Coating thickness is one of the most frequently discussed specifications in PVD and DLC applications, and one of the most commonly misunderstood. The assumption that thicker coatings provide better protection is intuitive but incorrect for thin-film vacuum deposition. In PVD and DLC, performance comes from the coating's material properties, including hardness, friction, thermal stability, and adhesion, not from adding more material to the surface.
Advanced Coating Technologies (ACT) applies coatings from 0.5 µm to 7 µm depending on the type and application. Here is how thickness relates to performance, why more is not always better, and what engineers should consider when specifying coating thickness for their parts.
To put the numbers in perspective: a human hair is approximately 70 µm in diameter. ACT's thinnest coatings (X-LC at 0.5 to 2 µm) are roughly one-fortieth the width of that hair. The thickest standard PVD coating (TiN at 1 to 7 µm) is still one-tenth of a hair's width at its upper range.
At these thicknesses, dimensional change is minimal. A 3 µm coating adds 6 µm to the total diameter of a cylindrical part. For most machined components, injection molds, medical instruments, and firearm parts, this falls within allowable tolerance bands. Post-coating grinding is not typically required, which is one of PVD's primary advantages over thicker surface treatments like electroplating (5 to 250+ µm) or thermal spray (up to 300 µm).
In thin-film coatings, increasing thickness beyond the optimized range introduces problems rather than solving them.
Internal stress builds as thickness increases. PVD and DLC films develop residual stress during deposition. Within the designed thickness range, this stress is manageable and the coating maintains adhesion. Push the thickness too high, and internal stress can exceed the bond strength between the coating and substrate, causing spontaneous delamination, edge chipping, or cracking.
Surface roughness increases with thickness. Thinner coatings replicate the substrate's surface finish more faithfully. As thickness grows, coating growth features (droplets in arc deposition, columnar structures in sputtering) become more pronounced, increasing surface roughness. For applications requiring smooth, low-friction surfaces, such as bearings, medical instruments, or sliding mechanisms, this roughness increase defeats the purpose of the coating.
Brittleness increases at excessive thickness. High performance coatings like AlTiSiN (HV 4,500) and nACO (HV 4,500) achieve extreme hardness, but hardness and brittleness are related. At optimized thickness (1 to 4 µm), these coatings resist abrasive wear without fracturing. At excessive thickness, the same coatings become more susceptible to cracking under impact or mechanical shock.
Each coating in ACT's portfolio has a specified thickness range that reflects its optimized performance window:
These ranges are not arbitrary. They represent the thickness window where each coating delivers its specified hardness, COF, adhesion, and surface finish properties without the internal stress, roughness, or brittleness problems that come from over-application.
For precision parts, engineers should confirm two things during the coating specification process. First, verify that the coating thickness at the specified range keeps the finished part within its dimensional tolerance. For most parts at 1 to 4 µm, this is not a concern. For ultra-precision components with single-digit micrometer tolerances, the conversation matters.
Second, verify that the coating provider measures and documents thickness on every batch. In-house testing with Calo Testers (ball-crater thickness measurement) and Fisherscope X-ray systems (non-destructive thickness and composition analysis) provides objective verification that the applied coating falls within the specified range.
A 3 µm AlTiSiN coating at 4,500 HV outperforms a 50 µm chrome plate at 800 to 1,000 HV in abrasive wear resistance. A 2 µm DLC coating at COF 0.05 to 0.1 reduces friction more effectively than a 25 µm anodized layer at COF 0.30 to 0.50. Thickness is a parameter to control, not a metric to maximize. The coating's hardness, friction, temperature resistance, and adhesion determine performance. The thickness determines whether those properties are delivered reliably or undermined by internal stress. At ACT, every PVD coating is applied within its optimized range and verified before it ships, because the right thickness is the one that lets the coating do its job.
Copyright © 2012 - 2025 | Advanced Coating Technologies, Inc.
