1997 Volume 38 Issue 7 Pages 630-635
In order to improve friction and wear characteristics, surface modification of aluminum matrix composites was carried out by applying a new method named Electrical Discharge Alloying, in which a conventional electrical discharge machine can be utilized. Titanium contained in a green compact electrode, and also carbon and silicon decomposed from a working fluid are transferred to the substrate surface through a single discharged arc. An increase in the gap voltage widens the gap distance. Since the pressure due to the evaporation of working fluid in the vicinity of a discharged arc decreases with a gap distance widened, it is hard to blow off the top layer of discharged craters with enriched titanium and carbon if the gap voltage is high. Consequently, the volume fraction of TiC in the modified surface increases with increasing gap voltage, and then the hardness of modified surfaces becomes high. The process, electrical discharge alloying, makes it possible not only to coat a composite layer containing TiC precipitates with a thickness of nearly 80 μm within a few minutes, but also to get different volume fractions of TiC by changing the gap voltage, which is one of the process parameters. Hardness of the modified surface can be controlled to have any value of 7–14 GPa by varying the volume fraction of TiC. It is also recognized that the process improves wear resistance of the modified surfaces.
