Formation of TiC/Ti<SUB>2</SUB>AlC Composite Layer and Improvement on Surface Roughness

Abstract

In order to improve surface hardness, surface modification of die casting aluminum alloys was carried out by applying a new method called Electrical Discharge Alloying with ultrasonic vibrations, in which a conventional electrical discharge machine can be used. The layer deposited on the substrate consists of TiC and Ti 2 AlC formed by the reaction between titanium contained in the green compact electrode, the aluminum in the electrode and the substrate and also the carbon decomposed from a working fluid. When the ultrasonic vibration is applied to the substrate, especially at a frequency of 94.2 kHz, the discharged craters are bigger than those obtained when alloying without ultrasonic vibration. Also, for single discharge, the amount of deposited Ti and C increases near the edge of the crater. When the ultrasonic vibration is applied to the electrode for single discharge, many convex-shaped craters are generated on the substrate. The cross-sectional hardness of the alloyed area increases with increase in the concentration of carbon and titanium. The secondary elaboration using the cast Ti-36 mass%Al solid electrode is effective for the improvement of surface roughness of the modified layer. When the green compact electrode is used in the primary Electrical Discharge Alloying and the cast solid electrode is used in the secondary elaboration, surface roughness is not so different between the process with and that without ultrasonic vibration. However, the modified layer's thickness obtained with ultrasonic vibration is thicker than that without ultrasonic vibration.