Study On The Microscopic Mechanism Of Irradiation-induced Structural Evolution In Zr-based Amorphous-nanocrystalline Alloy

Irradiation-induced performance degradation of structural materials is the main factor that affects the development of clean nuclear energy with low-cost and high-energy-density.To guarantee the safety,efficiency and longevity of operation of nuclear plants,it is important to design and develop new nuclear structural materials with excellent resistance against irradiation.It is reported that both the nanocrystals and amorphous alloys possess high resistance to neutron irradiation.Besides,stable nanocrystals can be precipitated in the matrix of amorphous alloys under appropriate conditions,forming amorphous-nanocrystalline composite materials,which could greatly ebhance the mechanical properties of amorphous alloys.However,whether the composite materials made up of nanocrystalline and amorphous structures would exhibit excellent neutron irradiation resistance,further investigations and demonstrations are required to be carried out.As well known,it is a great deal of challenge to study the irradiation damage mechanism of neutron on the materials by experiments.Therefore,the classic molecular dynamics（MD）method is adopted in this work.The Zr₂Cu is selected as the research object,and a Zr-based amorphous-nanocrystalline alloy model（the Zr₂Cu ANA model）is successfully constructed by inserting the nanocrystals into the amorphous model with the same composition.Then,the process of irradiation damage induced by a primary knock-on atom（PKA）of 12.2 ke V in the composite structure model is investigated by using a series of simulations and calculations.It is found that,during the irradiation process,the range and size of collision cascade zones changed with the simulation time.In the amorphous region,free volumes can spontaneously and fully recover after the cooling and structural relaxation processes,the value of which is quite similar to that of initial state,regardless of the complex behavior exhibited under the collision cascades phenomenon.In the nanocrystal region,the collision cascades could induce some melted local regions,but the migration of phase boundary between the nanocrystalline and amorphous（or liquid）phases would make the irradiation-induced vacancies be rapidly and fully annihilated.And there is an effective self-healing property in the nanocrystal region,because the nanocrystal phase is more competitive than the amorphous phase during quenching.In addition,no atomic diffusion mechanism is found between the nanocrystal grain and the neighboring amorphous zone,because most of the knocked-on atoms can be readily and spontaneously absorbed by the phase boundary.In summary,this work is well done and reveals a unique and effective structural self-healing mechanism in the amorphous-nanocrystalline alloy materials,which will shed light on the development of new alloy materials with high irradiation resistance.