Under different deposition temperature (500 ℃, 600 ℃, 700 ℃ and 800 ℃), keeping the composition proportion and the inlet content of WF₆ and H₂ the same amount, the cross section metallographic microstructure of the tungsten tube processed by CVD (Chemical Vapor Deposition) is different.

When the deposition temperature is lower(500 ℃), the organization of the deposited layer presenting fine crystalline column;

When the deposition temperature reach 600 ℃, the speed of the tungsten atoms generated by the chemical reaction of the reduction will accelerate. In the deposition process, some grain grow ing occasionally get the lateral growth space and grow, which will make deposit layer of column grain structure coarsening.

Some occasional rapid growth of the grain growth to obtain the lateral growth space and growth

When the deposition temperature is raised to 700 ℃, the speed of the tungsten atoms generated by the chemical reaction of reduction has been very fast, these tungsten atoms deposited on surface of deposition will restart growth interface nucleation and further growth. In this process, morphology of the deposited layer will change significantly. Re-nucleation process will result in, firstly, columnar crystal growth pattern of the deposition layer will tend to clutter; secondly, the crystal grain of deposition layer will obviously refined.

If the deposition temperature rising to 800 ℃, re-nucleation process will be more obvious, at the same time, the microstructure of the deposited layer has lost columnar crystal growth characteristics, and its organizational form is messy and grain size is uneven.


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As the CVD (Chemical Vapor Deposition) process, by constantly absorbing tungsten atom, initially formed thin polycrystalline grain, which will grow in all directions and form the randomly oriented growth area of deposition microstructure.

After a further depositing and growing, since the cross growth of these crystal grains in all directions will stop growing due to the mutual contacting and blocking among crystal grains, so only the growth in a direction which is perpendicular to the surface of copper matrix is able to obtain required crystal grains growth space, in order to continue to grow. Because there is such a competitive growth way, so a columnar grain structure is ultimately formed, whose direction is perpendicular to the growth development of the surface, whereby the region is mainly composed of deposition layer.


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CVD tungsten tube morphology:

In the CVD (Chemical Vapor Deposition) process, due to the chemical reaction with H₂, WF₆ adsorbed on the surface of the copper matrix reduce to tungsten atom, and these tungsten atoms will gather nucleation on the copper matrix surface and grow, at last, the tungsten tube is formed by cutting and other process.

The formation of the first layer of the microstructure is related to the forming process of the initial crustal nucleus of tungsten layer and nuclei initial growing up process.

Tungsten atoms will deposit and diffuse on the surface of the deposition matrix and gather on the surface of the active matrix position, these positions are usually near the grain boundary, surface level position and the crystal defect surface outcrops.

When nucleation aggregated reach a certain degree of supersaturation, the deposited layer of crystals will form initial nuclei. Because those active sites presented on the deposit surface distribution is not uniform, so, from the microscopic point of view, the initial deposition surface nuclei are not uniformly distributed.


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Due to its high density, excellent absorption behaviour against radiation, and environmental friendly characteristic, tungsten alloy can be the best choice to produce container inspection tungsten radiation shield. Container inspection tungsten radiation shield is usually used in container inspection system as the main components of gamma radiation detectors, gamma radiation detectors, and neutron radiation detectors. Those detectors can be used in ports, prisons, and border, which can detect weather mass destruction weapons, explosives, weapons, drugs and undeclared goods are hiding in the vehicles.

The photograph below shows the tungsten alloy radiation shielding in container inspection.

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Tungsten carbide buttons are widely applied in geological prospecting, coal mining and oil well boring. Because of its high wear resistance, high bending strength and high hardness, tungsten carbide button is ideally suited for wear parts, other machine parts and dies which are subject to severe service conditions, such as high temperatures, corrosion and abrasion.
Proper usage of tungsten carbide button can avoid button cracking and bending, save physical labor and working time, promote work efficiency.

Figure out the essence of rock drilling is very important. Through study the density and hardness of rock, use the proper grade of tungsten carbide button. Thus avoid the improper use of tungsten carbide button which may cause severe damage due to the over-high pressure. During the drill process, observe the drilling pressure, use the correct drilling method, and stop using tungsten carbide button if it gets blunt. 


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During the rock drilling process, tungsten carbide button works by impact crushing on hard rock in order to drill holes on the rock. As a result tungsten carbide button will have friction and crash with the rock. It will cause unavoidable abrasion. Before it cracks, abrasion is a normal failure mode of tungsten carbide button.

Tungsten carbide button bit fails because of abrasion which can not drill rock any more. During the crashing and friction, hard grain in the rock penetrates into the soft binder layer of tungsten carbide button. In the later process, tungsten carbide grain spalls and a small part of tungsten carbide button is worn. Under the continuous pressure of rock drilling machine, tungsten carbide button keeps being abrasive and the contact area between rocks enlarges, tungsten carbide grain spalls little by little. At last tungsten carbide button can no longer be used.


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As mentioned in the chemical vapor deposition method, the coatings of tungsten carbide insert could increase the plastic deformation resistance, but the tool properties like edge toughness is impaired.

Difficultly from CVD method, the coatings generated by physical vapor deposition are thinner, although the ability of protection against heat and plastic deformation is weak, they offers great edge integrity which in turn yields an desired protection against edge chipping.

Generally, it is quite difficult to simultaneously lever up all tungsten carbide insert properties as there are numerous properties of both the protective coating and tungsten carbide substrate and the combination.


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For coated tungsten carbide insert,the main coating issues related to machining of steel , stainless steels or cast iron and other milling operations are delamination or cracking of the protective coating.

It is known that, during machining, the cutting edges of tungsten carbide insert are worn because of different wear mechanism such as, chemical wear, abrasive wear and adhesive wear. In addition, if the cutting speed is high, there will be a considerable amount of heat occurs in cutting zone and a plastic deformation is likely to generate, which for a payback, an enhanced wear will be triggered as a consequence of delamination or coating cracking.


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As an alternative option, adding cubic carbides such as TiC, Tac or NbC also could increase the coated tungsten carbide insert plastic deformation resistance. But it should be noticed that it also has a negative effect on edge chipping tendencies.

Since the constitution of the applied wear resistant surface coating is a vital factor in the tool properties, it could also increase the plastic deformation resistant. When adopting chemical vapor deposition , the coating tends to be thicker and more wear resistant, and the insert’s plastic deformation resistant is improved however a larger extent impair edge toughness is likely to occur.


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It is claimed that the cutting performance of coated tungsten carbide insert regarded to specific wear type could be improved by single actions but the side effect will be pronounced at the same time when examining other wear properties. As a result, in order to get an optimization tool performance, a decent design of coated tungsten carbide insert should take all these properties into account and make balance  among them. One important balance in terms of milling alloyed steels with tungsten carbide insert is between cutting edge plastic deformation and edge chipping resistance.

Decreasing the binder content is one of the most common way to level up the resistance to plastic deformation and abrasive wear resistance. However this method will bring down the toughness of the cutting insert, as the vibrations and presence of casting or forging skin are affected by these factors, what’s more it will largely short the tool life.


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