Ceramic hard. Or ultra-slick. Both thin films.

DLC has sp3 bonding similar to diamond (as opposed to sp2 bonding of graphite). Result: extreme hardness (approaching diamond), chemical inertness, low friction. But amorphous (non-crystalline) — not actually diamond. Can be deposited at lower temperatures than crystalline coatings, compatible with heat-sensitive substrates. Trade-off: temperature limit around 300°C vs diamond's 700°C stability.

TiN (gold): older, lower cost, general steel machining. 2500 HV. TiCN (gray): harder than TiN, for abrasive materials. 3000 HV. TiAlN (violet-black): better at high temperature, standard for aerospace machining. 3500 HV, stable to 800°C. AlTiN: modified TiAlN with higher aluminum — better oxidation resistance. For tough materials (stainless, Inconel): AlTiN. For general steel: TiCN or TiN. For aluminum: diamond-like or uncoated (ceramic coatings can weld to aluminum).

Yes — DLC low-temperature deposition (150-250°C) compatible with many plastics and other heat-sensitive substrates. Standard PVD typically requires 400°C+, damaging plastics. DLC used for: plastic optics (scratch-resistant coating on sunglasses), plastic consumer products (wear-resistant surfaces), medical plastics. Specialty application but growing market.

Both PVD and DLC are line-of-sight processes — coating deposits preferentially on surfaces facing the source. Complex internal geometry: incomplete coverage. Workarounds: (1) Part rotation during deposition for better uniformity. (2) Multiple sources in chamber. (3) For critical internal coverage, different process (electroless nickel for uniform coverage). For mostly-external-surface parts: PVD and DLC work well.

PVD: established process, many vendors, competitive pricing. Small parts: $20-50. Large parts: $50-150. DLC: specialty process, fewer vendors, higher cost. Small parts: $40-100. Large parts: $80-200. Both add 50-200% to base part cost. Justified when: tool life improvement, premium product differentiation, specific performance requirement. Not economical for general industrial.

PVD: 5-10 days typical. DLC: 7-14 days. Both require shipping to coating vendor and back — plan into project timeline. For urgent orders, air freight between coater and customer reduces transit time. Some PVD shops offer 3-day rush service at premium. DLC rarely has rush availability.