Tensile Properties Investigation Of Bionic Layered Al_xCrMnFeCoNi High Entropy Alloy Processed By Laser Additive Manufacturing

CrMnFeCoNi high entropy alloy is favored by many researchers because of its unique properties and single microstructure,but its strength at room temperature is low.Adding Al element can improve the strength of CrMnFeCoNi,but greatly reduce the plasticity.Therefore,it is expected to find a strengthening method that can both improve the strength and maintain the plasticity.Shell,shell and other natural biological structures not only have high strength,but also have high plasticity and toughness,which is mainly due to the existence of lamellar spiral structure inside,through the thickness of the direction of stacking layer by layer,improve the comprehensive mechanical properties.Laser additive manufacturing technology is a kind of fabrication technology which can realize multi-lamellar structure of metal materials.In this paper,the laser direct deposition technology is used to simulate the multi-layer structure in nature,and the Al_xCrMnFeCoNi（x as mass fraction）high-entropy alloy with different layered structure is prepared by designing and regulating the composition in the layer.The microstructure and mechanical properties of the alloy were analyzed,and the influence of the addition of layered structure on the properties of high entropy alloy was studied.The following conclusions were obtained:（1）With the continuous increase of Al content,Al_xCrMnFeCoNi high entropy alloy（4%≤x≤12%）has a phase transition process,that is,the single FCC phase gradually changes to FCC+BCC two-phase and finally changes to a single BCC phase.At the same time,BCC phase can promote the reduction of the alloy grain size.Thus the strength and hardness of the alloy increase and the plasticity decreases.（2）The“double layer”high entropy alloy with“soft and hard”collocation was designed and prepared."Double layer"structure with coarse grain and fine grain group differences,achieve the uneven structure,this kind of structure to improve the strength of high entropy alloys,because with the improvement of the degree of grain refinement,soft and hard area because of the performance differences between causes uncoordinated deformation between interface,deformation degree aggravate realized alloy strengthening.However,the plasticity of high entropy alloys is still not ideal because the outer hard zone breaks earlier than the soft zone.（3）The“sandwich”high entropy alloy with“soft+hard+soft”structure was designed and prepared,and a high entropy Al₆-Al₁₂-Al₆ alloy with excellent plasticity matching was obtained.The yield strength and tensile strength of this alloy at room temperature were 625MPa,760 MPa and 15.2%respectively.“Sandwich”structure of high entropy alloys first appeared in the hard section of micro cracks,grow and expand into a big crack,then crack extension of the crack tip motion slowed only after it reached the hard and soft interface,and a slight turning to release stress,the existence of interface obstacles the crack through rapidly,alleviate the plastic sacrifice,and most of the soft area crack formation is slow and in the sample edge.