Ａｕ‐ＺｒＢ２分散めっきの表面特性

Abstract

For the purpose of obtaining a new type of electrical contact material, layers of Au-ZrB2 composite were electrodeposited from an acidic Au plating bath containing suspended ZrB2 particles, which have such advantageous properties as a high melting point, excellent hardness, good corrosion-and oxidation-resistance and high electrical conductivity. Some properties of the codeposited surface layers were investigated.It was observed by scanning electron microscope that the diameter of the ZrB2 particles codeposited with Au on the substrate was about 5μm or less, independent of the size of the ZrB2 particles in the plating bath. Using a micro Vickers hardness tester, the hardness Hv of 165-180 of the ZrB2 composite layer was found to be clearly different from the value of 120 for a pure Au deposit layer. In abrasion tests using a tester of our own devising, 35μm layers of pure Au deposit were completely worn down but Au-ZrB2 composite layers retained over 90% of their thickness after the same number of rotations of the rub head. Some test pieces of Cu substrate covered with Au-ZrB2 were set in the contact points of relay switches and a 100V, 50Hz, 60W resistive load (candescent light bulb) was switched on and off in accordance with JIS C 5441. After 5×105 switching cycles very little change was detected in contact resistance, or in the surface roughness of the contact points caused by the heat of arc discharge.These facts indicate that a composite layer of Au-ZrB2 may be suitable for use in contact material for electronic devices.