Metal Bionic Design Based On Shell Pearl Layer Features And Research Of Wire Arc Additive Manufacture

There is an optimal matching law between the structure and mechanical properties of natural shell materials.The nacre of shell has "soft-hard" interleaved-compound structure and excellent mechanical properties,which provides a new idea for the design and manufacture of high performance biomimetic materials.In the process of studying biological materials,the development of new manufacturing methods of biomimetic materials has become a research focus.This paper is focus on the material composition,microstructure and mechanical properties of the freshwater mussel,and analyze the relationship between its structure and mechanical properties.The workpiece with bionic structure is designed according to the structural characteristics of the nacre and printed by TIG Wire Arc Additive Manufacture method,which microstructure and mechanical properties are studied to verify the strengthening and toughening mechanism of natural shell materials.The main mineral component of freshwater mussel is CaCO₃,which is composed of prismatic layer and pearl layer.The surrounding density is larger,the center is smaller.The flexural strength of fresh shells was 29.8MPa,which was significantly lower than that of heated,which was 3.37MPa.The hardness of the prism layer is 4?5GPa and the elastic modulus is about 60GPa.The hardness of the pearl layer is 3.5GPa and the elastic modulus is about 70GPa.So we can conclude that the prism layer is harder than the pearl layer and has poor elastic deformation resistance.The crack propagation path of the nacre layer shows that the "soft and hard" interweaving structure is the key factor of the nacre layer's toughness.It is concluded that the toughening mechanism of natural shell materials is crack deflection,aragonite extraction and the connection of organic matter.The width and height of the weld are inversely proportional to the welding speed and are proportional to the welding current.The increasing of the overlap rate can make the top surface of the buildup layer more smooth,it is good for the manufacturing of the structure.When the overlap rate is 33%,the forming quality is the best.When the overlap ratio is more than 50%,it will lead to the collapse of metal structure to one or two side.The microstructure of the bottom weld of stainless steels is y-austenite with few worm-like 8 ferrite;the middle part is ?-austenite and ?-ferrite;the structure of the final weld is ?+?phase region,in which y-phase region is divided into cellular y-phase and columnar ?-phase.The grains are getting smaller and smaller along the stacking direction from bottom to top.The growth direction of microstructure in the remelting area is perpendicular to the fusion line to the center of the molten pool.The growth direction of the internal structure is from the bottom to the top,and the top area changes with the cooling direction.The hardness of stainless steels and high nitrogen steels gradually increased along the stacking direction from the bottom to the top,but the hardness of high nitrogen steels changed in the shape of "V" on the local scale.The hardness of the two kinds of interwoven structures changed in the shape of" sinusoid",the peaks are the hardness of high nitrogen steels and the trough of waves are the hardness of stainless steel.The tensile strength and ductility of stainless steel and high nitrogen steels and the two kinds of matreial interwoven structures along the direction perpendicular to accumulation are better than that of direction of accumulation.the strength of stainless steel is lower than that of high nitrogen steel,but the plasticity of stainless steel is higher.The plasticity of two kinds of matreial interwoven structures is higher than high nitrogen steel,but lower than stainless steel,the tensile strength is higher than stainless steel and lower than high nitrogen steel.With the high nitrogen steel and stainless steel composition ratio increases,tensile strength increases but plasticity decreases.The impact energy of stainless steels and high nitrogen steels in the direction perpendicular to the unit layer is smaller than that in the direction parallel to the unit layers.The impact energy of high nitrogen steel is less than that of stainless steel.The impact energy of two kinds of materials interwoven structures is higher than that of high nitrogen steel,but it does not reach the level of stainless steel.When the ratio of high nitrogen steel and stainless steel components increases,the impact energy of two kinds of materials interwoven structures will be reduced.