The key characteristics of CVD tungsten carbide coatings are as follows:

1、Outstanding chemical and corrosion resistance
2、Free from through porosity, thus effectively protecting mild steel substrate from corrosive media without sealing the coating
3、Superior resistance to sulfide stress cracking
4、Provides effective protection against mineral acids such as sulfuric acid and hydrochloric acid
5、Resists Aqua Regia at room temperature
6、Superior wear resistance; Wear rate of CVD tungsten carbide coatings is four fold lower when compared to thermal spray WC, 12 fold lower than hard chrome, and 40 fold lower when compared to abrasion resistant steel AR-500
7、Demonstrates better erosion rate when compared to chrome carbide weld overlay, hard chrome, white iron, cemented carbide, and various other hard materials
8、Better fatigue resistance and toughness
9、Superior resistance to impact and deformations
10、Deposition from the gas phase enables coating of internal surfaces and intricate shapes.

A micro-photograph of a cross-section of 50-microns thick CVD Tungsten Carbide coating type T on thread. The uniform coating follows the substrate; even slight imperfections are accurately followed (magnify. 20X).

Comparison results of ASTM G65 tests of CVD tungsten carbide coating abrasion resistance against other hard materials is depicted.

Results of ASTM G65 tests of CVD Tungsten Carbide coating abrasion resistance as compared to the results for other hard materials.

Corrosion resistance of CVD tungsten carbide coatings is demonstrated.

Samples of three different coatings after salt spray corrosion tests: left - HVOF after 480 hours; centre – Hard Chrome after 288 hours; right – CVD coating type T after 480 hours.
Applications of CVD Tungsten Carbide Coatings

CVD tungsten carbide coating is suitable for applications with many different components operating in extreme erosive and abrasive atmospheres, such as critical components of metal seated ball valves, downhole tools, and pumps handling abrasive fluids.

Ball valves coated with CVD tungsten carbide coating, demonstrate increased valve life thanks to the coating as it make them scratch-proof and able to resist erosion and abrasion.

Ball valves coated with CVD Tungsten Carbide coating.

CVD tungsten carbide coating extends the life and reduces downtime costs of downhole tools such as grippers for down-hole tractors, high loading bearings pins, and mud-driven hydraulic parts for directional drilling tools.

CVD tungsten carbide coating type T is applied on outside piston and inside cylinder of a positive displacement pump transporting abrasive viscous fluids at pressures as high as 2800 psi to reduce wear, thus increasing pump life threefold.

CVD tungsten carbide coating is an ideal alternative to phase-out hard chrome plating because it involves carcinogenic hexavalent chromium, thus causing negative impact on environment, health and safety.
Conclusion

With these qualities, CVD tungsten carbide coating becomes an ideal solution to improve the performance and life of critical components of valves, downhole tools, and pumps operating in power generation, cryogenic equipment, refineries, food manufacturing, and oil and gas facilities.
About Hardide Coatings

Hardide Coatings produce a range of advanced surface engineering coatings that protect the internal and external surfaces of components from wear, erosion and acidic corrosion.

The coatings are proven to extend the life of metal parts operating in harsh environments for a variety of industries including oil & gas, valves, pumps, aerospace and advanced engineering.

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Tungsten carbide is a main raw material in the making of tungsten carbide alloy, it is also know as Wolfram Carbide. Tungsten carbide has metal gloss and has hardness similar to adamas, it is also a good conductor of electric current, its melting point is 2870℃ and boiling point 6000℃，relative density is 15.63 （at18℃）. This kind of material does not dissolve in water, hydrochloric acid and vitriol.

Owing to these physical properties, tungsten can be used in making, attrition-resisting, strike-resisting and corrosion-resisting moulds, the use of tungsten in moulds can extent the their service lives. Thus will effectively save the cost of moulds in production and improve economic performance. This sort of mould can be used in our special processing, too. It is known that China is the largest manufacturing country in the world, the application of mould is wide in many areas. Tungsten carbide moulds will undoubtedly receive warm welcome from a great number of enterprises. Experts therefore expect that tungsten carbide moulds will have board prospects in the market. 

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The life of critical components and tools can be increased by many different hard coatings and surface treatments such as boronizing, nitriding, hard chrome plating, plasma and thermal spray coatings, physical vapor deposition (PVD) and chemical vapor deposition (CVD) coatings. However, each technique has its own disadvantages. This article discusses the innovative CVD tungsten carbide/tungsten coating named as Hardide, Which exhibits exotic properties.
Types of CVD Tungsten Carbide/Tungsten Coatings

CVD tungsten carbide coatings are different from other tungsten carbide coatings as they do not use cobalt or nickel metal matrix binder. CVD tungsten carbide/tungsten Coatings are available in four different types.

The hardest coating type H comprises pure tungsten carbides, thus demonstrating high hardness but with only 'satisfactory' toughness. The multi-layer coating type M features layers of different hardness. It is possible to modify the overall coating characteristics by changing the ratio between the thickness and properties of individual layer based on specific application requirements. CVD tungsten carbide coating type T is the most widely used coating.
Nano-Structure of CVD Tungsten Carbide Coating Type T

Coating type T is a sophisticated nano-structured material comprising a metallic tungsten matrix with dispersed tungsten carbide nano-particles with a typical size range of 1-10 nm.

High resolution electron microscopy image of precipitate in CVD coating type T deposited on Cu substrate. The atomic distances (1.49 and 1.76 Å) directly taken from the precipitate region are matched best to the lattice constants of W2C (110- 1.49 Å and 102 - 1.74 Å).

The coating type T demonstrates abrasion resistance up to twelevefold higher than that of hard chrome and improved hardness of more than 1100 Hv. The coating can be formed on titanium, low alloy and some tool steels, stainless steel, and Ni-, Co- and Cu-based alloys. This nano-structured material shown unprecedented impact resistance, crack resistance and toughness by tolerating 3000 microstrain deformations without any deterioration.
CVD Tungsten Carbide Coating Porosity

CVD tungsten carbide coating is devoid of through porosity from a thickness of below 1 µm thanks to its deposition mechanism. The crystallization of the coating takes place from the gas-phase atom-by-atom, and the defects and micro-pores in the coating are filled by the highly mobile reaction products as the coating grows.

SEM image of a cross-section of CVD coating layer on cemented carbide substrate. The coating as deposited has exceptionally low porosity and it can isolate substrate material against attacks of aggressive media, such as acids.

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It was uncommon to see Tungsten Alloy Shells filling with explosive until the middle of the 16^th century. In the early days, it was common to find duds in carronades, as the fuse tubes in the carronades are made of synthetic powder which burned slow and thus caused instability when igniting the black power.

It was not until 1823, cannons which could be filled with explosive shells were finally invented by A French General named Henri-Joseph Paixhans. In the 19^th century, most of shells that can be seen are made from cast iron, tungsten alloy shells were used in piercing amour initially, as cast iron shells were incapable of bearing the knockings of new type of powder.   

In World WarⅠ, 70% of injuring of infantries in battle fields were caused by the shell fragments from tungsten alloy shells.   

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