HTS Coatings — machining & grinding

Chrome Oxide · Silicon Oxide · Titanium Dioxide

93% Cr₂O₃, 4% SiO₂, 3% TiO₂

  • Plasma

When the seal face has to run quiet, tight, and forever, this is the oxide we reach for. Chromium oxide with minor additions of silicon dioxide and titanium dioxide — roughly 93% Cr2O3, 4% SiO2, 3% TiO2 — is the premier ceramic for rotating mechanical-seal duty. Commercial analogs are Oerlikon Metco 136F and Höganäs AMPERIT 716. A plasma gun melts the pre-fused-and-crushed blend and slams it onto the part; the SiO2 acts as a flux in the plume, wets the Cr2O3 splats, and the TiO2 fills intersplat voids. Result: 1000-1200 HV, 1-4% porosity, 5,500-7,000 psi bond over a NiCrAl tie layer, and a surface that laps to 2-4 µinch Ra — sub-micron — for hydrodynamic seal-face duty.

The minor silica and titania buy you what pure Cr2O3 cannot: tolerance to mechanical shock and thermal cycling without chipping. That is why this blend owns pump plungers, compressor rods, textile thread guides, and fourdrinier components — anywhere a pure chrome oxide coating would crack when the part sees startup transients or abrasive upset.

Pick it over straight Cr2O3 when the duty mixes abrasion with shock or thermal cycling, or when the finish spec demands sub-micron Ra. Stay with 99% Cr2O3 when the duty is pure low-impact abrasion and every point of hardness counts.

Got a seal face that keeps failing or a plunger chewing through chrome plate? Send us the drawing — we'll quote the right Cr2O3-SiO2-TiO2 blend and finish spec.

Technical data

Hardness
1000-1200 HV300 typical APS (macrohardness ~Rc65); sits between straight Cr2O3 (1100-1300 HV) and the tougher 45% TiO2 blend (900-1100 HV)
Bond strength
4,000-6,000 psi on low-carbon steel without a bond coat; 5,500-7,000 psi with a NiCrAl or Ni/Al tie layer (28-48 MPa) — ceramic-limited, not binder-limited
Max service temp
~1000°F sustained (abrasive wear); 350-400°F sealed for wet/corrosive service; TiO2 phase transformation above ~1000°F caps the ceiling
Max service temp
~540°C sustained; 175-205°C sealed wet-corrosive
As-sprayed porosity
1-4% APS — the SiO2 acts as a flux in the plume, wets the Cr2O3 splats, and closes intersplat voids tighter than pure Cr2O3
Typical thickness
4-12 mils (100-300 µm) on seal faces and plungers; 6-25 mils (150-625 µm) on rolls, dryer cans, and larger cylindrical parts
Surface finish (Ra)
200-400 as-sprayed; 8-20 diamond-ground; 2-4 diamond-lapped for mechanical-seal faces — sub-micron Ra is routinely achievable

Where it earns its keep

  • Seal-face ceramic of choice — laps to 2-4 µinch Ra (sub-micron), holds dimension, runs quietly against carbon or sintered-SiC mating rings, and outlasts straight Cr2O3 on rotating-seal duty
  • Tougher than 99% Cr2O3 — the minor SiO2 addition fluxes the plume, improves interparticle bonding, and the TiO2 fills splat voids so the coating tolerates mechanical shock and thermal cycling without chipping
  • Denser than pure chrome oxide — 1-4% porosity vs. 2-6% for straight Cr2O3; less leak path for corrosive process fluids, better hydraulic integrity on seal faces and plungers
  • Retains most of pure Cr2O3's hardness (1000-1200 HV) and chemical inertness — handles acids, alkalis, and process liquors below ~400°F when phosphate-sealed
  • Bond strength comparable to the best APS ceramics — 5,500-7,000 psi with a NiCrAl tie layer, good enough for high-PV mechanical-seal service

Where it doesn't

  • More expensive than straight Cr2O3 — blended, pre-fused-and-crushed powders (Metco 136F, AMPERIT 716) carry a premium over single-oxide chrome
  • Slightly lower hardness than 99% Cr2O3 (1000-1200 HV vs. 1100-1300 HV) — when duty is pure three-body abrasion with no impact or thermal shock, straight chrome still wins on wear life
  • Still requires diamond grinding and lapping — you do not finish this in the grinding room with conventional wheels; plan for diamond tooling and superfinishing time in the quote
  • Service temperature capped near 1000°F — TiO2 phase transformation embrittles the coating above that; step up to Cr3C2-NiCr for hotter abrasion duty
  • Ceramic, not metallic — do not specify for heavy impact, shock loading, or flexing substrates; for those, Stellite 6 or WC-Co hardfacers are the right call

Typical applications

  • Mechanical-seal faces and seal rings — the premier oxide for rotating seal duty
  • Pump plungers and reciprocating compressor rods in abrasive service
  • Centrifugal pump impellers, casings, and wear rings
  • Textile thread guides, godet rolls, heater plates, creel bars
  • Printing rolls — impression, anilox, and laser-engravable cell surfaces
  • Paper-mill fourdrinier components, breast rolls, and doctor-blade wear surfaces
  • Yankee and can dryer shells (wear + mild corrosion)
  • Plug-valve and choke-valve trim in mildly abrasive wet service

Wear modes addressed

  • Adhesive sliding wear against mechanical-seal faces (primary)
  • Low-stress abrasion from fibers, paper, and slurries
  • Particle erosion and cavitation in pump internals
  • Chemical/corrosive wear in wet process service (when sealed)
  • Thermal cycling and mild mechanical shock (SiO2 + TiO2 advantage over pure Cr2O3)

Industries

  • Pump and mechanical-seal OEM/MRO
  • Pulp and paper
  • Textile and synthetic-fiber manufacturing
  • Printing and packaging (flexo, gravure, label)
  • Chemical and petrochemical process
  • Oil & gas (reciprocating compressor rods, plunger pumps)
  • Water and wastewater

Substrates

  • Carbon and low-alloy steels (1018, 4140, 4340) with a bond coat
  • Stainless steels (304, 316, 410, 17-4 PH)
  • Gray and ductile cast iron (pump casings, dryer cans)
  • Aluminum bronzes (pump internals, with bond coat)
  • Ni-base alloys for corrosion-critical seal faces

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.

  • Oerlikon Metco — Metco 136F Product Listing (myMetco)

    “Metco 136F: chromium oxide-silica thermal spray powder, fused-and-crushed, atmospheric plasma spray process. Blended Cr2O3/SiO2/TiO2 oxide ceramic for wear and corrosion-resistant coatings.”

  • A&A Coatings — Plasma Chromium Oxide-Silica

    “Chromium Oxide Balance, Silicon Dioxide 5%, Titanium Dioxide 3%; macrohardness Rc65, cross-sectional DPH300 900; bond strength 4,000 psi without bond coat; service below 540°C (1000°F) abrasive, 175-205°C sealed corrosive; lap finish 2-4 microinches AA; applications include pump impellers, reciprocating pump and compressor rods, centrifugal pump seals, mechanical seal applications, and textile machinery components contacting fibers. Silica addition provides impact absorption, prevents grain loosening, and adds impact resistance atypical of ceramic coatings.”

  • H.C. Starck / Höganäs — AMPERIT 716.066 Cr2O3-TiO2-SiO2 (92-3-5) Datasheet

    “Chemistry: Cr2O3 91.3-95%, TiO2 2.0-3.5%, SiO2 3.0-5.0%, Fe2O3 ≤0.20%. Blended fused-and-crushed APS powder; direct analog to Metco 136F for mechanical-seal and pump-component service.”

  • Gordon England Thermal Spray Forum — Metco 136F Coatings Discussion

    “The silica content in 136F helps toughen and seems to make coatings more wear resistant compared to pure chromium oxide coatings; the silica may function as a flux, improving wetting and lowering melting point. Plasma-sprayed 136F shows slightly better density, hardness, bond strength, finishing capability, and wear resistance than flame-sprayed variants.”

  • Stanford Advanced Materials — Chromium Oxide 93% / 4% SiO2 / 3% TiO2 Thermal Spray Powder

    “Cr2O3-SiO2-TiO2 blended thermal-spray powder (fused-and-crushed or mechanically clad); produces coatings with high toughness, extreme wear resistance, and high impact resistance; service temperature to 540°C (1000°F); applications include pump impellers, mechanical seal applications, and textile manufacturing.”

  • Höganäs AMPERIT Oxide APS Powder Range

    “AMPERIT oxide range includes blended Cr2O3-TiO2-SiO2 grades engineered for atmospheric plasma spray; applications span mechanical-seal faces, textile and paper-industry wear components, and pump internals.”

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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