Nickel plating

[tadd]

Howdy all:
Just thought I would pass along my dealings with Electronic Chrome and Grind. They did a hard nickel plate on my centerlock hubs. I have used home Ni plate on my unimog so I don't have to ever sweat corrosion on those parts ever again (in my lifetime anyways ). I didn't trust myself to do something 'delicate' yet.

So in this thread you can see the vintage hub is a bit crusty.

Question about centerlock hubs for braintrust

This is after ECG's magic! They even went to the trouble of over plating thickness and ground to the correct dimensions so all the pits in the seal surface and bearing race surfaces are gone. They even did a Rockwell test to determine if they needed to heat process for hydrogen embrittlement when I brought it up.

They are not inexpensive, but the results were well worth the cost IMHO. Its nice to get back something better than I could do.

One with da shiny is the vintage, the other is a repop that was yellow cad.

[chris_seven]

Tadd,

Was the plating technique used Electroless or Electrolytic?

Clearly Electroplating Nickel can introduce problems due to hydrogen depending on the base material and its heat treatment condition.

Do you know the hardness of the steel used for the manufacture of these hubs as it would be interesting to know?

Depending on the plating technique used Nickel deposits can also have very high levels of residual tensile stress which can result in a significant reduction in fatigue life.

Watts Nickel is particularly bad in this respect but even deposits plated using a Nickel Sulphamate solution can reduce the fatigue endurance limit of hardened and tempered 4340 by as much as 50%.

Nickel Sulphamates tend to provide plated finishes that are stronger than those developed by the Watts process so would be the preferred method.

The reduction in fatigue life is due to the fact that the cracks that develop easily in the brittle coating act as stress raisers into the substrate.

One of the issues is that the presence of hydrogen in the Nickel layer causes embrittlement of this layer.

This effect is subtly different to the hydrogen cracking that can sometimes occur in the substrate.

It has been shown that baking at 300 degC can dehydrogenate the surface layers and significantly improve fatigue life back to the levels of an unplated part.

If baking temperatures are increased above 300 deg then fatigue life can again reduce as the material can start to either lose a little strength or suffer from temper embrittlement.

Electroless Nickel deposits have relatively high strength but tend to be brittle depending on the Phosphorous content.

The residual stresses can vary from compressive when a bath is new and phosphorous content is high to tensile when the bath ages or Phosphorous content is low.

In general it would be conservative to consider that Electroless Nickel does cause a reduction in fatigue life.

Classic Hydrogen embrittlement will not be an issue.

[tadd]

Chris:
I'm not anywhere near the metallurgist you are but I am aware of hydrogen issues. I may have misused the term hydrogen embrittlement. I will adjust my lexicon. As always when you post thank you for the schooling .

Its hard nickel which IIRC is less stressed than watts. I have a literature paper around here somewhere. It is an electrode process.

The plating engineer told me that they heat treat for anything over Rockwell 35 although the mil spec says R45 (if I am remembering that conversation correctly). Much like when I got my cylinders Ni-SiC re-coated it was very interesting talking to the engineer at Millennium plating. The ECG engineer said he would check hardness, so I will try to follow up on that.

I haven't found what alloy is used, but it is my understanding that it is a 2xxx series not a 4xxx series.

t

[chris_seven]

Tadd,

Sorry to go over this again but I would probably still like to bake these parts at 300degC - although I would accept that I am probably being very conservative.

It seems as if you have used a Nickel Sulphamate process which I would agree is the best option.

I also agree abut the hardness limit for hydrogen embrittlement in the conventional sense and there is nothing wrong with your understanding.

Nascent hydrogen which develops on the surface of steels when electroplated can cause cracks in the substrate ad the stronger the steel the more likely there is to be a problem.

The issue with the Nickel Sulphamate process is not due to substrate problems but due to hydrogen cracking in the Nickel coating.

Even relatively low stressed Nickel has a relatively short critical crack length and the hydrogen causes very short cracks to develop in the plated layer.

When subjected to fatigue loading these short cracks reduce the stress needed to initiate a crack into the substrate and make it easier for the crack to propagate into the steel.

We did some work some years ago on nickel plated turbine discs which is where the information on fatigue life comes from but this was using a 4340 steel.

The use of an SAE 2XXX Series also known as Nickel Steel is interesting and these steel are normally used for their low temperature properties.

Their impact strength at low temperature tends to be quite good due to a relatively low transition temperature so they are often used for the construction of storage tanks, rivets and a number of specialised parts used in very cold climates.

Their fatigue lives are not so great as at best this series of alloys have tensile strength of around 100ksi at best and more commonly 70ksi.

There is not too much fatigue data available as most interest is in the area of Charpy and K1D testing.

Its just worth a quick estimate of fatigue stress to see if there is anything to worry about. but any cracks in the plated layer may have less effect on fatigue life than in a higher strength steel.