Structural Control of Surface Modified Layrs through Ultrasonically Distributed Electrical Discharges.

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In order to improve friction and wear characteristics, surface modification of aluminum matrix composites was carried out by applying the new method named Electrical Discharge Alloying, in which each electrical discharge is forcibly scattered by ultrasonic vibration. Titanium contained in the green compact eletrode, and also carbon and silicon decomposed from the working fluid are transferred to the substrate surface through a single discharged arc. Sinece the application of ultrasonic vibration to the aluminum alloy substrate makes the amount of transferred elements increase, the thickness of modified layrs remarkably become thicker. Then, the volume fraction of in situ TiC in the modified surface increases with applying ultrasonic vibration, so that the hardness of modified surfaces becomes high. The process, electrical discharge alloying, makes it possible not only to coat a composite layr containing in situ TiC with a thickness of nearly 80 mum within a few minutes, but also to get high volume fractions of TiC by applying ultrasonic vibration, which is an additional process parameter to discharge conditions. Hradness of the modified surfaces can be controlled to have any value of 4-14 GPa by varying the volume fraction of TiC.It is also recognized that the process improves wear resistance of the modified surfaces.