Hard Coatings

Hard coatings are thin, wear-resistant surface layers (often PVD/CVD) that reduce friction and improve hardness without changing core part geometry.

Overview

Hard coatings (commonly PVD/CVD films such as DLC, TiN, and TiAlN) add a dense, thin, high-hardness layer to a finished part. They’re used to increase abrasion resistance, reduce galling, lower friction, and improve tool/part life while keeping the base material’s bulk properties.

Choose hard coatings when the part already meets dimensional requirements and the failure mode is at the surface: sliding wear, adhesive wear, or high contact stress. They’re common on cutting/forming tools, wear components, and mechanisms where lubrication is limited.

Tradeoffs: coating performance depends heavily on substrate material, heat treatment, surface finish, and edge condition. Coatings can change critical dimensions by a few microns, may not cover deep blind features uniformly, and can chip at sharp edges. Specify the coating type, target thickness, and any post-coat masking/inspection up front.

Common Materials

  • Tool steel D2
  • H13 tool steel
  • 440C stainless steel
  • 17-4 PH stainless steel
  • Titanium Grade 5
  • Carbide

Tolerances

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Applications

  • End mills and drill bits
  • Injection mold cores and cavities
  • Punches and dies
  • Valve stems and seats
  • Sliding pins, bushings, and wear plates
  • Medical instrument jaws and cutters

When to Choose Hard Coatings

Hard coatings fit parts where surface wear, galling, or friction limits life, and the base material already provides required strength and toughness. They’re best on finished, accessible surfaces with controlled surface finish and edge geometry. Works well for low to high volumes when repeatable durability matters more than cosmetic appearance.

vs Machined Surface Finishing

Choose hard coatings when the machined finish alone won’t survive sliding contact, abrasion, or repeated cycles. Coatings add a hard, low-friction surface that machining can’t provide, while preserving the bulk properties of the substrate.

vs Polishing

Choose hard coatings when low friction must be maintained under load and over time, not just improved initial smoothness. Polishing can reduce asperities, but it doesn’t add hardness or chemical wear resistance the way DLC/TiN/TiAlN do.

vs Coatings

Choose hard coatings when you need high hardness, low friction, and wear resistance in thin layers with minimal dimensional impact. Many general-purpose coatings prioritize corrosion resistance, appearance, or thickness build rather than contact-wear performance.

vs Heat Treatment

Choose hard coatings when you need a hard surface without making the entire part brittle or changing core strength. Heat treatment changes bulk properties and may distort parts; coatings target surface performance on already-finished geometry.

vs Painting

Choose hard coatings when the surface sees contact, sliding, or abrasion where paint will rapidly wear through. Hard coatings are engineered for tribological performance and can survive high contact stresses that decorative/protective paints cannot.

Design Considerations

  • Call out coating type (DLC/TiN/TiAlN), target thickness range, and any critical surfaces to coat or mask
  • Control edge conditions; add small radii/chamfers to reduce chipping and improve coating durability
  • Specify pre-coat surface finish where it matters (e.g., bearing/sliding surfaces) and avoid deep tool marks
  • Avoid deep blind holes and very high aspect-ratio features on coated functional surfaces unless the supplier confirms coverage capability
  • State post-coat dimensional/fit requirements and inspection method if microns matter (e.g., pin gauges, CMM, witness coupons)
  • Confirm substrate heat treatment/hardness before coating; inconsistent hardness or residual stress drives adhesion failures