| The processing and application of environmentally friendly electrical contact material is profound studied in order to replace the Ag/CdO electrical contact material which is harmful to human body as well as the environment.In recent years,researchers pay increased attention to the Ag/SnO2 environmentally friendly electrical contact material due to its nontoxicity,high welding resistance and high arc erosion resistance.However,poor ductibility,machinability and low contact resistance are still the great fault of the Ag/SnO2 electrical contact material,which keeps it from being widely applied.In order to solve the mentioned technology difficulties,the company of western country and Japan developed comercial Ag/SnO2-In2O3 and low cost Bi2O3 doped Ag/SnO2 electrical contact materials.However,the domestic Bi2O3 doped Ag/SnO2 electrical contact materials are still under development and have not gone into production.In this paper,Ag/SnO2-Bi2O3 electrical contact material was prepared via Self-propagating High-temprature Synthesis(SHS)combined with Mechanical Alloying(MA)and Powder Metallurgy(PM)using AgSnBi alloy powders prepared by melting-atomization process as precusor.The effect of processing parameters on the microstructures,physical performance and electrical endurance of Ag/SnO2-Bi2O3 electrical contact material was profoundly studied.The stress-strain relationship of the Ag/SnO2-Bi2O3 electrical contact material was studied,basing on which the heat fabrication technology was established.The Ag/SnO2-Bi2O3 electrical contact material with great physical performance and long electrical endurance was successfully prepared through recipe formulation,process optimization and electrical endurance test The main results are as follows:(1)AgSnBi powder with average particle size of 10?m was prepared via melting-atomization process,and the Ag/SnO2-Bi2O3 intermediate composites were obtained by SHS-MA technique.The effect of the parameters such as oxidation temperature,oxidation speed and concentration of Bi element on the oxidation behavior,microstructures,phase transformation and physical performance was studied.It was revealed that the oxidation rate of AgSnBi powder firstly increased with increasing oxidation temperature and then changed to steady.The relatively high oxidation rate could be obtained in the range of 700 to 800?.The oxidation weight gain and SHS oxidation rate also increased with increasing oxidation rotation rate.When the oxidation rotation rate was increased to 300rpm,the The oxidation weight gain and SHS oxidation rate of the powder were respectly 99.02%and 85.27%.It is revealed that Sn firstly reacted with O to form SnO2,and then Ag4Sn phase reacted with O to form Ag and SnO2.(2)The effect of ball milling speed,particle size and forming-sintering process on the microstructures,metallurgical structure and physical performance of the Ag/SnO2-Bi2O3 electrical contact materials prepared by MA technique was researched.The creep behavior of the Ag/SnO2-Bi2O3 electrical contact materials at high temperature was also studied.Hot working technology was established based on the fact that the effect of deformation temperature and strain rate on stress-strain relationships.The ball milling speed has little influences on the microstructures and phases of Ag/SnO2-Bi2O3 composite powder.All the powders obtained with different ball milling speeds consisted of Ag and SnO2 and was agglomerates.The resistivity,hardness and density of Ag/SnO2-Bi2O3 electrical contact materials increased with increasing forming pressure.The optimized Ag/SnO2-Bi2O3 electrical contact material with average resistivity of 2.35??·cm,average hardness of 70?8OHV0.5and average density of 9.283g·cm-3?7.425 g ·cm-3 was obtained under forming pressure of 1200MPa.When the sinter temperature(Ts)was in the range of 900 to 920?,the resistivity,hardness and density of Ag/SnO2-Bi2O3 electrical contact material were optimal,which were 2.30?2.45??·cm,74.3?78.2 HV0.5 and 9.286?9.352 g·cm-3,respectively.It is revealed that the rheological properties of Ag/SnO2-Bi2O3 electrical contact material at high temperature was optimal when the deformation temperature was 800?-850?,the strain rate was 0.01?0.1S-1 and the strain was-0.7,which based on the analysis of stress-strain plot of Ag/SnO2-Bi2O3 electrical contact material.(3)The electrical endurance performance of Ag/SnO2-Bi2O3 electrical contact materials was obtained by electrical endurance test.The effect of process parameters such as operation times and particle size on the electrical endurance performance and the arc-erosion behavior were profoundly studied.The weight loss(Am)of moving contact of Ag/SnO2-Bi2O3 electrical contact material decreased with increasing particle size.The weight loss(?mD)of dynamic contact with particle size of 9.83 ?m reached-0.0192g,while the weight loss(?mJ)of static contact with particle size of 6.89 ? m reached-0.0192g.The arcing time and arcing energy of arc eroded Ag/SnO2-Bi2O3 electrical contact material were around 68ms and 5000mJ on closed state,respectively.And while the arcing time and arcing energy were around 23ms and 1000mJ on open state,respectively.The particle size had great influences on the initial arcing time and initial arcing energy.The arcing time and arcing energy of Ag/SnO2-Bi2O3 electrical contact material were higher on closed state compared with that of Ag/SnO2-Bi2O3 on open state.The surface morphology of the arc eroded Ag/SnO2-Bi2O3 electrical contact material included flower-like and rod-like microstructure,Ag-rich area,arc vacancy,holes,micro-crack,white floc particles,etc.the crack propagation mechanism that the micro-crack spreaded along the Sn-rich area was put forward by SEM/EDS analysis. |
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