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

Nuclear power is one of the important ways to solve energy problems,it has become an important indicator to measure a country's comprehensive national strength and international competitiveness.The fuel element composed of the Zr-4 alloy cladding tube and the Inconel718 alloy positioning grid is the place where the fission reaction occurs in the nuclear power system.The cladding tube as the first barrier for radiation protection and its interior withstand long-term radiation damage,while the flow-induced vibration causes severe fretting wear between the cladding tube and the positioning grid.Therefore,studying the effect of irradiation on the fretting wear performance of zirconium material have great significance for improving the service life of nuclear power plants and ensuring the safe operation of nuclear power equipment.In this thesis,Zr-4 alloy material before and after irradiation is taken as the research object.On the self-developed multifunctional fretting wear experimental machine,the fretting wear experiments of zirconium alloy samples with different degrees of irradiation damage was carried out by ball-plane contact.Through the optical microscope(OM),scanning electron microscope and supporting energy spectrum analysis(SEM and EDX),X-ray photoelectron spectroscopy(XPS)and white light interference analysis,studying the fretting wear behavior of zirconium alloy before and after irradiation.In addition,the finite element simulation software ABAQUS was used to simulate the fretting wear under different working conditions,and the simulation results can explain the fretting phenomenon with reference to the viewpoint of contact mechanics.The main results as follows:(1)Fretting experiments were carried out under different normal loads(10?80 N),displacement amplitude(5?60?m),and tangential frequency(1 Hz,5 Hz,10 Hz,50 Hz).According to the evolution rules of friction coefficient curve and F_t-D curve,combined with the wear scar morphology,the Zr-4 alloy running condition fretting map(RCFM)was established.The fretting operation diagram includes three operating mechanisms:partial slip regime,mixed regime and slip regime.The contact surface of partial slip regime is only slightly scratched,and the wear mechanism is adhesive wear.The contact interface in the mixed regime can be divided into the central adhesion zone and the edge sliding zone and the center of the wear mechanism is adhesive wear,and the edge is abrasive wear.In slip regime,wear mechanism is adhesive wear and abrasive wear accompanied by oxidative wear.(2)Irradiation hardening occurs on the surface of irradiated zirconium alloy,the hardness increases and the brittleness increases.Compared with the non-irradiated samples,the contact surface of the partial slip regime showed less scratch,and the wear mechanism was still adhesive wear.The contact surface of the mixing regime and the slip regime showed fine abrasive particles,and the wear mechanism was from adhesive wear changes into abrasive wear;this conversion trend becomes more obvious with the radiation dose increases.(3)The finite element software ABAQUS was used to simulate the fretting wear of Zr-4alloy under different working conditions.From the viewpoint of contact mechanics,the simulation results give a reasonable theoretical explanation for the phenomenon of fretting wear.The normal load and displacement amplitude work together to determine the contact status of the interface.In the partial slip status,the center stick edge slip,and appear a stress singularity at the stick-slip junction,which is the maximum value of the equivalent stress and shear stress and the edge slip part wears seriously.The whole slip status stress maximum value shifts to the direction of frettin,there is no stress singularity,the contact center wears seriously.