With modern machinery industry are developing towards high-precision, high-speed cutting, grinding, low cost, and environmental protection and other directions, tungsten carbide cutting tool has higher requirement on the properties. Theoretically, the efficiency of cutting process, the precision and the surface quality depend on the hardness and the strength of the cutting tool. But it is difficult to balance the relationship between the hardness and the strength. In general, the strength of the material with higher hardness is relatively lower, and the increase of the strength is also base on the decrease of the hardness frequently. Therefore, in order to reconcile this contradiction and further improve the wear resistance of tungsten carbide cutting tools, the relevant researchers develop tungsten carbide coating layer. It deposits a tungsten carbide layer on the base and forms a chemical barrier and a thermal barrier, which effectively reduce the wear of the cutting tools. Furthermore, coating layer with higher coefficient of friction can remarkably improve the service life of the cutting tools.Generally, the requirements of tungsten carbide cutting tool coating layer as follow:
1. High hardness and excellent wear resistance;
2. The coating film has a little effect on the toughness of the base material;
3. Reduce the friction coefficient of the cutting tool and the workpiece;
4. Longer service life.

At present, the most used tungsten carbide coating technologies include CVD (Chemical Vapor Deposition), PVD (Physical Vapor Deposition), MTVD (Medium Temperature Vapor Deposition), PCVD (Plasma Chemical Vapor Deposition) and so on. Wherein the chemical vapor deposition is the most widely used one. The principle is that a mixed gas of the coating material in cemented carbide surface interaction at high temperatures, the mixed gas of some component decomposed and carbide surface coating metals or compounds formed. It should be noticed that deposition reaction must be carried out under certain conditions activation energy. In addition, high-temperature CVD has many advantages, such as:
1. Relatively easy source of coating material;
2. Can obtain TiC, TiN, TiCN, TiB, Al2O3 and other single or multiple composite coating layers;
3. High bonding strength between the base and the coating layer, excellent wear resistance.

With the development of science and technology, the quantity demand and requirements of transport facilities, such as tunnels, subways, bridges and other infrastructure projects, has become higher and higher. Tungsten carbide has high hardness, high strength and excellent wear and corrosion resistance, so it has been widely used in those constructions. Shield tungsten carbide is a kind of tungsten carbide products, which usually assembled on the underground tunneling shield machine. Since unknown geological composition and shield machine is a kind of high-power equipments with large propulsion force, shear force, conventional tungsten carbide will be easily broken and fractured in the high intensity mixing thrust and shear forces. The common used shield tungsten carbide products are shield tungsten carbide buttons and shield tungsten carbide blade.

Shield tungsten carbide button is similar to common tungsten carbide button, but is has a broader application range, the force can be uniformly dispersed throughout the surface of the buttons, and it has better performance in wear resistance and toughness. Shield tungsten carbide blade is composed of tungsten carbide blade and steel base, which mainly withstand the squeezing, impacting, scratching and other effects caused by continuous changes in subsoil, water pressure. There is a experiment shows that the most important influencing factors as follow: one is the content of Co, the other is the granularity. According to the analysis of experimental data, the content of Co has a optimum range, below this range is correspondingly decreased shield carbide toughness and easily to be broken; instead, the Co content higher than this range, the strength of the shield alloy will drop and easily to be worn. The influence of grain size is also similar to Co content, too small grain size will cause the fracture of shield tungsten carbide; too large grain size will easily to be worn.

Vacuum plating is a PVD (physical vapor deposition) phenomenon. Injecting the argon gas under a vacuum condition, argon impact target, the target is separated into molecule and to be absorbed by the conductive goods and forming uniformly smooth surface layer. It includes vacuum deposition, sputtering and ion plating and other types. They are processing based on a vacuum condition to deposit various metals and non-metallic thin film on distillation or plastic surface by sputtering, distillation, etc., thin surface coating film can be formed in such method, it also has other outstanding advantages such as fast speed and good adhesion. However, the price is higher, there is less metal type can be operated, so it is generally used for functional coatings of more high-end products, such as an internal shield.

There are two common plastic products plating process: water vacuum ion plating and electroplating. Ion plating is a physical vapor deposition (PVD) process that is sometimes called ion assisted deposition (IAD) or ion vapor deposition (IVD) and is a version of vacuum deposition. Vacuum plating approach is now a more popular approach, which can make a strong sense of metal products with high brightness. And compared with other coating methods, it needs lower cost and less pollution to the environment, which is now widely used in various industries.

This method uses a tungsten heater has the following characteristics:
1. The metal film obtained by vacuum deposition is thin (typically between 0.01 ~ 0.1μm), and it is possible to copy the shape of injection mold parts surface strictly.
2. Operating voltage is relatively low (200V), which is easy to be operated, but the price of the device is relatively high.
3. Pot bottles volume is small, and production efficiency is low.
4. The melting point of coating piece should be lower than tungsten metal (such as aluminum, silver, copper, gold, etc.).

With the rapid development of the chip technology of integrated circuit, microelectronics packaging field has been required further, which has the developing trend towards small, thin, low cost and lead-fee. And with the integrated scale of microelectronic integrated circuit expanding gradually, the power per unit area and heat of integrated circuit increases correspondly, which is also the main challenge microelectronic packing material confronted with. At present, microelectronic packaging materials include three types: PMC (Polymer-matrix Composites), MMC (Metal-matrix Composites), CCC (Carbon-carbon Composites). And the metal-based electronic packaging material is the key directions of research and development. Furthermore, add high-performance ceramics with low coefficient of thermal expansion or other additives into metal matrix can further improve the comprehensive properties of metal-based microelectronic packaging materials.

Tungsten copper heat sink or called as microelectronic packaging material is a kind of metal-based composite material. It can be well matched with silicon, gallium arsenide and other semiconductor material and ceramic materials in microelectronic devices by adapting the proportion of ingredients of W and Cu to achieve reasonable expanding coefficient. And it can also avoid the thermal fatigue damage caused by thermal stress. At the same time, the better performance in electrical and thermal conductivity and excellent microwave shielding function can be obtained. In addition, tungsten copper as a kind of efficient radiating heat sink sweating material, when the temperature exceeds the melting point of copper, due to the melting point of W much higher than Cu, Cu liquefied even evaporated remove the most of heat, which keeps the related equipment working steadily. Therefore, tungsten copper composite material has been widely used in LSI (Large Scale Integrated Circuit) and high-power microwave devices in recent years, such as microprocessors, microwave components, radio communication devices and RF power devices and other high-tech products, it remarkably improve the using power of microelectronic devices and promote them miniaturization.

Compared with conventional crystalline materials, nano-structure tungsten copper composite material has different specific properties, such as higher density, higher strength, better hermeticity and thermal and electrical conductivity. So it has attracted wide concern of the researchers around the world. Through different preparation process of tungsten copper nano composite powders, the powder granularity has been greatly refined and dispersion improved, which can effectively improve the sintering characteristics of W-Cu system and it beneficial for tungsten copper composite material get the fully densification.

At present, the focus of nano-structure tungsten copper composite material includes the manufacturing process and sintering characteristics. There are some manufacturing processes studied, such as MA (Mechanical Alloying), Mechanical Thermo-chemical Process, Spray Drying Method, Sol-Gel Method and so on. Some studies have shown that a total reduction of tungsten copper oxide powder in a highly dispersed state, only rely on capillary action can cause the rearrangement of particles so as to achieve full densification. By spray drying combustion combined nanostructure tungsten-copper composite powders prepared by the subsequent reduction treatment, the content of Cu is 20%-40%, by 1250 ℃ insulation 1h sintered density can be obtained more than 98%; combined mechanical thermo-chemical method with liquid-phase sintering can manufacture W grains 1μm in average grain size without adding sintering additives; by mechanical alloying method, at lower temperature (1100 ℃) liquid phase sintering performance can be effectively enhanced sintering powders. It is for the reason that the interaction between same types of W-W particles and different types of W-Cu particle in tungsten copper pseudo alloy. In addition, from the sintering characteristics, since nano grain is fine (usually less than 100nm in granularity), has larger specific surface area, stronger surface activity, the larger contact area of the powders and higher sintering driving force, the required sintering temperature is lower and the speed of densification improved.

The main failure forms of YG8 tungsten carbide drill bits includes the broken and shedding of tungsten carbide insert sheet. It is for these reasons that the residual stress, lack of welding and low strength of brazing after the welding. Welding strength is the most direct criterion for testing the quality of welding quality and the main influencing factor is the welding gap. During the welding process, if the welding gap is too small, the parts of tungsten carbide insert sheet will contact with the steel closely, so that the molten solder after soldering can not spread to the entire surface to reduce the joint strength; if the welding gap is too large, after welding the supporting role of the matrix is weakened, solder large gap casting columnar structure, grain is relatively coarse, loose tissue, strength and toughness relative decline, a direct result of the strength of the joint is reduced.

The reasons of residual stress appearing include the difference of the coefficient of thermal expansion and uneven temperature distribution. There is a great difference in the coefficient of thermal expansion between tungsten carbide and steel (the linear expansion coefficient of WC-Co is 5-7×10^-9, the linear expansion coefficient of steel is 12.6×10^-9), so it will produce great internal stress by the large difference of shrinkage after cooling, which is also the main causes of tungsten carbide and welding gap cracking. In addition, the brazing process accompanied by thermal expansion and contraction phenomenon and thermal stresses within the material, with the increasing temperature difference, thermal stress is increasing, tungsten carbide insert sheet will appear cracks easily. There are some solutions to reduce the stress as followed:
1. Control heating and cooling rates to avoid excessive temperature difference, especially the cooling rate after welding;
2. Take the necessary measures to prevent partial hot or cold phenomenon;
3. Uniform heating, minimize solder liquefaction process, to avoid the volatile low-melting phase, resulting in weak tissue and pores and also reduce the phenomenon of the brazing surface oxidation;
4. To enlarge the welding gap appropriately to reduce the additional stress on the cemented carbide piece.

During the experiment, the tester uses thyristor controlled DC TIG welding power source and the model is YC-300TSPVTA. Electronic stopwatch model is TREREX. Vernier caliper Model is 025 and No. is 096 583. Electronic balance model is AEL-200 and digital multimeter model is Bestillingsnr.

Arcing performance:           
Operating specifications: tungsten wire diameter 2.4mm, tip taper angle 45 °, the protruded length of the tungsten electrode 8mm, arc current 80A, arc duration 10S, arc length 3mm, repeating 30 times, argon gas flow rate 8L / min, DCSP TIG welding

Testing results: composite rare earth tungsten electrode at 30A, 80A and 150A welding current, arcing repeated 30 times were successful and the success rate was 100%, indicated it has good arcing performance.

Arc static characteristic curve:
Operating specifications: tungsten wire diameter 2.4mm, tip taper angle 45 °, tungsten electrode protruding length 3mm, arc length 3mm, argon gas flow rate 8L / min, DCSP TIG welding, tungsten  wire as cathode and water-cooled copper as anode

Test Results: Form the test result Fig. 4-24 shows that the static characteristic curve of the composite electrode is less than thorium tungsten electrode, indicating that it has low work function and strong electron emission capability, so it has good weldability.

Electrode burning rate:
Operating specifications: electrode diameter 2.4mm, welding current 180A, arc duration 20min, the electrodes extended length 3mm, arc length 3mm, argon gas flow 8L / min, water-cooled as copper anode, DCSP TIG welding

Test Results: From the test result Fig. 4-5 can see the burning property of composite rare earth electrode is better than thorium tungsten electrode.

After commercial welding machine testing found the result is consistent with the component screening test result, indicating optimized manufacturing technology can obtain high performance composite rare earth tungsten electrode, which is better than same specifications thorium tungsten electrode.