Interface Damage Evolution Of Ag-SnO₂ Contact Materials And Improvement Mechanism For Mechanical Property

Silver based electrical contacts undertake the task of breaking and conducting current in low-voltage electrical appliances.The stability and reliability of the entire electrical system are directly affected by the properties of electrical contacts.Environmentally friendly Ag-SnO₂ contact materials have attracted much attention in the field of the low voltage electrical appliances due to their high stability,resistance to arc erosion,and resistance to fusion welding.However,the physical properties of SnO₂ particles and Ag matrix are completely different,which lead to poor interfacial wettability.Moreover,during the processing process,severe stress concentration occurs inside the Ag-SnO₂ material,which significantly reduce the ductility of the Ag-SnO₂ material.Poor interface wettability and low ductility make it difficult to process Ag-SnO₂ materials,which cannot meet the miniaturization requirements of devices.Meanwhile,during service,the Ag-SnO₂ contact materials are constantly subjected to mechanical forces,and the low SnO₂/Ag interface bonding strength induces crack initiation and propagation,accelerating material failure.The effects of in-situ loading additives and their types on the mechanical behavior,interface damage and failure mechanism of Ag-SnO₂ contact materials were systematically studied by a combination of tensile experiments and finite element simulations.The main research contents are as follows:（1）The influence of the geometric characteristics and content of SnO₂ reinforced particles on the stress-strain distribution of Ag-SnO₂ contact materials was studied using ABAQUS finite element software.The preparation work before the experiment has been further improved.The simulation results indicated that when the mass fraction of SnO₂ particles was 8 wt%,the comprehensive mechanical properties of Ag-SnO₂ contact material were the best.（2）The initiation and propagation of internal cracks in Ag-SnO₂ contact materials were studied,and the mechanism of CuO additives was analyzed.The experimental results showed that the in-situ loading of CuO additives on SnO₂surface can significantly improve the fracture toughness of Ag-SnO₂ contact materials and inhibit the formation of intergranular cracks.The presence of CuO additives effectively suppressed the initiation of secondary cracks near the main crack tip and significantly reduced the propagation rate of the main crack.Large dimples and tear ridges were formed around SnO₂ particles,which significantly improved the plastic deformation ability and fracture toughness of Ag-SnO₂ contact materials.（3）The effect of the in-situ loading of CuO additives on the mechanical behavior of Ag-SnO₂ contact materials was systematically studied.The experimental results showed that the elongation of electroless plating with the addition of nano CuO increased by 400%;The elongation of Ag SnO₂ material with physical mixture CuO increased by 200%.There were numerous cracks on the fracture surface of Ag-SnO₂material without additives,resulted in interfacial debonding failure,which manifested as brittle fracture.Electroless plating loaded with CuO can improve the interfacial bonding strength.The high interfacial bonding strength suppressed the initiation and propagation of intergranular cracks,which resulted in many dimples and tearing edges on the fracture surface of Ag-SnO₂（CuO）tensile specimens.The fracture mode of Ag-SnO₂（CuO）materials changed to Ag matrix tear,which was a ductile fracture.（4）The interface damage evolution process of Ag-SnO₂ contact materials was simulated and analyzed using ABAQUS software.The simulation results showed that the in-situ loading of CuO additives can significantly improve the interfacial bonding strength of Ag-SnO₂ contact materials.The deformation ability between SnO₂ and Ag phases was coordinated by CuO additives,which effectively improved load transfer ability and significantly alleviated stress concentration.The plasticity and tensile strength of Ag-SnO₂（CuO）materials have been significantly improved.The initiation of cracks in Ag-SnO₂ contact materials without CuO was caused by stress concentration at the sharp corners of SnO₂ particles.The induced cracks propagated along the high stress zone,forming a 45°angle with the horizontal,leaded to the fracture of the Ag matrix.The damage initiation position of Ag-SnO₂（CuO）materials transferred from the Ag/SnO₂ interface to the Ag matrix,and the failure mode changed from brittle debonding at the interface to ductile matrix fracture.This was due to the increase in the bonding strength of the Ag/SnO₂ interface and the decrease in the degree of SnO₂ particle aggregation.（5）The mechanical behavior of Ag-SnO₂（NiO）contact material under uniaxial tensile load was studied,and the stress and strain distribution patterns were simulated using finite element software ABAQUS.The results indicated that the interfacial bonding strength and plastic deformation ability of Ag-SnO₂ contact materials can be also improved by adding nano NiO additives in chemical plating.Compared with Ag-SnO₂,the tensile fracture surface intergranular cracks of Ag-SnO₂（NiO）contact materials were significantly reduced,with many dimples and tear edges.The elongation of Ag-SnO₂（5%NiO）contact material was increased by 140%.At the initial stage of loading,there was a severe stress concentration zone in the area where SnO₂（NiO）particles aggregation,and cracks initiated and propagated at the Ag/SnO₂interface.In addition,the stress and strain at the time of damage were smaller than those of Ag-SnO₂（5 wt%CuO）materials under the same conditions.