Study On Methods And Mechanisms Of Compositing/Jointing Of Immiscible Tungsten And Copper

W/Cu composites with high melting point,high sputtering resistance,good thermal conductivity and other outstanding comprehensive performances have been widely used in the fields of electronic processing,aerospace,military industry and other industries.It has also become one of the preferred materials for plasma facing components(PFCs)in thermonuclear experimental reactors.However,since W and Cu have no solubility of each other through the whole composition,and the distinct differences in physical properties such as melting point and thermal expansion coefficient,it is very difficult to realize the direct metallurgical combination of W and Cu by the current conventional process.This work is carried out to realize the interdiffusion bonding between the immiscible Cu and W without using interlayer metals by the direct diffusion bonding and the Cu electroplating process after W surface nano-treatment methods.It means a continuous W/Cu metallurgical interface can be formed,that is,a true metallurgical bonding.The mechanical performance test,electrochemical measurement,adhesion test,DSC test and SEM,HRTEM,XRD characterization methods were used to systematically study the W/Cu composites obtained via the two compositing/joining processes.The main results are as follows:(1)Through the direct diffusion bonding process,including appropriate surface treatment,uniform pressure assembly(the pressure is 106 MPa)and diffusion annealing(the annealing temperature is 980?,holding time is 3 h),a W/Cu joint with high strengths can be obtained.The thickness of the W/Cu diffusion layer is about 22 nm.The maximum tensile and bending strengths of the as-obtained W/Cu joints are 172 and 232 MPa,respectively.After a low temperature annealing for long time,the as-obtained W/Cu joints still maintain a high tensile strength of 166 MPa,which shows a good stability.(2)Nanoporous active W metal layers are prepared via a two-step anodization process(anodizing at 60 V for 60 min firstly and then at 40 V for 60 min)in a fluoride containing electrolyte and then deoxidized annealing in H2 atmosphere(the annealing temperature is 700?,holding time is 3 h).The obtained nanoporous active W layer is with uniform and homogeneous nanopores,higher specific surface area and superior hydrogen evolution reaction activity.The appropriate Cu electroplating 9 parameters are that the current density is 1 A/dm2,the plating time is 30 min and the temperature is 40?.The obtained Cu coating of the W/Cu electroplate is smooth,homogeneous,dense and has good adhesion to the substrate W.After diffusion annealing,the thickness of the W/Cu diffusion layer is about 13 nm.(3)Based on Miedema's theory and Alonso's calculation method,a thermodynamic model of the alloying between W and Cu has been established.Combining the DSC test for the storage energy in W and Cu,the analysis results based on the model show that the alloying between immiscible W and Cu is thermodynamically feasible.The initial energies of W-Cu system including the surface energy,the storage energy and energy caused by external pressure are able to overcome the positive reaction heat and serve as the driving forces for the alloying.