What makes a good wear resistant coating?
- High hardness. As a rule, higher hardness means higher abrasion resistance, especially if paired with 2
- High fracture toughness. Fragile coatings will sustain wear worse than a ductile one
- High bond. Even hard and ductile coatings will not be worth a penny if they delaminate
- Low porosity. Chemical resistance is important while through porosity gives liquids a way to the base material which could result in under-film corrosion
- Uniform quality. Any coating is as good as its weakest point.
Until recently we knew for sure that HVOF tungsten carbide cobalt chrome is the best wear resistant coating in thermal spray technology.
It has changed.
Please read further to find out why and how our HVAF WC-10Co-4Cr outperforms any HVOF version or visit our Coating Services page to see how we apply wear resistant coatings.
Kermetico HVAF Wear Resistant Coating Features
Kermetico HVAF carbide coatings are superior to HVOF rivals regarding wear resistance, corrosion protection, and production cost. The high velocity of the in-flight particles (greater than 1,000 m/s | 3,300 ft./sec.) in our HVAF process enables the production of very dense coatings with high bond strength.
Moreover, the low combustion spraying temperature (1,960-2,010°C | 3,560-3,650°F depending on the fuel gas) and gentle particle heating lead to minimal feedstock phase transformation and almost nonexistent elemental depletion/decomposition of the in-flight particle.
Furthermore, the replacement of pure oxygen in the HVOF process by using the HVAF process with air significantly reduces the oxide content in the coatings, which is desirable for high-performance coatings.
Key features of HVAF and HVOF Tungsten Carbide Coatings
|WC-10Co-4Cr Coating Features||A Typical HVOF||Kermetico HVAF Modes|
|Deposition efficiency, %||40-55||60-70||48-58||36-42|
|Young’s Modulus E, GPa||300||400||450||450|
|Apparent metallographic porosity||<0.8||<0.8||<0.5||<0.1|
|Bond Strength, MPa (PSI)||80+ (12,000+)|
|Range of as-sprayed roughness, µm (µ in.)||3.5-4.5 (150-180)||1-3.2 (40-130)|
The Kermetico HVAF process produces WC-based coatings with the highest fracture toughness, substantially exceeding known HVOF coatings. Since the main mechanism of wear of WC-base coatings is attributed to the material brittleness, Kermetico’s HVAF coating exhibits better wear resistance.
A Few Comparisons of Abrasive Wear and Erosion Protection Properties of Popular HVOF and Kermetico HVAF Coatings
There has been a great deal of scientific research conducted recently showing the superiority of our HVAF tungsten carbide coatings. Let’s review some of them.
Schlumberger conducted a slurry erosion test in 2012.
In this trial an Economy mode, Kermetico HVAF WCCoCr coating was compared to coatings of the same material deposited by industry-leading HVOF and detonation systems.
The following charts are courtesy of the Central Power Research Institute of India.
Could the reason for this result be that our coatings have been compared to less than the best available coating equipment?
You may also be interested in a comparison of Kermetico HVAF WCCoCr coatings with one of the most advanced HVOF systems on the market.
Are you interested in how our HVAF Balanced and Ultra modes provide such excellent results?
A Scientific Research of HVAF and HVOF Wear Resistant Coatings
As Prof. Wang has shown in his article “Wear and corrosion performance of WC-10Co-4Cr coatings deposited by different HVOF and HVAF spraying processes”:
“Three WC-10Co4Cr coatings were deposited by HVOF and HVAF processes, and their microstructure and properties were investigated in this study. The following conclusions were drawn as a result.
(1) The WC-10Co4Cr coating deposited by the HVAF spraying process exhibited nearly the same phase composition as its initial feedstock powder, which included mainly the WC and some Co3W3C and crystal Co phases with nearly no decarburization. The JK coating sprayed with Jet Kote III-HVOF equipment exhibited the most severe decarburization with high-intensity W2C and even metallic W phase. The phase composition of the JP coating deposited by the JP8000-HVOF system was composed of main WC and minor W2C peaks and exhibited a light degree of decarburization.
(2) The wear resistance and mechanism of the HVOF/HVAF-sprayed coatings were influenced not only by their hardness but also by their fracture toughness. The high hardness of carbide coating could effectively hinder the cuts caused by the abrasives, and their high toughness could make the binder absorb some of the energy caused by abrasive attacks with some degree of plastic deformation.
(3) The WC-10Co4Cr coatings, which had different degrees of decarburization, exhibited different dominant wear mechanisms.
(4) The electrochemical corrosion resistances and mechanisms of HVAF- and HVOF-sprayed WC-10Co4Cr coatings were influenced by their phase compositions and microstructures.”
Scientists tell us that Kermetico HVAF provides better wear and erosion resistance than HVOF. But a lot of companies still use HVOF to protect equipment from wear.
Why is that?
Maybe HVAF is too expensive?
The Economic Aspects of Abrasion Resistant Coatings
The list price of our HVAF equipment is lower than the price of good HVOF equipment.
With Kermetico HVAF thermal spray systems we are not limited to the “best coating possible.”
We can choose how to spray a tungsten carbide abrasion resistant coating:
- save money spraying in HVAF economy mode, getting HVOF quality with lower costs;
- apply the highest coating quality in HVAF U-mode to achieve high hardness, ductile, non-porous, abrasion and cavitation resistant coatings;
- or choose HVAF Balanced mode to gain a competitive edge in both cost and quality.
Hard Metal HVAF Coatings for Wear and Corrosion Protection
Kermetico HVAF equipment is the perfect instrument to apply WCCoCr erosion resistant coatings, but there are other wear-resistant materials which display their best qualities after being deposited with our HVAF systems.
|Kermetico №||Common name||Nominal Composition, wt.%||Hardness, HRC||Bond strength, PSI||Temperature Limit, °C (°F)|
|SS-430||Stainless Steel 430SS||Cr-15. C-0.4, Fe-balance||36-38||9,000||540 (1,000)|
|SS-350||Super-stainless||Ni-15, Cr-29, Mo-4, C-1.8,|
|6AB||Hard Steel||Cr-14, Ni-6, B-3.3, Si-3, C-2|
|431SS||Stainless Steel||Cr-16, Ni-2, C-0.2|
|SHS-717||Nanosteel**||Cr-25, Mo-8, W-10, C-2, Si-2, Mn-5, B-5, Fe-balance||65+||12,000||700(1,300)|
|LM-M||Armacor M||Cr-45, B-6, Si-1, Mn-1|
|ST-6||Stellite* 6||Cr-27, W-4, C-1, Co-balance||50-52||12,000||650 (1,200)|
|ST-1||Stellite 1||Cr-30, W-12, C-1|
|T-400||Tribaloy* T400||Cr-8.5, Mo-26, Si-2.6|
|T-800||Tribaloy T800||Cr-17, Mo-28, Si-3.4|
|NI-1662||Nickel-chrome-tungsten-boron||Cr-15, W-9, B-3, Si-4, C-0.8|
|NI-1620||Nickel-boron||B-2, Si-4, Ni-balance||35-38||12,000||500 (930)|
(*) – “Stellite” and “Tribaloy” are trademarks of Kennametal Stellite Company
(**)– “Nanosteel” is a trademark of NanoSteel Company
Kermetico HVAF and HVOF Thermal Spray Coating Technology
Kermetico designs and manufactures three families of HVAF and HVOF thermal spray equipment.
- Convertible HVOF and HVAF wear resistant coating equipment:
- Multi-purpose HVAF AK systems, with a range of spray guns:
- AK7 – a high-power gun for the thermal spray of large parts
- AK6 – a universal gun to spray a balanced mix of parts in a job shop
- AK5 – a compact gun to spray smaller parts, thin walls and complex surfaces
- AK-ID – an 80 mm (3.15”) and larger internal diameter spray gun
- AK-IDR – a rotating ID gun to spray 4” (100 mm) and larger bores
- AK-HH – a handheld gun for on-site coating
- Specialized HVAF S equipment:
- Additional equipment:
Kermetico, Inc. – Material Science Excellence, HVAF and HVOF Equipment Manufacturing and Thermal Spray Coating Services Since 2006
We create equipment that helps material scientists, engineers and business managers achieve their goals.
We have installed more than 60 Kermetico HVAF and HVOF systems in the USA, Europe, Japan and China.
Some of these systems are at work in Universities and National Labs, but most of them are used in production thermal spray shops.
We proudly design and produce our thermal spray equipment in California and install it all over the world.
You can visit our R&D center in Benicia to meet our designers and see our HVAF and HVOF equipment in action.
We also deposit abrasion resistant coatings for customers in North America – ourselves and through our network of partners