As we know, some manufactory would add a little TaC, which can improve alloy binder component for enhancing the wear resistance, toughness and strength. While it means that more cost and if add excessively, the results would reverse. After the addition of Ni, P in WC-Co cemented carbide can be formed Ni-Co-P, Ni-P and Co-P. The eutectic temperature of Co-P is 1020 degrees, the eutectic temperature of Ni-P is 880 degrees, and Co 1340 degrees lower than the melting point of 1495 degrees and WC-Co's. The main reason is that P atomic adsorption and segregation in Ni, Co particle surface, thereby reducing the energy of surface of Ni, Co particles. Therefore, such alloys in the liquid phase, and it makes early appearance dissolution and precipitation and the formation of the skeleton of solid particles also occurred in advance to make the process more fully sintered at a relatively low temperature. So it can effectively accelerate the speed of hard densification and improve the performance of tungsten carbide button.

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Using low-temperature molten salt method to produce tungsten cobalt and the producing processes are as follow:

1. In accordance with the mass ratio of 1.17: 1 obtain LiNO3-Na2WO4 mixed molten salt.
2. The Co and W at quantity relative ratio of 1: 1, respectively formulated into aqueous solubility is 1mol/L and then under vigorous stirring, the solution was slowly dropped into Na2WO4 and CoCl2 solution with stirred 30min so that the two solutions were thoroughly mixed.
3. The mixture was filtered, precipitate and washed, dried at 80 ℃ in the oven to give the precursor of CoWO4.
4. to weighed molten salt and precursor by mass ratio of 6: 1 in the mortar mix evenly put it into alumina clamp pot, the pot will be placed in the electric furnace holding 8h at 210,270,340 ℃.
5. After the synthesis reaction was allowed to cool to room temperature, to obtain a solid product, which was after distillation, washing, filtration and drying to obtain the final powder sample.

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With the development of deep drilling and oilfield excavation, the performance of tungsten carbide button is also concerned. Most of profiles of tungsten carbide button are ball-shaped, and bullet-shaped. But it would be easily deactivate when we use the ball-shaped and the bullet-shaped would be vulnerable because of lackness of the matrix under a large impact. Based on the effective mechanism of spherical broken rock and bending stress curve theory, some researchers design blunt-resistant tungsten carbide button. It combines the advantages of the ball-shaped with the bullet-shaped, which is composed of two parts, a spherical cap and a cone. Spherical side is used in ball-shaped pressing die, and another approximate cone side is used in wedge pressing so that the effect of rock breaking is improved.

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With the requirement of rock drilling higher and higher, which means that it should has good toughness against impact and high abrasive resistance. And the use of crystallization of ultra-fine structure can obviously improve the performance of tungsten carbide ball button. There is research data shows that carbide binder phase content unchanged, while WC grain size of less than 1μm, alloy hardness and strength of will get obviously improved. What’s more, with the size of WC grain reduced further, the promotion will be more visible.

As the particle has small size, large surface area, and surface strong reactivity, which makes it certain specific properties will be able to simultaneously increase the strength and hardness of tungsten carbide button. Therefore, many of the scholars or researchers study set the goals and directions on the refinement of carbide grains to nanometer so that both of hardness and strength can be enhanced. It can extend the working life of tungsten carbide button and decrease the cost of production.

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Tungsten cobalt chemical formula is CoWO4 and molecular weight is 307.78. It has wolframite structure, CAS number: 12640-47-0. Tungsten cobalt as a functional material widely used in anti-knock, paint additives, catalysts, microwave dielectric ceramics and optical anode materials.
There are many methods for producing CoWO4 which are traditional solid-phase method and wet chemical methods including co-precipitation method, hydrothermal method, spray pyrolysis method and so on. However, these method more or less are some problems, such as conventional solid-phase method need high synthesis temperature, larger energy consumption, the resulting powder particle size is large, irregular shape. While co-precipitation method can effectively realize the reaction components are homogeneously mixed at the atomic scale, but get precipitate requires high temperatures calcination process. Besides, the hydrothermal method more strict on equipment and has complex operation. After a series of studies found that low-temperature molten salt method produce tungsten cobalt not only process simple, and do not ask more of technical equipment, it is conducive to large-scale production.

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The composition performance of tungsten copper points on electrical life experiment table

A TDR-40A vacuum single-grains furnace can be employed to measure the electrical erosion. Tungsten copper points is used for a contact material, which act as a cathode material, and has been polishing after being processed into metallographic sample, pure tungsten of Φ = 2mm is acting as a anode material, placing the two electrodes into a vacuum furnace. Then energize DC (Direct Current) voltage between the anode and the cathode, which is 8000V to get higher stability. Therefore, with the speed of 0.2mm / min, the cathode will rise slowly to make it close to the anode until the arc between the anode and the cathode can ignite, a precision of 0.1mg analytical balance is used for weight loss measurement of samples, arc each 30 times, and the total number of arc times is 300 times around.
A 1000-B-type scanning electron microscope is used for scanning electrical erosion of morphology, and a electron spectroscopy for changes analysis on sample composition.

 

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Tungsten copper contacts composition performance table of electrical life experiment

Electrical erosion can be measured in a TDR-40A vacuum single-crystal furnace. Cathode material is tungsten copper contacts, a contact material, which has been processed into metallographic sample after polishing, anode material is pure tungsten (Φ = 2mm), they are placed in a vacuum furnace. Plus DC voltage of 8000V (in order to obtain a higher stability) between the anode and the cathode, so that the cathode can rise slowly with the speed of 0.2mm / min, let it close the anode until arc ignite between the anode and the cathode, arc every 30 times, using a precision (0.1mg) analytical balance to measure weight loss of a sample, total arc times is 300 times.

Employ 1000-B-type scanning electron microscope to scan morphology electrical erosion, and electron spectroscopy to analyze changes in the sample composition.



 

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Sample 1: WCu30, prepared by powder metallurgy, size of 10mm * 10mm * 10mm;
Sample 2: Fibrous structure tungsten copper points, Φ = 0.12mm, size of 10mm * 10mm * 10mm;

The arc erosion of WCu30 and fibrous structure tungsten copper points, which increase with the arcing erosion increase. Along with the increase of arcing time, mass loss of both points’ arc erosion increase rapidly at first; then during 15-20 times, it increases slowly; and then after 30 times, it increases quickly. What is more, sample 2’s mass loss is less than sample 1’s. The reason why mass loss of the two samples increasing rapidly lies that: original burr, unevenness and impurities on the surface of cathode material are subject to strong electron and ion sputtering under thermal action of discharge arc, leading to a large loss of material; Because sample 2’s raw material is tungsten fiber(can enhance mechanical properties), therefore, its hardness and strength of the sample will increase, and whose loss can be reduced; At the same time, due to capillary suction, the molten copper can make melt filling in tungsten skeleton under the action of arc, so that splash and losses of cathode materials can also be reduced. Since the mass loss of Sample 2 is less than sample 1’s, so sample 2 owns lower arc corrosion resistance.



 

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New tungsten copper contacts material: tungsten copper contacts (with fibrous structure)
Sample 1: WCu30 prepared by mixing, sintering and other process;
Sample 2: fiber structure of tungsten copper contacts (Φ = 0.12mm);
Sample size: 10mm * 10mm * 10mm.

The arc erosion of new tungsten copper contacts material and WCu30 are increasing with the increase of arcing erosion. In the beginning, quality loss of arc erosion of both samples increase rapidly with the number of arcing time, then slowly increasing during 15-20 times, and then quickly increase after 30 times, besides, the quality loss of sample 2 is less than sample 1. The reason of quality loss increased rapidly of the two samples is: under the thermal action of discharge arc, the original burr, unevenness and impurities of the cathode material’s surface are suffering from strongly electron and ion sputtering, resulting in a large loss of material; since sample 2 is using tungsten fibers as its materials, which enhance its mechanical properties, so the strength and hardness of the material increases, and the loss can be reduced; the arc has played a role in it at the same time, the molten copper, due to capillary suction, can make melt filling in tungsten skeleton, such splash and losses of cathode materials can be reduced. Because the quality loss of Sample 2 is less than sample 1, so sample 1 with higher arc resistance to corrosion.

 

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Tungsten ores

Tungsten does not occur naturally in its pure metallic state; rather, it is found in several ores, but only two kinds of tungsten-bearing mineral rocks, called wolframite and scheelite, are mined commercially. Wolframite accounts for about 70% of the total tungsten resources in the world, and scheelite accounts for about 30%.

Scheelite

Scheelite is a calcium tungstate mineral that forms a series with the rarer mineral powellite, which contains molybdenum in place of the tungsten. Colors include golden yellow, brownish green to dark brown, pinkish to reddish gray, orange and colorless. Transparency ranges from translucent to transparent and crystal faces are highly lustrous. Its gravity is high and its hardness is low. It also fluoresces under shortwave ultraviolet.

Scheelite occurs in contact metamorphic skarns, in high-temperature hydrothermal veins and greisens, and less commonly in granite pegmatites. Notable occurrences include Hollinger Mine, Ontario, Canada; Saxony, Germany; Tong Wha, Korea; Sonora, Mexico; Cornwall, England; New South Wales and Queensland, Australia; Mill City, Nevada, Atolia, San Bernardino Co., California, Cochise Co., Arizona, Utah and Colorado, all in the USA; and Jiangxi, Hunan and Yunnan provinces, China.

Scheelite is a subordinate ore of tungsten, with wolframite supplying a greater quantity on a worldwide basis. Scheelite is synthesized via the Czochralski process to produce the material that is used to imitate diamond, as a scintillator, or as a solid state lasing medium.



 

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