Wettability And Spreading Dynamics Of Graphite And Al₂O₃ By Molten Metals

Discussing the wetting mechanism of metal matrix and solid reinforcement and revealing its spreading dynamic rules can provide important theoretical guidance for optimizing the preparation technology of metal matrix composites.Researchers have no consistent view of the wetting mechanism by now.Most of the spreading dynamics model established already is based on the relationship between contact angle or droplet spreading radius and time for their expression,so they do not reveal the nature of spreading driving force.On the base of the limited interfacial thermodynamic calculation model,a spreading kinetic model was established which was used for describing reactive wetting system in this dissertation.The wettability of Au-Si/graphite and Ag-Ti/Al2O3 system was studied using a modified sessile drop method,and the sample interface microstructure was analysed by XRD,EDS,and SEM means.The dynamic model established in this paper is used to predict the dynamic changing rules of the system.The main research results are as follows:(1)Under the condition of a certain temperature,the addition of Si can significantly improve the wettability of Au and graphite system.As with the increasing concentration of alloys,the time required to balance get shortened and the final contact angle decreased.This is mainly due to that the active element Si react with C dissolved from graphite and generated a comparatively continuous SiC layer between metal/graphite interface,thus a new metal/ceramic interface formed,which reduced the solid/liquid interfacial energy and led to contact angle decreased.(2)At the initial wetting stage,the dissolving of graphite and the surface adsorption of active element influence the spreading of Au-Si/graphite system,and the lower the temperature,the more obvious effects.But the interfacial reaction is the key factor of system wettability.At 1373-1473 K,the final contact angle of Au-30at.%Si/graphite system was between 100°to 160° The wettability changed from non-wetting to wetting and the time up to balance got shortened with the raising of temperature.(3)When temperature rangeing from 1373K to 1473K,the initial contact angle and final contact angle have a certain degree of dependency to temperature of Ag-4at.%Ti/Al2O3 wetting system.Both initial contact angle and final contact angle changed with temperature as an approximate linear relationship.The interfacial reaction and the adsorption of active element Ti on the solid/liquid interface decided the wetting of system collectively,but the interfacial reaction played the main role.As temperature rising,the interfacial reaction intensified and the thickness of product layer increased obviously,and the interfacial reaction products have obvious stratification which was attributed by the precipitate type and the different order.(4)Describing the reaction wetting process by the change of solid/liquid interfacial energy rate.It is found that the wetting process is closely related to the interfacial reaction.The spreading kinetic model explained the wetting mechanism from the angle of energy and predicted the solid/liquid interfacial energy decreasing with time in exponential relationship.The experimental results are in accord with the theoretical calculation in reaction-limited spreading.We also calculated the reactive activation of Au-Si/graphite system by the equation established in this paper.