Kinetic Theory Of Wetting And Diffusion Diffusion Of Sn-Based Solders On Zr₅₅Cu₃₀Al₁₀Ni₅ Metalic Glass

Since the discovery of the second generation of amorphous alloy in late 1980 s, they are called bulk metallic glasses(BMGs) for significant progress in their size. As Zr-Cu-Al-Ni system, Zr55Cu30Al10Ni5 BMG shows excellent performance, especially in the machinery manufacturing, aerospace, medical equipment, defense force, and many other engineering fields, reflecting the important potential application value. For practical application, the bulk amorphous alloy Zr55Cu30Al10Ni5 due to its preparation of rapid solidification process, is bound to face by connecting method to solve some homogeneous or heterogeneous amorphous alloy components of the application to large size and complicated. As a means of connection, and in view of the metallurgical melting point of Sn-based solders are lower than the glass transition temperature of Zr-base BMGs, this article is using the characteristics of pure Sn and amorphous Zr55Cu30Al10Ni5 as a typical object, to study the details of kinetics of interaction between pure Sn and Zr55Cu30Al10Ni5 BMG.As interaction between Sn and Zr55Cu30Al10Ni5 BMG, the kinetics of the whole process including wetting and interfacial diffusion growth are slow processes. Annealing treatment below the glass transition temperature of Zr55Cu30Al10Ni5 bulk metallic glass(BMG) specimens are investigated. Every 10 K temperature interval isothermal limited annealing treatment time will be selected to draw up time —temperature—transformation(T-T-T) curve. The apparent activation energy of crystallization is about 325±7k J/mol, higher than the values of supercooled liquid region conditions. Surface hardness of the samples before and after the limited annealing treatment are tested by nanoindentation, where the spherical-like crystallization morphology indicate the higher standard deviation of surface hardness of the BMG after the limited annealing treatment. The crystallization kinetics of the Avrami exponent is 4 in accordance with spherical-like crystallization morphology. A short review on mathematical setting of the problem could distinctly give the differences of the different crystallization behaviors at different temperature regions. Avrami exponent is from 4 to 3, explaining the crystallization morphology is from spherical-like to dendritic, could be ascribed to the concepts of symmetry breaking.Low temperature Sn-based solders including Sn-In eutectic solder show non-wetting on Zr55Cu30Al10Ni5 metallic glass(BMG) directly in vacuum sessile drop experiments. The results mean that wetting completely on Zr-based BMGs by adjusting the composition of Sn-based solders would fail usually. By utilizing pitting corrosion sensitivity of chloride of Zr-based BMGs, liquid Sn displays a slow wetting and spreading processes of experimental time window on Zr55Cu30Al10Ni5 BMG surfaces, which are pretreated by molten Zn Cl2. Six BMG specimens, which are treated in the same way in melting Zn Cl2, give different final contact angles by Sn. The different roughness of the BMG surface morphology, which is caused by molten Zn Cl2, determines the different final contact angles of Sn. The driving force is caused by liquid Sn nucleation at the interface on modified BMG surfaces, which determines the final contact angle and the time of the spreading to equilibrium states.Through theoretical analysis, mainly based upon the Fokker–Planck approach, which permits us to calculate directly the probability of the distribution of steady-state thickness fluctuations. Mathematical analysis results point out that as a result of the existence of structure relaxation of the BMG, diffusion layer of Sn/Zr55Cu30Al10Ni5 BMG interface as the metastable system, its growth process is divided into two stages. First is the stage I as diffusion controlled growth, whose growth time exponent is 1/2. With nucleation occurred near the interface, the phase transition process of coalescence, the diffusion layer get into the growth stage II, whose time exponent is suppressed to 1/3. The average size of clusters of new phase in the process of diffusion layer growth shows the exponet 1/3 law in stage II. According to quantum theory, the transmission of Sn particles through a disorder system of the BMG, scattered by the local fluctuation levels, is the source of the time exponent from 1/2 to 1/3 as a macroscopic cumulative effect. Subsequent experiments verified the existence of two stage growth of the diffusion layer. Meanwhile, the result of TEM confirmed the description of the existence of the stage II.