Study On Microstructure Of Ag-SnO₂-In₂O₃ Electrical Contact Material Prepared By Interal Oxidation

AgSnO₂ electrical contact materials are the optimum candidate for replacing the toxic "universal contact" AgCdO electrical contact materials,which have been widely used in the field of low voltage apparatus.Internal oxidation is one of its main production method,but there are many problems we need to solve such as uneven distribution of oxides,long growth cycle,poor processing performance and high cost.This article is based on the situation that majority studies of the Ag-SnO₂-In₂O₃ electrical contact materials given priority to its use of performance,and lack of theoretical analysis,this paper from the perspective of internal oxidation technology,using the theory of diffusion and the related knowledge of metallography,combined the macro properties with microstructure analysis,the oxidation process of Ag-6.0Sn-2.8In alloy has beed explored and studied.The metallographic,microstructure,chemical composition,microphology and microhardness were investigated by Metallographic?OM?,scanning electron microscope?SEM?,energy disperse spectroscopy?EDS?,X-ray diffraction?XRD?,and microhardness tester of the Ag-SnO₂-In₂O₃ materials prepared under different parameters?temperature and oxygen partial pressure?with the method of internal oxidation,the results are concluded as follows:The internal oxidation reaction can proceed smoothly relying on degrease treatment,alloys without degreasing treatment were hard to oxidize even under the high oxygen partial pressure of 1.5 MPa;And microstructure was influenced greatly by furnace charging mode,and we should choose the appropriate furnace charging way according to the alloy components.the main crystal phases of Ag-6.0Sn-2.8In alloy after oxidation are Ag,Sn O₂ and In₂O₃.And Ag diffraction crystal plane are?111?,?200?,?220?,?311?.In the process of alloy oxidation,the solute elements Sn and In generated to SnO₂ and In₂O₃,will inevitably causes the volume expansion,which lead to the internal stress.And there were two main ways to release of internal stress:?1?oxidative cracking;?2?the substrate metal Ag to spread out,resulting in rich Ag forms on the surface and white Ag belt in the internal of the alloy.The internal oxidation of Ag-6.0Sn-2.8In alloy are mainly about the internal diffusion of O atoms and reverse diffusion of Sn and In atoms.The oxidation rate,the size,shape,distribution of the generated oxides,the microstructure and macro properties vary with the condition of different temperature and oxygen partial pressure.Experimental analysis shows that the reverse atom diffusion of Sn,In atoms is influenced by oxidation temperature,and the internal diffusion of O atoms is influenced by temperature and oxygen partial pressure double roles.It is mainly for grain boundary diffusion under low temperature?550 ??,and intracrystalline diffusion under high temperature?650 ?,750 ??for Ag-6.0Sn-2.8In alloy.It shows bulky particles when under low oxygen partial pressure?0.021 MPa?,and tiny particles under high oxygen partial pressure?0.3 MPa,1.5 MPa?.Among them,under the condition of 650 ?,the oxidation of 0.3 MPa,metallography,SEM and EDS results show the microstructure uniformity of material,hardness is moderate,which is suitable for production and processing.