Formation of TiC/Ti2AlC composite layer and improvement on surface roughness

In order to improve surface hardness, surface modification of die casting a luminum alloys was carried out by applying a new method called Electrical D ischarge Alloying with ultrasonic vibrations, in which a conventional elect rical discharge machine can be used. The layer deposited on the substrate c onsists of TiC and Ti2AlC formed by the reaction between titanium contained in the green compact electrode, the aluminum in the electrode and the subs trate and also the carbon decomposed from a working fluid. When the ultraso nic 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 dep osited Ti and C increases near the edge of the crater. When the ultrasonic vibration is applied to the electrode for single discharge, many convex-sha ped craters are generated on the substrate. The cross-sectional hardness of the alloyed area increases with increase in the concentration of carbon an d titanium, The secondary elaboration using the cast Ti-36 mass%Al solid el ectrode is effective for the improvement of surface roughness of the modifi ed layer. When the green compact electrode is used in the primary Electrica l 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 thick ness obtained with ultrasonic vibration is thicker than that without ultras onic vibration.