增材制造成形件中位错的研究进展

A Review of Dislocations in Additive Manufacturing Forming Parts

增材制造是通过逐层堆积的方法制造实体零件的一种革命性技术,其成形性能受成形工艺、微观结构、沉积路径等影响,其中,位错作为晶体微观结构中广泛存在的一种线缺陷,是决定金属性能的一个重要因素。为深层次理解增材制造性能影响的本质机制,需进一步了解增材制造成形件中的位错特点。本文基于近年来增材制造成形件中位错的研究成果,梳理了位错的起源、特征和密度,分析了位错对强度等性能的影响。与传统制造相比,增材制造成形过程中因固有的循环加热-冷却而造成的压缩-拉伸应力循环使得增材制造成形件中的位错具有独特的结构和性质。在塑性变形中,位错随应变变化明显,不同的初始位错影响成形件对应变的响应;增材制造成形件中测量的位错密度高于锻件或铸件,不同位置、不同形状的位错密度也存在一定的差异;位错强化是增材制造成形件中的主要强化作用,与此同时,在钢的成形件中,位错还可诱发马氏体相变,促使再结晶,另外还影响成形件的腐蚀、蠕变和氢脆等。

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.