Why HVOF for WC-Co coatings?
HVOF generates supersonic particle velocities (400–700 m/s) and relatively low flame temperatures (2,700–3,200°C) compared to plasma spray (8,000–15,000°C). For WC-Co powders, the lower temperature is critical: WC decomposes to W₂C and free carbon above approximately 1,400°C under oxidising conditions. HVOF's high velocity and moderate temperature minimise WC decomposition and oxidation, producing coatings with:
- Hardness: 1,000–1,400 HV₃₀₀ (depending on grade and process) - Porosity: < 0.5–1% by image analysis - Bond strength: > 70 MPa (ASTM C633) - Wear rate: < 5 mm³/(N·m) in ASTM G65 Procedure B dry abrasion
HVAF (high velocity air-fuel) is increasingly used as a lower-cost, higher-velocity variant that further reduces WC decomposition versus conventional HVOF.
WC-12Co vs WC-17Co vs WC-10Co-4Cr: when to use which
The three most common HVOF WC-Co grades serve different application profiles.
WC-12Co (88% WC, 12% Co): The standard workhorse grade. Best balance of hardness (~1,150–1,300 HV) and toughness. Wear rates in ASTM G65 are the lowest of the three grades. Used for: pump plungers, hydraulic cylinder rods, paper machine rolls, steel mill guides. Limitation: Co binder dissolves in acidic or chloride environments — avoid in sea-water or strong acid service.
WC-17Co (83% WC, 17% Co): Higher cobalt content lowers hardness (~1,000–1,150 HV) but increases toughness and resistance to coating delamination under cyclic stress. Used for: aerospace landing gear, forming tools subject to impact, and substrates that flex in service. Coatings are slightly thicker for the same wear protection due to lower hardness.
WC-10Co-4Cr (86% WC, 10% Co, 4% Cr): Chromium addition produces a passive Cr₂O₃ surface layer on the Co binder, dramatically improving corrosion resistance. Hardness ~1,050–1,200 HV — slightly lower than WC-12Co. Used for: sea-water pump components, oil and gas offshore equipment exposed to brine, chemical processing pump seals, and marine applications. The go-to grade wherever both abrasion and corrosion must be resisted simultaneously.
Particle size distribution (PSD) for HVOF guns
HVOF powder PSD is critical — particles too fine burn or oxidise in the flame; particles too coarse arrive at the substrate incompletely melted and produce porosity or unbonded particles.
Typical HVOF size requirements: - Standard HVOF guns (DJ 2700, JP 5000, WOK 15): −45+15 µm (D10 ~18, D90 ~42 µm) - HVAF guns (M3, Kermetico): −45+15 µm or −38+15 µm (tighter distribution) - Fine-feature HVOF: −38+15 µm for thin coatings on precision parts - Plasma spray: −63+20 µm or wider distributions tolerated
PSD is measured by laser diffraction (ASTM B822 / ISO 13320). Request D10, D50, D90, and % below 10 µm (fines content) on the CoA — fines > 5% cause increased in-flight oxidation and reduce coating hardness. Also specify that the powder must be agglomerated-sintered (spherical morphology) for HVOF — not fused/crushed, which has angular morphology and poor flowability.
Carbon loss during HVOF: what to watch
WC-Co powder that has been incorrectly stored or processed may have surface decarburisation — the conversion of WC to W₂C or even free W by oxidation. In the HVOF flame, decarburisation continues. Coatings from decarburised powder show: - Reduced hardness - Increased brittleness (W₂C is more brittle than WC) - Brown or greyish coating appearance (not the characteristic dark grey of good WC-Co) - X-ray diffraction showing W₂C and/or free W peaks alongside WC peaks
On the powder CoA, monitor total carbon (min. ~5.5% for WC-12Co at 88% WC) and verify by XRD phase analysis that the powder is predominantly WC phase. Powder stored in humid conditions or subjected to excessive heating before spray can develop surface decarburisation.
At Jayanth Tungsten, each lot is supplied with total carbon by combustion analysis and XRD phase confirmation. Powder is sealed in nitrogen-flushed packaging to prevent storage degradation.
Sourcing WC-Co spray powder from India
The Indian market for WC-Co spray powder has developed as buyers in UK, Germany, UAE, and Southeast Asia seek alternative sources to European or Chinese suppliers. Jayanth Tungsten (Tumkur, Karnataka) produces agglomerated-sintered WC-12Co, WC-17Co, WC-10Co-4Cr, and WC-NiCr powders in standard HVOF size cuts (−45+15 µm) with full PSD (laser diffraction), chemistry (ICP-OES), flowability (Hall), and SEM morphology documentation on the CoA. ISO 9001:2015 certified.
For PTA hardfacing, we also supply fused tungsten carbide powder (macro-crystalline WC, angular morphology, −53+20 µm) for use in NiCrBSi matrix overlays on mining and drilling equipment.
Contact via WhatsApp +91 96111 57351 with your grade requirement (WC-12Co / 17Co / 10Co-4Cr), size cut, quantity, and destination port for pricing and a sample CoA.