The disc specimens, 8 mm dia., 1.5 mm thick, with ternary alloying component of gold, copper, indium or tin as a additive alloying element were prepared to investigate the influence of them on the segregation and chloride corrosion behavior of silver 75 gm palladium 25 gm the binary alloy.
To observe and compare the segregation degree of each metallic elements, the light microscopic view of cast structure and the secondary electron image with line profiles from EPMA were taken, and as the best test methods for comparing chloride corrosion behavior, a potentiodynamic polarization method in saline solution without aeration and stirring was selected. From potentiodynamic polarization curves drawn by potentiostat connected with saturated calomel and graphite electrode, critical current densities of each specimens were compared with each other. Corroded surfaces and corrosion products were observed and analyzed to find the most corrosive site.
After contact corrosion with nickel chromium alloys as anode for 60 days in physiologic saline solution, the micrographs of corroded surface of nickel chromium alloys were used as index for anticorrosive property of silver palladium based alloys. Transfer and deposit of nickel ion to the surface of silver-palladium alloys were observed also.
The result of the present study allow the following conclusions to be drawn:
Line profiles of gold and indium exhibit no segregated behavior and adding large amount of gold or indium into the basic composition decrease the degree of segregation of silver and palladium. However copper and tin were segregated prominently on the grain boundary with the segregation of palladium.
2. Specimens containing gold 5% show the corrosion resistance less than that of alloy with fundamental composition, and 13% gold alloy exhibit the most excellent corrosion resistance in all kind of tests.
3 Segregation and corrosion were diminished gradually by increasing the amount of indium, however at 6% indium content corrosion tendencies of specimens were increased by the formation of microcracks.
4 By increase in quantity of copper a insignificant rise of critical current density was observed, microporositiesat grain boundary were found as corrosion prone site.
5. Tin added to Ag-Pd binary alloy segregate the solid solution as Ag-Pd rich, Sn-Pd rich, and Ag-Sn rich eutectic phases the last was corroded prior to the other phases.
6. Adhesion of corrosion product were least on copper alloy, and during contact corrosion with nickel chromium alloys, alloys containing copper or tin were corroded themselves.
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