Wetting Of Amorphous And Crystalline Co/Ni/Fe-Based Alloys By Sn And Sn-Based Solders

Amorphous alloys have a series of excellent physical and chemical properties,and thus have potential value of engineering application.The amorphous alloys are usually in a thermodynamic metastable state,and are tended to stable crystalline state under heat.The transformations include structural relaxation,crystallization and etc.,which would cause the change of atomic distribution and energy state.Therefore,the heat input should be limited during the joining process.Soldering,as a low-temperature joining process,can achieve amorphous joining below the crystallization temperature and provide technical clue for the joining process.In this thesis,four kinds of solders（pure Sn,Sn-Cu,Sn-Ag-Cu and E-Sn-Pb）were used as the molten metal in the wetting process;amorphous and crystalline Co-based,Ni-based and Fe-based alloys were used as the substrate;the solderability was evaluated by wetting balance method.The main results of this study are as follows:（1）For Co-based alloy substrates,the reaction of oxide film removal plays a decisive role in the wetting process,and thus the wettability sequence is Sn≈E-SnPb>SnCu>SAC that based on reactivity between the solder and the oxide film.The wettability was improved with increasing temperature.In addition,compared with the amorphous and crystalline substrates,the amorphous alloy has higher reactivity,and thus the better wettability.（2）The Ni-based alloys in different states have the different wettability.For amorphous state,the effect of the deoxideation reaction on wettability is more serious than the physical porperties of solders.The higher Sn concentration in the solder has stronger reactivity,and better wettability was found.In the SAC solder,the formed（Cu,Ni）₆Sn₅ phase reduce the wettability,and thus the wettability sequence is:Sn>SnCu>SAC>E-SnPb;the crystalline substrate is relatively stable,and after the fully consideration of the factors that may affect the wettability,the wettability is dominated by the surface tension,the sequence is:E-SnPb>SAC>SnCu>Sn.（3）The Sn/Fe system has the weak reactivity.In the wetting process,the final wettability is greatly affected by the physical properties of solders and the reactivity,but it ultimately depends on the former factor.Therefore,in the practical joining process of Fe-based amorphous alloys,a flux with better deoxidation（or more active）than RMA flux should be further considered.（4）In the wetting process of the three kind amorphous alloys,the crystallization reaction were accompanied.This crystallization phenomenon is affected by the degree of chemical reaction at the interfacial front and the amorphous stability.Although Co-based alloys have the most stability among them,the crystallization behaviors was also found in them.Further,the wetting process and crystallization reaction were simultaneously performed in the amorphous interface front.In summary,this study may be helpful to explore the different wettability between amorphous and crystalline alloys,and provide some theoretical guidance for the soldering technology to achieve the joining of amorphous and crystalline metals.