Frequently Asked Questions

We are a UK-based specialist in diffusion coating technologies that protect metal components from high-temperature degradation such as metal dusting, oxidation, carburisation, sulfidation and wear. Our core processes are Aluminizing, Chromizing and Boronizing.

Over 60 years ago, we pioneered industrial Chromizing in 1955 and have grown to support gas turbines, process plants and clean-technology industries worldwide since then.

Our head office and processing facility is in Middlesbrough, UK and we serve customers across Europe, North America, the Middle East and Asia.

We offer:

• Aluminizing / Aluminide diffusion
• Chromizing / Chromide diffusion
• Boronizing / Boriding
• Silicon aluminide slurry coatings and advanced coating support

We also provide Lab Services, coatings engineering support and feasibility studies.

We serve:

• Clean technology (hydrogen, SOFC, energy storage, nuclear)
• Oil, gas and petrochemical
• Power generation
• General industrial and heavy engineering

Our coatings help extend service life and improve reliability in demanding environments.

We can process components from small parts up to very large items, up to ~18 metres long and large overall dimensions thanks to our bespoke furnaces.

Aluminizing (also called aluminide diffusion) is a thermochemical surface engineering process that diffuses aluminium into the base metal. In service, this creates a stable aluminium oxide (Al₂O₃) scale which protects the component.

It protects against:

• Metal dusting
• Oxidation
• Carburisation
• Sulfidation
• Hydrogen permeation
• Chromium leach and high-temperature corrosion

This makes it ideal for reformers, furnaces, reactors and process tubes.

Typical materials:

• Carbon and low-alloy steels
• Stainless steels
• Nickel-alloy materials (Inconel® 600, 601, 625, 718, 800HT, 602CA, etc.)
• Other alloys on request

Yes, including tubular bores or complex geometries, provided the internal access is suitable for the diffusion process.

Layer thicknesses are tailored by process conditions and typically range from tens to over 100 microns depending on the application.

Yes. Aluminized components can dramatically reduce metal dusting by restricting carbon ingress and forming a robust oxide barrier.

Yes, diffusion coatings result in metallurgical changes at the surface which can slightly change dimensions and roughness. We advise accounting for this in design tolerances.

Chromizing diffuses chromium into the surface to create a coating that is resistant to hot corrosion, carburisation and sulfidation. Chromizing of a carbon steel will produce a wear resistant coating.

• Chromizing builds a chromium-rich diffusion zone

• Aluminizing builds an aluminium-rich diffusion layer that forms Al₂O₃ in service
The right choice depends on operating gas chemistry, temperature and alloy.

Chromizing is suitable for ferrous alloys, stainless steels, nickel-base alloys and selected cobalt alloys.

Boronizing (also called boriding) diffuses boron into the surface, forming a hard boride layer that improves wear resistance, erosion resistance, abrasion resistance and surface hardness.

• Very high surface hardness (up to ~1900 HV)
• Abrasion resistance
• Reduced coefficient of friction
• Solid bond with the substrate

It is commonly used for tooling, shafts, valves and wear-exposed components.

Most steels and cast irons, nickel alloys and selected cobalt and titanium alloys (subject to evaluation). Materials that contain greater than 0.8% silicon are not suitable for boronising.

Yes, high-temperature diffusion may affect heat-treated alloys. For critical mechanical performance, discuss post-coating heat treatment or alternative specifications.

Post-coating machining or welding is possible in many cases, but must be reviewed case-by-case.

In most cases, pressure testing is completed prior to coating, unless project specifications require otherwise.

Yes we offer selective masking techniques to coat only required regions.

Please email detailed enquiries to sales@diffusion-alloys.co.uk with:

• Drawings (PDF/STEP)
• Material specification
• Quantity
• Operating temperature & environment

Lead times depend on part complexity and process, typically from a few weeks for trials/prototypes to longer for larger production runs.

Our core business is diffusion coating services. Supply of powders or furnace systems can be discussed separately.

Yes we cater for low-volume R&D to high-volume series production including millions of fasteners.

Yes all coatings are produced under controlled processes and can be verified through thickness measurement, hardness testing and metallographic analysis.

We operate with strong health, safety and environmental practices in line with industry expectations.

Diffusion coatings form a metallurgical bond with the substrate, offering far superior resistance to spalling and thermal cycling compared with sprayed or plated layers.