| The realization of stable and sustainable development of nuclear power is an urgent problem to be studied to cope with climate warming and complete the low-carbon transformation of energy.In a pressurized water reactor nuclear power plant,the reactor core in the first loop system is the core of the nuclear power plant,and its main components,the fuel cladding tube and the grid spacer,will vibrate due to the circulating flow of the coolant,resulting in relative motion,which is unavoidable to cause random fretting wear between components.At the same time,nuclear fission releases a large amount of heat to make water warm up,and the contact atmosphere of fretting wear more complicated.In order to ensure the safe operation of nuclear reactors,it is crucial to improve the service performance of key components in the reactor.Therefore,the research on fretting wear of fuel assembly materials(Zirconium-4 alloy)under high temperature conditions is helpful to provide effective guidance for the operation and maintenance of nuclear fuel assembly in the future.In this thesis,the dry tangential fretting wear tests of Zr-4 alloy tubes at different temperatures were carried out by using the orthogonal contact mode of tube/tube to simulate the relative motion of the fuel cladding tube and the grid spacer working conditions.The damage surface morphology of Zr-4 alloy tube was detected by surface micro-analysis,and the main conclusion are as follows:(1)The change of displacement amplitude and normal load has a significant influence on the wear characteristics of Zr-4 alloy in different fretting operation regime.When the fretting is in slip regime,the Zr-4 alloy tube wears seriously and the surface is oxidized seriously,the wear mechanism in this operation regime is abrasive wear,fatigue wear and oxidation wear.In the mix regime,the damaged surface morphology is complex,there was a certain degree of adhesion in the center and microcracks and furrows were observed on the surface,and the wear mechanism includes abrasive wear,adhesive wear,and fatigue wear;The damage of the Zr-4 alloy tube running in the partial slip regime is least,and the morphology is characterized by central adhesion and adge slip.The oxidation mainly occurs in the annular microslip area,and the wear mechanism is mainly adhesive wear and delamination.(2)Changing the temperature,and taking the displacement amplitude of 60 μm and the normal load of 15 N(SR),30 N(MR)and 60 N(PSR)as the research objects.When the fretting operates in the slip regime,the increase of temperature does not affect the fretting operation state of Zr-4 alloy,but it will cause the increase of friction coefficient,material damage and wear amount;in the mix regime,the fretting operation regime will slowly change to the partial slip regime with the increase of temperature,and the friction coefficient will decrease,and the wear amount will decrease to a certain degree;when the fretting operation is in partial slip regime,there is little change in the damage area,and the friction coefficient and decrease first and then increase,but the overall change is not significant with the increase of temperature.(3)Keeping the temperature at 350 °C,random displacement tests were carried out by changing the random displacement spectrum and changing the normal load.When the displacement spectrum changes,the damage of the Zr-4 alloy tube is more serious under the action of the random spectrum with the larger average displacement amplitude;when the displacement spectrum is kept constant,the relative displacement of the two contact bodies decreases with the increase of load,and the material damage is slight. |
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