Rapid electrolytic deposition of diamond turnable nickel phosphorus alloy coating

High phosphorus and thick electroless nickel (EN) coating is a diamond turnable hard metal used for making optical mold inserts by single-point diamond cutting technology. The EN plating process, however, has drawbacks such as low deposition rate (< 10 μm/h), existence of defects, and high cost. In this study, we have developed a rapid electroplating process (> 60 μm/h) to deposit high phosphorus (> 12 wt%) nickel alloy (NiP) coating for diamond turning of optical mold inserts, by proper electrolyte formulation and process optimization. The coating was characterized in crystallinity (by XRD), phosphorus content (by XRF/EDS), microstructure (by SEM and optical microscope), and micro hardness. Diamond turning tests were also carried out by an industrial partner, and the machined surface finishes and diamond cutter wear condition were evaluated. The results showed that electroplating is superior to EN plating process to deposit diamond turnable NiP alloy coating due to low cutter wear rate, high deposition rate and low production cost. Furthermore, no defects were observed on the diamond turned electrodeposited NiP coating surfaces during the diamond cutting of 50,000 m.