Metal finishing Q&As since 1989

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Phosphorus in all nickel plating and hardness

2007

1-I want to know approximately what is the chemistry besides Nickel in Electroless Ni plating, Sulfamate Nickel plating and Electrolytic Ni Plating, especially the amount of Phosphorus for each one of those plating process.

2-Second question I have is what is the hardness of all nickel plating and chrome plating?

3-Is it true that if you heat a part that has been Chrome or Nickel plating to approximate 500F+, the hardness of the chrome plating and nickel plating will somewhat get hardness and then drop off at a still higher temperature.

Thomas P. Posten
Metallurgist - Long Beach, California, USA

As plated, electroless nickel (EN) is an amorphous solid solution of Ni+P. There are three grades. Low P (less 4% P), mid P (in between) and high P (above 9%P). Hardness at this point goes from 46 Rc for high P to over 58 for low P. All can be hardened by a short low temp HT which induces crystallization and precipitation of nickel phosphide. Chrome as plated is around 64-68Rc and is 99.5% pure. Prolonged exposure to high temperature greatly softens chrome as well as hardened ENs. Other nickel processes like sulfamate, conventional Watts or special formulations are all electrolytic, softer and almost 99.5% pure. There are exceptions but typical hardnesses go from 20 to 30Rc. These nickels also soften with temperature though not as much.

Guillermo Marrufo
Monterrey, NL, Mexico
2007