Compressive Mechanical Properties and Irradiation Hardening Constitutive Model of Beryllium with γ-Irradiation AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY25010011

Chinese Library Classification Number:TG146.24

Citation Information:

As a rare light metal exhibiting exceptional nuclear and physicochemical properties，beryllium has found extensive utilization in nuclear energy，high-energy physics，aerospace engineering and other fields. Owing to its unique combination of attributes including low density，high specific strength，superior corrosion resistance，remarkable thermal conductivity，minimal neutron absorption cross-section，and significant neutron scattering cross-section，beryllium serves critical functions as：1） moderator and reflector components in nuclear reactors；2） beam pipe material in particle accelerators for high-energy physics experiments；3） structural elements in spacecraft and inertial guidance systems；and 4） reflector substrates in optical systems. However，prolonged exposure to γ-radiation during operational service induces crystallographic defects （e.g.，point defects and dislocations） that progressively degrade the mechanical integrity of beryllium components. It is necessary to study the effect of γ-irradiation on the mechanical properties of beryllium. Three groups of beryllium specimens were subjected to γ-irradiation at dose levels of 10，100，and 1000 kGy respectively，with an unirradiated group serving as the control. Triplicate specimens were tested in each group. The compression test，scanning electron microscopy （SEM） and X-ray diffraction analysis （XRD） were performed on the beryllium specimens before and after irradiation to investigate the effects of γ-irradiation on the compression mechanical properties，surface microstructure and crystal structure of beryllium. The true stress-strain curves，compression mechanical properties，SEM images，roughness，XRD patterns and dislocation density of beryllium specimens with varying γ-irradiation doses were analyzed. And according to the data obtained from the compression test of beryllium specimens with different γ-irradiation doses，the irradiation hardening constitutive model was established. The results showed that irradiation hardening and embrittlement affected on beryllium specimens by γ-irradiation，resulting in enhanced strength and reduced ductility. With the increase of γ-irradiation dose，the compressive elastic modulus and compressive strength showed continuous growth，while the maximum strain continued to decrease. At the maximum tested dose of 1000 kGy，both the compressive elastic modulus and compressive strength of beryllium specimens reached their peak values，the compressive elastic modulus increased by 97.6% from 56.58 to 111.78 GPa，the compressive strength increased by 55.0% from 221.00 to 342.54 MPa，while the maximum strain decreased to its lowest value，decreasing by 32.6% from 0.555% to 0.374%. The irradiation hardening and embrittlement of beryllium were attributed to the substantial irradiation defects generated by γ-irradiation. During the irradiation process，γ-rays bombard the lattice atoms，resulting in a large number of point defects within the beryllium specimens，such as vacancies and interstitial atoms. These point defects migrated and interacted to form cavities and dislocation loops and accumulated at crystal boundaries in the specimens. When beryllium specimens underwent plastic deformation under external forces，irradiation defects increased the resistance to dislocation movement，making it difficult for crystal slip to occur，leading to material hardening and enhancing the compressive strength and elastic modulus of beryllium. On the other hand，the irradiation defects weakened crystal boundaries，causing crystal boundary cracks to initiate from the microscopic crystal slip，resulting in material embrittlement and reducing the maximum strain of beryllium. In XRD patterns of beryllium specimens，the diffraction angle corresponding to the （101） diffraction peak of Be decreased with the increase of irradiation dose，which indicated that the aggregation of a large number of irradiation defects expanded the interplanar distance of beryllium crystals. This structural evolution led to irradiation expansion in beryllium specimens. Meanwhile，γ-irradiation destroyed the microstructure of beryllium，concurrently enlarging the size of internal cavities and elevating dislocation density in beryllium. Notably，the higher the γ-irradiation dose，the larger the size of internal cavities and dislocation density in beryllium，but the increase in dislocation density gradually tended to saturate. At low irradiation doses，the dislocation density increased rapidly with the increase of γ-irradiation dose. When the irradiation dose reached a certain level，the size of internal cavities grew，and the increase in dislocation density became more gradual. As the size of internal cavities expanded to a certain extent，the surface of internal cavities absorbed vacancies and interstitial atoms，promoting the recombination of irradiation defects，and the growth of dislocation density tended to saturate. The increase in the size of internal cavities and dislocation density drove the aggregation of irradiation defects，resulting in the formation of micropores and protrusions on the surface of beryllium specimens，and the surface roughness increased with the increase of irradiation dose. By analyzing the compression test results of beryllium specimens with different γ-irradiation doses，an irradiation hardening constitutive model for beryllium was established based on Johnson-Cook constitutive model. Compared to the traditional Johnson-Cook model，the modified model incorporated an irradiation dose parameter G to quantify the effects of irradiation hardening on the mechanical properties of beryllium. The irradiation hardening constitutive model could accurately describe the compressive mechanical behavior of beryllium specimens within the range of irradiation doses from 0 to 1000 kGy.