Study On High Temperature Tangential Fretting Wear Characteristics Of Zirconium Alloy Affected By Irradiation

With the gradual depletion of non-renewable energy sources such as oil and coal,nuclear energy,as a clean energy that can develop sustainably,has become an effective way to solve energy crises and environmental problems.Zr-4 alloy is widely used as a cladding material for nuclear fuel elements because of its high strength and good corrosion resistance at high temperatures.In actual operating conditions,as the first barrier for radiation protection,the inside of the cladding tube is damaged by radiation for a long time,and the outside of the tube is subjected to the action of fast-flowing high-temperature and high-pressure water.Under the action of flow-induced vibration,fretting wear occurred between the cladding tube and the positioning grid,which caused partial damage to the tube wall,which seriously affected the safe operation of nuclear power plants.Therefore,preliminary research on the fretting wear properties of zirconium alloys affected by nuclear radiation under high temperature environments is of great significance to solving the fretting wear of cladding tubes and ensuring the safe operation of nuclear power plants.This paper selects the nuclear power cladding tube material Zr-4 alloy as the research object,and systematically carries out the fretting wear test of Zr-4 alloy before and after irradiation under high temperature environment on the self-developed multifunctional fretting wear tester.Combine optical microscope(OM),scanning electron microscope(SEM),EDX energy spectrum analysis,laser confocal and other analytical instruments to analyze and discuss the test results.The main results achieved are as follows:(1)Under 300? high temperature environment,keep the tangential frequency constant at 5Hz,and carry out a large number of fretting wear tests under different normal load(10-80N)and displacement amplitude(5-60?m)working conditions.Combining the Ft-DN three-dimensional graph and wear scar morphology characteristics,the Zr-4 alloy operating condition fretting diagram(RCFM)was established,and it was found that the fretting operating characteristics of the Zr-4 alloy at a high temperature of 300 ? can be divided into parts.There are three typical areas: slip regime,mixed regime and slip regime.The damage mechanism of part of the slip regime is mainly adhesive wear;the damage mechanism of the mixed regime is mainly manifested as fatigue wear,abrasive wear and oxidative wear,and cracks are generated near the contact edge and expand into the matrix.In the slip regime,the wear mechanism is mainly manifested as surface fatigue wear,abrasive wear and oxidative wear.In addition,the steady-state friction coefficient decreases with the increase of the normal load,and increases with the increase of the displacement amplitude;the increase of the displacement amplitude and the load will lead to the increase of the amount of wear.(2)Carry out fretting wear tests at 200?,300? and 400? respectively to study the influence of temperature on the fretting wear behavior of Zr-4 alloy.The results show that when the working condition is T=200?,Fn=10N,D =10?m,the inching operation area is in the partial slip regime.When the temperature is increased to 300°C,the fretting operation zone changes from a partial slip regime to a mixing regime.In addition,as the temperature rises,the steady-state friction coefficient decreases and then rises in part of the slip regime and mixing regime,and increases with the increase of temperature in the slip regime;the increase in temperature will lead to the depth of wear and the amount of wear rise.In addition,the effect of frequency on high-temperature fretting wear of zirconium alloys was studied by changing the tangential frequency(2Hz,5Hz,10Hz)at a high temperature of300?.The results show that the steady-state friction coefficient will increase with the increase of the tangential frequency.But it has no significant impact on the micro-motion operating state.When the frequency is 10 Hz,the wear depth and wear amount under this condition reach the maximum value.(3)Under a high temperature environment of 300?,the effects of nuclear radiation and the degree of radiation(1dpa,3dpa,5dpa,7dpa)on the fretting wear behavior of Zr-4 alloy were studied.The results show that the effect on the fretting operation state is not significant.The fretting friction coefficient and wear volume after irradiation are significantly higher than those of the unirradiated sample,and with the increase of the degree of irradiation,the friction coefficient and wear volume show a downward trend.The fretting damage mechanism after irradiation mainly including adhesive wear,abrasive wear,fatigue wear,surface fatigue wear and oxidative wear.