The sintered tungsten, and alloys commonly used direct sintering, sintering indirect. Direct sintering method used for smaller size for bars, rods, wire and other tungsten alloy powder metallurgy and production of billets. Indirect sintering method used for large slab. Partial liquid phase sintering method for the preparation of tungsten and its alloy powder metallurgy products, such as tungsten slab, high density tungsten alloy, tungsten - copper alloy.

Tungsten furnace burn down preform is placed between two electrode holder, burn preform in a protective atmosphere of hydrogen (and other protective atmosphere or vacuum) in low voltage, high current, resistance heating sintering method called direct sintering method.

Direct sintering equipment: direct sintering of major equipment for the pre-burning furnace and vertical furnace, furnace structure common is hanging bell-type water-cooled, single and multi-hood-type hood.

Direct Sintering Process

Pre-Sintering

The purpose of pre-sintered compacts to exclude the fusible and volatile substances, improving spoon compacts conductivity and strength. Pre-sintering system based on blank grades and specifications determined.

Vertical Melt Sintering

Melting down the sintering process is mainly for controlling the current value system, the heating time and holding time, the cooling water temperature and flow. Generally vertical melt production, each batch of tungsten blanks in determining the technological system before, do first fuse test to determine the fusing current. Production of the highest vertical melt fusing current operating current of approximately 88% -93%.


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Tungsten and tungsten alloy compacts and pre-sintered preform is placed resistance furnace, induction furnace and other forms of legislation in the sintering furnace sintering method called indirect.

Indirect Sintering Equipment

Horizontal molybdenum wire furnace: for sintering tungsten - nickel alloy, tungsten heavy alloy (W-Ni-Fe, W-Ni-Cu, etc.), tungsten - copper and tungsten - silver alloy.

High temperature resistance furnace, induction furnace, etc.: for sintering pure tungsten and unit-based or multi-line solid-phase sintering of tungsten alloy.

Indirect sintering process: indirect sintering pure tungsten and unit production lines or multicomponent solid-phase sintering products.

The indirect heating furnace sintering sintering temperature below the sintering temperature pendant melting method. Therefore, the use of indirect sintering tungsten powder particle size and compaction pressure demanding.
Indirect sintering process developed in addition to choosing the right tungsten and its alloy powder, the blank size and weight are also important basis for requiring a slow warming and sufficient intermediate temperature holding time.

Indirect Production of Sintered Tungsten Heavy Alloy

Common high density tungsten-based alloy: W-Cu-Ni series and W-Ni-Fe series. Tungsten alloy commonly used in the production of this type of horizontal molybdenum wire furnace. To 90% W +2.5% Cu +7.5% Ni as an example. This is typical of the surface tension of the liquid and the solid - liquid interfacial tension, liquid phase sintering can be divided into three distinct phases boundary is.


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Compacts small size , shape and relatively simple tungsten alloy powder metallurgy products, can suppress the production of steel , but the large size, complex shape compacts ordinary steel can not be formed , should be used isostatic molding and other methods . Including isostatic cold isostatic pressing and hot isostatic pressing , cold isostatic pressing in which industrial production has been widely applied .

Isostatic high-pressure pump by means of action of the fluid medium ( gas or liquid ) into the pressure -resistant sealed container steel body , the static pressure of the fluid pressure acting directly on the elastic modulus comprising a powder , the powder is at the same time balanced in all directions on the pressure and density distribution and intensity to obtain high green compacts .
Cold isostatic fluid medium used is usually water or oil , soft mode with high-quality rubber or plastic.

Isostatic molding die press forming compared with the general , its advantages are: isostatic pressing , through the colloid applied to the soft mode is pressed over the entire outer surface of the body , can be made of complex shape , density , height and diameter ratio can be arbitrarily selected compacts , pressed , the powder with a small elastic relative movement of the mold , so the friction loss is small, the desired unit low pressure, density, green density and intensity are high, easy to transport and mechanical processing, and soft mold manufacturing cost is also low.

Isostatic pressing equipment : isostatic pressing Major equipment for isostatic press , the combination of mold and automatic loading machinery. In this case, only introduce cold isostatic pressing machine and soft mold production.

Cold isostatic pressing machine: cold isostatic pressing machine mainly by the high pressure vessel and fluid pressure pump components with fluid storage tank , pressure gauge , high pressure fluid transport pipes, high-pressure valves.

Industrial application of cold isostatic presses are mainly three types : rod isostatic press , screw-type isostatic presses , isostatic presses rack cabinet .

Soft mold making and technical requirements

Mold material selection and mold making : The different powder materials in the isostatic molding require different pressures , the static pressure of the metal powder 43-219MPa, carbide ceramics 70. 4-219MPa. Accordingly , the tungsten powder, isostatic pressing mold material need to be a certain degree of strength and flexibility should , loaded powder can keep the original geometry ; has a high anti-wear properties; ease of processing ; no pressure medium from physical and chemical effects ; material is not easy on the adhesion of the compacts , long life and low price .


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Producing dense tungsten, and alloys in addition to powder metallurgy methods, there are melting, chemical vapor deposition, physical vapor deposition method.

Consumable Electrode Vacuum Arc Melting

Modern electric arc smelting, melting usually consumable tungsten electrode and the copper and copper alloy arc melting crucible. In a vacuum state, the molten metal is cooled copper crucible inflows (ingot mold) cooled into ingots, the thermal conductivity of copper, the heat transfer is easy, so that the liquid metal contacts to the water-cooled copper crucible rapidly solidified, thus eliminating the tungsten, and copper alloy and the reaction between the crucible. Tungsten metal is melted in the arc flame, electric arc occurs in the upper electrode (consumable) and the lower electrode (copper ingot mold tungsten and its alloys) between. Consumable electrode vacuum arc melting the cathode, the molten metal as the anode.

Tungsten arc melting ingots having a coarse grain structure, therefore, brittle, can be eliminated after the melting heat stress treatment, or adding other elements as an impurity scavenger, and a gap to control the grain size.

Electron Beam Melting

Electron beam melting high purity tungsten and alloys thereof, but not particularly coarse grain, not the pressure processing. Industrially used by the primary electron beam melting and then vacuum consumable arc melting. Electron beam melting tungsten alloy products and the intensity ratio of output arc melting and powder metallurgy products low and plastic - brittle transition temperature close to or slightly above them.

Zone Melting

Electron beam heating method using tungsten, and alloys of zone melting, can be obtained by zone melting high purity tungsten, having a Vickers hardness of 2842-33430, tungsten has also been greatly improved toughness.