Stainless steels are highly resistant to corrosion. They are tough and ductile, with excellent strength properties.

Mostly, stainless steels consist of iron, chrome, and nickel.

They are a great material for welding, but difficult to solder. They also need a special treatment before they can be electroplated.

There are different strategies concerning the pretreatment of stainless steel. But all methods aim to create an adhesive “bonding” layer by reducing the resistant chrome oxide layer to chrome.

Iron- and nickel oxides are easy to activate in a pH acidic environment which explains the use of very acidic media.

The three treatments:

• Nickel-Strike – A very acidic nickel-chloride electrolyte

• Gold-Flash – A sulfuric gold electrolyte

• Copper-Flash – A sulfuric copper electrolyte

Assessment of our treatments

Nickel-Strike

Advantages

• Relatively cost efficient treatment

• Good throwing power

• Established treatment

Disadvantages

• Very corrosive medium (Cl^– emits HCl)

• Only allows the use of nickel anodes, since any other anodes (like Pt, PtTi, MOXTi) cause chlorine gas emissions

• The layer is ferromagnetic, therefore, the application on stainless steels with low permeability is questionable at best.

• The initial permeability rises with heat treatment (350°C, vacuum)

• The deposition can corrode, immediate subsequent processing is highly advisable

• Optical assessment of the deposition is difficult since stainless steel and nickel look very much alike

Gold Flash

Advantages

• Good throwing power

• Not ferromagnetic

• Easy to assess optically (yellow deposit on stainless steel)

• The use of different anodes is perfectly possible (Pt, PtTi, MOX-Ti, Graphite, Au)

• Application with “tampon” method works well

Disadvantages

• Expensive (electrolyte contains at least 3g Gold per liter)

• The electrolyte is toxic

Copper Flash

Advantages

• Very good throwing depth (adjustable via copper content)

• Not ferromagnetic

• Fast (1-2 minutes)

• Very good color indicator (red on stainless steel)

• Different Anodes are possible (Cu, Pt, PtTi, MOX-Ti

• Easily applicable by “tampon” method

• Affordable

Disadvantages

• Hardly researched, so far not in external use. All internal tests have been successful and reproducible.

Internal Test for Strike and Flash Electrolytes

Base material: Typically, 1.4301 stripes. If possible, we use the material the customer provides

Quench Test:

• Degreasing of the strip

• Potential pickling (to get rid of machining structures, not always needed)

• Flash treatment (internal procedure)

• A la prima coating with 25 µm bright copper

• 3 cycles of the following test:

  • Heating auf the coating until it’s red hot

  • Quenching in cool water

  • Visual control for bubbles and delamination

• Bending test of the base material and copper deposit until brittle fracture

• Close visual examination of the fracture under a microscope (no delaminations are allowed to pass the test)