Nanostructured （NS） W-Cu composite powder was prepared by mechanical alloying （MA）, and nanostructured bulk of W-Cu contact material was fabricated by hot pressed sintering in an electrical vacuum furnace. The mic...Nanostructured （NS） W-Cu composite powder was prepared by mechanical alloying （MA）, and nanostructured bulk of W-Cu contact material was fabricated by hot pressed sintering in an electrical vacuum furnace. The microstructure, electric conductivity, hardness, breakdown voltage and arcing time of NS W-Cu alloys were measured and compared to conventional W-Cu alloys prepared by powder metallurgy. The results show that microstructural refinement and uniformity can improve the breakdown behavior, the electric arc stability and the arc extinction ability of nanostructured W-Cu contacts materials. Also, the nanostructured W-Cu contact material shows the characteristic of spreading electric arcs, which is of benefit to electric arc erosion.展开更多
One of the common characteristics of the electrothermal breakdown in an underwater discharge acoustic source（UDAS） is the existence of a pre-breakdown-heating phase.In our experiment,two phenomena were observed：（1...One of the common characteristics of the electrothermal breakdown in an underwater discharge acoustic source（UDAS） is the existence of a pre-breakdown-heating phase.In our experiment,two phenomena were observed：（1） the breakdown time that takes on high randomicity and obeys a ＂double-peak＂ stochastic distribution;（2） the higher salt concentration that reduces the residual voltage and causes 100% non-breakdown.The mechanism of electrothermal breakdown is analysed.To specify the end of the pre-breakdown-heating phase,a ＂border boiling＂ assumption is proposed,in which the breakdown time is assumed to be the time needed to heat the border water around the initial arc to 773 K.Based on this ＇border boiling＇ assumption,the numerical simulation is performed to evaluate the effects of two heating mechanisms：the Joule heating from the ionic current,and the radiation heating from the initial arc.The simulation results verify the theoretical explanations to these two experiment phenomena：（1） the stochastic distribution of the radius of the initial arc results in the randomicity of the breakdown time;（2） the difference in efficiency between the radiation heating and the Joule heating determines that,in the case of higher salt concentration,more energy will be consumed in the pre-breakdown-heating phase.展开更多
基金supported by the National Natural Science Fundation of China under grant No.50071043the Natural Science Fundation of Shaanxi province under grant No.2004E105.
文摘Nanostructured （NS） W-Cu composite powder was prepared by mechanical alloying （MA）, and nanostructured bulk of W-Cu contact material was fabricated by hot pressed sintering in an electrical vacuum furnace. The microstructure, electric conductivity, hardness, breakdown voltage and arcing time of NS W-Cu alloys were measured and compared to conventional W-Cu alloys prepared by powder metallurgy. The results show that microstructural refinement and uniformity can improve the breakdown behavior, the electric arc stability and the arc extinction ability of nanostructured W-Cu contacts materials. Also, the nanostructured W-Cu contact material shows the characteristic of spreading electric arcs, which is of benefit to electric arc erosion.
文摘One of the common characteristics of the electrothermal breakdown in an underwater discharge acoustic source（UDAS） is the existence of a pre-breakdown-heating phase.In our experiment,two phenomena were observed：（1） the breakdown time that takes on high randomicity and obeys a ＂double-peak＂ stochastic distribution;（2） the higher salt concentration that reduces the residual voltage and causes 100% non-breakdown.The mechanism of electrothermal breakdown is analysed.To specify the end of the pre-breakdown-heating phase,a ＂border boiling＂ assumption is proposed,in which the breakdown time is assumed to be the time needed to heat the border water around the initial arc to 773 K.Based on this ＇border boiling＇ assumption,the numerical simulation is performed to evaluate the effects of two heating mechanisms：the Joule heating from the ionic current,and the radiation heating from the initial arc.The simulation results verify the theoretical explanations to these two experiment phenomena：（1） the stochastic distribution of the radius of the initial arc results in the randomicity of the breakdown time;（2） the difference in efficiency between the radiation heating and the Joule heating determines that,in the case of higher salt concentration,more energy will be consumed in the pre-breakdown-heating phase.
