Effects Of Alloying Elements On The Wettability Of Alumina,boron Carbide And Carbon Nanotubes By Molten Al

Based on the“Materials genome engineering”national key scientific project and the“High-throughput preparation and development of discontinuous reinforced metal matrix composite and its application”national key research and development program,the present study investigated the wettability of three types of ideal reinforcing phases including alumina,boron carbide and carbon nanotubes by molten Al alloying with Si,Ti and Cu.On the one hand,we accurately measured the wettability of above three types of systems by using the dispensed and modified sessile-drop methods in a high vacuum in order to provide basic thermal/kinetic data related to wettability for the R&D program.On the other hand,we deeply explored the influence mechanism of the alloying elements on the wettability,aiming at providing theoretical guidance for the optimization of the preparation of the Al matrix composite and the improvement of the comprehensive performance of the composite from the perspective of wettability.Through the observation and analysis of the interfacial microstructure combined with thermodynamic/kinetic calculations,this study revealed the effects of alloying elements on wettability in non-reactive and reactive systems.The major results obtained are as follows:（1）The influence mechanisms of Si,Ti and Cu on the wettability of Al/α-Al₂O₃system are revealed.The addition of Si contributes to improve the wettability of both polycrystalline and（0001）single crystalα-Al₂O₃ by Al.The presence of C-facet（0001）single crystal on polycrystalline surface which has the strongest adsorption affinity for Si is the main factor to improve the wettability.Ti tends to adsorb at the solid-liquid interface and reduces the interfacial tension,leading to the improvement of wettability.The addition of Cu reduces the activity of Al in the alloy melt and thus weakens the deterioration of the final wettability of pure Al/（0001）α-Al₂O₃ system due to the surface structural reconstruction.（2）It is found that the influences of Si and Ti on the interfacial reactivity and wettability of Al/B₄C system are correlated with the alloying content.The lower Si addition（5–12 wt.%）does not significantly change the interfacial composition of Al/B₄C and has little effect on the final wettability.However,sufficient amount of Si addition（20 wt.%）transforms the interfacial product for Al/B₄C system from Al₃BC to numerous Si C,and the formation of Si C dominates the spreading kinetics at the later stage of spreading and improves the final wettability.The addition of Ti（0.5–3 wt.%）promoted the transition of the superficial interfacial product layer for Al/B₄C system from Al B₂ to Ti B₂,and the formation of Ti B₂ continuous layer phase improved the final wettability.The spreading kinetics of the Al-Ti/B₄C system is generally controlled by the diffusion of Ti to the triple line.The increase of Ti within the lower concentration range（≤1 wt.%）significantly increase the initial spreading rate and improves the wettability.（3）The influence mechanisms of Si and Ti on the interfacial reactivity and wettability of Al/CNTs system are revealed.The lower Si addition（5–15 wt.%）slightly deteriorates wettability.Whereas sufficient amount of Si addition（20 wt.%）contributes to the formation of Si C in large quantities at the interface,leading to the increase in the spreading rate and the improvement of the final wettability.The addition of Ti（1–3wt.%）promotes the formation of Ti C_x at the interface and enhances the initial spreading rate,and the final wettability of Al-Ti/CNTs system depends on the composite product layer of Ti C_x+Al₄C₃ at the interface.（4）The common mechanism for the influence of alloying elements（Si,Ti and Cu）on the wettability of different systems is as follows.（i）For the non-reactive system,alloying elements may segregate at the solid-liquid interface or on the surface of the droplet,resulting in the decrease of interfacial tension or surface tension,thereby regulating the wettability.Other element without absorbability（e.g.Cu）may also affect the wettability by changing the activity of matrix component.（ii）For the system involved in reactions,the addition of alloying elements can be divided into two cases.For the first case,referring to the addition of reactive elements to the non-reactive system,the spreading of such system is only controlled by the reaction kinetics process involving active components.The wettability depends on the property of the interface product and its rate of formation.For the other case where reactive elements are added to the reactive system,such as Al-（Si,Ti）/（B₄C,CNTs）system,the effect of alloying elements on the wettability is often related to their contents.When the alloying concentration exceeds the critical concentration in reaction thermodynamics,the transformation of interfacial products occurs.The property of the new product layer and its continuity determine the final wettability.On the contrary,the new product phase is difficult to form,resulting in a negligible effect of alloying elements on the wettability.