采用液接法制备Zn/CuxTiy扩散偶, 利用SEM和EDS等对扩散偶在663 K保温不同时间后的反应区进行分析. 结果表明, 除Zn/CuTi2和Zn/CuTi体系以外, 其它5个扩散反应体系能够形成周期层片型结构, 分别是Zn/Cu9Ti, Zn/Cu4Ti, Zn/Cu7Ti3, Zn/Cu3Ti2, Zn/Cu4Ti3. Zn/CuxTiy体系靠近反应区前沿的周期层片结构由单相CuZn2和双相CuZn2+TiZn3交替构成, 而且周期层片型结构的层片厚度与CuxTiy合金的成分有关: CuxTiy合金中Cu原子含量越高, 对应反应区的周期层片厚度越小. 上述实验结果符合扩散应力模型的预测.
Periodic-layered structure during solid state reactions is one of the most complicated and interesting structures in the solids, which consists of a periodic sequence of layers that grow perpendicularly to the expected macroscopic diffusion flow. Since the Zn/Fe3Si system was first discovered, much research work has been done on the characterization of the microstructures, the understanding of the formation mechanism and discovery of new systems. However, the exact nature of this phenomenon still remains a controversial topic. In the spirit of thermodynamic instability mechanism, the periodic-layered structure consists of single phase α layer and single phase β layer arrange alternately, while in that of dynamic instability mechanism, which is based on a diffusion-induced stress model, the structure is considered to be composed of regular multilayers of single phase α and two-phase α+β. In the present work, the solid state reactions of various Zn/CuxTiy diffusion systems annealed at 663 K for different times were investigated by using melting contact method, SEM and EDS. The results show that both the polished sections and the in situ fracture surfaces of periodic-layered structure, 5 new systems, i.e. Zn/Cu9Ti, Zn/Cu4Ti, Zn/Cu7Ti3, Zn/Cu3Ti2, Zn/Cu4Ti3 are found to form periodic-layered structure within the diffusion zones. The periodic-layered structure is composed of the CuZn2 single phase and CuZn2+TiZn3 two-phase layers distributing alternately within the reaction area near the CuxTiy side. Furthermore, the thickness of the periodic layers relates to the composition of CuxTiy substrates: the higher the content of Cu atom in the Cu-Ti substrate, the thinner the layer will be. In addition, the adjacent two-phase layers show mated topography and the interface between the periodic layers illustrates typical tear characteristics in mechanics, which are in good accordance with the prediction of the diffusion-induced stresses model. Therefore, the present work provides new and convincing evidence for the dynamic instability mechanism in the interpretation of periodic-layered structures in solids.
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