Carbide Insert Coatings Explained: TiN, TiCN, TiAlN, AlCrN

April 22, 2026

Carbide Coatings Explained: TiN, TiCN, TiAlN, AlCrN

Walk into any tool shop and you'll see inserts and drills in a rainbow — gold, violet, grey, bronze, black. Those colours aren't cosmetic. They tell you the coating, and the coating tells you what the tool is optimised for. This post maps coating colour to chemistry to application.

TiN (Titanium Nitride) — the gold one

Visible signature: bright yellow-gold. The original industrial carbide coating. Hardness ~2,300 HV, oxidation at ~600°C. Improves wear resistance over uncoated carbide by 2-3×. Workhorse for general-purpose turning and drilling.

Best for: general steel, non-ferrous, mild cutting conditions, HSS tool upgrades.
Avoid for: high-temperature work, stainless at elevated speeds, hardened materials.

TiCN (Titanium Carbonitride) — the violet-grey one

Violet-grey appearance. Harder than TiN (~3,000 HV), better wear resistance but lower oxidation limit (~400°C). Often applied as a multi-layer stack with TiN on top.

Best for: cast iron, high-speed steel workpieces, abrasive materials, continuous cutting.
Avoid for: stainless (heat issues), hardened steel.

TiAlN (Titanium Aluminium Nitride) — the black one

Dark grey to black. Hardness ~3,200 HV. Critical difference: oxidation limit ~800°C — nearly double TiN. When TiAlN heats up, it forms an Al₂O₃ (aluminium oxide) film on the surface that acts as a second protective layer. This makes it the dominant coating for high-speed CNC work.

Best for: steel at high cutting speeds, stainless steel, hardened steel up to HRC 55, dry/near-dry machining, CNC production.
Avoid for: low-carbon aluminium (chemical affinity — chip buildup), very low-speed manual work.

AlTiN / nACo (Aluminium Titanium Nitride nano-composite) — darker black

Evolution of TiAlN with inverted Al/Ti ratio. Darker appearance. Oxidation limit ~900°C. Dominant for hardened steel work, turning above HRC 50, and high-feed milling.

Best for: hardened steel turning (HRC 50-65), stainless at high speeds, Inconel and exotic alloys.
Avoid for: aluminium, copper — same BUE (built-up edge) issues as TiAlN.

AlCrN (Aluminium Chromium Nitride) — dark violet/purple

Newer generation. Oxidation limit ~1,100°C — the highest in common industrial coatings. Lower hardness than AlTiN (~2,800 HV) but better toughness, better edge-chipping resistance, exceptional in interrupted cuts.

Best for: interrupted cutting, stainless steel, Inconel, difficult-to-machine alloys, milling applications with rough entry/exit.
Avoid for: pure continuous-cut finishing where AlTiN or TiAlN deliver better wear.

Diamond coatings (CVD and PCD)

For aluminium alloys with silicon content (A380, ADC12), MMC composites, graphite, carbon-fibre reinforced plastics. Diamond coatings (CVD) or polycrystalline diamond (PCD) tips deliver 10-50× the life of uncoated carbide in these materials.

Best for: Al-Si alloys, graphite electrodes (EDM manufacturing), CFRP, non-metallic composites.
Avoid for: ferrous materials — at high temperature, diamond decomposes against iron.

Uncoated carbide — still relevant

Bright silver appearance (no colour). Used for aluminium and non-ferrous where coatings interfere with chip flow. Also for low-speed manual turning on older machines where heat isn't an issue. Cheaper than coated equivalents.

Best for: aluminium (dedicated uncoated polished grades like Korloy H01, Mitsubishi TF15), copper, brass, plastics.
Avoid for: steel at CNC speeds, stainless, any elevated-temperature work.

Multi-layer coatings (CVD)

Many modern CVD coatings stack multiple layers — TiN + Al₂O₃ + TiCN is a common three-layer recipe. Each layer does a specific job: outer TiN for friction, Al₂O₃ for heat, TiCN for abrasion. You'll see these in premium Japanese and Korean grades (Mitsubishi UE6110, Korloy PC9030, Kyocera CA4120).

PVD vs CVD — how coatings are applied

PVD (Physical Vapour Deposition) — applied at ~500°C. Thinner coating (2-5 µm). Preserves substrate toughness. Dominant for sharp-edge finishing, stainless work, milling.
CVD (Chemical Vapour Deposition) — applied at ~1,000°C. Thicker coating (5-20 µm). Slight toughness reduction but more durable under heat. Dominant for roughing and continuous cutting.

Rule of thumb: PVD for finishing + interrupted cuts; CVD for roughing + continuous cutting. Modern grades mix both (CVD base + PVD top layer).

Quick reference — which coating for which job

Workpiece	Recommended coating
Mild steel (finishing)	TiN or TiAlN PVD
Carbon steel (roughing)	CVD multi-layer (Al₂O₃ + TiCN)
Stainless steel	TiAlN or AlCrN PVD
Cast iron	TiCN or uncoated
Hardened steel (HRC 45+)	AlTiN / nACo PVD
Aluminium (general)	Uncoated polished
Al-Si / MMC / CFRP	Diamond (CVD or PCD)
Inconel / titanium	AlCrN or AlTiN PVD