# Electroless nickel plating

Autocatalytic nickel deposition, phosphorus and boron variants, preparation, thickness distribution, dimensional buildup, and conditional coating properties.

Reviewed: 2026-10-29

Tags: processes, finishing, plating, nickel

An ideal **10 µm electroless nickel layer per wall** closes a **20.000 mm bore** to **19.980 mm**. The same layer takes a **20.000 mm shaft** to **20.020 mm**. Account for preparation, underlayers and local buildup. Specify the Ni-P or Ni-B chemistry and heat treatment separately from thickness.

## Identity and mechanism

Chemical reduction deposits nickel alloy without external current. APT identifies nickel-phosphorus, nickel-boron, composite deposits and multielement alloys as distinct variants. [APT process guide](https://advancedplatingtech.com/wp-content/uploads/2013/10/Electroless-Nickel-Plating-A-Guide.pdf)

In nickel-phosphorus deposition, hypophosphite supplies the chemical reduction mechanism. Deposit properties depend on phosphorus content and subsequent heat treatment. Solution composition and use also affect porosity and corrosion resistance. [ASTM B733-22(2026), public scope](https://store.astm.org/b0733-22r26.html)

The process belongs to [Surface-finishing processes](index.md). The deposited alloy, incoming base material, and any additional layers are separate parts of the finished coating system.

## Alloy families and terminology

| Family | Meaning and bounded applicability |
| --- | --- |
| Nickel-phosphorus, Ni-P | A nickel alloy with codeposited phosphorus. APT's guide uses 2–5% for low phosphorus, 6–9% for medium phosphorus, and 10–12% for high phosphorus. These are that guide's descriptive bands. [APT guide](https://advancedplatingtech.com/wp-content/uploads/2013/10/Electroless-Nickel-Plating-A-Guide.pdf) |
| Processor-specific Ni-P products | Micron describes low phosphorus as 1–4%, medium as 5–9%, and high as above 10%. Its NIPLATE 600 and NIPLATE 500 are named medium- and high-phosphorus systems. [Micron technical reference](https://www.microncoatings.it/en/electroless-nickel/hardness-and-heat-treatments/) |
| Nickel-boron, Ni-B | ASTM B607 distinguishes Type 1 with 0.1 to less than 3.5 mass% boron and Type 2 with 3.5–6 mass% boron and at least 90 mass% nickel. These are specification classifications, not Ni-P phosphorus bands. [ASTM B607-21(2026), public scope](https://store.astm.org/b0607-21r26.html) |
| Composite electroless nickel | A deposit containing dispersed particles. Atotech lists PTFE and silicon-carbide composite products separately from its ordinary phosphorus families. Particle identity is part of the coating identity. [Atotech product portfolio](https://www.atotech.com/products/general-metal-finishing/wear-resistance/electroless-nickel-coatings/) |

**Synthesis.** A qualitative phosphorus label alone does not establish a composition interval. A named product, measured composition, and applicable specification retain more information than the label. Ni-B and composite properties cannot be assigned from an ordinary Ni-P reference.

## Base material and preparation

APT identifies steel, aluminum, copper, and copper alloys as base materials on which good adhesion is possible. Its guide identifies surface preparation and activation as major determinants of adhesion. Possibility on a material family does not establish adhesion on every alloy, temper, oxide condition, or previously treated surface. [APT guide, adhesion](https://advancedplatingtech.com/wp-content/uploads/2013/10/Electroless-Nickel-Plating-A-Guide.pdf)

Anoplate's ENhanced Nickel family also includes stainless steel, zinc die castings, powdered metal, and nonconductive materials in its stated applicability. This is processor-family evidence, rather than proof that untreated nonconductive material initiates deposition or that every EN product supports every listed material. [Anoplate ENhanced Nickel](https://www.anoplate.com/capabilities/enhanced-nickel/)

**Synthesis.** Compatibility is a relationship between the incoming material condition, preparation and activation sequence, deposit, and post-treatment. A substrate name alone does not define that relationship. Preparation details and any undercoat remain consequential unknowns when only "electroless nickel" appears in a requirement.

## Thickness distribution and dimensions

ASTM B733's public scope conditions uniform coating thickness on free circulation of plating solution over the surfaces. The absence of a plating-current distribution problem does not remove that condition. A blind cavity or internal passage is therefore not evidence of equal thickness merely because the external surface has a specified deposit. [ASTM B733-22(2026), scope 1.4](https://store.astm.org/b0733-22r26.html)

Anoplate describes similar buildup at thread crests and roots for its ENhanced Nickel coatings. That claim concerns coating distribution, not preservation of the original thread fit. [Anoplate ENhanced Nickel](https://www.anoplate.com/capabilities/enhanced-nickel/)

**Geometric synthesis.** For an ideal cylindrical surface with a uniform coating thickness `t`, measured perpendicular to the surface, and no preparation removal or later finishing:

| Feature | Ideal final dimension |
| --- | --- |
| External cylinder of initial diameter `D` | `D + 2t` |
| Cylindrical bore of initial diameter `d` | `d − 2t` |
| Plate with both broad faces coated | Initial thickness plus `2t` |
| One coated flat face | Outward displacement `t` |

For an illustrative `t = 10 µm = 0.010 mm`, a 20.000 mm outside diameter becomes 20.020 mm. A 20.000 mm bore becomes 19.980 mm. These calculations express ideal buildup, not achievable tolerances. Unequal local thickness, preparation removal, underlayers, thermal change, and later material removal change the result. Thread pitch diameter needs the thread geometry rather than direct reuse of the cylindrical-bore equation.

## Hardness, heat treatment, and corrosion

Micron reports approximately 650 HV for its medium-phosphorus coating and 550 HV for its high-phosphorus coating before hardening. It reports about 800 HV after 8 hours at 260–280 °C and about 1000 HV after 4 hours at 340 °C. These are its stated coating-treatment combinations, not universal schedules. Its explanation relates hardening to the formation of nickel-phosphide phases. It also reports that high-phosphorus deposits regain magnetic response after sufficient heat treatment. [Micron hardness and heat-treatment reference](https://www.microncoatings.it/en/electroless-nickel/hardness-and-heat-treatments/)

APT distinguishes preplating stress-related treatments, lower-temperature postplating treatments for adhesion or hydrogen-embrittlement relief, and higher-temperature hardening. Its discussion states that hardening of medium- and high-phosphorus deposits can increase hardness while reducing corrosion resistance. [APT corrosion and heat-treatment reference](https://advancedplatingtech.com/blog/corrosion-protection-benefits-electroless-nickel-plating/)

APT's process guide identifies hot, highly alkaline solutions as an environment where lower phosphorus can improve corrosion resistance. [APT guide, corrosion](https://advancedplatingtech.com/wp-content/uploads/2013/10/Electroless-Nickel-Plating-A-Guide.pdf)

Nickel-boron has a separate limitation. ASTM B607 describes microporous coatings with limited corrosion protection. Its public scope links boron content to properties and notes that electronic coatings commonly remain without heat treatment to preserve solderability. [ASTM B607-21(2026)](https://store.astm.org/b0607-21r26.html)

**Synthesis.** "Heat treated" is incomplete without its purpose, temperature, time, alloy composition, and base-material constraints. A harder coating is not automatically the coating with better corrosion performance. These references establish no universal hardness, wear rate, corrosive-service lifetime, or hydrogen-relief schedule.

## Specification scope and quantities

| Reference or quantity | Interpretation |
| --- | --- |
| ASTM B733-22(2026) | Ni-P on metallic products for engineering uses. Its public abstract distinguishes phosphorus type, service condition linked to minimum thickness, and post-heat-treatment class. Those designations describe different attributes. [Publisher scope and abstract](https://store.astm.org/b0733-22r26.html) |
| ASTM B607-21(2026) | Autocatalytic Ni-B coatings for engineering use. It is a separate alloy specification. [Publisher scope](https://store.astm.org/b0607-21r26.html) |
| ISO 4527:2003, edition 2 | Requirements and test methods for autocatalytic Ni-P on metallic substrates. The public abstract excludes Ni-B, Ni-P composites, and ternary alloys. [ISO record](https://committee.iso.org/standard/36258.html?browse=ics) |
| Thickness | A length, commonly µm or mm. Nominal, minimum local, and measured thickness are different quantities. One mil is 0.001 inch, equivalent to 25.4 µm. |
| Composition | Mass percentage where the cited source identifies a mass basis. Particle volume percentage in a composite is a different quantity. |
| Hardness | A result tied to a scale and test conditions. HV denotes Vickers hardness. The Micron values above are reported as HV without a stated load in the inspected text. |

**Synthesis.** A reference number alone does not establish a complete coating requirement or acceptance result. Alloy, thickness basis, post-treatment, substrate condition, and acceptance criteria remain separate. This page does not establish equivalence among ASTM, ISO, military, aerospace, or customer specifications.

## Source provenance and limits

Sources were inspected on **29 October 2026 PDT**. This is an unpublished research draft. The public ASTM records identify B733-22(2026) and B607-21(2026) as active, updated 5 October 2026. Their older unreapproved records are historical. Only public abstracts and scopes support this page, not the purchased full standards.

The inspected ISO record identifies edition 2, May 2003, confirmed in 2021, with a systematic review opened in July 2026. That record establishes scope and status at access, not a new edition or contractual applicability.

APT's 12-page process guide has no verified issue date in its text. Its URL directory date is not treated as an edition. The separate APT corrosion article is dated 6 June 2016. Micron, Anoplate, and Atotech pages have no verified issue dates. Their product claims remain tied to the named processor or manufacturer. Differences in phosphorus bands are retained above.

Coverage excludes bath recipes, a universal preparation sequence, acceptance sampling, customer qualifications, approved suppliers, pricing, processing rates, and lead times. Full standards, lot-specific measurements, and application-specific qualification evidence were not available. The generic relationships above establish no customer's confirmed capability or approved process.