Abstract
The feasibility of using various nitrides as wax pattern coating material for an Ag-Pd-Cu-Au alloy was studied. Nitrides used in this experiment were h-BN, AlN and Si3N4. Wax patterns were painted with the nitride coating materials, and were then outer-invested with a mixture of gypsum-bonded investment and water. The temperature of the mold was 700ºC, and the heat source was a blow pipe. Thin specimens (thickness: 0.55 mm) were cast in the 45 Ag-20 Pd-18 Cu-12 Au alloy (melting point: 930ºC) using a centrifugal casting machine. The cast specimens were investigated macroscopically and by scanning electron microscope, surface-roughness analyzer, X-ray diffractometer and micro-vickers hardness meter.
The results were summarized as follows. BN showed the benefit of separation that indicated improved cleansability and work efficiency. The BN coating layer remarkably inhibited the formation of CuO on the cast surface, only Cu2O was detected. The color of the cast surface coated with BN was rusty red, which agreed with the color of Cu2O. The surface-roughness (Rz) of the cast specimens decreased to less than 2/3 of the control with the use of BN. It was suggested that BN restrained the decrease in hardness of the surface layer. Nitrides did not influence interior hardness of the cast specimens.
