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CVD Alumina

CVD coatings · Chemical bath

CVD alumina is an electrically insulating ceramic layer used as a thermal and oxidation barrier on carbide cutting inserts.

CNC machiningHigh cost $$$$Insulating
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CVD Alumina on a machined part

What is CVD alumina?

It is commonly 5–20 µm within multilayer systems deposited around 900–1050 °C.

How it works

Aluminum-bearing and oxidizing gases react at high temperature to grow dense aluminum oxide on a compatible underlayer, commonly TiCN on cemented carbide. Alumina has low thermal conductivity and chemical stability at cutting temperatures. Conventional CVD temperature excludes aluminum, polymers, and most finished steels.

Why specify it

  • Strong hot chemical stability
  • Thermal barrier for carbide inserts
  • About 1800–2200 HV hardness
  • 5–20 µm conformal layer

Where it falls short

  • Brittle in interrupted cutting
  • Electrically insulating
  • 900–1050 °C process
  • Requires compatible nucleation layer

CVD alumina at a glance

CVD alumina is strongest on corrosion protection (70 of 100) and surface hardness (85 of 100), at a high cost.

Corrosion protectionVery good70 / 100
Surface hardnessExcellent85 / 100
Cosmetic qualityFair35 / 100
LubricityFair35 / 100
Relative costHigh95 / 100
CorrosionHardnessCosmeticLubricityEconomy

Each score is 0–100 against every finish in this catalog. Corrosion comes from salt-spray life (ASTM B117, log scale) and hardness from the finish layer's Vickers or pencil hardness; cosmetic, lubricity and cost are FabDigit's engineering assessment. Economy on the radar is the inverse of cost.

CVD alumina key numbers

Typical values from the governing specifications and shop practice; bars are this finish against the highest value among cvd coatings finishes.

Thickness5–20 µm0.2–0.79 mil
Hardness1,800–2,200 HV
Max service temp.1,000 °C1,832 °F
Thickness
5–12 µm within an insert stack
Hardness
1,800–2,200 HV — Typical CVD alumina indentation range.
Electrical
Insulating
Colours
  • black
  • dark grey
Appearance
Dark grey to black in cutting-tool grades, often with a coloured top identification layer.

Where CVD alumina sits among all finishes

Surface hardness (Vickers, log scale) against corrosion protection (salt-spray hours, log scale) for every coating FabDigit offers, one cloud per finish group. CVD alumina is highlighted; hover a dot for its name or open the full map.

02550751000255075100Corrosion protection (0–100)Surface hardness (HV, log scale, 0–100)Plating — 19 finishesHard coatings — 17 finishesAnodize & conversion — 8 finishesPaint & powder — 7 finisheshard, low corrosion protectionhard and protectiveprotective, softsoft, little protectionType II anodize — corrosion 71, hardness 54BSA anodize — corrosion 71, hardness 52Type I anodize — corrosion 71, hardness 49Hard anodize — corrosion 71, hardness 61PTFE hard anodize — corrosion 71, hardness 61Nitriding — corrosion 55, hardness 73PEO — corrosion 70, hardness 74Sherardizing — corrosion 83, hardness 56Brass plate — corrosion 35, hardness 44Bronze plate — corrosion 40, hardness 49Cadmium plate — corrosion 70, hardness 26Copper plate — corrosion 32, hardness 39Decorative chrome — corrosion 64, hardness 71Electroless copper — corrosion 20, hardness 41Electroless nickel — corrosion 70, hardness 68Nickel plate — corrosion 51, hardness 55Gold plate — corrosion 68, hardness 39Hard chrome — corrosion 40, hardness 73Hot-dip zinc — corrosion 90, hardness 42Nickel-PTFE — corrosion 72, hardness 57Silver plate — corrosion 55, hardness 39Solder plate — corrosion 42, hardness 9Tin plate — corrosion 34, hardness 0Zinc plate — corrosion 60, hardness 30Zinc-nickel — corrosion 86, hardness 60Cerakote — corrosion 83, hardness 27E-coat — corrosion 83, hardness 15Epoxy coat — corrosion 83, hardness 15Powder coat — corrosion 83, hardness 14Wet paint — corrosion 59, hardness 10AlCrN PVD — corrosion 58, hardness 93AlTiN PVD — corrosion 52, hardness 94CrN PVD — corrosion 62, hardness 83DLC — corrosion 55, hardness 93MoS2 PVD — corrosion 20, hardness 26TiAlN PVD — corrosion 50, hardness 93TiCN PVD — corrosion 40, hardness 92TiB2 PVD — corrosion 40, hardness 94TiN PVD — corrosion 45, hardness 87WC/C PVD — corrosion 48, hardness 77ZrN PVD — corrosion 52, hardness 90CVD TiCN — corrosion 38, hardness 92CVD TiN — corrosion 45, hardness 87Multilayer CVD — corrosion 62, hardness 88HVOF coating — corrosion 78, hardness 77Plasma spray — corrosion 60, hardness 68Plastic chrome — corrosion 72, hardness 71Electroless plastic — corrosion 58, hardness 39Clear coat — corrosion 20, hardness 12Soft-touch — corrosion 20, hardness 5PLATINGHARD COATINGSANODIZE & CONVERSIONPAINT & POWDERMultilayer CVDAlCrN PVDType II anodizePowder coatZinc plateZinc-nickelHard chromeTiN PVDTin plateCadmium plateE-coatCerakoteWet paintHot-dip zincNitridingHVOF coatingCVD alumina — corrosion 70, hardness 85CVD alumina
02550751000255075100Corrosion protection (0–100)Surface hardness (HV, log scale, 0–100)Plating — 19 finishesHard coatings — 17 finishesAnodize & conversion — 8 finishesPaint & powder — 7 finishesType II anodize — corrosion 71, hardness 54BSA anodize — corrosion 71, hardness 52Type I anodize — corrosion 71, hardness 49Hard anodize — corrosion 71, hardness 61PTFE hard anodize — corrosion 71, hardness 61Nitriding — corrosion 55, hardness 73PEO — corrosion 70, hardness 74Sherardizing — corrosion 83, hardness 56Brass plate — corrosion 35, hardness 44Bronze plate — corrosion 40, hardness 49Cadmium plate — corrosion 70, hardness 26Copper plate — corrosion 32, hardness 39Decorative chrome — corrosion 64, hardness 71Electroless copper — corrosion 20, hardness 41Electroless nickel — corrosion 70, hardness 68Nickel plate — corrosion 51, hardness 55Gold plate — corrosion 68, hardness 39Hard chrome — corrosion 40, hardness 73Hot-dip zinc — corrosion 90, hardness 42Nickel-PTFE — corrosion 72, hardness 57Silver plate — corrosion 55, hardness 39Solder plate — corrosion 42, hardness 9Tin plate — corrosion 34, hardness 0Zinc plate — corrosion 60, hardness 30Zinc-nickel — corrosion 86, hardness 60Cerakote — corrosion 83, hardness 27E-coat — corrosion 83, hardness 15Epoxy coat — corrosion 83, hardness 15Powder coat — corrosion 83, hardness 14Wet paint — corrosion 59, hardness 10AlCrN PVD — corrosion 58, hardness 93AlTiN PVD — corrosion 52, hardness 94CrN PVD — corrosion 62, hardness 83DLC — corrosion 55, hardness 93MoS2 PVD — corrosion 20, hardness 26TiAlN PVD — corrosion 50, hardness 93TiCN PVD — corrosion 40, hardness 92TiB2 PVD — corrosion 40, hardness 94TiN PVD — corrosion 45, hardness 87WC/C PVD — corrosion 48, hardness 77ZrN PVD — corrosion 52, hardness 90CVD TiCN — corrosion 38, hardness 92CVD TiN — corrosion 45, hardness 87Multilayer CVD — corrosion 62, hardness 88HVOF coating — corrosion 78, hardness 77Plasma spray — corrosion 60, hardness 68Plastic chrome — corrosion 72, hardness 71Electroless plastic — corrosion 58, hardness 39Clear coat — corrosion 20, hardness 12Soft-touch — corrosion 20, hardness 5PLATINGHARD COATINGSANODIZE & CONVERSIONPAINT & POWDERAlCrN PVDPowder coatZinc plateCVD alumina — corrosion 70, hardness 85CVD alumina
Anodize & conversionPlatingPaint & powderHard coatings

Specifications for CVD alumina

The documents a drawing cites to define this finish, with the Type / Class rows that apply. Each links to a page explaining the standard.

Drawing call-out

CVD COAT CARBIDE INSERT Al2O3 OVER TiCN BOND LAYER, Al2O3 5–10 µm THICK, TOTAL COATING 10–18 µm; PROCESS 900–1050 °C

Which materials take CVD alumina?

Verdict per material family, with the grades that behave differently. Each family links to its datasheets in the material library.

Material familyVerdictNotes
Tungsten Alloy
YesCemented carbide with a compatible underlayer is standard.
Aluminum
NoProcess temperature is incompatible.
Brass
NoProcess temperature is far above the melting and softening range of brass.
Copper Alloy
NoProcess temperature anneals or melts copper alloys.
Magnesium Alloy
NoProcess temperature is incompatible with magnesium alloys.
Polymer
NoProcess temperature is incompatible.
Stainless Steel
NoThe 900–1050 °C cycle destroys typical stainless tempers and corrosion performance.
Steel
NoAlumina CVD is specified on carbide inserts, not finished steels.
Titanium
NoCVD temperature produces severe alpha case and property loss.
Zinc Alloy
NoProcess temperature is incompatible with zinc alloys.

How CVD alumina is applied, and what it does to the part

  1. 1Prepare carbide and underlayer
  2. 2Heat reactor
  3. 3Nucleate alumina
  4. 4Grow Al2O3 layer
  5. 5Cool and edge-treat
DimensionsInclude 5–20 µm alumina plus all underlayers in edge and chipbreaker geometry.
Build-up per side5–20 µm — Allow full layer thickness on exposed sides; total stack may be thicker.
MaskingUsually needed. Fixture or mask surfaces that cannot accept an insulating ceramic layer.
ElectricalInsulating
Temperature limit1,000 °C (1,832 °F) continuous
AppearanceDark grey to black in cutting-tool grades, often with a coloured top identification layer.
Added lead time7–14 working days on top of the bare part

Design rules for CVD alumina

What to decide on the drawing before the part goes to the finisher.

  1. Use cemented carbide support.The substrate must tolerate high temperature and support brittle alumina.
  2. Avoid fragile sharp edges.Thick alumina can chip in interrupted cuts.
  3. Specify the complete layer stack.Alumina normally depends on an underlayer.
  4. Account for electrical insulation.The surface no longer conducts reliably.

CVD alumina versus the alternatives

Finishes engineers weigh against CVD alumina, and when each wins.

FinishCorrosionHardnessCosmeticCostThicknessChoose it when
CVD alumina
this page
708535$$$$5–20 µm—
Multilayer CVD Tool Coating
CVD alumina vs Multilayer CVD Tool Coating →
628845$$$$5–20 µma complete TiCN/Al2O3/TiN system is required
Aluminum Chromium Nitride PVD
CVD alumina vs Aluminum Chromium Nitride PVD →
589352$$$$1–5 µmlower process temperature and sharper edges are required
CorrosionHardnessCosmeticLubricityEconomy
CVD aluminaMultilayer CVD Tool Coating

The radar overlays CVD alumina with Multilayer CVD Tool Coating, its most common alternative — chosen a complete TiCN/Al2O3/TiN system is required. Scores in the table are 0–100 across every finish in the catalog.

Cost, lead time and compliance

Relative cost

CVD Alumina is a high-cost finish ($$$$): more expensive than about 97 % of the finishes FabDigit quotes.

Finishing is priced per part with a lot minimum, from FabDigit's own China-side rates. The exact figure appears on the instant quote once the part is uploaded.

Lead time and compliance

Added lead time7–14 working days
RoHSCompliant
NotesAlumina is generally RoHS-compliant; CVD gases require controlled exhaust treatment.

What CVD alumina is used for

  • Steel-turning inserts
  • Cast-iron inserts
  • High-speed finishing inserts
  • Thermal-barrier tool layers

CVD alumina — frequently asked

Why is alumina used on carbide inserts?

Alumina is chemically stable and thermally insulating at hot cutting edges. A 5–12 µm layer reduces heat flow into the carbide.

How thick is CVD alumina?

Catalog systems commonly use 5–20 µm, with about 5–12 µm typical inside a multilayer stack. Total stack thickness includes TiCN and any top layer.

Is CVD alumina electrically conductive?

No; aluminum oxide is electrically insulating. Do not rely on coated surfaces for grounding.

PVD vs CVD alumina: why use CVD?

Conventional CVD gives conformal, dense layers at about 900–1050 °C. The tradeoff is a thicker film and a substrate restricted mainly to carbide.

Can alumina CVD coat aluminum?

No for conventional tool CVD because 900–1050 °C is far above aluminum's safe processing range. Lower-temperature specialty processes are separate technologies.