Study On Doping Modification And Electrical Endurance Performance Of Ag/SnO₂ Electrical Contact Materials Fabricated By Internal Oxidation

As a key material of electronic components,Ag/SnO₂ electrical contact materials are widely used in contactors,relays,low-voltage switches and other related fields due to their good thermal stability,arc erosion resistance and fusion welding resistance.The internal oxided Ag/SnO₂In₂O₃ electrical contact materials are being developed from Germany and Japan.Especially in the fields of high-end relays and high-performance contactors,this internal oxidation combined with deep processing techniques has been monopolized.Although many relevant scholars have carried out a series of studies on preparation techniques of Ag/SnO₂In₂O₃ electrical contact materials,such as multi-component modification,In element substitution have made some progress.However,the research on the thermodynamics and dynamics of AgSn alloy oxidation,dopant types and contents,electrical performance under theactrual working conditions has not been completely solved,which is in urgent need of systematic in-depth research and demonstration,so as to providean important reference value for downstream customers to optimize reasonable preparation process and appropriate dopant prescription according to thereal application scenarios.Therefore,a series of X-component doping modified Ag/SnO₂In₂O₃ electrical contact materials（Me=Ni,Cu and Zn）were designed from the perspective of partially replacing expensive In elements and improving the electrical properties of electrical contact materials.The influence of doping component types and contents,internal oxidation process parameters,electrical performance parameters and other important factors on the micro structure and electrical performance of the modified Ag/SnO₂In₂O₃ electrical contact material was emphatically investigated,and the electrical service life capability were evaluated when installed in thereal application scenarios.Based on the internal oxidation thermodynamic calculations,the internal oxidation process parameters of X-modified Ag-Sn-In alloys were established.The temperature rise test platform and electrical life capability test system were used to evaluate the temperature rise and electrical life performance of Me-modified Ag/SnO₂In₂O₃ electrical contact material.The 3D micro dynamic evolution process of Me modified Ag/SnO₂In₂O₃ materials before and after arc erosion was detected by ex-situ VR 3D projection technique,and the failure mechanism of its electrical life service ability was explored.The main research contents and conclusions are as follows:（1）Based on "Williamson-hall diagram",with the increase of Ni content from 0.0 wt.%to 0.5 wt.%,the grain size and micro strain of AgSnInNi alloys show a downward trend.The addition of Ni increases the nucleation rate,inhibits the crystal growth process in the crystallization process,and leads to the reduction of grain size.However,when the Ni content increases to 1.5 wt.%,the grain size and strain of AgSnInNi alloys increase,which is attributed to the presence of globular large-size alloy particles with high nickel content in the alloy.Only Ag phase was detected in Cu Modified AgSnIn alloys,and no other phases were detected.This shows that Sn,In and Cu elements are all dissolved into the Ag lattice.The diffraction peak positions of 1.1～4.0wt.%Cu modified alloys have shifted to the left in varying degrees,which is mainly due to the distortion of Ag lattice caused by solid solution Sn,In,Cu atoms,which changes the lattice spacing,resulting in the shift of XRD diffraction peak of the phase.The micro structure of Zn modified AgSnIn alloys is basically the same,and there are some twin boundary structures in the grains.With the increase of Zn content,the grain boundary contents increase,and the twin boundaries within the grain also gradually increase.（2）The effective internal oxidation of modified AgSnIn alloys can be achieved by adjusting the internal oxidation temperature,internal oxidation time and oxygen partial pressure of Ni and Cu element doped alloys.However,the samples modified by Zn element are difficult to realize oxidation.The optimal parameters for Ni doped alloys to realize uniform oxidation isatthe oxidation temperature of 700℃,theoxygen partial pressureof 5MPa and theoxidation timeof 96h,while that for Cu doped alloys is at the oxidation temperature of 700℃,the oxygen partial pressure of 5MPa and the oxidation time of 48h.0.5 wt.%Ni modified AgSnIn alloy shows the best resistivity（3.238 μΩ·cm）and a suitable hardness value（120 HV）.And 2.15 wt.%Cu modified AgSnIn alloy shows the best resistivity（3.21 μΩ·cm）and a suitable hardness value（137.6 HV）.（3）For the Ni modified AgSnO₂In₂O₃ contact material system,the appropriate Ni doping content（S3-i）is helpful to reduce the temperature rise,improve the fusion welding resistance and AC-4 electric life service ability.This is attributed to the strengthening effect of grain refinement and layered fibrous arrangement,as well as fine grain and layered fibrous arrangement.Compared with the AC-4 life cycle ability of commercial Ag/CdO12 samples,the AC-4 service life of Nickel modified Ag/SnO₂In₂O₃ samples（S3-i）is 48015 times,which is not only much better than the modified Ag/SnO₂In₂O₃ samples without Ni and with a Ni content of 1.5wt%,but also better than the traditional commercial Ag/CdO samples.For Cu Modified Ag/SnO₂In₂O₃ contact material system,when the copper doping amount is 2.15 wt.%,the electrical life performance of Cu doped Ag/SnO₂In₂O₃ material can reach 27945 times.The electric life failure mode of series Cu Modified Ag/SnO₂In₂O₃ materials is fusion welding and largearea droplet splashing,but the electric life service capability is different.The corresponding order of electric life service capability is as follows:Cu（2.15）>Cu（1.65）>Cu（1.1）>Cu（3.4）>Cu（4.0）>Cu（6.8）.（4）The electrical life cycle service cycle sequence of Ag/SnO₂In₂O₃ materials modified by multi doping vary with the kinds and contents of different composite doping elements,and the order of electric life service life is positively related to the surface hardness characteristics of the materials.The failure mode of the three materials of S15-i,S16-i and S19-i is lackingphase;The failure mode of the two materials of S17-i and S18-i is fusion welding.All materials have similar failure characteristics such as little carbon deposition,thermal cracks,silver rich layers and oxide particle segregation zone,which are mainly attributed to the poor wettability between the silver matrix phase and the oxide reinforcement phase,and also the escape of partially molten silver in the form of droplet splashing or silver vapor volatilization.