Tungsten carbide is a widely employed coating material across diverse industries.
Explore the nature of these tungsten carbide coatings, their applications, and the distinctive properties that set them apart, including exceptional resistance to erosion, corrosion, and abrasion.
Applying tungsten carbide coatings through the high-velocity Oxygen Fuel (HVOF) process involves directing high kinetic energy into powder particles during thermal spraying.
While these particles exhibit high energy, upon impact with the substrate, their velocity diminishes to zero, and the kinetic energy is absorbed.
This results in the particles flattening and rapidly bonding with the workpiece. As additional particles arrive in the HVOF Tungsten Carbide Coating process, the coating accumulates at a swift pace.
The utilization of HVOF thermal coating spray for carbide coatings yields high bond strength, low porosity, excellent corrosion resistance, notable wear resistance, resistance to erosion, and low residual stress.
Moreover, the HVOF thermal spray process allows for relatively customizable coatings.
The wear resistance, strength, and hardness depend on factors such as the volume fraction and grain size of the particles and the types and ratios of the metallic binder used.
This adaptability enables the tailoring of tungsten carbide coatings' hardness and other properties to meet specific requirements for a given item.
EWS LLP provides various options for tungsten carbide coating process chemistry, which can be optimized to protect against erosion, abrasion, or corrosion of the coated part.
These coatings find application in diverse sectors, including aviation parts, deep-sea oil/gas wells, zinc galvanizing rolls, and many more.
The HVAF coating or metal spray process is distinguished by its low combustion temperature (1,960-2,010°C | 3,560-3,650°F) and high particle velocities (800 to over 1,000 m/s | 2,625-3,281 ft./sec.), resulting in the production of low-oxidized, ductile, non-porous, high-bond carbide, and metal coatings.
With a spray rate reaching up to 550 g (about 1.21 lb)/min (73 lbs./hr), this process significantly accelerates, offering a notable advantage over HVOF.
HVAF process equipment harnesses the energy from gas combustion in the air to effectively spray powders.
Notably, the combustion temperature in an HVAF coating gun is typically 1,000°C (1,830°F) lower than that in a high-velocity oxy-fuel coating system.
This lower temperature proves ideal for gradually heating feedstock particles of metals and cemented carbides to, or slightly above, the metal’s melting temperature.
Additionally, the initial oxygen content in the combustion gas mixture is five times lower in the HVAF coating process compared to any high-velocity oxy-fuel coating process.
Both of these factors play a crucial role in preventing the oxidation of metals and the decomposition of carbides.
HVAF and HVOF tungsten carbide coating processes demonstrate outstanding resistance to sliding wear, abrasion, and erosion, even though their corrosion resistance is lower than that of WCCoCr.
The HVAF WCCo coatings exhibit gas-tight properties, preventing the permeation of gas and liquid, up to a thickness of 50 microns (2 mils).
WC-12Co thermal spray coatings typically exhibit greater hardness when compared to coatings of WC-17Co, mainly due to higher coating tungsten carbide levels.
The WC-12Co tungsten carbide coatings provide resistance to sliding wear, impact, abrasion, and fretting at temperatures up to 510°C (950 °F), particularly in non-corrosive environments.
For higher-temperature applications, chromium carbide coatings are recommended.
Coatings incorporating tungsten carbide offer effective protection to substrates against fretting, abrasive grains, particle erosion, and dynamic contact with hard surfaces.
These tungsten carbide coatings on steel find utility in abrasion-resistant coatings within dry, non-corrosive settings.
Although HVOF Process technology is commonly employed for WC coating applications, noticeable material oxidation, and WC decomposition can still occur during HVOF deposition.
The decomposition of WC-Co coatings is directly linked to a high combustion temperature, typically exceeding 3,000°C (5,432°F), along with the presence of oxygen in HVOF combustion products.
This leads to coating tungsten carbide embrittlement and subsequent reduction of its service lifetime under conditions of abrasive and erosive wear.
HVOF, short for high-velocity oxy-fuel coating, is the most sought-after thermal spray coating service at EWS LLP.
Commonly utilized for machining part repair or overhaul, it delivers robust and enduring surface coatings.
Applied robotically with a thickness as thin as three-hundredths of an inch, HVOF Tungsten Carbide Coating can easily meet OEM (original equipment manufacturer) dimensions or tight tolerance requirements.
This method accommodates harder coating materials, such as tungsten carbide, and can spray a variety of metal-based materials.
HVOF thermal coating spray involves the combustion of either hydrogen and oxygen or kerosene and oxygen to generate a high-velocity spray jet.
The coating tungsten carbide material is introduced into the spray jet through argon gas and applied to the component surface.
The HVOF spray jet operates at such high velocity that it produces diamond shockwaves, providing an inherent quality check during the thermal spraying process.
HVAF coating stands for high-velocity air fuel, which is closely linked to HVOF spray. However, it has notable improvements in its methods.
HVAF tungsten carbide coating produces more robust and uniformly distributed coatings. The flame temperature in the HVAF tungsten carbide coating process is closer to the melting point of most coating materials, eliminating breakdown due to particle overheating.
This feature results in HVAF providing the most consistent mechanical coatings among the types available at EWS LLP. These advantages make HVAF coatings highly resistant to abrasion, wear, and corrosion.
Additionally, the lower spray temperature makes HVAF the most ductile coating, contributing to protection against cavitation damage.
The HVAF Tungsten Carbide Coating technology involves the combustion of propane in a compressed air stream, similar to the HVOF process, generating a uniform high-velocity jet.
HVAF sets itself apart by incorporating a heat baffle to further stabilize the thermal spray mechanisms.
Material injection into the air-fuel stream propels coating particles toward the part.
HVAF thermal spray coating offers faster coatings at a lower spray temperature while enhancing wear and corrosion resistance.
Know more - What is HVOF? What are the key advantages of high-velocity oxyfuel coatings?
Tungsten carbide has diverse applications, with one notable use being in thermal spray carbide coatings, often applied to brake discs for high-performance cars.
In this context, the tungsten carbide coating process enhances performance, extends service intervals, and reduces brake dust.
Another crucial application of tungsten carbide coating lies in the manufacturing of machining tools, capitalizing on the material's abrasion resistance and heat resistance.
These tools are especially valuable in scenarios where steel would wear down rapidly, such as in high-precision or high-volume production settings.
Tungsten carbide, or its variants like tungsten carbide cobalt composite, is commonly employed in the production of armor-piercing ammunition.
Its strength is also prevalent in mining and foundation drilling. Additionally, in the realm of sports, it serves as a popular material for trekking poles or ski pole tips.
Furthermore, tungsten carbide finds use in the creation of jewelry due to its durability, and it is also utilized in the manufacture of surgical instruments.
In medical applications, it outperforms stainless steel but comes with a higher cost and requires more delicate handling.
When evaluating wear resistance, the primary consideration is hardness. At its core, the material's toughness correlates with better wear resistance. In a comparison between high velocity oxy fuel coating or HVAF tungsten carbide thermal spray and hard chrome plating, the former exhibits superior hardness and experiences less volume loss in tests.
In thermal spray applications, cracking is often tied to coating ductility and a minimal amount of binding strength.
Ductility can be calculated using Young’s Modulus of the coating, which depends not only on the coating material but also on the coating process.
HVAF tungsten carbide thermal spray has demonstrated higher ductility compared to hard chrome plating.
Regarding fracture toughness, as measured by the stress intensity factor, HVAF tungsten carbide thermal spray and hard chrome plating show similar performance.
This suggests that the critical stress threshold for a sharp fracture, where crack propagation rapidly increases, is approximately the same for both solutions.
Corrosion is a natural chemical process that occurs in parts exposed to harsh industrial environments or during normal operation.
Ensuring the security of parts is crucial. Corrosion rates vary among materials, with porosity playing a vital role in coatings.
Porosity in hard chromium plating can be challenging to assess due to natural cracking during coating development.
HVAF tungsten carbide thermal spray can endure a 1000-hour salt spray corrosion test, while hard chrome plating withstands a 150-hour test.
Friction is a significant aspect where hard chrome plating traditionally excelled until the emergence of HVOF and HVAF coating.
Previously, thermal spray required extensive polishing and grinding to compete with hard chrome plating, making it economically unfeasible.
HVAF tungsten carbide coatings now exhibit an as-sprayed roughness of around 32 Ra, are applied in thinner layers, and can be easily polished to 0 Ra without grinding. This leads to cost and time savings.
EWSLLP is an ISO-certified company specializing in advanced thermal spray coating services across a range of industries, including steel mills, paper and pulp processing, oil and gas, power generation, and hard chrome replacement.
By customizing coating solutions to meet specific customer needs, the company caters to orders of different scales, serving both individual clients and large-scale manufacturers.
Also Read in Detail - What is Thermal Spray Coating – Processes, Fundamentals, Applications, Guide 101
Also Read in Detail - 10 Types of Thermal Spray Coating Processes You Should Know
The various types of tungsten Carbide Coatings include Tungsten Carbide Cobalt – Which provides abrasion and fretting resistance.
Tungsten Carbide Nickel – It offers unique properties and applications. Tungsten Carbide Cobalt Chrome – It is another option with distinctive characteristics.
Tungsten Carbide (WC) is a highly durable ceramic material presented as fine grey powder particles.
Renowned for its exceptional hardness, this material demonstrates outstanding resistance to wear, abrasion, and scratches.
Its robust properties shield surfaces from potential damage and various surface-related challenges, including corrosion, erosion, and fatigue.
Research indicates that the HVAF process deposits coatings at a rate approximately four to five times faster than the HVOF process.
Consequently, employing a single HVAF unit can achieve the same results as using multiple HVOF tungsten carbide Coating units.
Due to coating tungsten carbide’s impressive hardness and exceptionally low density, this material serves as a reinforcing agent for aluminum in military armor and high-performance bicycles.
Moreover, its notable wear resistance has led to its use in applications such as sandblasting nozzles and pump seals.
Materials composed of tungsten carbide and cobalt exhibit certain limitations, with resistance to corrosion and oxidation standing out as the two most noteworthy drawbacks in the application of this common cermet.
Tungsten Carbide (WC) is a highly resilient ceramic material, appearing as fine grey powder particles.
Renowned for its exceptional hardness, this material boasts remarkable resistance to wear, abrasion, and scratches.
It effectively safeguards surfaces from potential damage and various surface-related challenges, including corrosion, erosion, and fatigue.
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