Isothermal Section Of The Zn-Ti-Si System At 450℃ And The Research Of Periodic Layered Structure Of X(Ni,Ti)₃ Si/Zn

The phenomenon of periodic layed structure attracted a great attention of inverstigators. And several diffusion models have been proposed. However, so far there is no comprehensive theory for academics to embrace, and the mechanism of this unusual phenomenon still remains controversial. So more research is needed to strengthen the theoretical basis for the work. A series of diffusion couple experiments were carried out based on the experimental study of the relevant department of Zn-Ti-Si system at 450oC, and using the reaction path and the interface response theory to study the periodic layered structure.As a series of investigation, the isothermal section of the Zn-Ti-Si system at 450℃was studied using the equilibrated alloys. The specimens were investigated by means of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The experimental results indicate that ten three-phase equilibrium phase regions exist in the 450oC isothermal section, including TiZn₈+Ti₅Si₃+TiZn₁₆, Liq.+TiSi₂+Si, Liq.+TiSi₂+TiSi, Liq.+Ti₅Si₃+TiZn₁₆, TiZn₈+Ti₅Si₃+TiZn₃, TiZn₃+Ti₅Si₃+TiZn, Ti₅Si₃+Ti₂Zn+α-Ti, Ti₅Si₃+Ti₂Zn+TiZn, Liq.+Ti₅Si₃+Ti₅Si₄. while Ti₅Si₃ is a very active phase which equilibriumed with other phases. There is aΤphase exists at 450oC which composition range is Zn (36.5-69.3at.%) Ti (19.6-37.3at.%) Si (11.8-26.14at.%). When through a short holding time it will appear in the edge of Ti5Si3, while after the long holding time it will disappear, these indicated that theΤphase is a metastable phase, by reparating sample accordanced with the composition ratio range at 450oC, there has not been a single-phase, so the composition and structure of theΤphase needs to be further studied.According to the relevant experimental results, the diffusion couple experiments were carried out in the Zn-Ti-Si and Zn-Ni-Si system, and the results showed that periodic layered structure was observed in Zn/Ti₃Si solid state diffusion couples and liquid-solid diffusion couples. while in Ni₃Si/Zn system, using field emission scanning electron microscopy and electron probe, we have analysised the microstructure morphology of the nucleation station, the results agree with the formation mechanism of periodic layered structures which we have proposed that Ni enriched in the interface of T/Ni₃Si, when the concentration of Ni reaches a certain critical value required for the nucleation of theγphase, theγphase may precipitates from theΤphase which eventually formed a continuous layer. The new system of Ti₃Si/Zn was studied respectively, the results indicated that incomplete periodic layers formed in the liquid-solid diffusion region of Ti₃Si/Zn, which maked up of the T phase and TiZn₃, while T-phase was only formed in the forefront of the Ti₃Si phase alonged the diffusion direction.