Research On The Kinetics Of The Periodic Layered Structure In The Co₃W/Al And Ni₃Si/Zn Diffusion Couples And The Phase Relation Of Relative System

The formation of periodically layered structures during solid-state reactions wasfirst discovered by Osinski accidental when they studied the effect of content of Sielement on the properties of hot dip galvanized products in1982. Since then, scholarsbegin to concern this phenomenon and also find periodically layered structures in theAgTi/Si, Co₂Si/Zn, NiCoFe/Mg, NiCo/Mg, Ni₃Si₂/Zn, SiC/Ni, SiC/Pd, SiC/Pt,SiO₂/Mg,（Ni,W）/Al and CuTi/Zn diffusion couples system. There are some theoriesand models about the periodic layered structure, up to now, but they are controversial.As part of the project “Thermodynamic and kinectic study on the periodiclayered structure”, the kinetics and relative phase relation of the periodic layeredstructure in the Co₃W/Al and Ni₃Si/Zn diffusion couples are researched in this paper:In this paper the phase diagram of the Al-Co-W system at600oC and Sn-Ni-V systemat300oC was determined. The interface reaction about the Co₃W/Al、Ni₃V/Sn andNi₃Si/Zn diffusion couples were studied. The kinetics of the periodic layered structurein Ni₃Si/Zn diffusion couples was described. The formation mechanism of theperiodic layered structure in the Ni₃Si/Zn diffusion couples was proposed withdiffusion paths. The main conclusions within this thesis are:（1） As a series of investigation, this work have completed the phase diagram ofthe Al-Co-W system at600oC, and found14three-phase equilibrium regions:（Al）+γ+Al₉Co₂, δ+γ+Al₉Co₂, δ+ε+Al₉Co₂, Al₁₃Co₄+ε+Al₉Co₂, Al₁₃Co₄+ε+Al₃Co,Al₅Co₂+ε+Al₃Co, Al₅Co₂+ε+（W）, Al₅Co₂+AlCo+（W）, T+AlCo+（W）, T+Co₇W₆+（W）,T+Co₇W₆+Co₃W, T+Co₃（Al,W）+Co₃W,（Co）+Co₃（Al,W）+Co₃W,（Co）+Co₃（Al,W）+T,（Co）+AlCo+T. Three-phase equilibrium regions （Co）+AlCo+Tis speculated based on the phase rules. T is a new phase and its average compositionis Al-65.1at.%Co-11.8at.%W.（2） This work also completed the Sn-Ni-V system at300oC and9three-phaseequilibrium regions were found: Ni₃Sn₄+VSn₂+（Sn）, Ni₃Sn₄+VSn₂+V₃Sn,Ni₃Sn₄+V₃Sn+T, Ni₃Sn₄+Ni₃Sn₂+T, V₃Sn+（V）+T, VNi₂Sn+Ni₃Sn₂+Ni₂V,Ni₃Sn+Ni₃Sn₂+Ni₃V, Ni₃Sn+（Ni）+Ni₈V and VNi₂Sn+σ+Ni₂V, and6three-phaseequilibrium regions are speculated base on the phase rules. They areNi₃Sn₂+VNi₂Sn+T,（V）+VNi₂Sn+T, Ni₃Sn₂+Ni₂V+Ni₃V, Ni₃Sn+Ni₈V+Ni₃V, （V）+VNi₂Sn+σ and （V）+NiV3+σ, and the average composition of T in this system isV-43.1at.%Ni-36.4at.%Sn.（3） The interface reaction in the Co₃W/Al、Ni₃V/Sn and Ni₃Si/Zn diffusion coupleswere studied in this paper: the formation mechanism of the periodic layered structurein Co₃W/Al diffusion couples was investigated. The reaction zone in Ni₃Si/Zndiffusion couples was found to grow by a parabolic law, and the growth process iscontrolled by Zn diffusion to Ni₃Si substrate and Ni diffusion to the T/γ interface.Combing with diffusion path and the phase diagram of the Zn-Ni-Si system, thenucleation process of periodic layered structure in Ni₃Si/Zn diffusion couples isinterpreted.