Pevnost v tahu a ve smyku dvojčatového a ideálního NiTi martensitu

Tensile and shear strength of perfect and twinned NiTi martensite

abstract

en

Twinning in the NiTi martensite represents a large planar defect that is responsible for its unique material properties like the shape memory effect, and therefore the NiTi marten-site reversible deformation depends on the ability of twin's reinforcement in the marten-site. Thus, twinning plays an essential role in the shape memory effect. To obtain a better understanding of the twinning reinforcement in the martensite from the atomic scale point of view, we've computed the tensile and shear strength for perfect and twinned NiTi martensite by the means of the density functional theory. The perfect martensite crystal lattice has been described by the experimentally observed martensite structure parameters as well as by the BCO parameters that have been predicted by the ab initio methods. The model of the twinned martensite is represented by a supercell containing (100) compound twinning arranged in two variants of the martensite. For comparison, the strength of a perfect austenitic B2 structure is also studied. The obtained results have shown that the presence of the selected compound twinning in the martensite only slightly reduces the tensile and shear strength. The results have also shown that the ten-sile and shear strengths for austenite are significantly higher than those for martensite.

Dvojčatění v NiTi martenzitu představuje velkou rovinnou vadu, která je odpovědná za své jedinečné vlastnosti materiálu, jako je tvar paměťovým efektem, a proto NiTi reverzibilní deformace závisí na vlastnostech těchto dvojčat, jenž hraje zásadní roli v efektu tvarové paměti. Pro získání lepší pochopení dvojčat v martenzitu v atomovém měřítku byla vypočítána na pevnost v tahu a pevnost ve smyku pro dokonalé a dvojčatový martenzit NiTi pomocí DFT simulací. Perfektní martenzit krystalová mřížka byla popsána v experimentálně zjištěných parametrů martenzitických struktur, jakož i ze strany BCO parametrů, které byly predikovaných podle ab initio metod. Model zdvojeného martenzitu je reprezentován superbuňkou obsahující (100) dvojčatění. Pro srovnání je vypočtena také pevnost dokonalé austenitické struktury B2. Získané výsledky ukázaly, že přítomnost vybrané sloučeniny twinningy v martenzitu jen nepatrně snižuje pevnost v tahu a pevnost ve smyku. Výsledky také ukázaly, že smykové síly austenitu jsou významně vyšší než ty, pro martenzitu.

Twinning in the NiTi martensite represents a large planar defect that is responsible for its unique material properties like the shape memory effect, and therefore the NiTi marten-site reversible deformation depends on the ability of twin's reinforcement in the marten-site. Thus, twinning plays an essential role in the shape memory effect. To obtain a better understanding of the twinning reinforcement in the martensite from the atomic scale point of view, we've computed the tensile and shear strength for perfect and twinned NiTi martensite by the means of the density functional theory. The perfect martensite crystal lattice has been described by the experimentally observed martensite structure parameters as well as by the BCO parameters that have been predicted by the ab initio methods. The model of the twinned martensite is represented by a supercell containing (100) compound twinning arranged in two variants of the martensite. For comparison, the strength of a perfect austenitic B2 structure is also studied. The obtained results have shown that the presence of the selected compound twinning in the martensite only slightly reduces the tensile and shear strength. The results have also shown that the ten-sile and shear strengths for austenite are significantly higher than those for martensite.

NiTi, dvojčatění, tvarová paměť, pevnost tahu a smyku

NiTi, twinning, shape memory, tensile and shear strength

06.07.2014

Spain

International Conference on Martensitic Transformations 2014 - ICOMAT 2014

27–27

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