Tool coatings can extend cutting edge life by 3–10× compared to uncoated tools and enable higher cutting speeds. In deep hole drilling — where heat generation and chip friction are extreme — coating selection directly determines whether a tool lasts 50 holes or 5 holes.
This guide compares the five main PVD coatings used in deep hole drilling, with material-specific recommendations.
1. Coating Properties Overview
| Coating | Hardness (HV) | Max Temp (°C) | Friction vs Steel | Typical Life vs Uncoated |
|---|---|---|---|---|
| TiN | 2,300–2,500 | 600 | 0.4–0.55 | 2–5× |
| TiCN | 3,000–3,500 | 450 | 0.2–0.4 | 4–5× |
| TiAlN | 3,300–3,500 | 900 | 0.3–0.6 | 4–8× |
| AlTiN | 3,600–3,800 | 900 | 0.6–0.7 | Up to 10× |
| AlCrN | 3,200–3,600 | 1,100 | 0.35–0.5 | Up to 10× |
Sources: AIMS Industrial coating guide; RUKO TiN/TiAlN/AlTiN comparison; Oerlikon Balzers; Seco Tools.
2. Coating Selection by Material
| Workpiece Material | Recommended Coating | Why |
|---|---|---|
| Mild / low-carbon steel | TiN or TiAlN | TiN cost-effective at low speed; TiAlN for production |
| Medium-carbon steel (1045) | TiAlN | Higher temperature tolerance at production speeds |
| Alloy steel (4140, 4340) | TiAlN | Best balance of heat resistance and toughness |
| Stainless 304/316 | TiAlN (essential) | Work-hardening requires thermal stability |
| Hardened steel > 45 HRC | AlCrN or AlTiN | TiN/TiAlN cannot survive the heat |
| Cast iron | TiCN or TiAlN | TiCN’s hardness resists abrasive carbides |
| Aluminum | AlCrN or uncoated polished | ⚠️ NEVER use TiAlN on Al (chemical reaction → BUE) |
| Titanium (Ti-6Al-4V) | TiAlN or AlCrN | Low thermal conductivity needs high-temp coating |
| Inconel / superalloys | AlCrN | Highest thermal stability required |
| Copper / brass | Uncoated polished | Coatings generally unnecessary |
Sources: AIMS Industrial; Travers Tool coating chart; GARR Tool; AC Coating.
3. Application by Drilling Method
| Method | Typical Speed Range | Recommended Coating | Reason |
|---|---|---|---|
| Gun drilling (small dia) | 10–80 m/min | TiAlN or AlTiN | Heat concentration at small diameters |
| Gun drilling (large dia) | 30–90 m/min | TiAlN | Balance of cost and performance |
| BTA drilling (steel) | 60–100 m/min | TiAlN | Standard production coating |
| BTA drilling (stainless) | 40–80 m/min | TiAlN (essential) | Work-hardening protection |
| BTA drilling (Inconel) | 15–25 m/min | AlCrN | Extreme heat requirement |
4. Critical Compatibility Note: Aluminum
TiAlN must never be used for aluminum deep hole drilling. The titanium in the coating chemically reacts with aluminum at cutting temperatures, forming built-up edge (BUE) and rapidly destroying the cutting edge. For aluminum:
| Coating | Compatibility | Notes |
|---|---|---|
| TiN | ✅ | Works but not optimal |
| TiCN | ❌ | Reacts with aluminum |
| TiAlN | ❌❌ | Causes BUE |
| AlCrN | ✅✅ Best | No chemical reaction |
| Uncoated polished | ✅ | Cost-effective for low volume |
5. Coating Selection Decision Matrix
| Condition | Recommended Coating |
|---|---|
| General steel drilling (production) | TiAlN |
| Hardened steel > 45 HRC | AlCrN or AlTiN |
| Stainless steel | TiAlN |
| Cast iron (abrasive) | TiCN or TiAlN |
| Aluminum | AlCrN (or uncoated polished) |
| Titanium | TiAlN or AlCrN |
| Inconel / superalloys | AlCrN |
| Maximum heat resistance | AlCrN (1,100°C) |
| Maximum wear resistance | AlTiN (3,800 HV) |
| Lowest friction | TiCN (0.2 μ) |
| Budget priority, soft materials | TiN |
Key Sources
- AIMS Industrial, “Cutting Tool Coatings — TiN, TiAlN, AlCrN, TiCN” — comprehensive comparison
- RUKO, “TiN, TiAlN, AlTiN: A Comparison of the Coatings” — temperature and hardness data
- Travers Tool, “Choose the Right Drill Coating” — material compatibility chart
- GARR Tool, “What Tool Coatings Do You Offer?” — application guidance
- Seco Tools, “What Do Coatings Do?” — coating function principles
- Oerlikon Balzers, coating portfolio — technical specifications
- AC Coating, PVD coating overview — process details