Preparation And Characterization Of Reactive Nanomultilayers And Its Application In Joining Trial

As a new kind of nano energetic material,the reactive nanomultilayer?NML?foils exhibit self-propagating reaction after ignited by an external source of low energy with the higher amount of exothermic heat,which can instantly produce high temperature in the range of 1000-3000? and the reaction front velocity could reach the maximum100m/s.The application of reactive nanomultilayer foils in brazing and diffusion welding of microelectronic chips,metal and non-metal?ceramics,carbon foam,etc.?as well as metal and amorphous alloys in vacuum or atmospheric environment,has become research focus in materials micro-nano-joining area.The reactive nanomultilayer foil represented by Ni/Al system has been widely used in the field of interconnecting,3D stack packaging,and has broad application prospects in the military and aerospace fields.The research on compositions,microstructure,thermal stability,thermodynamic characteristics of the reactive nanomultilayer foils and their application in joining processes has great guiding significance for the preparation of nanomaterials and joining of new materials.In this paper,two new kinds of Ti/Ni and Ti/Si reactive nanomultilayer film were prepared by magnetron sputtering and their microstructures were characterized.The exothermic process,the reaction front velocity of self-propagation wave under low-energy initiation and the reaction products were analyzed.Ti/Ni reactive nanomultilayer foils were used for TLP diffusion bonding of titanium alloys in vacuum.The effects of nanomultilayers compositions and joining process parameters on the joint properties were systematically studied.And the potential of Ti/Si nano-multilayer as a heating source in self-propagating reaction joining of carbon foams with Sn-based solder was explored.The results are as follows:?1?The cross-sectional morphologies of Ti layer and Ni layer is smooth and clear.Ti/Ni nanomultilayer film possesses good periodic modulation structure,but there is a certain interfacial diffusion between Ti and Ni layer.Self-propagating reactions can occur in the atmosphere,with a propagation velocity of 0.47 m/s.TiNi₃ and TiO₂products are formed after the reaction.?2?Ti/Si nanomultilayer film possesses a clear cross-sectional morphology between the titanium and silicon layers with good periodic modulation structure.The heat release for the film with a Ti to Si atomic ratio of 5:3 is larger than that with an atomic ratio of 1:1.The velocity of self-propagating reaction of self-sustained Ti/Si nanomultilayers foils on different substrates in the atmosphere varies,while it reaches a highest average value of 9.6m/s on the heat insulation cotton.The main products of exothermal reaction were Ti₅Si₄,Ti₅Si₃,and TiO₂.?3?The joint strength of TLP diffusion bonded Ti6Al4V alloy by using Ti/Ni nanomultilayer foil increases obviously with the increase of bonding temperature,and the atomic ratio of Ti and Ni has a significant effect on the joint strength.When the bonding temperature is 800? and the pressure is 5MPa,the joint has a low shear strength.When the temperature increases to 875?,the joint strength are all larger than1000MPa for Ti/Ni system with a Ti to Ni atomic ratio of 1:1 and 1:2.The nanoscale effect of nano-multilayers successfully reduces the melting point of the film,and the transient liquid phase can be formed at a lower temperature of 650? according to DSC results.As the bonding temperature increases to 800?,Ni atoms in the film rapidly diffuse into the base metals,which accelerates the gradual composition homogenization of the joint with decreased porosity.Finally,under a pressure of 5MPa and a temperature of 900?,the TLP process produces a strong,interface-free joint with no remnant reacted Ti/Ni nanofoil interlayer.?4?The potential of Ti/Si nano-multilayer for soldering carbon foam was proved.As a local heat source,overlayed Ti/Si nanofoil with a total thickness of 25mm melted partial SnAgCu solder,and the molten solder entered the pores of carbon foams,which contributes to wetting and metallurgical bonding at interface.It is considered that the small single layer thickness and the non-uniformity of the prepared nanofoil result in that the heat release is not enough to fully melt the solder.However,Ti/Si nanomultilayer foil still show a promising prospect in self-propagating exothermic joining applications.