Design Of Interface Wettability Of TCO_p/Cu Electrical Contact Materials And Its Arc Resistance Performance

Copper-based electrical contact materials represent promising trend in developing silver-saving and environment-friendly electrical contact materials.The primary drawback that blocks the application of copper-based materials in low-voltage electrical contacts is the contact instability due to the oxidization,and the keypoint is to solve the wettability between second phases and the matrix.In this work,transparent conducting oxide powders（TCO_p）possessing excellent electrical conductivity are proposed in the design of new copper-based electrical contact materials.Focousing on the wettability of TCO_p/Cu interface,TCO_p/Cu electrical contact materials were rationaly designed through first-principles calculations and prepared by powder metallurgical method in this work.The effects of wettability between TCO_p and Cu on the densification,sintering properties and arc erosion resistance were systematically studied.The main work is listed as follows:First-principles calculations based on the Density Functional Theory（DFT）were utilized to investigate the interface wettability of TCO_p/Cu.The effects of doping on bonding characteristic of SnO₂/Cu interface were explored.It was found strong affinity between Cu and O atoms were generated by low-valence cation doping.The interface wettability was intimately associated with the defects in SnO₂ induced by doping.That is,electron holes introduced by acceptor doping improved the interface stability,while excess electrons aroused by donor doping played the opposite roles.The holes in SnO₂faciliated charge transfer from Cu atom to O atom,resulting in the formation of mixed ionic-covalent bonds.Zn₂SnO₄,as a production of complex modification of SnO₂,showed strong adhesion with Cu.In comparsion with Cu-O bonds at SnO₂/Cu and ternary TCO_p/Cu interfaces,the stonger Cu-O bonds across Zn₂SnO₄/Cu were endowed with directional properties to form a stable tetrahedral coordination structures.Analysis of electronic structures of Zn₂SnO₄/Cu interface by density of state,charge density and charge density difference revealed that the charge transfer from Cu to O atoms generated Cu-O bonds with mixed ionic-covalent character,which contributed to enhance interface wettability.The influences of Zr atom on the adhesion properties of TCO_p/Cu interfaces were evaluated.The results indicate that Zr alloying could improve the adhesion strength of the interfaces.By high-temperature sessile drop testing,metal drop spreads on the Zn₂SnO₄ substrate,resulting a lower wetting angle that that between metal drop and SnO₂.The results indicate Zn₂SnO₄ can effectively improve the interfacial wettability,and verify the validity and reliability of caluculated W_sep and wettability of TCO_p/Cu by first-principles calcaulations.TCO_p/Cu electrical contact materials were prepared by powder metallurgical method.It was found that,after sintering at 950°C,the shrinkage degree of specimens decreased with the increasing of the initial pressure.From the results,the optimal pressure of 250-300 MPa for TCO_p/Cu compacts were determined,followed by hot-extrusion and rolling process.Furthermore,the influence rules of wettability on the densification and sintering properties were investigated.It revealed that low-valence cation doping and complex modification on SnO₂ could facilitate the enhanced sintering of compacts.Analysis of sintering necks showed that the above modification process could effectively improve the wettability of SnO₂/Cu.The effects of TCO_p on the interface wettability is consistent with the results from first-principles calculations,indicating that DFT calculations can open a versatile approach to evaluate sintering properties by calculating the wettability of ceramic/Cu interfaces,and provide a design principle for the preparation of Cu-based electrical contact materials.During arc erosion,the surface morphology of electrical contact materials changed signicantly,forming island-like protuberance,gas pores,erosion craters and rapid cooling structures.As for Cu electrical contact material,oxygen was prone to diffuse into Cu grain boundary.Consequently,the oxidation film generated outside the Cu grain induced a sharp increase of contact resistance,resulting in the contact welding.The addition of Sn-based oxides in Cu matrx could effectively address the problem of welding failure.Anaylsis of the distribution of SnO₂ and Cu²⁺-doped SnO₂ on the contact surface revealed that the low-valence cation doping on SnO₂ could maintain the contact stability by improve the interface wettability.Zn₂SnO₄/Cu electrical contact materials possessed stable contact resistance and low mass loss during 10000 arc erosion,which was ascribed to the excellent wettability of Zn₂SnO₄/Cu interface.The best concentration of Zn₂SnO₄is 1%by weight,which could make the volume fraction of Cu to excess the thresfold for conducting during the process of second metallurgy and recrystallization.Furthermore,the oxidation of Zr occurred along with the oxidation of Cu during arc erosion,which considerably consumed the oxygen.Consequently,the oxide of Zr and Zn₂SnO₄ could improve the viscosity of molten pool,maintaining the contact stability.Therefore,Zn₂SnO₄/Cu composite can be considered as one of the promising candidates of new-type copper-based low-voltage electrical contact materials.Additionaly,according to the investigation on the wettability by first-principles calculations,the correlation between wettability and arc erosion resistance of TCO_p/Cu electrical contact materials,extending the design of high-performance copper-based electrical contact materials.