After decades of continuous development, the hardness of tungsten carbide cutting tools has reached 89 ~ 93HRA, at a high temperature of 1000 ℃ still has good red hardness, which is several times the durability of high-speed steel cutting tools. tungsten carbide is WC, TiC, TaC, NbC, VC and other refractory metal tungsten carbides and prepared by powder metallurgy from iron group metals as a binder. Compared with the high-speed steel, it has high hardness, wear resistance and red hardness; compared with superhard material, it has a higher toughness. Because of tungsten carbide cutting tools has a good overall performance, so in the tool industry has been widely used.

Diverse types of tungsten carbide cutting tools. In the past, the International Organization for Standardization (ISO) has the tools, tungsten carbide cutting tools are divided into three categories: P class, mainly used for cutting steel; K class, mainly used for cutting cast iron; M class, for the ordinary type tungsten carbide. In recent years, the increasing number of types of processed materials, ISO and the addition to the three types of tungsten carbide, namely H class, mainly for high cutting hard materials such as hardened steel, chilled cast iron; S class for cutting heat materials, high-temperature alloys; N class for cutting non-ferrous metals.



 

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Vacuum electronic devices have a wide application in civil and military fields such as communication, radar and industrial heating. Cathode is an important component in the device since it provides the required electronic beam for the device. Among all the electron emitters, scandate cathodes have aroused great attention among all the cathodes due to their copious emission property.

It has been found in the previous work, the raw powder properties such as morphology, particle size and size distribution greatly affected the emission property of the cathode. The diffusion and distribution uniformity of rare-earth elements would be enhanced if the structure dimension of the emitter decreased from micrometer to sub-micrometer even to nanometer, i.e., the electron emission property of emitter would be improved with the diminution of the micro-structure dimension of cathode matrix.

Scandium oxide doped tungsten powders have been prepared by a new method of spray drying combined with two-step hydrogen reduction. Spray drying has some advantages such as the particle size can be controlled in the single step.

The addition of Sc2O3 shifted the hydrogen consumption peak to the lower temperature side. Namely, the reduction temperature of tungsten oxide decreased with Sc2O3 addition. Adding scandia could decrease the particle size of tungsten. The scandia doped tungsten powder prepared by spray drying method had sub-micrometer size in the range of 0.1μm to1μm in semispherical shape and scandium distributed evenly in the powder. Using scandia doped tungsten powder, sub-micro-structure cathode matrices with semispherical grains and homogenous distribution of scandium was obtained.

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The films annealed at 200C and 300 C display violet–red under the sunlight as well as the as-deposited ones. Nevertheless, the film annealed at 400C exhibits transparency and appeared to be blue colored. The film annealed at 200C is amorphous, i.e. does not exhibit diffraction peaks while those annealed at 400C exhibit several sharp diffraction peaks, indicating the crystallization of this film happened. The peaks shown in Figs. 1(b) and 1(c) can be attributed to a mixture of polycrystalline phases, which includes hexagonal h-WO3 phase (JCPDS PDF-33-1387) and triclinic t-WO3 phase (JCPDS PDF-30-1387). It is also seen that the films annealed at 400C were dominated by hexagonal h-WO3 phases. Acosta et al. had prepared the tungsten oxide thin films by sputtering WO3 bulk. Their results indicated that the films mainly contained hexagonal h-WO3 phase and monoclinic α-WO3 phase. Usually, the polycrystalline monoclinic and triclinic phases can be observed in the films deposited by reactive magnetron sputtering from W target, but few reports have also shown the presence of hexagonal phases. we can see that the growths of the film along (002) and (200) orientations of the triclinic phases are enhanced when thermal treatment time at 400C is prolonged from 60 min to 180 min.

Under our experimental conditions, the thickness d of the as-deposited film has been determined to be about 220 nm by an observation of its section SEM. SEM images of the thin films annealed at different temperatures. All the sample films are very compact. The sizes of the sputtered tungsten oxide grains look very uniform and are a little less than 100 nm. The grain boundaries become more and more discernable as the annealing temperature increases from room temperature to 400C, whereas they become very indistinct again owing to the growth of the grains when the annealing time is prolonged from 60 min to 180 min at 400C. This process indicates the structure transformation of the sample films from the complete amorphous nature to crystallization and is in complete agreement with the results confirmed by XRD. The surfaces of the deposited films become rougher as the annealing temperatures rise. When the annealing time at 400C increases from 60 min to 180 min, the nanorod-like structures have grown from the surface of the deposited film. This kind of surface morphology of the samples is very different from those of the films prepared by sol–gel methods and by reactively sputtering tungsten metal target.

It is well known that during the sputtering, the interaction between Ar plasma and WO3 bulk can highly distort and tilt the form works of the WO6 octahedra and thus results in an amorphous film. At the same time, a large number of oxygen vacancies and defects, which can reduce the tungsten ions from W6+ to W5+ or W4+,would be produced in the deposited films. This is responsible for the violet–red color and the amorphous XRD data of the films annealed below 300C. The obvious crystallinity of the deposited films at 400C for 60 min implies that the defects and disordered structures in the films have been effectively activated by this temperature. Consequently, increasing the annealing time at 400C is obviously favorable to the crystallinity and the growth of the films.

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Scandia doped tungsten powders were prepared by spray drying combined with two-step hydrogen reduction. The particle size of doped tungsten powder, powder morphology and doped tungsten matrix were characterized by scanning electron microscope, X-ray diffraction and laser diffraction particle size analyzer, respectively. The reduction behavior of Sc2O3 doped tungsten oxide and the effect of Sc2O3 onthe property of tungsten powder were studied by the temperature programmed reduction. The experimental results showed that the precursor powders prepared by spray drying had spherical shape. The addition of Sc2O3 could decrease the reduction temperature of tungsten oxide. The scandia doped tungsten powder had sub-micrometer size in the range of 0.1 to1 μm and scandium distributed evenly in thepowder. By using this kind powder, sub-microstructure cathode matrices with semispherical grains and homogenous distribution of scandium were obtained.

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