http://www.rowantechnology.com - 1 -

Choosing a Hard Chrome Alternative

Keith Legg

Rowan Technology Group, http://www.rowantechnology.com

klegg@rowantechnology.com, 847.680.9420

What is wrong with chrome plating?

Chrome plating has been in use since the 1940’s and is a powerful, simple and cheap process. The plating 

solution is very simple (chromic acid, sulfuric acid, and sometimes brighteners and other additives) and the 

process is quite forgiving. Unfortunately chromic acid (CrO3) is a hexavalent chromium (Cr6+) compound, and 

the process is quite inefficient, with most of the current going to hydrolyze the water, producing copious 

amounts of hydrogen and oxygen bubbles. When they rise to the surface these bubbles burst, throwing a fine 

mist of hexavalent chrome into the air. To protect workers and the environment, this mist has to be sucked 

away in an efficient air-handling system.

Chrome plating generates several different waste streams:

• Cr6+ mist air emissions – worker health and safety issue in the plant, air pollution issue outside, must 

be trapped in scrubbers

• Cr6+-contaminated waste water – must be treated before release to public treatment plants or water 

courses

• Solid wastes – must be disposed of as hazardous waste:

o Cr6+-contaminated sludge and masking material

o Cr6+-contaminated air filters, solids and water from air-handling systems

• Groundwater contamination from leakage and spills (this is rarely a problem with modern plants, 

which have double-containment, but used to be a serious source of contamination in older brownfield plants).

Note that the problem with chrome plating is the deposition process. Chrome plating itself is benign.

Over the last decade emissions from chrome plating plants in the US have become very small as plating shops 

have had to meet the very stringent EPA Clean Air Act emission requirements. They have done this through a 

combination of stringent engineering controls and the use of PFOS fume suppressants in plating tanks. 

However PFOS is a long chain fluorinated hydrocarbon that has been found to be very persistent in the 

environment, and is being phased out, leaving the plating shops to control emissions by engineering controls 

(scrubbers, tank lids, etc.).

What is hard chrome plating used for?

Hard chrome is used throughout manufacturing industry for a very large number of wear resistant applications 

in industrial equipment and vehicles, and for almost all metal fabricating tooling except cutting tools (which 

are usually carbide tools with very hard CVD or PVD thin coatings):

1. Wear resistance – Put down by OEMs on hydraulic actuators, shaft journals, railway engine shafts, 

aircraft landing gear, and thousands of other components for wear resistance (and to provide a 
http://www.rowantechnology.com - 2 -

measure of corrosion protection). Almost all hydraulic actuators on earth movers, snow plows, road 

repair equipment, backhoes, car transporters, farm machinery, mining equipment, etc. are chrome 

plated. In vehicles most stems on all of the engine valves are chrome plated, as are many shock 

absorbers.

2. Industrial tools – Rolls for producing steel, aluminum, and other alloys, as well as most other 

materials that come in sheets, such as paper and plastic sheet, stamping tools and dies for everything 

from tiny electrical connectors to car doors, molds for manufacturing almost anything in plastic. In 

short, almost everything that is manufactured from metal, plastic, or even paper relies on chrome 

plating for its production.

3. Reclamation and rebuild – Chrome plate is used by overhaul shops in the mining and aircraft industry 

to bring worn or corroded parts back to dimensional tolerances, so that they can be repaired rather 

than having to be replaced. This is done on many components that are never plated by the OEM, as 

well as plated components whose plating has become worn or scored.

4. Decorative uses – Hexavalent chromium plating is also very commonly used in the form of a very thin 

coating for decorative chrome on car and truck trim, motorcycles, kitchen and bathroom appliances 

such as faucets drains, and numerous other items that require a bright, shiny appearance. Trivalent 

chromium plating can be used (and is used) on many decorative items, but it is not as easy to do and 

does not always look identical to hex chrome coated surfaces.

Hard chrome plating alternatives

There are several hard chrome plating alternatives that are now used, depending on the application and on 

whether it is an OEM part or a component to be repaired: 

• Thermal sprays (HVOF) – Primary replacement for most commercial and military aircraft repair, and 

for large actuators on mining equipment. Best performance. Cannot be used for deep internal 

diameters and high strain fatigue applications.

• Electro and electroless plates (usually based on Ni or Co) – Good for internals.

• Vacuum coatings – OEM applications only. Not for rebuild.

• Heat treatments – OEM applications only. Not for rebuild.

• Laser and weld coatings – Localized repair.

See below for more detailed descriptions of these alternatives.

Thermal spray and HVOF

The most commonly used technology for replacing hard chrome plating is thermal spray (primarily, but not 

exclusively, HVOF). While this is the technology of choice for most applications it is not necessarily the best 

choice for all.

There are a large number of companies around the US and the world who supply thermal spray services, and 

the equipment and supplies (thermal spray powders) are available from a number of international companies.

Thermal spray is the general term for a number of processes in which particles of coating material are heated 

and sprayed using high speed gas onto the surface to be coated. It is a fully commercial industrial process that 

is used for coating everything from bridges and radar towers to aircraft parts and prosthetic knee joints. Since 

thermal spray coatings are readily sprayed up to 0.020” (500 microns) thick, they are good for rebuilding worn 

components, which is the primary use for hard chrome plate.

If you are currently using hard chrome plating you will find thermal spray to be a considerable culture shock. 
http://www.rowantechnology.com - 3 -

Thermal spray is not all that difficult, but it means doing things in a very different way.

• If done well, thermal spray will give you a higher quality, more reliable coating with much longer 

service life. If done poorly, coatings will flake off or be very porous, or they will turn into efficient 

cutting tools that tear up seals and mating surfaces.

• Unlike hard chrome, where there are only minor choices of plating additives and hard chrome is what 

you always get, there is a large choice of coating materials, starting powders, gases, types of 

equipment and deposition conditions. The most common coating materials for chrome replacement 

are chrome carbide-nickel chrome (Cr3C2-NiCr) and tungsten carbide-Co (WC-Co and WC-CoCr). 

(Note that the Cr in these materials is not hexavalent, despite the misinformation in the California 

CARB regulations.)

• Hard chrome plating is very forgiving and makes acceptable coatings without a lot of attention. 

Thermal sprays require proper process definition and careful control.

• Workers require a lot more training and skill to do thermal spray reliably that to do chrome plating.

• You cannot always use the same finishing methods. Chrome plate is usually ground with an aluminum 

oxide wheel to a finish of about 16m” Ra for bearing surfaces, but the carbide sprays must be ground 

with a diamond wheel or belt, and sometimes superfinished with a stone or belt to <6m” Ra.

• If you need to coat internal diameters or complex shapes, HVOF is not a good choice, and you may 

need to use plasma spray for larger diameters or alternative electroplates or electroless nickel for 

smaller diameters.

• The way thermal spray fits into the production system is different. Chrome plating requires products 

to be cleaned and masked, then left in the plating bath for a day or more. Large items are sprayed 

one at a time for 15-60 minutes, while batches of small items can be sprayed at the same time in 

special fixtures. Thus thermal spray is much faster, but requires constant attention.

Because most users are not very familiar with all these choices, we offer consulting assistance to make the 

best choices, as well as training and coating optimization for a consistently high quality product.

Electroplates, electroless nickel and composite plating

As drop-in replacements for chrome plating, electroless- and electro-plates have the advantage that they are 

bath processes able to be done with the same sort of technology with which chrome plating users are familiar. 

Most non-chrome hard electroplates are based on nickel, although there are some plates that are based on 

other materials:

• Ni-W, Ni-W-B and Ni-W-B with SiC (the Takada process). All of these are alloy coatings, which typically 

are more complicated to deposit than the simple elemental coatings. Coatings with particles codeposited (such as SiC, diamond, PTFE, etc.) are particularly difficult as particle suspension and 

deposition uniformity are difficult to control, and in some cases the particles have been known to 

wreak havoc with air handling systems.

• Cobalt-based electroplates avoid the Ni ESOH problems, although Co is a more expensive metal and 

often termed a strategic metal because its sources lie mostly in unstable areas of the world, with little 

available in North America or Europe. Co-based electroplates include Co-P nanophase alloys 

developed specifically as chrome replacements and only just now becoming commercially available, 

and Co-SiC composites, which have been used in some aircraft engine applications for some years in 

the UK.

Electroless nickel (often just called EN) is a standard and widely available plating process. There are a great 

many platers offering electroless Ni, and the plating equipment and solutions are commercially available.
http://www.rowantechnology.com - 4 -

Unlike chrome plating and other electroplating methods, which use an electric current to deposit the coating, 

electroless Ni is an “autocatalytic” process – i.e. the Ni deposits out of the bath onto the parts just because 

they are there, without any need for anodes and robbers, and all the associated fixturing used in 

electroplating. This makes it a very flexible process, able to coat even very complex parts and small internal 

spaces easily and uniformly. But because the bath is a delicate balancing act of keeping the Ni in solution, but 

allowing it to deposit out onto anything put into the bath, it requires careful attention to bath chemistry and 

cleanliness of the surface being coated. Unlike chrome plating baths, which last essentially for ever, electroless 

Ni baths typically require complete replacement periodically.

There are several types of electroless Ni available commercially:

• Electroless Ni-P is the most common type, with a typical hardness up to.

• Electroless Ni-B is used for some aerospace and other specialized applications. It is much less widely 

available than Ni-P. Because lead or thallium are required for the bath chemistry, Ni-B coatings 

usually contain from 0.1-1wt% of these toxic materials. Therefore these coatings are not always 

RoHS-compliant.

• Electroless Ni-P composite coatings are available with a variety of additions to the base Ni-P coating. 

These include SiC or diamond for wear resistance, PTFE for lubricity, or even both for a hard, 

lubricious coating.

Because it is a plating process electroless Ni is not a big step for most companies used to using chrome plating,

although it is a much less forgiving process:

• Electroless Ni is not usually as wear resistant as hard chrome and must be heat treated at 400°C 

(750°F) to create the phosphide precipitates that give the coating its hardness. As-deposited the 

hardness of electroless Ni-P is 500-700 HV as deposited and up to 1,100 HV after heat treating, while 

Ni-B is typically 650-750 HV as-deposited and up to 1,200 HV after heat treating. This makes it 

unsuitable for alloys and products that cannot take this temperature.

• The coating is very corrosion resistant as-deposited, provided there are no holes or scratches, but 

loses some corrosion resistance on heat treating.

• It is usually a thin coating (<0.003” (75mm), although some bath chemistries now allow coatings that 

are much thicker), and so it is not usually used for rebuilding worn items, which is the primary use for 

hard chrome.

• Electroless Ni coatings can take a very smooth finish, and are often used for mirrors and very smooth 

dies and molds. The coating is not microcracked as hard chrome is.

• Electroless Ni is most useful for small components, although some companies are able to plate items 

several feet across weighing several tons. While small components can usually be cleaned and plated 

fairly easily, it is often difficult to prepare and clean large items perfectly over their whole surface. As 

a result large components frequently exhibit small poorly adhered areas.

• Because the process requires a fine chemical balance it is critical to maintain bath chemistry 

accurately. Some users set up systems to do this automatically to maintain consistent quality.

• Especially with large items the cleanliness and finish of the surface to be plated is critical as 

contamination can prevent the autocatalytic reaction and leave holes in the coating.

The presence of Pb in electroless Ni-B coatings makes them non-compliant with RoHS. The alternative, 

thallium, is not covered under RoHS, but it is also a heavy metal cumulative poison. Neither of these materials 

is used in EN-P.
http://www.rowantechnology.com - 5 -

Vacuum Coatings

For most of the applications for which chrome plating is used, vacuum coatings are not the answer because of 

their relatively high cost and their inability to build the dimensions of worn or damaged components back to 

spec. However, for some applications these types of coatings can be cost-effective, especially for small 

components that must last a long time.

There are two primary types of vacuum deposition methods:

1. Physical vapor deposition (PVD) – In this method the coating material is created from a solid, either 

evaporated by an electric arc or an electron beam, or sputtered. It goes through a plasma (to allow 

the ions to be accelerated) and lands on the component surface, forming a very thin but very hard 

layer.

2. Chemical vapor deposition (CVD) – CVD processes have a lot in common with PVD, including cost and 

the size of items that can be coated. However, in the CVD method the coating material comes from 

gases that combine on the hot surface to form a coating.

These types of coatings are usually expensive because they are relatively complex technologies that require 

vacuum chambers. This limits the sizes of products that can be coated to less than a foot or so (30cm).

Facts about PVD coatings:

• PVD coatings are usually deposited at temperatures of 250°C (480°F). They can be deposited at lower 

temperatures, but, depending on the method coating quality and adhesion tend to suffer at low 

temperature. This limits the alloys that can be readily coated.

• PVD coatings are highly sensitive to contaminants on the surface being coated, which must be 

scrupulously clean and must not expose the vacuum to water, oils, paints, or other contaminants that 

will contaminate the process.

• They are only a few microns thick (typically 3 microns, or 0.0001”) and cannot be used for rebuilding 

worn components. Thick PVD coatings often have such high stress internal stress that they spall off. 

Some Japanese automotive companies do, however, make PVD CrN coatings 60mm (0.0025”) thick.

• PVD nitride and carbide coatings are hard – 2,000 - 3,000 HV (three times as hard as chrome plate), 

and some can even be up to 5,000 HV (half as hard as diamond). For this reason they are used as 

erosion coatings in some aircraft engines

• PVD is not in general a good method for coating internals, although some techniques have been 

developed specifically to coat the insides of tubes, pipes and gun barrels.

• Among the most commonly-used PVD coatings are TiN, CrN, and the various diamond-like coatings 

(DLCs).

• PVD nitride coatings are essentially inert and do not corrode, but they do not provide any protection 

once scratched or damaged.

• IVD (Ion Vapor Deposition) aluminum is an example of a PVD process that is used quite widely in the 

aircraft industry. While there have been attempts to modify the method to deposit hard coatings, 

none of these have gone beyond the R&D stage.

• PVD coatings are often used for decorative surfaces, to create “lifetime coatings” on door hardware 

and plumbing fixtures. Many of the nitrides have gold or other attractive colors.

• PVD is environmentally benign in that the only gases that go through the process generally are 

nitrogen and argon, and the source materials are solid metals, although some processes do use 
http://www.rowantechnology.com - 6 -

methane or acetylene gas. Vacuum chambers do have to be cleaned, and care must be taken to avoid 

worker exposure to fine metal dusts.

Facts about CVD coatings:

• CVD is used to create many of the same hard nitride coatings as PVD, with similar hardness.

• The primary advantage of CVD coatings is that, because they use gases, they can be used to coat very 

complex objects, including internals, even down to micron sizes.

• For CVD coatings to grow on a surface the surface must usually be red hot (around 1,000°C,1,830 °F), 

which limits what types of alloys it can be used to coat. As a result it is seldom used for coating high 

strength alloys, which are heat-sensitive. CVD can be done at lower temperatures by using plasmas or 

more expensive metalorganic gases. This lowers to temperature to around 500°C (930°F), which is 

still above the tempering temperature of many alloys.

• Coatings are usually a few microns thick, although the method can be used to create materials 

several centimeters thick (such as infrared windows).

• CVD materials are usually hazardous (some highly so) – poisonous, pyrophoric, explosive, or combine 

with water vapor in the air to create hazardous fumes such as HCl. The process must therefore be 

used with proper safety systems and methods of trapping the used gas.

If you are used to using chrome plating, you will find adopting vacuum coating methods to be very challenging. 

Very few companies outside the cutting tool industry use CVD coatings because of the safety issues. PVD 

coatings have been brought in-house by manufacturers of plumbing products and some aircraft engine parts 

manufacturers and overhaulers. However, the cost of equipment can be very high ($1-3million for a coating 

system, with additional costs for a cleaning line). Running a coating operation also requires a sophisticated 

workforce able to handle and troubleshoot vacuum systems, cooling systems, gas handling systems and 

electronics. PVD coatings require very careful attention to cleanliness, both of the product to be coated and of 

the vacuum chamber, which requires proper equipment and a well-trained workforce.

In general, unless production volumes are high, most users will find it most cost-effective to a coating service 

vendor rather than bringing the process in-house. Vendors can be found in most areas of the world.

Heat Treatments

Heat treating is the general name for a set of technologies in which the product is heated to give the proper 

alloy properties (tensile strength, hardness, toughness) or to modify the surface. These types of technologies 

are also known as diffusion treatments when they also involve the diffusion of metal atoms from a packed bed 

into the surface – primarily Al, Cr and B.

The most widely used surface modifications are nitriding, carburizing and nitrocarburizing. Older processes 

used to involve the use of molten salt baths (frequently cyanides) or packed beds, but these methods have 

been largely displaced by gas methods of nitriding, carburizing and nitrocarburizing, and by plasma nitriding. 

New technologies such as ion implantation have been adopted into the surface treatment industry from the 

semiconductor industry, but have found only small niches.

Because they cannot be used to build up worn material, heat treatments are not used in repair. Their primary 

usage is to create wear-resistant surfaces on products (carburizing of gears, for example), or to make surfaces 

resistant to corrosion or oxidation (e.g. boiler tubes, hot section turbine blades). The exception to this is ion 

implantation, which is a room temperature process in which ions are fired into the surface to form a very thin 

(0.1 mm) layer. Although the layer affected is extremely thin, the process appears to change the wear 

mechanism so that it has an impact on wear long after the thin surface has been worn away.

Facts about heat treatments:
http://www.rowantechnology.com - 7 -

• Heat treatments generally take place at temperatures of 500-1,000°C (930–1,830°F). This limits the 

alloys and products that can be treated.

• At these temperatures, some alloys can grow as they go through phase changes, and products can 

distort.

• These treatments are not coatings. They cannot come off as coatings can, but they also cannot be 

used to build up worn surfaces.

• Not all alloys can be nitrided or carburized. These processes are usually used on nitridable or 

carburizable steels, but can be used on some other alloys.

• The exception to this is ion implantation, which is done at room temperature, usually using nitrogen 

ions. It has very limited market niches (medical prostheses such as hip and knee joints, certain molds, 

dies and metal forming tools). The method has been shown to reduce wear in hard chrome plate, and 

so some companies have used the process to improve the life of plated products.

Nitriding, carburizing, ferritic nitrocarburizing and implantation are clean processes and the surfaces are RoHScompliant. Metallizing treatments (chromizing, aluminizing, boronizing) can product chlorine and HCl gas and 

leave the packed bed a hazardous waste that must be disposed of properly. Some newer metallizing methods 

have been developed to alleviate these problems.

Laser and Welding Methods

Some of these welding methods have been in use for many years – weld cladding has long been a simple do-ityourself method for repairing and reducing wear of farm machinery, while explosive welding used to be used 

for welding railroad track. However, these methods have been modernized and some of the newer 

technologies, such as laser cladding, are beginning to make headway as hard coating and repair methods in 

place of chrome plate.

Laser cladding is a technology that has only become industrially viable on a large scale in the past few years as 

more robust and reliable lasers, such as diode lasers, have become widely available. The technique uses a laser 

to melt a powdered metal onto the surface. This heats the surface but not the bulk of the material, so it does 
http://www.rowantechnology.com - 8 -

not have the limitations of most heat treatments, but this can an issue for aerospace parts.

Electrospark deposition (alloying) (ESD, ESA) is a microwelding technique in which an electrode is used to 

weld coat the surface or fill in small damage areas. It is often used to repair dies and molds, but has been 

adopted in some other limited applications. The heat-affected zone is very small and the method is used for 

repairing some aircraft engine components that are not fatigue-critical. Its primary use is the repair of damage 

and wear in molds and dies. The equipment is very inexpensive and easy to use with minimal training, and 

there are several suppliers around the world.

Facts about laser and weld methods:

• Welding involves melting the material to be welded. This limits the alloys and products that can be 

treated to materials that can be welded and products that can withstand the heating involved or can 

be heat treated back to their original properties.

• The various standard torch and electric arc welding methods input the most heat. They are ideal for 

large items. However, welding of stainless steel can generate Cr6+ in significant quantities because of 

evaporation from the weld rod.

• Laser welding is best for external surfaces. It can be highly controlled and automated and can even be 

used to produce 3-dimensional near net shapes.

• ESD can be done in such a way that it has almost no effect on fatigue. It is a very small area, slow 

deposition process and is primarily used for repair rather than coating.

These methods are all RoHS-compliant. Weld coating with any Cr-containing electrode material or laser 

cladding with Cr-containing powder could be OSHA non-compliant.

What option is best?

It depends on the application, the item being plated, whether it is contracted or done in-house, and how the 

process needs to fit with your production system.

Treatment Typical applications Pros and Cons

Thermal spray (HVOF, etc.) Aircraft landing gear, 

hydraulic rods for most 

purposes, industrial rolls

Harder and more wear resistant, can rebuild. 

Not for IDs, must be superfinished.

Electro and electroless 

plating

Anywhere hard chrome is 

used, internals (esp 

electroless Ni)

Mostly easy to use for internals and externals. 

Generally no better than chrome.

Heat treats Hydraulic rods, gears, 

bearings

Almost any size and shape, cannot delaminate. 

Cannot be used for rebuild, cannot be used for 

heat-sensitive materials.

Vacuum coatings Typically small, high value

items, molds and dies

Extremely hard and wear resistant. Complex 

and expensive.

Welding methods Rebuild of worn or corroded 

items

Good for thick coatings, mostly on externals. 

Not for heat sensitive materials, must be 

refinished.