The properties of electrodeposited silver films from succinimide baths were iuvestigated using a bath composed of 0.45mol/L of CH3SO3Ag and 1.5mol/L of succinimide. The silver film grain size was similar to that from a bright cyanide bath. The optimum conditions for bright silver plating were a pH of 10, a bath temperature of 25°C, and a current density of 2A/dm2. The plating bath throwing power was 40-42% and increased with the pH. The solderability of these silver deposits was better than those from a bright cyanide bath and the film electric contact resistance was less than 2mΩ at a load of 5g. The deposited silver hardness was Hv (125-130) and became Hv (86-90) after backing at 200°C for 1h.
The critical current density at which massive Zn deposition began was measured in Zn and Zn-Ni alloy plating baths containing sodium citrate. Results were as follows: (1) The Zn deposition potential from citrate-containing baths was 0.1V less positive than from citrate-free baths, iudicating that citrate behaves as a complexing agent with Zn ion. (2) Ni partial polarization curves also shifted to a less positive region with the addition of citrate in Ni and Zn-Ni alloy plating baths. (3) The addition of sodium citrate and a decrease in pH in baths increased the Zn critical current density. (4) pH in the cathode layer attained the value for Zn hydroxide formation at the critical current density in both citrate-containing and citrate-free baths. Since the pH for Zn hydroxide formation is higher in citrate-containing than citrate-free baths, the critical current density at which adsorbed Zn hydroxide suppresses the hydrogen evolution rate to initiate massive Zn depositions is increased by the addition of citrate to baths.
Coated cutting tools with CVD diamond film requires high adhesion strength between the diamond film and substrate. We studied the adhesion strength of diamond-coated WC-Co tools using Microwave Plasma CVD (MWPCVD) and an Al-18%Si alloy cutting test using diamond cutting tools. Diamond was coated onto tools using an MWPCVD apparatus. The reaction gas was a mixture of methane and hydrogen. Substrate temperature was varied from 673K to 1173K by controlling the microwave output power and growth pressure. SEM observation revealed that grain size grew with increasing substrate temperature. All deposits were clear diamond crystals. XRD showed that deposits were cubic diamond. Raman spectroscopy showed that deposits synthesized at a lower substrate temperature (673K) were of higher quality than those synthesized at a higher substrate temperature (1173K). A scratch adhesion strength test, from 673K to 873K showed that adhesion strength increased from 873K to 1173K, but it decreased with increasing substrate temperature. Deposition synthesized at 873K showed the best adhesion strength. In Al-18%Si alloy cutting test of using diamond-coated tools synthesized at 873K, diamond film did not peel after a 800m cutting test and the surface of Al-Si work pieces turned with diamond coating tools synthesized at 873K presented uniform roughness. The cutting performance of Al-18%Si alloys using diamond-coated WC-Co tools was related to adhesion strength.