What is HVAF and HVOF Tungsten Carbide Coating? Why do you need it?

Introduction 

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. 

What are HVAF and HVOF Tungsten Carbide Coating? 

HVOF Tungsten Carbide Coating  

Applying tungsten carbide coatings through the High-Velocity Oxygen Fuel (HVOF) process involves spraying powder particles at high speeds onto a component's surface. When the particles hit the surface, they flatten and bond with the material, gradually building up a strong, durable coating. HVOF tungsten carbide coatings offer high bond strength, low porosity, and excellent resistance to corrosion, wear, and erosion. They also help minimise residual stress, making them suitable for demanding industrial applications. The HVOF thermal spray process allows tungsten carbide coatings to be customised for specific applications. Their wear resistance, strength, and hardness depend on factors such as particle size, carbide content, and the type and proportion of metallic binder used. EWS LLP offers different tungsten carbide coating compositions that can be optimised to protect components against erosion, abrasion, and corrosion. These coatings are used across various industries, including aviation, deep-sea oil and gas operations, and zinc galvanising rolls.

HVAF Tungsten Carbide Coating 

Both of these factors play a crucial role in preventing the oxidation of metals and the decomposition of carbides. 

Why do we need HVOF and HVAF  Tungsten Carbide Coating? 

HVOF and HVAF tungsten carbide coating processes provide excellent resistance to sliding wear, abrasion, and erosion. However, their corrosion resistance may be lower than that of WC-CoCr coatings.

Key Benefits and Applications

WC-12Co thermal spray coatings are generally harder than WC-17Co coatings due to their higher tungsten carbide content. These tungsten carbide coatings resist sliding wear, impact, abrasion, and fretting at temperatures up to 510°C (950°F), particularly in non-corrosive environments. Chromium carbide coatings are recommended for higher-temperature applications. Tungsten carbide coatings on steel protect components from abrasive particles, erosion, and repeated contact with hard surfaces, making them suitable for dry, non-corrosive environments. HVAF WC-Co coatings can also provide gas-tight protection against gas and liquid penetration at thicknesses of up to 50 microns (2 mils).

Limitations of HVOF Tungsten Carbide Coatings

Although the HVOF process is widely used for tungsten carbide coating applications, high combustion temperatures exceeding 3,000°C (5,432°F) and oxygen in the combustion gases can cause material oxidation and tungsten carbide decomposition. This can make WC-Co coatings brittle and reduce their service life under abrasive and erosive conditions.

What Is HVOF and HVAF Spray? 

Know more - What is HVOF? What are the key advantages of high-velocity oxyfuel coatings?

What Is Tungsten Carbide Coating Used For?

Tungsten carbide coatings are used in various industries because of their hardness, durability, and resistance to wear and heat.

• Automotive Industry: Tungsten carbide coatings on brake discs can improve performance, extend service intervals, and reduce brake dust.
• Machining and Manufacturing: Tungsten carbide is used in cutting and machining tools that need high abrasion and heat resistance, especially in high-precision or high-volume production.
• Mining and Drilling: Its strength and wear resistance make it suitable for mining equipment and foundation drilling.
• Aerospace and Industrial Applications: Tungsten carbide and tungsten carbide-cobalt composites are used in specialised applications, including certain high-strength components.
• Sports Equipment: Its durability makes tungsten carbide useful for trekking pole and ski pole tips.
• Jewellery: Tungsten carbide is popular for durable jewellery due to its hardness and scratch resistance.
• Medical Instruments: Tungsten carbide is used in some surgical instruments because of its hardness and wear resistance, although it can cost more and require careful handling.

What Are The Benefits Of HVOF and HVAF Tungsten Carbide Coating? 

Wear and Abrasion Resistance: 

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. 

Cracking: 

In thermal spray applications, cracking is influenced by coating ductility and bond strength. A coating’s stiffness can be assessed using Young’s modulus, which depends on both the coating material and the application process. HVAF tungsten carbide thermal spray coatings have demonstrated higher ductility than hard chrome plating. However, both coatings show similar fracture toughness when measured using the stress intensity factor. This means they have a similar critical stress threshold at which cracks can begin to grow rapidly.

Corrosion Resistance: 

Corrosion is a natural chemical process that affects components exposed to harsh industrial environments or normal operating conditions. Protecting these components is essential for extending their service life. Corrosion resistance varies depending on the material and coating porosity. In hard chrome plating, natural cracks that develop during coating formation can make porosity difficult to assess. HVAF tungsten carbide thermal spray coatings can withstand up to 1,000 hours in a salt spray corrosion test, compared with approximately 150 hours for hard chrome plating.

Friction: 

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: Thermal Spray Coating Specialists 

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

FAQ 

What are the different types of tungsten carbide coating? 

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. 

What is the purpose of tungsten carbide coating? 

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. 

What is the difference between HVOF and Hvaf? 

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. 

What makes tungsten carbide a unique material? 

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. 

What are the disadvantages of tungsten carbide? 

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. 

What is the benefit of tungsten carbide coating? 

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.