The effects of the alloying elements (Ti, Zr, Hf, Al and Si) on the wettability and spreading dynamics in the Cu/B4C system were investigated by a modified sessile drop method at 1373 K. The addition of a small amount of Ti, Zr and Hf greatly improved the wettability while that of Al and Si did not show a significant effect even at a concentration of 10 at.%. The effectiveness was in the sequence of Ti>Zr>Hf>Al>Si. For the Cu-(Ti, Zr, Hf) alloys, the spreading showed different dynamic behaviors at different concentrations. When the concentration was low (no more than 3 at.%), the time variation in contact diameter exhibited a linear behavior until a characteristic contact angle was reached and then the triple line began to warp due to the formation of a non-wettable graphite crater at the front. The wetting was thus controlled by the interfacial reaction in the early stage and the dissolution of the B4C substrate at or close to the triple junction in the later stage. When the concentration was relatively high (5 at.%), the warping of the triple line was suppressed and the spreading was much faster with the final contact angle approaching zero degree. The excellent wettability should result from the joint contribution of the formation of continuous wettable reaction product layer and the adsorption of excessive active atoms at the interface. The spreading dynamics for the reaction-control and the adsorption-control possess similar mathematical expressions but different physical meanings in time factor, making the distinguishing between them difficult but not impossible.
Keywords: Wetting; Spreading; Reaction; Adsorption; Interface.