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.

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.

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High speed steel tools for machining were coated with WC and TaC by chemical vapor deposition (CVD), 25 and were used in a high speed milling machine. The physical integrity of the tools coatings were analyzed by scanning electron microscopy at the end of the trials and materials surface roughness were compare in order to predict best behaviour too. The relevant analyses indicate that the deposits form heterogeneous films. The results suggests that the TaC coating resist higher attrition than made of WC's.

Tungsten Carbide Coating Tools: Chinatungsten Online - http://www.tungsten-carbide.com.cn
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CVD tungsten carbide coatings are different from other tungsten carbide coatings as they do not use cobalt or nickel metal matrix binder, the main characteristics of CVD tungsten carbide coatings are including,

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

 Tungsten Carbide Coating Tools: Chinatungsten Online - http://www.tungsten-carbide.com.cn
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Pyrochlore-type tungsten trioxide hemihydrate (WO₃·0.5H₂O) powder with the average particle size of 0.5μm was prepared successfully from the weak alkaline sodium tungstate solution by using organic substances of sucrose or cisbutenedioic acid as the acidification agent. The influences of solution pH and acidification agents on the precipitation process were investigated. The results showed that organic acidification agents such as sucrose and cisbutenedioic acid could improve the precipitation of pyrochlore WO₃·0.5H₂O greatly from sodium tungstate solution compared with the traditional acidification agent of hydrochloric acid. In addition, the pH value of the hydrothermal system played a critical role in the precipitation process of WO₃·0.5H₂O, and WO₃·0.5H₂O precipitation mainly occured in the pH range of 7.0 to 8.5. The precipitation rate of tungsten species in the sodium tungstate solution could reach up to 98 pct under the optimized hydrothermal conditions. This article proposed also the hydrothermal precipitation mechanism of WO₃·0.5H₂O from the weak alkaline sodium tungstate solution. The novel method reported in this study has a great potential to improve the efficiency of advanced tungsten trioxide-based functional material preparation, as well as for the pollution-reducing and energy-saving tungsten extractive metallurgy.

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