Walk into any industrial supply catalog and you'll see the same three coating abbreviations on HSS drill listings: TiN, TiAlN, and TiCN. Each one comes with a price premium over uncoated. The question is whether that premium is worth it for your work — and if so, which coating you actually need. The answer depends on material, speed, and how much heat you're generating.
What Coatings Actually Do
A drill coating serves three functions: it adds surface hardness, reduces friction at the cutting interface, and provides some degree of thermal barrier between the workpiece heat and the HSS substrate. None of these coatings make a dull drill sharp again. They extend the point where sharpness becomes critical — and they do it in different ways that favor different materials and cutting conditions.
Thickness of these coatings is measured in microns (typically 1–4 µm). That's thin enough that a correctly-resharpened coated drill retains coating on the flanks and body while the freshly-ground cutting edge is bare HSS. That's normal and acceptable — the main wear protection for the cutting edge comes from substrate hardness and geometry, while the coating protects the margins and lands from abrasion during the hole pass.
TiN — Titanium Nitride
TiN is the original performance coating and still the most widely recognized. That distinctive gold color means TiN. It delivers a surface hardness of around HV 2300 compared to the ~HV 900 of bare HSS, and it reduces the friction coefficient significantly over uncoated steel.
Where TiN Works Best
- General-purpose drilling in mild and medium carbon steels
- Aluminum and non-ferrous metals where built-up edge (BUE) is a concern
- Lower-speed, lower-temperature applications
- Shops that resharpen frequently — TiN is more forgiving of the marginal geometry that sometimes comes from resharpen cycles
TiN starts to oxidize around 600°C. Above that, the coating degrades rapidly. For high-speed or dry drilling in harder steels, TiN isn't the right choice.
TiAlN — Titanium Aluminum Nitride
TiAlN is the step-up coating for higher-temperature environments. It doesn't necessarily start out harder than TiN (also around HV 2300–2800 depending on Al content), but its defining property is thermal stability. TiAlN forms an aluminum oxide layer at the cutting surface under heat — this layer is thermally insulating and actually increases in hardness with temperature rather than softening. The useful operating temperature range extends to roughly 800–900°C.
Where TiAlN Works Best
- Stainless steel, hardened steel, and difficult alloys
- Higher-speed drilling where heat buildup is unavoidable
- Dry or minimal-coolant applications
- Any situation where the drill runs hot by design
Important: TiAlN performs poorly in aluminum. The aluminum oxide reaction that makes it heat-resistant becomes a liability when cutting aluminum — it can promote chip welding. Use TiN or uncoated for aluminum.
TiCN — Titanium Carbon Nitride
TiCN adds carbon to the titanium nitride structure. The result is the hardest of the three coatings — typically HV 3000 or above — and a lower friction coefficient than TiN. It's recognized by its gray-violet or gray appearance rather than gold.
Where TiCN Works Best
- Abrasive materials where coating hardness (not heat resistance) is the priority
- Cast iron, graphite-filled materials, and fiber-reinforced plastics
- Medium-temperature applications — TiCN doesn't handle extreme heat as well as TiAlN
- Materials that cause rapid flank wear through abrasion rather than thermal degradation
Side-by-Side Comparison
| Property | TiN | TiAlN | TiCN |
|---|---|---|---|
| Color | Gold | Violet/Black | Gray-Violet |
| Hardness (HV) | ~2300 | ~2800 | ~3000+ |
| Max temp (°C) | ~600 | ~900 | ~400–450 |
| Friction coeff. | 0.4 | 0.45 | 0.2–0.3 |
| Best for | General steel, aluminum | Stainless, hardened, dry cutting | Abrasive, cast iron, composites |
| Avoid in | High-temp dry cutting | Aluminum, copper | High-heat applications |
The Resharpening Question
Coated drills can and should be resharpened. The cutting edges are the critical wear zones, and resharping them to correct geometry restores cutting performance even after the coating at the edge is removed. The coating on the flanks, margins, and body continues to provide friction reduction and wear protection throughout the hole pass.
Some shops hesitate to resharpen coated drills thinking they'll "ruin" the coating. This is a false economy. A correctly-resharpened coated drill outperforms an unsharpened, full-coating coated drill with worn edges. Geometry drives performance far more than surface chemistry at the cutting edge itself.
Resharpen Your Coated Drills
MachinistPost resharpens HSS drills — coated or uncoated — with correct geometry by mail. Don't throw out drills with worn edges and good bodies.
Start Your Order