Tungsten alloy is a kind of alloy, which based with tungsten and added some other elements. In metals, tungsten has the highest melting point, high temperature strength, good creep resistance, good thermal conductivity, good electrical conductivity and electron emission properties and large specific gravity. In addition to be greatly used in the manufacture of carbide alloy and additives of alloy, tungsten and its alloys are not only widely used in electronics, electric light industry, but also used in aerospace, casting, weaponry and other sectors for producing rocket nozzles, casting molds, penetrator, contacts, heating element, heat shields and so on. In addition, high-density tungsten alloy are often used to make the tungsten radiation shielding,which been used in many fields.

The studies have confirmed that the radiation shielding ability has a close relationship with the density of materials, the greater the density, the better the radiation shielding performance. In another words, higher density means better-ray absorption capacity and radiation shielding capability. Due to the high density of tungsten alloy than other materials, the tungsten alloy radiation shielding of γ-ray has better radiation shielding properties, thereby can reduce the volume of the shield without affecting the radiation shielding performance. The same volume of tungsten alloy radiation shielding will have better radiation shielding performance compared to lead.

Tungsten alloy combines high density (the density is 60% higher than lead), machinability, good corrosion resistance and high radiation absorption capacity(better than lead and steel), high strength, etc., so it can be seen that the tungsten alloy materials are the best raw materials to prepare radiation shielding.

Non-destructive testing is a method or relevant means that usually been used without damaging the product structure, without compromising the performance of the product. The detection of products can be divided into two kinds, which included destructive products and non-destructive products, the latter focused on appearance, it means that should be tested one by one, but can be as long as qualified. For the former usually takes some samples, and focuses on the intrinsic quality of the designated products suspected inherent defects were dissected. Since the destructive testing will eventually be used at the cost of a product, so using non-destructive testing method to test products can balance that, i.e., it can certainty not destruct the product and handle the intrinsic quality of the product.

Non-destructive testing(NDT) methods may rely upon use electromagnetic radiation, sound and inherent properties of materials to examine samples, which includes examining the materials external surfaces in details by microscope. Although samples preparation techniques for matallographic, optical microscope and electron microscope are generally destructive as the surfaces must be made smooth through polishing or the samples must be electron transparent in thickness. Therefor the interior of samples can only be examined with penetrating electromagnetic radiation, such as X-rays or 3D X-rays. Therefor,Tungsten radiation shielding could be used effectively for radiation protection from the harm radiation when testing the defects of products by X-ray or 3D X-ray.

PS:TUNGSTEN ALLOY RADIATION SHIELDING

Experts find that radiation exposures could be reduced by maxing shielding. The density of tungsten alloy radiation shielding materials is related to its radiation stopping ability. Higher density means better stopping and absorbing radiation ray ability.

Due to a higher density that most other materials,tungsten radiation shielding has a much higher ability of absorbing and stopping almost rays than other metals, such as the traditional radiation shielding-lead. Tungsten radiation shielding has greater linear attenuation of gamma radiation and means that less is required for equal shielding. Altematively equal amounts of tungsten shielding provide diminished exposure risks than equivalent lead. So, tungsten alloy is the right and suitable material for radiation protection, as its combination of high density, good machinability, good corrosion resistance and high radiation absorbing ability. Besides, tungsten alloy is a kind of toxic pollution material, it would be better for environmentally friendly.

Compared with traditional powder metallurgy (PM), tungsten copper electrode nano composite material including powder milling, compacting and sintering process, but due to the characteristics of nano particles, there are some differences between traditional powder metallurgy and nano copper powder preparation.

1. Gas Evaporating

Copper evaporates in inert gas atmosphere, then a conflict with an inert gas and the particles, cooling, condensation forming nano copper particles. The forming powder process including 3 stages: one is metal evaporates and produces vapor, another one is metal vapor diffuses in inert gas and nucleation and crystal nucleus growth. The powder particle size is mainly determined by the growth process from the evaporation surface to this temperature region, and this process is affected by evaporation temperature and the pressure and the type of inert gas, the influence of temperature gradients within the device and convection conditions. Metal ultra micro powder with 10nm-1μm can be fabricated by the process parameters controlling. This method is the most direct and effective in metal ultra micro powder fabricating, a company from France uses induction heating to improve the gas evaporating and succeed in fabricating copper ultra micro powder.

2. Plasma

Plasma has high temperature and high reaction speed, you can get a uniform, nano-powder of small particles, easily to achieve mass production, can be prepared almost any nanomaterials. It can be specifically divided into direct current arc (DC), high frequency (RF) and mixture (HP). DC has many advantages, such as simple equipment and operation, high efficiency and wide application, but it will easily melt and evaporate at high temperature, which will pollute the product; RF has no pollution of electrode, high speed of reaction, but its energy utilization rate is lower and instability. HP is combined with DC and RF, which has large space of plasma, high purity, high efficiency and good stability.

Tungsten copper has been widely used in electrode (EDM or ECM), electronic packaging materials and some fields because of its high density, strength and excellent thermal and electrical conductivity. Due to the large differences physicochemical property between two metals (tungsten and copper), which called binary psudoalloy, tungsten copper uses powder metallurgy (PM) to manufacture replace casting process. It uses tungsten and copper powder with fine grain and high purity, the general process is: powder milling → mixed → compacting → sintering → infiltration → cold working.

This paper concentrates on analyzing the relation between sintering mechanism and densification of tungsten copper material. Generally, the traditional sintering theory said that if a system intend to achieve higher densification, it should has good wettability and the solid phase can dissolve in the liquid phase and proper amount of liquid phase. According to the relationship of tungsten and copper in the process of sintering, the copper-tungsten binary phase diagram can be drew as follow:

The diagram shows that tungsten copper system belongs to completely insoluble system. In addition, the wettability of copper solution is not so well to tungsten skeleton in common conditions. Recently, more and more researchers and scholars find that tungsten copper powder with nano composite structure has better sintering properties. It is due to tungsten copper compacts in solid phase state, although tungsten copper powder with nano composite structure does not dissolve the segregation. They though it is related with one solid phase sintering and liquid particle rearrangement effects.

Except the cementation of powder particle, densification and the change of constituent of pure metal, there is no dissolve and appear new phase in the process of one solid phase sintering. Then we will use the model of tungsten copper pressed compact to show the varieties of powder in the process of solid phase, which will intuitively describe the relation between sintering mechanism and densification of tungsten copper electrode.

After coarse pestle, it should be fine pestle on vertical steel ball machine. It uses grinding plate as grinding tool and the lower grinding plate opening 90 ° symmetrical V-groove, milled plate installation alignment groove runout less than 0.02mm, which groove also should be pre-grinding by standard ball to ensure the precision.

Afterwards, tungsten carbide ball should be polished by vertical lathe and uses oak plate as grinding tool to turn arc groove with 0.5R. It has grooved boards with four claw chuck clamping, alignment grooves within 0.1mm, with W5 / W7 diamond paste (Old GB model, or about 4000 mesh / 3000 mesh) as a polishing paste, applied to certain pressure on the grinding plate does not move, speed control in 60r / min, the polishing process can be carried out for 4-6 hours, making the ball appear like a mirror.

Finally, cooling tungsten carbide polished ball about 5min. Then use kerosene to remove the stains on the surface and wipe out by clean cloth. Testing and packaging: The amount of change in the diameter of the grant requested diameter ball is detected using a micrometer or ruler for detecting extremely; roundness detected; the surface roughness using observation and comparison assay. It is required soft cushion apart between the balls and the ball use soft cushion apart, to prevent the collision of the balls and the ball, so that it is deformed or worn.

The specific requirements of each procedure of tungsten carbide polished ball as follow: Coarse grinding at the beginning, machined by vertical steel ball machine and uses 100# diamond resin grinding wheel (grain size is 100). Before the grinding, the grinding wheel to be ball milled with the corresponding specifications of the groove. In addition, the groove depth is generally equal to 1/5-1/3 of tungsten carbide polished ball and runout groove should ensure that within 0.03mm.

Then the fine grinding, which also machined on vertical steel ball grinding machine and uses 150# diamond grinding wheel (the grain size is 150, finer suitable for fine grinding). It is similar to coarse grinding, the grinding wheel to be ball milled with the corresponding specifications of the groove. The groove depth is generally equal to 1/5-1/3 of tungsten carbide polished ball and runout groove should ensure that within 0.03mm.

The next is coarse pestle, which uses grinding plate for machining on vertical steel ball machine. The lower grinding plate opening 90 ° symmetrical V-groove, milled plate installation alignment groove runout less than 0.02mm. Before the grinding, the groove should be pre-grinding by the standard ball, which adopts concentration 30% grinding fluid and 140/170# SiC （grain size is 140/170） as grinding compound. Disposable add a little abrasive, with a smaller flow, pressure control in 4KN-6KN, speed 25-30r / min, grinding to a balance of + 0.03mm-0.04mm, 0.001mm in control of roundness, approved changes in diameter assurance within 0.002mm, the surface roughness of less than Ra0.4.

Reduction of Ammonium Paratungstate Generated during Hydrometallurgical Processing of Tungsten-Copper Borings

Tungsten-copper (W-Cu) alloy is employed for manufacturing heavy duty contactors, relays,switches etc. During production of such components, W-Cu turnings/borings are generated. At CSIR-NML, a process for recovering tungsten and copper from tungsten-copper borings containing 46.01% W, 53.78% Cu, 0.13% Fe and other minor metals as high purity tungsten powder and copper powder has been developed. In the present work, a detailed investigation on reduction of ammonium paratungstate (APT) having purity 99.95% by hydrogen gas to produce high purity tungsten powder is presented. The various process parameters such as temperature, time and flow rate of hydrogen gas have been optimized. At the temperature of 800°C and 0.1 l pm flow rate a reduction of 77.78% was observed up to 2h time. At 900°C, with increase in flow rate from 0.1 l pm to 0.3lpm the increase in reduction was found to be from 63.88% to 99.99% at 1h time.At still high temperature of 1000°C, almost complete reduction was obtained at 0.1 l pm flow rate in 1h time. The effect of bed-depth was also carried out. At all temperatures chemical reaction was the rate determining step.