摘要
The laser powder bed fusion(L-PBF)additively manufactured CoCrFeNi high-entropy alloy(HEA),with face-centered cubic(FCC)crystal structure,demonstrates better comprehensive mechanical properties in the building direction(BD).Loading quasi-static,dynamic fatigue,and dynamic separated Hopkinson press bar(SHPB)impact stress conditions along the BD of the L-PBF processed HEA exhibit intriguing mi-crostructural evolution characteristics.The L-PBF generates hierarchical dislocation grids containing nu-merous cell substructures within the HEA FCC grains,impeding dislocation motion during deformation and improving the strength.When subjected to dynamic fatigue loading,the dislocation grids restrict the mean free path of dislocations and thus trigger the activation of abundant stacking faults.Hence,nu-merous nanotwins form near the end of the fatigue life.Multiple twinning systems can also be activated under dynamic high-speed impact loading.Especially at a low temperature of 77 K,the stacking fault energy of the CoCrFeNi HEA decreases,resulting in increased activation of nanotwins,exhibiting excep-tional toughness and resistance to dynamic loads.Additional twin boundaries also impede dislocation movement for the strain hardening.These findings hold valuable implications for the study of additively manufactured HEA parts working in extreme environments.
基金
sponsored by the National Natural Science Foundation of China(Grant No.52175140)
National Key R&D Program of China(Grant No.2022YFB4602102)
Fundamental Research Funds for the Central Universities in China(Grant No.JKG01231610)
Pre research project of Civil Aerospace Technology(Grant No.D020301)
Equipment Pre-research Sharing Technology Key Project(Grant No.JZX7Y20210422004601).
作者简介
Corresponding author:Bo Li.E-mail address:libo@ecust.edu.cn。
