CVD vs PVD Coatings on Turning Inserts: How to Read the Grade and Pick Right
The coating string inside a grade description — CVD TiCN+Al2O3+TiN in Sandvik 4325, PVD TiAlN in ISCAR IC807 — is a process label, a layer stack and a use-case hint at once. This guide decodes both coating families, shows what the layer stacks in a real cross-brand database look like, and gives the decision order for picking between them.
Every grade record on InsertBase carries a descriptive string straight from the catalogue. Sandvik's grade 4325 reads 4325 / HC / CVD TiCN+Al2O3+TiN; ISCAR's IC807 reads PVD TiAlN tough general turning grade. Those strings pack three decisions into one line: the process (CVD or PVD), the layer stack (which compounds, in which order) and the substrate pairing (hard or tough). Read them and you can predict how a grade will behave before you ever see it cut.
The grade-selection guide covers the six ISO 513 workpiece groups and where grades sit in them. This guide zooms into the coating decision itself — the single most consequential choice inside a grade, because the coating takes most of the heat and wear while the substrate carries the load.
Two processes, two personalities
CVD (chemical vapour deposition) grows the coating from reactive gases at high temperature — around 1,000 °C on a typical carbide. The coating builds up slowly and thick, which is why CVD grades carry multi-layer stacks 5–12 µm thick: a bonding layer, mid layers for wear resistance and a top layer for oxidation resistance. The trade-offs are thermal and mechanical: the process temperature changes the substrate surface (which is why CVD substrates are engineered around it), and the residual stress profile is less favourable for interrupted cuts. The edge ends up moderately honed rather than razor sharp.
PVD (physical vapour deposition) does the opposite. The coating is condensed from a vapour at roughly 400–600 °C — cool enough that the substrate is barely touched — and lands thin and dense, typically 2–4 µm, under compressive residual stress. That combination buys a sharper, more chipping-resistant edge on a fine-grain substrate. What PVD cannot do is thickness: on a long, hot, continuous cut in steel, a 3 µm layer simply has less material to give than a 10 µm one.
| Property | CVD | PVD |
|---|---|---|
| Deposition temperature | ~1,000 °C | ~400–600 °C |
| Typical thickness | 5–12 µm, multi-layer | 2–4 µm, fine-grain |
| Residual stress | Tensile-prone | Compressive |
| Edge character | Honed, robust | Sharp, chipping-resistant |
| Signature layers | TiCN + Al2O3 + TiN | TiAlN / AlTiN / TiAlCrN |
| Weak spot | Interrupted cuts, sharp edges | Extreme hot hardness on long steel cuts |
What the layer stacks actually say
The compounds in the descriptive string are not decoration — each layer has a job. TiCN is the workhorse wear layer against abrasive flank wear. Al2O3 (aluminium oxide) is the thermal barrier: it barely conducts heat and resists oxidation, which is exactly what a cutting edge needs at high speed in steel, where most of the cutting heat wants to flow into the tool. TiN on top gives low friction and a gold colour that makes wear inspection easy. A CVD stack of TiCN+Al2O3+TiN is therefore tuned for high-speed, high-temperature, continuous cutting — the classic turning regime in steel and cast iron.
PVD stacks read differently. TiAlN and AlTiN form a hard aluminium-rich nitride that develops its own thin aluminium-oxide skin at cutting temperature — a built-in thermal barrier in a thin film. TiAlCrN adds chromium for further oxidation resistance; TiCN+TiN appears on the softer end of the PVD range. These layers are engineered to stay intact on a sharp edge running at moderate speed in sticky, work-hardening or heat-resistant material.
A sample of the stacks catalogued in InsertBase's own database — every row is the literal descriptive string from the manufacturer's record:
| Grade | Coating | Catalogued stack / focus |
|---|---|---|
| Sandvik 4325 | CVD | TiCN+Al2O3+TiN on hard substrate — steel and cast iron turning |
| ISCAR IC5005 | CVD | TiCN+Al2O3+TiN — nodular cast iron, high speed |
| ISCAR IC428 | CVD | TiC+Al2O3 multi-layer on hard substrate — grey and nodular cast iron |
| Sandvik 1115 | PVD | TiAlN+TiAlN — finishing in steel at sharp edges |
| ISCAR IC807 | PVD | TiAlN on sub-micron substrate — tough general turning |
| ISCAR IC806 | PVD | TiAlN on ultra-fine substrate, SUMOTEC treatment — superalloys and titanium |
What a cross-brand database shows
Aggregate the coating fields across InsertBase's 335 catalogued grades from twelve manufacturers and the split is unambiguous. Among the 198 grades where the manufacturer declares a coating family, 123 are CVD and 65 are PVD (10 are uncoated). Filed by workpiece group, the two families barely overlap in emphasis:
| ISO 513 group | CVD grades | PVD grades |
|---|---|---|
| P — steel | 70 | 32 |
| K — cast iron | 46 | 17 |
| M — stainless | 36 | 51 |
| S — superalloys | 3 | 35 |
| H — hardened | 1 | 17 |
| N — non-ferrous | 2 | 12 |
Counts are grades whose manufacturer files them under each group; most grades cover two or three groups, so columns sum to more than the grade count. Data from the InsertBase grade index at time of writing.
The pattern mirrors the physics. CVD dominates where cuts are hot, long and continuous — steel and cast iron turning. PVD dominates where the edge needs toughness and sharpness — stainless, superalloys, titanium and hardened steels, often at lower speed or with interruptions. Neither family is "better"; they are tuned for different failure modes.
Substrate: the other half of the string
The coating never works alone — the descriptive string pairs it with a substrate class, and the pairing is deliberate. Hard substrates support CVD stacks in stable, high-speed cuts; tough substrates support the same stacks for heavier or less stable conditions, sometimes with a cobalt-enriched surface layer that resists crack propagation — ISCAR's IC9250 (CVD, cobalt-enriched, "general purpose machining of steel under a wide range of conditions") is the textbook example.
PVD grades lean the other way: ultra-fine grain and sub-micron substrates give the thin coating a smooth, strong foundation and keep the edge sharp. That is why PVD grades like IC706 specify "hard ultra-fine grain substrate" — the fine grain is what lets a sharp edge survive abrasive titanium rather than micro-chip along it.
How to choose, in order
1. Start from the workpiece group. Steel and cast iron at productive speed → shortlist CVD grades first. Stainless, superalloys, titanium or hardened steel → shortlist PVD. The group table above is the prior; the specific grade is the evidence.
2. Check the stability of the cut. Continuous, well-clamped turning tolerates CVD's tensile-prone thick layers. Interrupted surfaces, thin-walled parts or unpredictable entry → PVD's compressive stress and sharp edge are the safer bet.
3. Match speed to the Al2O3 layer. If the plan is high surface speed in steel or cast iron, the Al2O3 barrier of a CVD stack is the mainline defence — grades like 4325 exist for exactly this. Moderate speed with finish demands → PVD or even an uncoated fine-grain grade.
4. Read the substrate and the operation tag together. Hard substrate + high-speed descriptor = wear-led design; tough substrate + cobalt-enriched = crack-led design. Pair the choice with the right chipbreaker duty band, and let the nose radius absorb the rest of the edge-strength question.
5. Verify against real offers. The same grade name can appear on many geometries with different availability — confirm the full code on the model page, or find catalogued cross-brand matches with the cross-reference finder and decode the geometry with the ISO 1832 decoder.
The short version: CVD is a thick, hot-process armour built around an Al2O3 thermal barrier — reach for it in high-speed steel and cast iron turning. PVD is a thin, cool-process skin with compressive toughness — reach for it in stainless, superalloys, titanium and any cut that punishes a fragile edge. When in doubt, read the descriptive string: the process, the stack and the substrate are printed right there.