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Nickel vs Chrome Coating on Machined Parts: Thickness, Function, and How to Choose

Coating selection for CNC components · Boyang Hardware, Zhongshan, China

Direct answer Nickel plating (5–25 µm) is the workhorse corrosion barrier on machined steel, brass and copper parts, depositing uniformly enough for predictable dimension growth. Decorative chrome (0.5–2 µm) is a thin bright topcoat applied over nickel. Hard chrome (20–100+ µm) is a separate engineering coating for extreme wear and hardness. On most machined components the right answer is nickel alone, nickel-plus-chrome for appearance, or hard chrome only for heavy-wear surfaces.

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Nickel and chrome side by side

Table 1 — Practical comparison of the three plating routes commonly specified on machined parts. Typical layer ranges from electroplating practice; exact thickness is set per specification.
Attribute Nickel (electro) Decorative chrome Hard chrome
Typical thickness 5–25 µm 0.5–2 µm (over nickel) 20–100+ µm
Main function Corrosion barrier, uniform build Brightness, tarnish resistance Wear resistance, hardness
Hardness Moderate (~200–400 HV) Thin — contributes little mechanically High (~800–1000 HV)
Corrosion role Primary barrier layer Thin top layer; depends on nickel underneath Good in mild environments, micro-cracked
Dimension effect ± predictable, near-uniform Negligible Significant; often ground after plating
Typical parts Fittings, valve components, electrical contacts Consumer hardware, knobs, visible trim Ram rods, hydraulic bores, die surfaces

Plating and tolerances: the dimension-growth problem

Plating is an addition, not a conversion: a 10 µm nickel layer raises every plated surface ~10 µm, doubling on diameters. Precision bores, threads and press fits therefore need one of three treatments:

  1. Masking — the feature is plugged or taped and stays unplated.
  2. Machining undersize — the feature is cut to compensate so the plated part meets the drawing.
  3. Post-plate finishing — common for hard chrome, which is applied oversize then ground to final dimension.

State on the drawing whether dimensions apply before or after plating — this single note prevents most plating-related rejections. Dimensional verification after plating is part of our 100% inspection process (see inspection reports).

Choosing by application

Honest limits: plating reproduces the substrate — scratches and machining marks show through chrome and are magnified by bright nickel, so the pre-plate surface finish matters (see the surface finish guide). Hard chrome changes hydrogen content in high-strength steels; where hydrogen embrittlement is a risk, baking is specified by the customer's engineering standard and should be stated up front. Plating is done by audited partners, not in-house — we coordinate and re-inspect.

FAQs

What is the difference between nickel and chrome plating on machined parts?

Nickel (5–25 µm) is the corrosion barrier and build-up layer; decorative chrome (0.5–2 µm) is a thin bright topcoat over nickel; hard chrome (20–100+ µm) is a stand-alone wear coating.

How does plating thickness affect the final dimensions of a machined part?

It adds material — 10 µm of nickel grows a diameter by about 20 µm. Precision features are masked, machined undersize, or ground after plating so the finished part meets the drawing.

Do you plate in-house?

Plating is performed by audited local partners under our specification; parts are re-inspected dimensionally before shipment. Machining, coating coordination and quality control stay in-house.