HTS Coatings — machining & grinding

Aluminum Oxide

99.5% Al₂O₃

  • Plasma

Aluminum oxide — white alumina — is the ceramic every thermal-spray shop starts with, and the one most jobs end with. At 99.5% purity, plasma-sprayed to a few thousandths thick, it gives you three things at once: a hard wear surface, an electrical insulator, and a chemically inert face that shrugs off alkalis, most detergents, and food-contact exposure.

We apply it by atmospheric plasma spray — a torch running at roughly 15,000°F shoots fused-and-crushed alumina powder (think Metco 105SFP, AMPERIT 740, or Saint-Gobain equivalents) at your part. The result is a coating around 820 to 1150 on the Vickers hardness scale, roughly Rc60-65, with 300 to 500 volts per mil of dielectric strength. Typical thickness is 5 to 20 mils. Past 20 we start to fight residual stress, so if you need more we build it in layers.

This is the coating for printing and corona rolls, textile guides, pump seal faces, vacuum-chamber liners, electrostatic chucks, and non-conductive rollers. The high-purity grades qualify for food-contact and medical tooling.

Honest caveats: alumina is brittle. It chips under impact. It has open porosity as-sprayed — in wet or corrosive service we seal it with phosphate, epoxy, or silicone. And it doesn't like thermal shock. If those matter, we'll say so up front and route you to the right chemistry.

Send us the part and the duty cycle. We'll tell you if alumina is the answer.

Technical data

Hardness
820-1150 HV0.3 typical APS; 850-1000 DPH300 for 99.5% premium grade; Rockwell equivalent Rc60-Rc65
Bond strength
2,000-5,000 psi (14-35 MPa) typical APS; up to ~7,400 psi (51 MPa) with suspension plasma
Max service temp
3000°F (material stability to 3000°F; most industrial service limited to ~1000°F for dimensional and wear stability)
Max service temp
1650°C material; ~540°C typical wear-service ceiling
As-sprayed porosity
1-10% typical APS; 1-4% with optimized parameters; near-zero in premium fine-powder grades
Typical thickness
5-20 mils (0.125-0.5 mm); >20 mils risks cracking and delamination

Where it earns its keep

  • Among the hardest thermal-spray ceramics at 820-1150 HV0.3 — superb abrasion, sliding, and erosion resistance for roll and seal duty
  • Excellent electrical insulator: 300-500 V/mil dielectric strength makes alumina the default for non-conductive rolls, insulators, and electrostatic chucks
  • Chemically inert and stable to 3000°F material limit; tolerates alkali, ammonia, and many oxidizing environments that attack metals
  • High-purity (99.5%) grades are FDA-compatible and biomedically qualified, so the same chemistry works for printing rolls, food-contact surfaces, and medical tooling
  • Economical ceramic feedstock with a mature APS process — wide gun compatibility (F4MB, 9MB, SinplexPro, TriplexPro) and global powder availability (Metco 105SFP, AMPERIT 740, Saint-Gobain alumina)

Where it doesn't

  • Brittle — chips and spalls under impact or shock loading; not the right pick where parts are struck, dropped, or thermally cycled hard
  • Low thermal conductivity vs metals means thermal-gradient cracking if the coating sees rapid localized heating or quenching
  • As-sprayed coatings carry 1-10% open porosity; severe corrosion or wet-chemistry service almost always requires a sealer (epoxy, silicone, or phenolic) to block liquid ingress
  • Maximum practical thickness ~20 mils — beyond that residual stress drives cracking and delamination; build multi-layer or redesign the part if more stock is needed

Typical applications

  • Printing and corona rolls (non-conductive, wear-resistant sleeve)
  • Textile guides, thread guides, and fiber-handling rolls
  • Paper-mill press and guide rolls, knife edges
  • Pump mechanical seal faces and wear pads
  • Electrical insulators, electrostatic chucks, vacuum-chamber liners, semiconductor handling surfaces
  • Medical and biomedical components (hip, knee, dental tooling with qualified high-purity grades)
  • Rocket-nozzle liners, furnace linings, induction-coil coatings, food-contact wear surfaces

Wear modes addressed

  • Two-body and three-body abrasion by hard grains and fibers
  • Sliding wear against hard counterfaces
  • Particle erosion at low impingement angles
  • Dielectric breakdown (electrical insulation failure)
  • Cavitation in fluid-handling components

Industries

  • Printing and packaging (corona, anilox, impression rolls)
  • Pulp, paper, and textile manufacturing
  • Semiconductor and electronics (chucks, liners, carriers)
  • Medical and biomedical device OEMs
  • Food and beverage processing (FDA-compatible high-purity grades)
  • Aerospace and defense (rocket nozzles, furnace tooling)
  • Chemical processing and pump manufacturing

Substrates

  • Low-alloy and carbon steels (with NiAl or NiCr bond coat)
  • Stainless steels (304, 316, 410, 17-4 PH)
  • Aluminum alloys (with bond coat)
  • Titanium alloys (Ti-6Al-4V for medical and aerospace)
  • Copper, brass, and bronze (specialty applications)
  • Nickel-base alloys and select superalloys

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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