| The development of electronic technology is getting more and more advanced,and the power of electronic components in intelligent equipment,construction machinery,transportation equipment,military missiles,aerospace and other fields is increasing.How to discharge heat efficiently becomes a problem to be solved urgently,the development of new packaging thermal management materials is one of the feasible ways to solve the problem.Copper(Cu)has excellent electrical and thermal conductivity,but its mechanical strength is poor;Carbon nanotubes(CNTs)not only have excellent conductivity,but also have excellent mechanical strength,but they cannot be directly applied to the packaging process.In this project,the composite of the two materials is expected to meet the increasingly stringent thermal management requirements.In order to improve the agglomeration state and interface bonding strength,CNTs after electroless copper plating(Cu@CNTs)were used as raw materials,so as to obtain the Cu@CNTs /Cu composite with good performance to meet the requirements of industrial use.In this project,Cu powder and Cu@CNTs were used as original materials to prepare composite materials by powder metallurgy.The experimental process is mixing-pressingsintering-extrusion.With the help of OM,SEM,XRD,hardness,physical properties and other relevant test equipment,I analyzed the mechanical strength and physical properties of the Cu@CNTs/Cu material.In the process of Cu@CNTs/Cu composite powder at 100 h,the structure of the original material has not been destroyed.The uniformity of the powder was studied by scanning the metallographic and elemental surfaces.It was found that when the addition of Cu@CNTs increased,the agglomeration phenomenon was gradually aggravated and the uniformity of the powder gradually decreased.In the process of pressing,it was found that when the pressing pressure increased,the density increased accordingly,and the density change was no longer obvious after 900 MPa.Under the same conditions,when the addition of Cu@CNTs increased,the sample density decreased.In the process of sintering,the surface of the steel cladding sample was bright and clean without cracking,and the XRD analysis of the sample after hot extrusion indicated that there was no oxidation phenomenon during the processing.The sample density was constantly improved along with the process flow,and finally reached above 0.965.The hardness of the samples decreased during sintering,which was related to the elimination of work hardening,and finally reached more than 145 HV.When the addition of Cu@CNTs increased,the yield strength of the material gradually increased,up to 248MPa(1.5wt%Cu@CNTs/Cu),however,too much additives did not significantly improve its mechanical strength.The main reason may be closely related to the agglomeration phenomenon.The main strengthening mechanisms include fine crystal mechanism,load transfer mechanism and thermal mismatch mechanism,etc.The strength model based on load transfer and thermal mismatch has some rationality.The physical properties of Cu@CNTs/Cu extrusion samples in thermal expansion,conduction and conduction were analyzed.In terms of thermal expansion performance,compared with pure Cu,the addition of Cu@CNTs could effectively reduce the linear expansion coefficient in the extrusion direction.Theoretical analysis showed that the reduction of linear expansion coefficient in the extrusion direction was related to the directional arrangement of Cu@CNTs.In terms of conductivity,the extrusion direction conductivity decreased with the increase of the addition of Cu@CNTs.In terms of thermal conductivity,the extrusion direction thermal conductivity increased significantly after extrusion,which was greatly related to the directional configuration and densification of Cu@CNTs.The measured performance of conductivity and thermal conductivity is low,which may be affected by the CNTs-Cu interface,CNTs-CNTs interface,residual pores,defects of Cu@CNTs and non-idealized orientation. |
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