Tungsten Powder Infiltrated with Copper-Titanium-Bismuth or Copper-Titanium-Tin

Tungsten powder is pure tungsten in powder, apparent black powder. The regular tungsten powder fearture with 2~10um, 99.90% or 99.95%. Tungsten powder used as material for tungsten product usually.

The purity of tungsten powder is of particular importance in PM manufacturing of tungsten metal, since during subsequent sintering further purification through evaporation is only possible to a certain extent. The demand for purity of tungsten powder has increased steadily during the last three decades. Considerable improvements in hydrometallurgy have led to concentrations fairly below 10 µg/g for most of the elements. This trend with time can be demonstrated by comparing today's usual specifications with those given in the last book on "Tungsten" by Yih and Wang, published in 1979.

It was found that using vacuum infiltration techniques, copper-titanium-bismuth or copper-titanium-tin alloys, titanium sandwiched between copper-bismuth or copper tin alloys and a tungsten powder body subsequently heated to form copper-titanium-bismuth or copper titanium-tin alloy, a tungsten powder body coated with titanium by electroplating or vapor phase plating, and the like, wet individual particles of the tungsten powder body so as to allow infiltration of the tungsten particles and the copper-titanium bismuth or the copper-titanium-tin alloy thereby raising the overall electrical conductivity of the copper alloy matrix. The use of vacuum infiltration techniques also decreases the volume of hydrogen present in the resultant tungsten-copper-titanium tin composites by more than an order and decreases the volume of all gaseous components by several orders.

Although complete and substantially instantaneous infiltration of copper into sintered tungsten bodies is conveniently carried out in an atmosphere of hydrogen, a copper melt shows no penetration into tungsten powder bodies in a vacuum atmosphere using comparable time temperature treatments and using standard metallurgical procedures. In carrying out the present invention, it was found that subjecting the tungsten powder body and a contacting copper-titanium-bismuth alloy or a copper titanium-tin alloy to a vacuum infiltration process, the copper-titanium-bismuth alloy and the copper-titanium tin alloy were absorbed into the tungsten body by capillary attraction. It is thought that in each instance the titanium promotes wetting of the tungsten particles by the copper titanium-bismuth alloy and the copper-titanium-tin alloy.

The bismuth and the tin are used in the resultant composite contact materials to sustain an are at low values of current and voltages during the operation of the composite contact material in vacuum environments.

Tungsten is used in electrical contact materials because of its inherent characteristics of hardness and of resistance to arcing which reduce pitting of the tungsten contact material. However, pure tungsten contact material possesses high electrical resistance which lowers the efficiency and reliability of the tungsten contact material.

It has been suggested that a composite of tungsten copper used as an electrical contact material would make advantageous use of the several outstanding characteristics of both metals. In the composite, the copper provides the current carrying capability and thermal conductivity while the tungsten contributes hardness, resistance to are erosion, and superior anti-weld properties. In order to utilize the aforementioned characteristics of the copper and the tungsten, it is necessary to fabricate the metal into a tungsten-copper composite.

Copper and tungsten are mutually insoluble and form no alloys in the metallurgical sense, but mixtures of the "ice two metals are usually referred to as alloys but are, technically speaking, composites. Composites of tungsten-copper may be prepared by pressing the mixed metal powders to the required shape in dies, and subsequently sintering in a hydrogen atmosphere above the melting point temperature of the copper, preferably between l250 and 1350 Centigrade. The hydrogen acts as a flux and the molten copper wets the tungsten particles and cements them together. Another method which provides a harder resultant body consists of first pressing and sintering the tungsten powder so as to form a coherent but porous body, which is then heated at a temperature of about 1200 C. to 1300 C. in a hydrogen atmosphere and in contact with molten copper. The copper is absorbed into the pores of the tungsten powder body by capillary attraction. The copper infiltrated imparts strength and ductility to the tungsten powder body and also provides the resultant body with higher current carrying capability and thermal conductivity. However, using standard metallurgical procedures, a copper melt shows no penetration into the tungsten powder body in a vacuum. It is thought that the lack of penetration of the copper into the tungsten powder body is due to the unfavorable surface energies that are present in the vacuum.

The additions of bismuth and tin to the composites provides a resultant composite contact material that does sustain an are at low magnitudes of current and voltages during the operation of the contact materials in a vacuum atmosphere environment. It is thought that the foregoing occurrence is due to the relatively high vapor pressures of bismuth and of tin.

Therefore, it provides composite materials suitable for use as contact materials in vacuum electrical switching devices.

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