I am trying to deposit a pure nickel coating on a stainless steel substrate by means of a conventional electroplating process. But the deposited coatings have not shown an acceptable mechanical strength, fracture toughness and adhesion to substrate. What is/are the easiest and most applicable way/ways for enhancing these properties?
Usually they use a precursor copper coating to provide better adhesion
Try subject the nickel coated steel specimens to thermal annealing. The interdiffusion between steel substrate and nickel coating improves both adhesion and strength of the coating.
Adhesion problem between stainless steel specimen and coating of pure nickel I am recommending to test on textured surface as trapping of nickel in microcavities shall increase effective contact area and hence strong adhesion/stable coating/long life of coating!!!!!
It is known that the microstructure and mechanical
properties of a plated thin film depend upon the plating
conditions such as temperature, concentration and current
density. Surprisingly, little effort has been made to
clarify the relationship between processing conditions and
mechanical properties of plated thin metal films, particularly
of plated Ni.
Hi Farid,
Try to proceed with electroless plating method. This method has the advantage to offer good adherence even on non-conducting substrate. Below, I suggest a bath formulation for electroless nickel plating:
Nickel sulfate: 80 g/L
Sodium hypophosphite: 24 g/L
Sodium acetate: 12 g/L
Boric acid: 8 g/L
Ammonium chloride: 6 g/L
Add Mn to the Ni deposit for mechanical strength. 1% Mn will suffice. It will enhance fracture strength greatly.
Hello,
For adherence:
1)electrolytic degreasing cathodic or anodic in alkaline bath;
after rinsing,immerse in
2)Wood's bath;comp.:NiCl2.6H2O:250gr/L;conc.200mL/L
Temp.:room temp.;make the piece first anodic at 2.5Amp/sq.dm for 1 to 2 min.then ,without removing piece from cathodic at 2.5 Amp./sq.dm.for 5to 6 min.
3)rinse
4)immerse in Ni sulphate or better in Ni sulfamate bath(100grNi/L,40gr boric acid,NiCl2 5gr/L) at T40-45 °C,pH4 , at current density of 5 to 10 mamp/sq.cm for the time necessary to desired thickness.
Rinse.
For strength , add to the sulfamate bath 8gr/L 1,3,5,or 1,3,6 or 1,3,7 naphthalene Trisulfonate or mixture of the 3 isomers.
Vickers Hardness will be of 400 to 450 units (< 250 VHN without Naphthalene Trisulfonate)
Surface preparation and process parameters of Ni plating plays major roll.
As Mr.Sergei said base coat copper coating minium 5 micron followed by Ni plating will improve adhesion.
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