping; the larger gap will make tungsten powder scratch the mold and produce the cracks on the surface of compact. From sintering process, porous tungsten skeleton sintered is the key process of tungsten copper manufacturing. High-temperature sintering is easy to remove impurities and ensure the electrical conductivity and the gas content meet the requirements. In addition, during the sintering process also need to consider the tungsten powder particle size, size distribution and pressing density. Too low temperature will increase the porosity and reduce the density and hardness of products; too high temperature will reduce the content of Cu and the electrical conductivity decrease. Overall, choose pure tungsten powder as raw material, mechanical molding, sintering furnace hydrogen reduction, hydrogen protection copper infiltration process to produce high-pressure vacuum switch tungsten copper material, it has high strength of porous W skeleton, low gas content, Cu has network-like distribution, tungsten copper matrix bonded tightly.

Cu Content Effect on Tungsten Copper Liner

Tungsten copper liner is considered as the heart of ammunition, which not only has high hardness, high strength and low coefficient of thermal expansion of W, but also has good plasticity and excellent thermal and electrical conductivity of Cu. Compared with single metal liner, this kind of composite liner has many advantages, such more reasonable energy conversion and absorption mechanism, fuller utilization of chemical energy, better performance in armor, lower cost, a broader application prospect and so on. With the production technology and process innovation, dense liner gradually is replaced by powder liners.

Since tungsten copper powder liner has high density, good ductility, deep penetration, less plugging and other advantages, it has been play an important role in shaped charge and some military fields. But in the process of tungsten copper liner, with the increasing temperature, Cu loss is always an inevitable problem. Cu loss will reduce the density and strength of materials. Related researchers based on pressure pressing, sintering temperature and time factors on the rate of variation of copper analyzed, and summed up the impact of copper and relative density on jet liner properties for the preparation of tungsten-copper powder liner offers theoretical basis. The experiments show that he rate of copper sintered samples with the pressing pressure increases with increasing sintering time and sintering temperature decreases, Cu loss is opposite. This is due to:

1. The pressure increases effectively narrows the distance of W grains, which reduces the Cu loss from the inside and slows internal material Cu particles outward evaporation rate;

2. The increasing pressure enlarges the contact area of Cu surface that the original Cu particles have a larger free energy in the melting process is easier and the adjacent Cu particles fuse to form larger particles. And it reduces the volatile rate of fine particles at high temperature that the content of Cu remained stable. Therefore, the content of Cu impact on the jet penetration is significant less than the relative density, but plays an important role in the stability of the jet. The smaller the rate of copper loss, the liner jet penetration is more stable.

Tungsten Powder Granularity Effect on Armor Capability of Tungsten Copper Liner

In recent years, tungsten copper is one of the most outstanding materials for the liner. Liner is the key part of shaped charge, which quality directly determines the penetration and armor capability of warhead blast. Compared with conventional liner, the powder liner has many advantages, such as high density, excellent thermal conductivity, good elongation, flexible composition ratio, better moldability and so on. Penetrating analysis based on fluid dynamics theory, it can be avoided to a large extent from the phenomenon of blocking pestle to form a longer and stable jet. Tungsten powder shape, size and size distribution can have a significant impact on the powder compaction and sintering process and the final product performance, thus affecting the performance liner shaped and penetration depth.

The experiment uses mixed - pressing sintering process, and put the compacting liner blank into high-temperature tube furnace, after 70min gradually warmed to 750℃ and holding 20min. Then use instantaneous electric detonator at the top of the midpoint detonating the static penetration power experiment. From the uniformity of powder liners isometric high radial position analyses, its runout and wall thickness substantially unchanged. The density distribution is analyzed in the axial direction, typically the maximum density at the top of the bottom of the minimum density, a decreasing trend was up and down. Detecting the use of Archimedes powder liners green density can be found in between 45-62μm tungsten powder particle granularity, with the decrease of tungsten powder particle size, density and relative density of the compact tungsten-copper powder liner and sintered density showed a trend of increasing. While maintaining the same quality with sub-fractions, process, particle size and other conditions of 60 ° tungsten powder copper shaped the static penetration test can be found with the decrease of the particle size of tungsten powder, powder liner break a depth showed an increasing trend and a significant improvement in the performance of armor.

Tungsten Copper Plasma Component Technology Breakthrough

Recently, French Atomic Energy Commission (CEA) / Institute of magnetic confinement fusion (IRFM) researchers announced a good news: Institute of Plasma Physics, Chinese Academy of Sciences has made key progress in the development of two types of tungsten copper heat load (HHF) test module towards plasma components (W / Cu-PFC) test. Tungsten copper towards plasma component mainly refers to perforated tube. Tungsten copper perforated tube is one of the parts of vertical divertor target plates, and the divertor has been playing an significant role in magnetic confinement fusion reactor.

The main role of divertor is that the interaction between plasma and materials processing separated in two chambers and separates the resulting doping source and the main plasma. In general, it uses High heat load irradiation for the divertor properties testing, which is an important criteria to evaluate the quality of tungsten copper perforated tube. Tungsten copper not only has high melting point, high strength, low coefficient of thermal expansion, low sputter rate, low retention and excellent wear and corrosion resistance, etc., which is recognized as the most suitable for future nuclear fusion reactor plasma-facing materials. Tungsten copper perforated tube is first to drill on tungsten block, followed by brazing or hot isostatic pressing (HIP) block and other technology tungsten chromium zirconium copper pipe connected. Since it has symmetry in structure, can relief the thermal stress concentration and eliminate the stress point so that it can withstand high thermal loads irradiation.

Tungsten copper perforated tube fabricated by HIP has well combining face and without any obvious cracks, but the wall thickness of the circumferential unevenness in the HIP process of collapse and cracking phenomenon occurs. This time, the Chinese Academy of Sciences has made a major breakthrough in the manufacture of technology in the international community for the first time to achieve mass production of tungsten copper PFC, tungsten plasma interaction to carry out a comprehensive study under the conditions of long-pulse high parameters and provides an excellent platform. According to IREM researchers report relevant results: W / Cu perforated tube (Mono-block) No. 4 block modules withstand 1,200 times 10MW / m2 and 300 20MW / m2 radiation heat load; No. 5 tungsten block withstood 500 10MW / m2 and 500 20MW / m2 radiation heat load beyond the International Thermonuclear Experimental Reactor ITER to 20MW / m2 radiation heat load 300 requirements. In addition, W / Cu plates (Flat type) module FT1 to withstand 102 times 10MW / m2,102 times 15MW / m2 and 302 times 20MW / m2 radiation heat load; Tablet Module FT2 withstood 302 times 10MW / m2,102 times 15MW / m2 and 102 times 20MW / m2 radiation heat load. Irradiation results far beyond the flat module 5 MW / m2 in the ITER design requirements, refresh the W / Cu plate member is known recording HHF tests. This also proves that the advanced nature of the plasma connecting tungsten copper PFC technology to some extent.

Tungsten Copper Contact — Ultrasonic NDT

Tungsten copper contact is also known as tungsten copper electrical contact or tungsten copper contact tip, which is a kind of psudoalloy that consist of W and Cu two kinds metals of immiscible and without the formation of intermetallic compounds. Consequently, it not only has high hardness, high melting point, high strength, low coefficient of thermal expansion and excellent wear resistance and corrosion resistance of W, but also has perfect electrical and thermal conductivity and plasticity of Cu. And it has been played an important role in some high-voltage switch, breaker, and instrument components.

Currently, preparation of tungsten copper contacts is mainly used in PM (powder metallurgy) technology, the corresponding method used for the performance testing, such as the density, the hardness, the strength, the tensile strength and micro-structure, etc., will have some damages on the integrity of tungsten copper products and lead to failure. And these tools to test for products in large quantities can only do a certain proportion of sample, which is difficult to have some representation. If the unqualified tungsten copper contacts undetected used in actual production is likely buried security risk, both for production or personal safety is extremely unfavorable. So the relevant researchers use Non-destructive testing techniques to measure and evaluate the mechanical properties of tungsten copper related products.

Ultrasonic NDT (Non-destructive Testing) is a kind of process that ultrasound can penetrate deep into the use of a metallic material, by entering a cross-sectional another cross-sectional; edge reflection occurs at the interface characteristics of the parts to check for defects. When the ultrasonic beam from the surface of the part by the probe pass to the metal inside encounter defects and Part underside of the reflected wave occurs, respectively, form a pulse waveform on the screen, based on these pulse waveforms to determine the location and size of the defect. Compared with other detecting methods, Ultrasonic NDT has many advantages, such as:

1. Ultrasound has perfect penetration ability, low transmission loss and the probing depth of up to several meters;

2. High sensitivity, it can be found with the diameter of the air-based reflectance 0.1-1mm equivalent reflector;

3. Accurate positioning, to assume the shape and the size are also more accurate;

4. Convenient in operation and it is suitable for the most materials;

5. The entire testing process will not cause environmental pollution, no harm to the human body completely.

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 correspond 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, electronics, 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 wide-band 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.