FORMATION OF COMPOSITE LAYER CONTAINING TIC PRECIPITATES BY ELECTRICAL-DISCHARGE ALLOYING

In order to improve friction and wear characteristics, surface modific ation of aluminum matrix composites was carried out by applying a new method named Electrical Discharge Alloying, in which a conventional el ectrical discharge machine can be utilized. Titanium contained in a gr een compact electrode, and also carbon and silicon decomposed from a w orking fluid are transferred to the substrate surface through a single discharged are. An increase in the gap voltage widens the gap distanc e. Since the pressure due to the evaporation of working fluid in the v icinity of a discharged are 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 volu me fraction of TiC in the modified surface increases with increasing g ap voltage, and then the hardness of modified surfaces becomes high. T he process, electrical discharge alloying, makes it possible not only to coat a composite layer containing TiC precipitates with a thickness of nearly XO mu m within a few minutes, but also to get different vol ume 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 TIG. It is also recognized that the process improves wear resistance of the modified surfaces.