1998 Fiscal Year Final Research Report Summary
Effect of Deformation Induced Transformation in B2-Type TiNi Alloys.
| Project/Area Number |
09650723
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical properties of metals
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| Research Institution | Kumamoto University |
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Principal Investigator |
NISHIDA Minoru Kumamoto University, Faculty of Engineering, Professor, 工学部, 教授 (90183540)
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| Project Period (FY) |
1997 – 1998
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| Keywords | Thermoelastic Martensite / B2-Type Intermetallic Compound / Ti-Ni Alloy / Deformation-Induced Transformation / Deformation Twinning / Twinning Shear Strain / Independent Slip System / Reverse Transformation |
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| Research Abstract |
Ti-Ni alloys of near-equiatomic composition exhibit the shape memory properties associated with thermoelastic martensitic transformation. The other peculiar characteristic is anomalous ductility around room temperature in both B2 parent and B19' martensite phases. The ductility of Ti-Ni alloys is about 40 to 60% in tensile elongation below Mssiguma which is upper limit temperature for the formation of stress induced martensite. The ductility is reduced to 30% above Mssiguma. The stress-strain curves of martensite is divided into three stages. The de-twinning of <011> Type II twin and the formation of (100) compound twin are observed in the first stage. The deformation mode in second and third stages is not only slip deformation but also twinning deformation with the (100), (001) and (20-1) compound twins. The ductility of the B19' martensite is attributable to the formation of (20-1) twin with large twinning shear of 0.4250 and the increment of independent slip system due to the formation of the three compound twins. The essentially same microstructures are developed at Ms to Mssiguma. Above Mssiguma, strain induced martensite is formed in B2 parent phase by tensile deformation. However, the martensite is not grown with increasing the strain. The Ti-Ni alloys exhibit good ductility at the temperature range where the martensite is stable. Goo et al., have suggested that the ductility of the Ti-Ni with B2 structure is attributable to the formation of {114} B2 compound twinning. In the present study, this twinning is derived from the (20-1)B19' twinning. That is, the (20-1)B19' twinning is remained as the {114}B2 compound twinning after reverse transformation. This Is consistent with the lattice correspondence between B2 parent phase and B19' martensite phase. Therefore, the anomalous ductility of B2-type Ti-Ni alloys around room temperature is related to the stress induced martensite.
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