Preparation And Microscopic Characterization Of Ti-Ni-Hf-Cu High Temperature Shape Memory Alloy Thin Ribbon

In this thesis,Ti-Ni-Hf-Cu shape memory alloy ribbons were prepared by rapid solidification ribbon method,and were totally studied by X-ray diffractometer,transmission electron microscope,optical microscope and differential scanning calorimeter,.The microstructure,phase transition method and mechanic properties of TiNi-Hf-Cu alloy ribbons explain the evolution mechanism of alloy ribbons during tensile deformation and analyze their deformation laws.The experimental results show that the microstructure of the Ti-Ni-Hf-Cu shape memory alloy is amorphous,and a small amount of crystallized B19' martensite exists in the free surface structure.After annealing at 600? for 60 s,the grains are equiaxed and the size is significantly smaller,less than 100 nm.Further,the room temperature phase composition of the Ti-Ni-Hf-Cu shape memory alloy ribbon is a B19' martensite phase and a?Ti,Hf?²Ni precipitate phase.The results of transmission electron microscopy of the alloy ribbon show that the martensitic variants in the alloy ribbon exhibit selfcooperative configuration,which is?011?type I twin relationship,and the interface between martensitic variants is curved.There are a large number of substructures between the bulk variants,which are?001?composite twins;the?Ti,Hf?²Ni precipitates are diffusely distributed at the interface between the martensite variants and inside the martensite variants.The DSC test results show that the phase transition temperature of the Ti-Ni-Hf-Cu alloy ribbon increases with the increase of Ni content,and the phase transition behavior also changes.In addition,as the annealing time increases,the martensitic transformation temperature also increases.The test results of shape memory effect show that the Ti₃₆Ni₄₁Hf₁₅Cu₈ ribbon has excellent shape memory performance.When the predeformation is 4%,the recovery rate is 100%.When the pre-variable is 6%,the recovery rate is as high as 96.7%.The transmission electron microscopy observation of the Ti-Ni-Hf-Cu alloy ribbon with different shape variables shows that when the deformation of the Ti₃₆Ni₄₁Hf₁₅Cu₈ ribbon is 3%,the alloy undergoes the reorientation process of the martensite variant,which is in a favorable orientation.The martensite variant swallows the malformed martensite variant,and the interface between the variants changes.When the shape variable of the Ti₃₆Ni₄₁Hf₁₅Cu₈ ribbon is 6%,the process of reorientation of the martensite variant is basically completed.At this time,the internal substructure of the martensite modification changes,and the demorphation process of the?001?composite twin is carried out inside the variant.Therefore,the micro-deformation mechanism of the rapidly annealed Ti-Ni-Hf-Cu alloy ribbon has been found.First,the elastic deformation of B19' martensite occurs,and then?011?re-orientation of type I twins occurs,and finally occurs?001?de-twisting of composite twins.In addition,there is a phenomenon of local stress concentration in the Ti-Ni-Hf-Cu alloy ribbon,which leads to the difference in the reorientation process of martensite variants in different regions.