Corrosion resistance of tungsten heavy metal alloys
Q. Does anyone have data on corrosion resistance of tungsten heavy metal alloys (90-95%W, remainder Fe and Ni)? Aerospace standards frequently call for cadmium plating and or/paint finishing of parts such as counterweights. Our experience is that corrosion of these alloys is rare and only occurs under extreme conditions.Aryeh Asher
- Ashkelon, Israel
A. Are you looking for information on the corrosion resistance of untreated tungsten heavy metal alloys, or for cadmium plated/paint finishing of these alloys? Under what service conditions?
If some organization has specified cadmium plating for the application, there is usually a good reason. Cadmium evaporates in the heat and vacuum of space, so I suppose the cadmium is for some lubricity or corrosion characteristic at standard temperature and pressure.
What do you mean by extreme conditions? Unless we know the application, it is difficult to answer the question.
A. We found out that Tungsten Alloy (95%W-3%Ni-2%Cu) with nickel electroplating were corroding after going through the damp tests for about 14 days. What causes the tungsten metal to corrode? Is it due to insufficient nickel coating that eventually results in corrosion.Lau shir ling
March 29, 2013
Q. Hi. We've been working with a company who uses WHA's for vibration dampening and employs a 90wt%W - 6wt%Ni - 4wt% Cu. We discovered through SEM/TEM and EDS that there is actually trace amounts of Fe and C in the matrix phase which binds the W grains together.
Due to the galvanic potentials, the more noble W vs. the matrix causes microgalvanic cells across the whole surface in contact with electrolyte.
We discovered, and verified with research, that any amount of copper in the matrix accelerates the corrosion, vs a matrix with say Ni-Co or Ni-Co-Fe. Its due to the solubility of tungsten in the matrix, where a higher % of W dissolved in the matrix reduces the galvanic potential difference.
Basically, we're looking for ways to finish it as well, and any moisture that touches it starts to eat at it. Unless we can plate it with Al or Cr and passivate it.
- Hamilton, ON, Canada
A. Hi Rob,
I have experienced exactly the problem you are seeing now. the galvanic potential of the copper and nickel against the tungsten was setting up corrosion sites and causing the part to bind.
In the end we have electroless nickel plated all over to about 0.002", this solved our problem. There was a lot of work necessary in getting the surface clean and active enough for plating, talk to a reputable plating house in your area and I'm sure they will be able to help you.
aerospace - Yeovil, Somerset, United Kingdom
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