Coating Selection Guide: TiN, TiAlN, AlTiN, AlCrN — When to Use Each
The coating on a carbide insert is its first line of defense against heat, abrasion, and chemical wear. But with so many coating options — TiN, TiCN, TiAlN, AlTiN, AlCrN, Al₂O₃, and multilayer CVD combinations — choosing the right one can feel like a chemistry exam. This guide breaks down each coating type by its properties, strengths, and ideal applications, with specific Korloy grade recommendations.
PVD vs. CVD: The Fundamental Divide
Before choosing a specific coating chemistry, understand the two main deposition methods:
| Property | PVD (Physical Vapor Deposition) | CVD (Chemical Vapor Deposition) |
|---|---|---|
| Process Temperature | 200–500°C | 800–1050°C |
| Coating Thickness | 1–5 µm (thin) | 8–20 µm (thick) |
| Edge Sharpness | Very sharp (near-zero hone) | Rounded (requires edge prep) |
| Residual Stress | Compressive (improves toughness) | Tensile (requires post-treatment) |
| Best For | Stainless, super alloys, interrupted cuts, sharp edges | Steel, cast iron, stable continuous cuts, high speed |
| Coating Adhesion | Good (mechanical bond) | Excellent (diffusion bond) |
| Typical Korloy Series | PC215K, PC3545, NC3225, NCM325 | PC5300, PC5335, PC5400, KC5305, KC5335 |
Coating-by-Coating Breakdown
TiN — Titanium Nitride
| Property | Value |
|---|---|
| Color | Gold |
| Hardness (HV) | 2,000–2,400 |
| Max Operating Temperature | ~550°C |
| Friction Coefficient | 0.4–0.6 |
| Thickness | 2–4 µm (PVD) |
When to use: TiN is the general-purpose baseline coating. It works well on low-to-medium carbon steels, non-ferrous metals, and plastics at moderate cutting speeds. Its gold color makes wear easy to detect visually. However, TiN is now largely superseded by TiAlN for most production applications due to its relatively low oxidation temperature.
Best for: Aluminum, brass, plastics, low-speed steel machining, and reconditioned tools.
TiCN — Titanium Carbonitride
| Property | Value |
|---|---|
| Color | Violet / blue-gray |
| Hardness (HV) | 2,800–3,200 |
| Max Operating Temperature | ~400°C |
| Friction Coefficient | 0.3–0.5 |
| Thickness | 2–4 µm (PVD), used as base layer in CVD |
When to use: TiCN is harder and more wear-resistant than TiN but has a lower oxidation temperature. It excels in applications requiring a sharp edge: stainless steel finishing, aluminum, and low-speed milling. In CVD inserts, TiCN serves as the inner wear layer beneath Al₂O₃.
Best for: Stainless steel finishing (PVD TiCN), threading, grooving, and as a CVD base layer.
TiAlN — Titanium Aluminum Nitride
| Property | Value |
|---|---|
| Color | Purple / violet |
| Hardness (HV) | 2,800–3,300 |
| Max Operating Temperature | ~750°C |
| Friction Coefficient | 0.3–0.5 |
| Thickness | 2–4 µm (PVD) |
When to use: TiAlN forms a protective Al₂O₃ oxide layer at high temperatures, giving it far better heat resistance than TiN or TiCN. It is the workhorse PVD coating for general steel and stainless steel machining. Korloy PC215K uses a TiAlN PVD coating optimized for austenitic stainless steel turning.
Best for: Stainless steel, general steel milling and drilling, interrupted cuts. Korloy grade: PC215K.
AlTiN — Aluminum Titanium Nitride
| Property | Value |
|---|---|
| Color | Dark purple / black-violet |
| Hardness (HV) | 3,200–3,800 |
| Max Operating Temperature | ~900°C |
| Friction Coefficient | 0.25–0.45 |
| Thickness | 2–4 µm (PVD) |
When to use: AlTiN has a higher aluminum content than TiAlN (typically 65–70% Al vs. 50% in TiAlN), which pushes its oxidation resistance to 900°C. This makes it the premier PVD coating for hard machining, dry milling, and super alloys. Korloy PC3545 uses PVD AlTiN for hardened steel and HRSA turning.
Best for: Hardened steel (H10–H20), titanium alloys, Inconel, dry machining, high-speed milling. Korloy grade: PC3545, NC3225.
AlCrN — Aluminum Chromium Nitride
| Property | Value |
|---|---|
| Color | Silver / gray |
| Hardness (HV) | 3,000–3,500 |
| Max Operating Temperature | ~1,100°C |
| Friction Coefficient | 0.25–0.40 |
| Thickness | 2–5 µm (PVD) |
When to use: AlCrN offers the highest thermal stability of any standard PVD coating, with oxidation resistance up to 1,100°C. It also has excellent chemical inertness, making it ideal for abrasive and adhesive materials. AlCrN is increasingly used for high-speed dry milling and for machining difficult-to-machine materials like hardened steels and abrasive composites.
Best for: High-speed dry milling, hardened steel, abrasive castings, composites. Often found on premium end mills and drills.
Al₂O₃ — Aluminum Oxide (CVD Layer)
| Property | Value |
|---|---|
| Color | Black / dark gray (in multi-layer) |
| Hardness (HV) | 2,500–2,800 |
| Max Operating Temperature | >1,200°C |
| Role in CVD Stack | Thermal barrier (outer layer) |
| Thickness | 4–10 µm (CVD) |
When to use: Al₂O₃ is the critical thermal barrier in CVD multi-layer coatings. It insulates the carbide substrate from the extreme heat generated at high cutting speeds. Korloy CVD grades (PC5300, PC5335, PC5400, KC5305, KC5335) all feature Al₂O₃ as the outer layer in their coating stack.
Best for: High-speed continuous turning of steel and cast iron. Essential for any CVD-coated insert.
Complete Coating Comparison Matrix
| Coating | Type | Hardness (HV) | Max Temp (°C) | Best Material | Korloy Grade | Sandvik Eq. |
|---|---|---|---|---|---|---|
| TiN | PVD | 2,000–2,400 | 550 | Al, brass, plastics | NCM325 (TiB₂ variant) | H10F |
| TiCN | PVD/CVD base | 2,800–3,200 | 400 | Stainless finishing | PC215K (inner layer) | 2220 |
| TiAlN | PVD | 2,800–3,300 | 750 | Steel, stainless, general | PC215K | 2220 |
| AlTiN | PVD | 3,200–3,800 | 900 | Hard steel, titanium, Inconel | PC3545, NC3225 | 4435, 7015 |
| AlCrN | PVD | 3,000–3,500 | 1,100 | Hard steel, dry milling | Premium end mills | — |
| Al₂O₃ | CVD layer | 2,500–2,800 | >1,200 | Steel, cast iron (high speed) | PC5300, KC5305 | 4225, 3210 |
| TiCN+Al₂O₃ | CVD multi | 2,800+2,500 | >1,200 | Steel, stainless, iron | PC2507, KC5335 | 2325, 3225 |
Coating Selection by Application
| Application | Recommended Coating | Korloy Grade | Why |
|---|---|---|---|
| General steel turning (P20–P30) | CVD TiCN/Al₂O₃ | PC5335 | Al₂O₃ thermal barrier allows high Vc |
| Stainless steel turning (M10–M20) | PVD TiAlN | PC215K | Sharp edge prevents BUE, good heat resistance |
| Duplex stainless (M30–M40) | CVD TiCN/Al₂O₃ | PC2507 | Thick coating resists abrasion + chemical attack |
| Gray cast iron (K10–K20) | CVD Al₂O₃/TiCN | KC5305 | Al₂O₃ resists crater wear at high speeds |
| Titanium alloy turning | PVD AlTiN | PC3545 | Tough coating + sharp edge for low-speed cutting |
| Inconel / HRSA milling | PVD AlTiN | PC3545 | 900°C resistance + compressive stress improves life |
| Hard turning >55 HRC | PVD AlTiN or CBN | NC3225 | AlTiN withstands extreme temperatures |
| Aluminum high-speed machining | PVD TiB₂ or uncoated polished | NCM325 | Low friction, anti-adhesion, sharp edge |
| Dry milling hardened steel | PVD AlCrN | Premium end mills | 1,100°C thermal stability without coolant |
How to Identify a Coating Visually
- Gold: TiN — the classic coating, widely used on drills and general-purpose tools
- Violet/Purple: TiAlN or TiCN — common on PVD turning and milling inserts
- Dark purple/black-violet: AlTiN — premium PVD for hard machining
- Silver/gray: AlCrN — high-end PVD for dry machining
- Black/dark gray (multi-layer visible): CVD TiCN/Al₂O₃ — standard on steel/iron turning inserts
- Bright silver (uncoated): Polished carbide for aluminum and non-ferrous
Not sure which coating suits your application? The technical team at hooguu.com can analyze your machining conditions and recommend the optimal coating and Korloy grade. We stock PVD and CVD coated inserts across the full ISO range — contact us for a free consultation.
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