Uniaxial strain-induced cascade defect evolution in molybdenum: An atomistic study with a new machine-learning potential

• A high-precision machine-learning potential for molybdenum has been developed and validated for irradiation damage studies. • Uniaxial tensile strain gradually increases the number of thermal-spike defects, whereas the stable-defect population is governed by both strain and temperature: it rises with tensile strain only in the low-temperature region. • Distinct from or strain, increasing uniaxial tensile strain (up to 2%) in molybdenum at 673 K uniquely induces preferential alignment of interstitial pairs along the strain axis. This alignment subsequently enhances defect cluster growth and nucleates 1/2 dislocation loops. The evolution of irradiation defects in nuclear structural materials is profoundly influenced by mechanical stress. However, a predictive understanding of this coupling at the atomic scale remains challenging. In this work, we develop a machine-learning moment tensor potential (MTP) suitable for cascade simulations and widely validate its accuracy. Utilizing this potential, we systematically perform molecular dynamics simulations of collision cascades with a focus on uniaxial 111 strain across a wide range of temperatures and PKA energies. These are supplemented by simulations under 100 and 110 strains at 673 K and 10 keV to assess crystallographic orientation effects. Our results reveal that the thermal spike defect yield increases monotonically with tensile strain, regardless of temperature; the stable defect number only increases with strain changing from compressive to tensile at low temperatures, while the strain effect is not significant at high temperatures. Moreover, the orientational response of self-interstitial atoms to strain is found to be highly dependent on the crystallographic direction of the applied strain. Tensile strain along 111 dirction increases the lattice spacing and reduces the formation energy of interstitials, causing self-interstitial atoms to preferentially align along the 〈1 1 1〉 direction and significantly increasing the yield of large-sized clusters and dislocation loops. This work provides an atomic-scale basis for understanding the irradiation defect evolution of Mo under actual service stress.