HTS Coatings — machining & grinding

Tungsten Carbide · Cobalt · Chrome

86% WC, 10% Co, 4% Cr

  • HVOF
  • HVAF

WC-10Co-4Cr is the coating people reach for when the part has to survive both wear and salt. Eighty-six percent tungsten carbide, ten percent cobalt, four percent chromium — that last four percent is what changes the story.

Chromium in the binder is the difference between a great abrasion coating and an aerospace-qualified chrome-plating replacement. WC-12Co is the workhorse for dry wear; it's also the wrong coating the minute you put it near salt spray, marine splash, or sour gas. Add the chromium and the corrosion numbers jump — 1,000+ hours ASTM B117 by HVAF where hard chrome plating typically fades around 150, dense and gas-tight microstructure, and the chrome-replacement wear numbers the aerospace industry qualified under ARP5935 and AMS 2447. Landing-gear inner cylinders, flap tracks, actuator rods, marine hydraulic rods, downhole mud-motor rotors, pump shafts in produced water — this is the chemistry.

We apply it by HVOF and HVAF. Hardness lands between 1,100 and 1,400 HV, bond strength past 10,000 psi (HVAF routinely past 12,000), porosity under one percent. Grind to 2-4 microinch Ra; superfinish below 1 µin if your seals demand it.

Compared to WC-12Co, you pay a little more powder cost and buy a lot more corrosion life. Compared to hard chrome, you lose the Cr(VI) tank, keep the fatigue life, and outlast the old coating four to five times over.

Send us the part and the service. We'll tell you if it's the right chemistry.

Technical data

Hardness
1100-1300 HV300 typical HVOF; 1200-1400 HV300 typical HVAF, up to 1600+ HV300 with fine-powder HVAF
Bond strength
10,000-12,000+ psi (69-83 MPa) HVOF; HVAF routinely >12,000 psi (>83 MPa), often exceeding the ASTM C633 glue-pull limit
Max service temp
930-1000°F
Max service temp
500-540°C
As-sprayed porosity
<1% (HVOF, often <0.5%); <0.3% (HVAF), gas-tight
Typical thickness
3-15 (75-380 µm); aerospace landing-gear builds commonly 6-18 mils
Surface finish (Ra)
90-120 as-sprayed; 2-4 diamond-ground; <1 superfinished

Where it earns its keep

  • Four percent chromium in the binder transforms corrosion performance versus WC-12Co — salt spray, marine splash, sour gas, and dilute acids no longer own the coating; HVAF-sprayed WC-10Co-4Cr clears 1,000+ hours ASTM B117 where hard chrome typically fails around 150
  • The qualified aerospace chrome-plating replacement on landing-gear inner cylinders and flap tracks (SAE ARP5935, AMS 2447) — wear resistance 4-5× hard chrome and negligible fatigue-life penalty versus the 50% hit that electroplated chrome can impose
  • Dense (<1% HVOF, <0.3% HVAF), high-bond (>10,000 psi, often >12,000 psi) cermet that grinds and superfinishes to mirror Ra (<1 µin) — sealing surfaces against packings and dynamic seals outlast hard chrome
  • No hexavalent chromium anywhere in the process — sidesteps OSHA 29 CFR 1910.1026 Cr(VI) PEL, EPA NESHAP 40 CFR 63 Subpart N, and EU REACH Annex XIV exposure for your supply chain
  • Drop-in chemistry for the shop that already runs WC-12Co — same HVOF/HVAF guns, same grinding practice; you pay a small premium on the powder and gain a large margin on corrosive-service parts

Where it doesn't

  • Decarburization — WC dissociates toward W₂C and W above ~500°C (930°F), which softens the coating and drops corrosion life; keep service below that or step up to a Cr₃C₂-NiCr for higher-temperature oxidizing service
  • Powder cost — the 4% chromium addition and tighter particle distributions make WC-10Co-4Cr meaningfully more expensive per pound than WC-12Co; spec it where corrosion pays for itself, not as a default
  • Spray parameters matter — gas-fuel HVOF, liquid-fuel HVOF (JP-5000), and HVAF each deliver different carbide retention, porosity, and corrosion performance; HVAF generally wins on decarburization, density, and corrosion, but the shop and the part have to be qualified together

Typical applications

  • Aircraft landing gear inner cylinders and flap tracks (hard-chrome replacement per SAE ARP5935)
  • Hydraulic cylinder rods in marine, offshore, and subsea service
  • Pump shafts, plungers, and sleeves in corrosive slurry and produced-water service
  • Oil & gas downhole tooling — mud-motor rotors, gate and ball valves, sucker-rod couplings
  • Food, pharmaceutical, and chemical process components where Cr(VI) is prohibited
  • Paper-mill rolls and print rolls in wet or acidic environments
  • Actuator rods and piston rods on airframe and industrial hydraulics

Wear modes addressed

  • Abrasive wear (two-body and three-body)
  • Sliding / adhesive wear
  • Erosion (particle, slurry, cavitation)
  • Corrosion-assisted wear and erosion-corrosion
  • Fretting wear
  • Fatigue (the coating is neutral-to-favorable versus chrome plate, which can drop fatigue life up to 50%)

Industries

  • Aerospace (airframe, landing gear, actuation — qualified chrome-plating replacement)
  • Oil & gas (downhole, wellhead, subsea, sour-service)
  • Marine and offshore (hydraulics, valves, cylinder rods)
  • Chemical and process (pumps, valves, shafts)
  • Food and pharmaceutical (hex-chrome-free surface)
  • Pulp, paper, and printing (wet rolls)
  • Power generation (steam-valve stems, hydro-turbine components)

Substrates

  • Low-alloy and medium-carbon steels (4140, 4340, 1045)
  • Stainless steels (17-4 PH, 410, 316)
  • Nickel-base superalloys (Inconel 718, Waspaloy)
  • Titanium alloys (Ti-6Al-4V, per qualified aerospace process)
  • Aluminum-bronze and Ni-Al bronze (marine pumps, propulsion)

Sources

Data points on this page draw on the following published references. Nothing here replaces a material-specific review by our process engineers — but it's the working starting point.

Material data on this page is provided as a general reference and can vary by lot, substrate, and application. Contact HTS to confirm the right material and specification for your specific part.

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