Study On Mechanism Of Wettability Improvement Of Brazing Alloy On TiC Cermet By Zn Volatilization

TiC cermet synthesized by SHS method is an important structure material because of its high hardness, good wear resistance and high elevated-temperature strength. Conventional brazing alloy has bad wettability on TiC cermet, while the wettability is greatly improved when AgCuZn brazing alloy with Zn vaporization is adopted. Thus the present thesis aims to study the mechanism of wettability improvement of AgCuZn brazing alloy on TiC cermet with Zn vaporization by means of experimental examination and theoretical analysis.The experiments of brazing alloy on TiC cermet in different atmosphere and AgCuZn brazing alloy with different Zn mass percentage make clear that Zn vaporization during vacuum has a great impact on wettability of AgCuZn on TiC cermet. Wettability of AgCuZn on TiC cermet is best with 25wt.% Zn. When AgCu brazing alloy was adopted, the microstructure was Ag(s.s)+Cu(s.s)/(Cu,Ni)+Ag(s.s)/TiC cermet+Ag(s.s) +Cu(s.s) /TiC cermet from the near exterior surface of the alloy to TiC cermet. However, with AgCuZn,the microstructure was Ag(s.s)+Cu(s.s)+(Cu,Ni)/Ag(s.s)+Cu(s.s)/(Cu,Ni)/ TiC cermet+Ag(s.s)+Cu(s.s)/TiC cermet. The configuration and amount of (Cu, Ni) are different at the interface of AgCuZn/TiC cermet with different Zn content, as well as the amount and diffusion distance of TiC particle.In this thesis, the classic Young's equation is modified using the change of S/L interface tension based on contact surface area percentage of (Cu,Ni) and Ni mass percentage in (Cu,Ni). The academic contact angles calculated from the equation tally with the contact angles obtained from the experiments. Further more, kinetics of AgCuZn brazing alloy wetting TiC cermet was studied. Based on Langmuir adsorption theory and the relationship between adsorptive capacity and wettability, the kinetic equation of AgCuZn on TiC cermet was established, and then modified using experiment datas.In order to explain the mechanism of wetting improvement of AgCuZn on TiC cermet by Zn vaporization during vacuum from the quantum mechanism, three cluster models were established in this paper.From analysis of density of state, partial density of state, bond population and bond length, it's determined that wettability of AgCuZn brazing alloy on TiC cermet is easier with Zn vaporization because of stronger interaction between Ni and Cu.