Shape memory and superelastic applications of NiTi based alloys have typically been limited to near room temperature or to bulk length scales. The objective of this work is two-fold: first, to investigate shape memory behavior at low temperatures in the context of the R-phase transformation in NiTiFe alloys by recourse to arc-melting, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and mechanical testing at low temperatures; and second, to investigate superelasticity and two-way shape memory behavior at reduced length scales in the context of NiTi by recourse to micro-compression, micro-indentation and TEM studies. Selected compositions of ternary NiTiFe shape memory alloys were arc-melted and thermomechanically processed to investigate the influence of composition and processing parameters on the formation of the R-phase. The methodology used for the processing and characterization of the alloys was established and included microprobe analysis, DSC, TEM and mechanical testing. No phase transformation was observed in alloys with Fe content in excess of 4 at.%. Thermomechanical treatments facilitated the formation of the R-phase in Ni-rich alloys. The range of the transformation between the R-phase and austenite, and the hysteresis associated with it were influenced by the distribution and size of metastable Ni4Ti3 precipitates. The investigation of the microstructural, thermal and mechanical properties of the R-phase transformation in NiTiFe alloys revealed a complex dependence of these properties on processing parameters. The present work also highlighted the hitherto unexplored competition between the two inelastic deformation modes operating in the R-phase (detwinning and stress-induced transformation) and established the preference of one mode over the other in stress-temperature space. iv The complete micromechanical response of superelastic NiTi was examined by performing careful micro-compression experiments on single crystal pillars of known orientations using a nanoindenter tip. Specifically, the orientation dependence of the elastic deformation of austenite, the onset of its transformation to martensite, the gradient and the hysteresis in the stress-strain response during transformation, the elastic modulus of the stress-induced martensite and the onset of plasticity of the stress-induced martensite were analyzed in separate experiments. A majority of the results were explained by recourse to a quantitative determination of strains associated with austenite grains transforming to martensite variants or twinning in martensite. Microstructural studies were also performed on a micro-indentation trained NiTi shape memory alloy specimen to understand the mechanisms governing the two-way shape memory effect. In situ TEM studies at temperature on specimens obtained at different depths below the indent showed the presence of retained martensite along with the R-phase. Previously, while such twoway shape memory behavior has typically been associated with large dislocation densities, this work provides evidence of the role of retained martensite and the R-phase in cases with reduced dislocation densities. Funding support for this work from NSF (CAREER DMR-0239512), NASA (NAG3-2751) and SRI is acknowledged.

The alloys FeMnSi and Fe2MnCrSi were obtained in arc furnace in a helium atmosphere at the water-cooled copper ingot mold with the double remelting. Homogenizing annealing of the samples was carried out in a vacuum furnace at 950°C. X-ray analysis was carried out for structure investigation of the alloys. The diffraction patterns were obtained on the X-ray diffractometer Bruker D8 Advance, measurement results were processed using software FullProf v.2.05. Measurement of magnetization isotherms and dependences of the magnetization of alloys on magnetic field were carried out with vibration magnetometer7407 VSM (Lake Shore Cryotronics) in magnetic fields up to 1.7 T at temperature 80 – 400 K. Changes in magnetic part of entropy in various magnetic fields from 0.01 to 1.7 T calculated from isotherms. For sample Fe1.75Mn1.25Si it is shown that at the Curie temperature dependence of the changes of entropy on the magnetic field is almost linear. Obtained dependence of the magnetization on the field at temperatures Tc - 50 K (Tc – the Curie temperature) for all investigated compounds showed that the magnetization of samples decreases with increasing concentration of manganese and chromium. The Curie temperature for alloys Fe3-xMnxSi decreases with increasing of manganese concentration. For alloys Fe2Mn1-xCrxSi the Curie temperature increase with with increasing of chromium concentration. ∆T-effect for all compounds was measured by direct method on an automated installation for measurement of the specific heat and magnetocaloric effect MagEq MMS SV3 (AMT&C) in magnetic field 1.7 T at temperature 85-370 К. The magnitude of the magnetocaloric effect of the investigated compounds kept constant in the investigated manganese and chromium concentration range including at room temperature. / В дуговой печи были получены сплавы FeMnSi и Fe2MnCrSi в атмосфере гелия на водоохлаждаемой медной изложнице с двухкратной переплавкой. Гомогенизирующий отжиг образцов проводился в вакуумной печи при температуре 950°С. Для исследования структуры всех сплавов был проведен рентгеноструктурный анализ. Дифрактограммы были получены на рентгеновском дифрактометре Bruker D8 Advance, результаты измерения были обработаны с использованием программного обеспечения FullProf v.2.05. На вибрационном магнитометре 7407 VSM (Lake Shore Cryotronics) в магнитных полях до 1.7 Тл в температурном интервале от 80 до 400 K проведены измерения изотерм намагниченности и измерена зависимость намагниченности сплавов от магнитного поля. Рассчитано по изотермам изменение магнитной части энтропии в различных полях от 0.01 до 1.7 Тл. Для образца Fe1.75Mn1.25Si показано, что при температуре Кюри зависимость изменения энтропии от величины поля почти линейна. Полученные зависимости намагниченности от поля при температурах Tc – 50 К (Tc – температура Кюри) для всех исследуемых соединений показали, что намагниченность образцов уменьшается при увеличении концентрации марганца и хрома. Температура Кюри сплавов Fe3-xMnxSi уменьшается с ростом концентрации марганца. При увеличении концентрации хрома в соединении Fe2Mn1-xCrxSi температура Кюри растет. На автоматизированной установке для измерения магнитокалорического эффекта и теплоемкости MagEq MMS SV3 (AMT&C) измерен прямым методом ∆T-эффект всех соединений в магнитном поле 1.7 Тл в диапазоне температур 85-370 К. Величина магнитокалорического эффекта изученных соединений сохраняется неизменной в исследованном диапазоне концентраций марганца и хрома в том числе и при комнатной температуре.

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Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: Geoffrey Brooks and Kenneth Coley. Includes bibliographical references (p. 152-164).

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The thesis is primarily concerned with the design, construction and preliminary commissioning of a novel polarimeter for full three-dimensional analysis of electron spin polarisation. The polarimeter is described in detail, together with the theoretical basis for its operation. Studies of an amorphous ferromagnetic alloy, Co66Fe4Ni1B14Si15, and its application as a secondary standard are presented. Finally, a design study of a GaAs polarised electron source, capable of providing both longitudinal and transverse polarisations, is detailed.

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