Diamond-like Carbon (DLC)

Diamond-like Carbon (DLC) is a thin PVD/PECVD hard coating that boosts wear resistance and lowers friction, often with a deep black finish.

Overview

Diamond-like Carbon (DLC) is a hard, low-friction carbon-based coating applied as a thin film (commonly ~1–4 µm) by PVD or PECVD variants. It reduces adhesive wear, scuffing, and galling, and can add corrosion protection depending on the substrate and coating stack. DLC is typically dark gray to black and is used when you need sliding performance without wet lubrication or when lubricants break down.

Choose DLC for moving interfaces: pins, plungers, seals, bearings, valve-train parts, cutting and forming tools, and mechanisms where friction drives heat or stick-slip. DLC is not a dimensional “build-up” process; it follows the base finish, so polish where you need low friction.

Tradeoffs: coating adhesion depends heavily on substrate, heat treat, and surface prep; sharp edges and high-contact-stress corners can chip. Some DLC processes have temperature limits that can affect heat-treated steels or certain aluminum alloys. Coating adds cost and lead time and should be specified with thickness, hardness, and any post-coat polish needs.

Common Materials

  • A2 tool steel
  • D2 tool steel
  • 17-4 PH stainless steel
  • 440C stainless steel
  • Titanium Grade 5
  • Aluminum 6061

Tolerances

±0.0002–0.0006 in (effective change from coating thickness; masking and edge effects vary)

Applications

  • Fuel injector needles and plungers
  • Piston pins and wrist pins
  • Hydraulic spools and valve components
  • Punches, dies, and forming tools
  • Bearing races and precision shafts
  • Medical and industrial cutting blades

When to Choose Diamond-like Carbon (DLC)

Choose DLC when sliding contact, adhesive wear, or stick-slip limits performance and you want a thin coating that preserves part geometry. It fits low to high volumes because the value is performance-driven rather than geometry-driven. Best results come from controlled surface finish, stable substrates, and contact designs that avoid sharp, highly loaded edges.

vs TiN

Choose DLC over TiN when friction and galling are the primary failure modes, especially in boundary-lubricated or dry sliding contact. DLC’s lower coefficient of friction typically reduces heat and scuffing more effectively than TiN on the same base part.

vs TiAlN

Choose DLC over TiAlN for sliding components and mechanisms where low friction matters more than hot hardness. TiAlN excels in high-temperature cutting, while DLC is usually the better lever for reducing stick-slip and adhesive wear at moderate temperatures.

vs Hard chrome plating

Choose DLC when you need a thinner, more uniform coating with lower friction and less risk of dimensional variation from plating thickness. DLC also avoids hydrogen embrittlement concerns common to some electroplated processes, but it requires good surface prep and may be less tolerant of edge impacts.

vs Nitriding

Choose DLC when you need a low-friction sliding surface rather than a deep diffusion-hardened case. Nitriding strengthens the substrate and supports high contact stress well, while DLC provides the friction and anti-galling benefit at the interface; many parts also combine nitriding plus DLC when specified correctly.

Design Considerations

  • Specify coating type/process (PVD vs PECVD), target thickness, and any required hardness or friction targets so the coater can select the right stack
  • Call out masking areas and allowable edge break; sharp edges and corners are common chip/adhesion failure points
  • Control pre-coat surface finish (Ra/Rz) on functional sliding faces; DLC will replicate scratches and tool marks
  • Define critical fits as pre-coat dimensions and allow for coating thickness variation on bores, shafts, and threads
  • Avoid highly concentrated contact stress at small radii; spread load with larger radii, wider contact bands, or better alignment features
  • State maximum allowable process temperature if heat treat or temper condition is sensitive