Research On Doping Modification And Arc Erosion Behavior Of AgTiB₂ Contact Materials

With the electrical system towards increasing miniaturization,multi-functionalization and high power,it poses the increasingly stringent requirements for the performance of the contact materials.The Ag TiB₂contact material is expected to be a novel high-performance and low-voltage Ag base contact material due to its excellent electrical conductivity,wear resistance,arc erosion resistance and material transfer properties.However,due to poor wettability between Ag matrix and TiB₂they presents weak interfacial bonding,and TiB₂particles are easy to aggregate during the service process,in which causes large fluctuation of arc duration,thus affecting the reliability and stability of the electrical system operation.So far,it is still lack of investigation on the improvement on the TiB₂/Ag interface,and the influencing mechanism of the interface characteristics on the physical properties and arc erosion behavior of the Ag TiB₂contact material is still unclear.Based on the above issues,it is proposed to improve the TiB₂/Ag interface bonding by introducing some metals or metallic oxides between Ag and TiB₂.In this work,the interface bonding characteristics between the added metals or metal oxides and TiB₂/Ag were firstly calculated through first principles,and the possible metallurgical reactions at the interface were analyzed according to thermodynamic calculation and metallurgical theory.It was found that Cu and Cu O can improve the TiB₂/Ag interface bonding.The TiB₂@Cu O（Cu）composite powder of Cu O（Cu）coated with TiB₂was further constructed by electroless plating.The bonding characteristics of Ag-4wt.%TiB₂@Cu O（Cu）interface were characterized.The effect of interface properties on the physical properties,mechanical properties and arc erosion properties of Ag-4wt.%TiB₂contact materials were studied and the mechanism was explored as well.In addition,some metal oxides（Me O）were also used to verify the above viewpoint.The following results can be drawn from above investigations.（1）Based on the first-principles calculation,it shows that Cu doping increases the TiB₂-Ti/Ag（111）interlayer charge product and charge transfer between the Ag（111）interface,which presents the maximum substitution doping separation work,indicating the enhanced bonding strength and stability of the TiB₂/Ag（111）interface.The charge at the TiB₂-Ti/Ag（111）interface was increased by two times by the introduction of Cu O,which also promotes the interface charge transfer and the interfacial atomic interaction,thus improving the stability of the composite configuration.In addition,thermodynamic calculations and metallurgical theoretical analysis show that,in the Ag/Cu O/TiB₂system,Cu O can react with TiB₂at the interface,and the generated Cu spreads into the Ag to form a solid solution,while Cu O also changes the interface characteristics of Cu O/TiB₂and Cu O/Ag,thus improving the interface bonding.However,in the Ag/Cu/TiB₂system,atomic diffusion only occurs at Ag/Cu interface,and the Cu/TiB₂has weak interface bonding.As a result,the interface bonding of the Ag/Cu/TiB₂system is weaker in comparison with the Ag/Cu O/TiB₂system.（2）The composite structure of Cu O and Cu coated TiB₂particles（TiB₂@Cu O,TiB₂@Cu）was first constructed by chemical plating,and the controllable preparation technology of TiB₂@Cu and TiB₂@Cu O composite powder was obtained,and the TiB₂@Cu and TiB₂@Cu O composite powder were successfully prepared.The TiB₂surface was effectively coarsened by pre-plating pretreatment,which can provide more nucleation points for Cu deposition.The uniform and dispersive coating of Cu O/Cu on the surface of TiB₂particles was finally achieved by regulation the HCHO concentration,primary salt concentration and complexation agent ratio.The optimal plating ingredients was 12.5g/L Cu SO₄·5H₂O,15g/L HCHO,22g/L EDTA·2Na,and 14g/L potassium tartrate with a loading capacity of 12g/L.（3）The Ag-4wt.%TiB₂contact material with uniform microstructure and good physical properties was obtained by optimizing repressing process and regulating microstructure,and the optimal coating content is determined as 0.7 wt.%Cu O.The interface characterization reveals that the Ag-4wt.%TiB₂contact material interface is mechanical binding,and the Cu that diffuses into Ag promotes the metallurgical bonding of the TiB₂/Ag interface,thus enabling more stable bonding interfaces for the Ag-4wt.%TiB₂@Cu O and Ag-4wt.%TiB₂@Cu contact materials.Compared with Ag-4wt.%TiB₂contact material,The hardness,compressive strength and limit deformation rate of Ag-4wt.%TiB₂@Cu O and Ag-4wt.%TiB₂@Cu contact materials are significantly improved,but the electrical conductivity decreases,in which Ag-4wt.%TiB₂@Cu O interface has been greatly improved,the hardness,compressive strength and limit deformation rate are higher than Ag-4wt.%TiB₂@Cu.Due to the shorter diffusion distance of Cu in the Ag-4wt.%TiB₂@Cu O as compared to Ag-4wt.%TiB₂@Cu,it has less damage to the electrical conductivity.（4）The electrical contact tests at 24V/16A show that the dispersive distribution of TiB₂particles is beneficial for decrease of the TiB₂aggregation on the contact surface,thus reducing the fluctuation of arc duration,enhancing the arc stability,and reducing the mass loss.Furthermore,since the improved interface bonding reduces TiB₂aggregation at the contact surface,the Ag-4wt.%TiB₂@Cu O contact material has less mass loss and higher arc stability as compared to the Ag-4wt.%TiB₂and Ag-4wt.%TiB₂@Cu contact material.To verify the effect of interfacial properties on arc erosion,other oxides with the same or opposite interface modification mechanisms as Cu O were selected for validation analysis.Among them,the interface reaction product of In₂O₃and TiB₂,In and Ag,promotes the interface bonding of TiB₂/Ag.Although the interface reaction product Ce₂O₃of Ce O₂and TiB₂cannot react with Ag,it also improves the interface bonding of TiB₂/Ag.The inert relationship of Y₂O₃,Ag and TiB₂causes the poor interface bonding between TiB₂and Ag.The validation results show that the In₂O₃addition significant improving the arc stability and arc erosion resistance of the Ag-4wt.%TiB₂contact material.