ASTM B733 – Electroless phosphating of nickel – The upper limit for phosphorus content is
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ASTM B733 specifies that the phosphorus content in chemically plated nickel-phosphorus alloys should be ≥10% for the high-phosphorus grade; what is the upper limit? What are the effects of too much phosphorus?
Relevant literature on \"The relationship between the physical and chemical properties of electroless nickel coatings and phosphorus content\" indicates that: (1) the microhardness of the coating at the as-deposited state decreases as the phosphorus content increases. After aging treatment, the coatings with different phosphorus contents all exhibited their maximum hardness at 400–420°C; this maximum hardness increased as the phosphorus content rose. Moreover, as the aging time increased, the hardness of coatings with low phosphorus content decreased more rapidly than that of those with high phosphorus content. (2) In the selected test medium. The corrosion resistance of high-phosphorus coatings is superior to that of low-phosphorus coatings. The corrosion resistance of the plated state is superior to that of the 400°C aged state.