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Shape Memory Effect And Martensite Transformation Of Fe-Mn-Si-Cr-Ni-N Alloy

Posted on:2006-05-12Degree:MasterType:Thesis
Country:ChinaCandidate:H N MaFull Text:PDF
GTID:2121360152991033Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
The shape memory effect of Fe-20.69Mn-4.93Si-8.15Cr-4.86Ni-0.05N alloy was studied by bending test and tensile test. Stress induced martensitic transformation as well as macroscopic lattice deformation in the alloy were studied by means of XRD, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and Atomic Force Microscope (AFM), shape memory mechanism of the alloy was discussed at the same time.From the study of shape memory effect, when solution temperature is 700 ℃ and bending deformation amount is 2.9% the shape recovery ratio is best (74.2%) and is improved by 9% than Fe-20Mn-5Si-8Cr-5Ni alloy without N in the same condition; when bending deformation amount is 9.4% the recoverable strain is best (4.0%). The shape memory effect of the alloy can be effectively improved by suitable thermomechanical training: the shape recovery ratio is 51.5% and the recoverable strain is 4.8% after two cycles trainning when solution temperature is 700 ℃, bending deformation amount is 9.4% and the quenching temperature is 700 ℃, the shape recovery ratio of the alloy is improved by 22% and recoverable strain improved by is 20% than the alloy without trainning.From the study of stress induced ε martensite transformation, the volume fraction of e martensite reaches maximum (47.8%) and e martensite show parellel form when the amount of tensile deformation is 3.8%; If the amount of tensile deformation is 6.2%, a'martensite appears due to intersection martensite and the volume fraction of s martensite begin to decrease(43.8%); If the amount of tensile deformation is 9.4%, the alloy has too much overlap and intersection and the volume fraction of a'martensite reaches maximum (54.3%). The suitable training can effectively decrease the volume fraction of a'martensite, after three cycles training when bending deformation amount is 9.4%, the volume fraction of a'martensite is 36.5% and decrease by 32.9% than the alloy without trainning.The martensite surface relief of the alloy was observed and analyzed by means of AFM. Itshows that thermal γ→ε transformation belongs to self-accommodating shear model, relief height is 8.33nm~57.69 nm, relief width is 0.53 × 103nm~3.26× 103nm and relief angle is 0.89°~0.90° ; Stress-induced γ→ε transformation belongs to single shear model, relief height is 47.06 nm~93.26 nm, width is 200.65 nm~312.50 nm and relief angle is 9.89° -17.93° ; The different transformation model can produce different shear strain, so they show different shape memory effect.
Keywords/Search Tags:shape memory effect, shape recovery ratio, thermomechanical trainning, surface relief, stress-induced martensite transformation
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