A Review of Dislocations in Additive Manufacturing Forming Parts

Additive manufacturing (AM)is a revolutionary technology to manufacture solid parts by layer-by-layer stacking. Dislocation,a kind of line defect widely existing in crystal microstructure,is an important factor in determining the properties of the formed parts. To further understand the characteristics of dislocations in parts formed by additive manufacturing and the essential mechanism of AM,the research achievements in the field over recent decades are summarized,with emphasis on the characteristics of dislocations,the densities of dislocations,and the effects of dislocations on the properties of the parts. Due to the compression-tensile stress cycle caused by cyclic heating and cooling in the forming process,AM-formed parts generally exhibit a high-density dislocation structure. The dislocation structure realizes its energy stability under cyclic action. The density and structure of dislocations in formed parts can be controlled by changing the heat input parameters during AM processing. The interactions among dislocations,microelements,phases,and different dislocations result in the accumulation of dislocations,dislocation loops,and dislocation tangles. The dislocation structure changes under heavy ion irradiation,which is of certain significance for the application of AM in the nuclear industry. The occurrence of dislocations reduces the elastic strain energy caused by lattice distortion,and the dislocation structure shows the mechanism of strain minimization in the solidification process. In the plastic deformation,the dislocations vary significantly with the strain. Different initial dislocations affect the response to the strain of the formed parts. Meanwhile,the initial dislocations induce martensitic transformation and promote recrystallization in the steel-formed parts,which in turn affect the mechanical properties. The dislocation density of the AM-formed parts is higher than that of the parts prepared by traditionally forged or cast methods. There are certain differences in dislocation density in various positions and shapes too. Additionally,different process parameters(such as heat treatment and aging treatment)also have an effect on the dislocation density,thus affecting the properties of the formed parts. Dislocation strengthening,as the main strengthening effect in AM-formed parts,endows them with the same mechanical properties as the forged parts. The unique dislocation structures generated by AM also affect the corrosion,creep,and hydrogen embrittlement of the formed parts. © 2024 Cailiao Daobaoshe/ Materials Review. All rights reserved.