Research On Surface Morphology And Microstructure Evolution Of CuZnAl Alloy Under He~+ Ion Irradiation

CuZnAl alloy is widely used in nuclear reactors,aerospace and other fields because it has advantage of shape memory effect,super elasticity,low price and easy processing,etc.However,under the irradiation environment,the irradiation effect is one of the main causes of material failure.Therefore,the surface morphology and microstructure of CuZnAl alloy irradiated by He~+ion was systematically investigated by SRIM,XRD,OM,SEM,EDS,TEM and AFM,and the results as follows:Firstly,the ion transport process in CuZnAl alloy irradiated by He~+ion was analyzed by SRIM simulation software.The range and concentration distribution of He~+ion in CuZnAl alloy were calculated by SRIM-2008 software under 50 keV He~+ion irradiation.The distribution of recoil atoms(Cu,Zn,Al)and the displacement energy,lattice binding energy and surface binding energy of each atom(Cu,Zn,Al)were calculated by SRIM.Besides,SRIM also simulated energy loss and sputtering phenomenon during He~+ion irradiation.It is concluded that the point defects(vacancies and interstitials)produced in the irradiated CuZnAl alloy by He~+ion were the source of irradiation effect.Although the sputtering process can aggravate the damage during the irradiation,the redeposition of the sputtered atoms can repair the damage to a certain extent.After He~+ion irradiation,no new precipitates were formed in the CuZnAl alloy.In addition,a large residual tensile stress was produced on the surface of CuZnAl alloy,and caused the diffraction peak in XRD to shift to a low angle.Irradiation pits were the main damage morphology of CuZnAl alloy surface irradiated by He~+ion,and it is found that the damage on the surface was mainly caused by the sputtering phenomenon.With relatively low irradiation doses(0.1 dpa and 1 dpa),increasing the irradiation dose(10 dpa)of He~+ion caused some irradiation pits to grow,but the redeposition during sputtering can repaire the defect to some extent.At the same time,the self-annealing effect during the irradiation process can also repair the defect well,which results in a reduction in the number of irradiation pits at high doses.The study also found that the surface roughness of CuZnAl alloy increased with increasing doses(0.1 dpa and 1 dpa),but decreased at the highest dose(10dpa).The main defects in CuZnAl alloy irradiated by He~+ion at different doses were dislocation,helium bubble,twins,stacking fault,dislocation wall and subgrain.Dislocation density was closely related to the dose of radiation.Because as the irradiation dose increased,the number of Frenkel defect pairs produced by ion irradiation increased,followed by the increase in dislocations,at low doses(0.1 dpa and 1 dpa),the number of dislocations was significantly increased compared to unirradiated samples.At the highest dose,the number of dislocations decreases due to high dose can enhance the recombination of interstitial atoms at the defect gathered site and the grain boundaries(GBs)can absorb point defects and defect clusters.In addition,Orowan mechanism was the main mechanism between dislocations and helium bubbles.Under the Orowan mechanism,there would be curved dislocation lines,straight dislocation lines and helium bubbles.Helium was easily trapped by vacancy(Vacancy,V)to form He-V clusters,then form helium bubbles during the process of He~+ion irradiation CuZnAl alloy.The sub-grains and dislocations formed at the highest dose(10 dpa)provided a large number of diffusion channels and nucleation sites for the helium bubble nucleus.The coarsening of helium bubbles at the grain boundaries led to the average diameter of the helium bubbles at the grain boundaries was slightly larger than that in the grains.According to the pinning action of helium bubbles by dislocations and grain boundaries,it can be concluded that the helium bubbles can escape from dislocations and grain boundaries only when they grow up beyond the critical size.In addition,the growth of helium bubble increased the Orowan stress,making the movement of dislocation blocked and then accumulated to form dislocation walls,and when the dislocation walls slided under external force,sub-grain structure was formed.This is the reason for the formation of a large number of dislocation walls and sub-grains under He~+ion irradiation(10 dpa).In the study,it was also found that massive deformed twins grew up with a stepped convex mechanism,while the slender deformed twins grew up by merging.As the adjacent sub-grains and the new sub-grains will invade stacking faults and twins,they caused the faults and twins to degenerate and disappear at the dose of 10 dpa.