| Shape memory alloy is a typical representative of smart materials at present,and additive manufacturing is hailed as a disruptive advanced manufacturing technology in the 21 st century.Using additive manufacturing to prepare shape memory alloy and its components,which a fourth dimension is added on the basis of "3D printing" become a research subject with great development potential and prospects in the field of smart material preparation.However,when the shape memory alloy is prepared by additive manufacturing,the memory function of the alloy will be lost.In response to this problem,this article proposes a new idea "using the micro-nano powder core wire as the material for additive manufacturing of memory alloys,which uses a high-boiling-point sheath to coat the low-boiling-point powder core to reduce the burning loss of alloy elements,and by nanonizing some of the elements in the powder core that is to carry out nano-doping to achieve the effect of strengthening the alloy master phase,thereby suppressing the adverse effect of additive manufacturing on the memory function of the alloy".In the research,taking the Fe-Mn-Si-Cr-Ni memory alloy,which is currently the most widely used and has the best corrosion resistance as the object.Research on the manufacturing process,organization and performance of the material,explored the preparation of Fe-Mn-Si-Cr-Ni memory alloy powder core wire and its additive manufacturing process,and analyzed five kinds of micro-nano powders doped with different proportions of nano-silicon core wire additive manufacturing Fe-Mn-Si-Cr-Ni memory alloy microstructure characteristics,investigated its shape memory performance and corrosion resistance.Thus,provide technical support for expanding the application field of iron-based memory alloy,while enrich and develop materials for additive manufacturing,especially powder-cored wire for additive manufacturing and related theories.The main work completed and the main results obtained in this paper are as follows:(1)The preparation of Fe-Mn-Si-Cr-Ni memory alloy powder core wire and its additive manufacturing process are explored.Through the research of the material distribution plan,vibration powder filling,wire drawing reduction and other links in the wire preparation process,the preparation process of the micro-nano powder-cored wire in the experimental process is obtained.At the same time,through the establishment of powder-cored wire additive manufacturing Fe-Mn-Si-Cr-Ni shape memory alloy process three-dimensional transient finite element model,analyzes the temperature field changes during the additive manufacturing process of Fe-Mn-Si-Cr-Ni memory alloy powder core wire under different output current I and arc scanning speed V,and clarified the influence of process parameters on the temperature field in the process of Fe-Mn-Si-Cr-Ni memory alloy additive manufacturing.The optimal process parameters of powder-cored wire for additive manufacturing of Fe-Mn-Si-Cr-Ni memory alloy are obtained,that is current I=210A and arc scanning speed V=0.45m/min.(2)The microstructure characteristics of additively manufactured Fe-Mn-Si-Cr-Ni memory alloy are analyzed.The microstructure and element composition of five Fe-Mn-Si-Cr-Ni memory alloys doped with different proportions of nano-silicon are compared and analyzed.The results show that doping with nano-silicon can interrupt the dendritic growth in the as-cast structure of the alloy and gradually transform it into cell crystals or equiaxed crystals with smaller grain sizes,and the effect is more obvious as the number of molten layers increases.At the same time,after homogenization and solution treatment,the alloy structure is composed of austenite grains.Among them,the degree of refinement of the 50% nano-silicon alloy is the most significant.In addition,in the alloy doped with 50% nano-silicon,the proportions of Si and Mn are the closest to the theoretical proportions and show an increasing trend,indicating that nano-doping can inhibit the additive manufacturing process element burning has a positive effect.(3)The shape memory performance of the additively manufactured Fe-Mn-Si-Cr-Ni memory alloy was investigated.The shape memory recovery of five kinds of Fe-Mn-Si-Cr-Ni memory alloys doped with different proportions of nano-silicon was measured,and the alloy deformation and the structure morphology after deformation recovery were observed at the same time.The influence of nano-silicon doping on the shape memory performance of the alloy was obtained,and the mechanism of inhibiting the shape memory performance of the alloy with nano-silicon doping was discussed preliminarily.The results show that with the increase of the doping ratio of nano-silicon,the shape memory recovery rate of the alloy shows a trend of first rising and then decreasing sharply.Among them,the shape memory recovery rate of the 50% nano-silicon alloy is increased by 34.97% compared with the conventional alloy,and the shape memory recovery rate of the doped 100% nano-silicon alloy is 80% lower than that of the conventional alloy.The analysis believes that nano-silicon doping is beneficial to improve the accuracy of alloy composition and matrix strengthening,while excessive nano-silicon doping will cause adverse effects due to its easy agglomeration.(4)The corrosion resistance of the additively manufactured Fe-Mn-Si-Cr-Ni memory alloy was investigated.The microstructure characteristics,polarization curve,corrosion resistance,corrosion products,etc.of five Fe-Mn-Si-Cr-Ni memory alloys doped with different proportions of nano-silicon were compared before and after corrosion in 3.5% Na Cl solution.The results show that with the increase of the doping ratio of nano-silicon,the corrosion resistance of the alloy increases first and then decreases,which is consistent with its effect on the shape memory performance.The corrosion resistance of the alloy is the best when the nano-silicon doping ratio is 50%,and the corrosion resistance of the alloy is the worst when the nano-silicon doping ratio is 100%.The analysis believes that nano-doping makes the alloy grain refinement and protects the important elements Si and Cr generated by the passivation film,so that the corrosion resistance of the additive manufacturing Fe-Mn-Si-Cr-Ni memory alloy is improved,and excessive doping of nano-silicon will deteriorate its corrosion resistance due to agglomeration. |
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