Study On Microstructure And Properties Of 3D Printing TiNi Memory Alloy

The TiNi Shape Memory Alloy has important application value in industrial intelligent control,connection and manufacturing of medical artificial joint and lightweight design.3D printing is a new technology for the integrated design and manufacture of the material structure developed in recent years.In which 3D printing of TC4 titanium alloy device has been practically applied,and 3D printing of the TiNi Shape Memory Alloy has been developed in recent years.Selective Laser Melting?SLM?technology is a kind of material manufacturing technology for typical?3D printing?,and has been widely concerned and applied in material science research and industrial production step by step.the SLM preparation of the TiNi Shape Memory Alloy is still in the initial stage,so the powder preparation process of the material,the adjustment of the printing parameters,the tissue and the performance and the heat treatment modification are improved,And the data accumulation of the comprehensive performance of the TiNi Shape Memory Alloy is particularly important for 3D printing.In this paper,the preparation of 240kg grade Ti-50at%Ni ingots,the preparation of Ti-Ni mixed powder by EIGA,and the laser selective melting forming of TiNi Shape Memory Alloy samples were studied.The printing parameters,sample microstructure and properties of SLM forming TiNi Shape Memory Alloy were studied.The microstructure of the sample was analyzed by optical microscope and scanning electron microscope,the sample density was measured by Archimedes drainage method,the phase transition process of the sample was measured by DSC,the Vickers hardness on the surface of the sample was measured by automatic microhardness tester,and the tensile behavior was measured by tensile tester.The experimental data were compared with the as-cast Ti-50at%Ni Shape Memory Alloy,and the causes and mechanism of the difference of microstructure and properties were analyzed.The effects of heat treatment on the density,phase composition,phase transformation process,defects,microstructure and tensile fracture of Ti-50at%Ni Shape Memory Alloy formed by SLM were analyzed.The laser power 200W,scanning speed 900mm/s,powder thickness 50?m,scanning spacing 120?m is the best process of SLM in this paper.The resulting Ti-50at%Ni memory alloy sample has a maximum density of 99.4%,and the phase composition is composed of B2,B19?,Ti₂Ni,Ti and Ni.The thermal treatment can increase the density of the SLM-Ti50at%Ni alloy memory sample to 99.7%,change the internal phase composition and phase change the numerical structure of the alloy,increase the surface hardness,and then decrease with the increase of the temperature of the phase change.The tensile behavior of the tensile samples of the Ti-50at%Ni memory alloy prepared by SLM is similar to that of the traditional two-phase Shape Memory Alloy.The fracture surface is characterized by a mixed fracture of brittle fracture and local plastic fracture,and the sample has a Shape Memory Effect.although some samples have defects such as stomata,cracks,and unfused materials,most TiNi Shape Memory Alloy samples prepared by SLM in this paper have Shape Memory Effect.