R. Tamm

Growth of epitaxial SmCo5 films on Cr∕MgO(100)

Although the hard magnetic SmCo5 phase has very attractive and well-known intrinsic magnetic properties, it has not been grown as an epitaxial thin film, so far. This letter reports the epitaxial growth of SmCo5 films by pulsed-laser deposition on Cr(100) buffered MgO(100) single-crystal substrates. The phase purity, crystal structure, epitaxial relation to the substrate, and magnetic properties have been determined by careful energy-dispersive x-ray analysis, pole figure measurements, transmission electron microscopy, and vibrating sample magnetometry. Compared to the formerly studied Sm2Co7 films, the preparation of the SmCo5 phase improves the remanent magnetization by 38%.Although the hard magnetic SmCo5 phase has very attractive and well-known intrinsic magnetic properties, it has not been grown as an epitaxial thin film, so far. This letter reports the epitaxial growth of SmCo5 films by pulsed-laser deposition on Cr(100) buffered MgO(100) single-crystal substrates. The phase purity, crystal structure, epitaxial relation to the substrate, and magnetic properties have been determined by careful energy-dispersive x-ray analysis, pole figure measurements, transmission electron microscopy, and vibrating sample magnetometry. Compared to the formerly studied Sm2Co7 films, the preparation of the SmCo5 phase improves the remanent magnetization by 38%.

Epitaxial growth,,of highly coercive Sm-Co thin films using pulsed laser deposition

Hard magnetic materials with a uniaxial magnetocrystalline anisotropy can be most efficiently used if the easy axis is well aligned along one crystallographic direction in the entire sample volume. Epitaxial growth is one suitable method to achieve this aim and therefore Sm–Co thin films on Cr-buffered single-crystal MgO (100) substrates were deposited. Pulsed laser deposition from elemental Sm and Co targets was used to prepare films of nominal Sm2Co7 stoichiometry. Pole figure measurements and magnetization measurements reveal an epitaxial growth of Cr on MgO onto which the c axis of the Sm–Co layer is aligned in plane, viz., MgO(001)[100]‖Cr(001)[110]‖Sm–Co(110)[001]. At higher deposition temperatures an additional Sm–Co (1 1 16) texture was observed. This corresponds to an additional epitaxial orientation relation, where the c axis is tilted 60° out of the substrate plane. However, at low deposition temperatures and with smaller pulse repetition rates a reduction in the amount of this unwanted compone...

Pulsed laser deposited epitaxial Sm–Co thin films with uniaxial magnetic texture

Sm–Co thin films have been grown epitaxially with pulsed laser deposition on Cr buffered MgO(110) substrates. The buffer microstructure plays a significant role in controlling the growth and hence the magnetic properties of the Sm–Co film. High deposition temperatures of the Cr buffer result in a rough and discontinuous microstructure, thereby resulting in an x-ray amorphous or nanocrystalline Sm–Co layer, as has been confirmed by transmission electron microscopy studies. By lowering the buffer deposition temperature from 700to300°C, the roughness decreases from 5to0.6nm. Sm–Co films grow epitaxially on these low temperature buffers with the epitaxial relation MgO(110)[001]∥Cr(211)011∥SmCo(100)[001] which implies a single in-plane orientation of the c axis along the MgO[001] direction. The strong in-plane crystallographic texture seen in the pole figure measurements leads to a very pronounced magnetic texture, quantified by a remanence ratio JrMgO[110]∕JrMgO[001] as low as 0.08 and a high remanence of 0.8...

Torsion Texture Measurements With High-Energy Synchrotron Radiation on NiAl

Diffraction with high-energy synchrotron radiation is a new experimental method to determine textures of materials, which due to the special properties of this radiation, in the future may have advantages in terms of accuracy of local texture measurements in comparison to established methods like Electron back scatter diffraction (EBSD). In the present study NiAl polycrystals with two different initial textures have been deformed in torsion at 727°C and 1000°C and their texture development has been measured with highenergy synchrotron radiation. Torsion enables the study of texture formation with strain as well as the exploration of large strains without changing the shape of the samples. The pole figures indicate the preferred alignment of ‹100› with the shear direction and {110} with the shear plane. High pressure torsion may also open new possibilities in terms of grain refinement and texture formation and thus ductilization of NiAl.

Texture induced plastic anisotropy of NiAl polycrystals

Abstract Textured stoichiometric NiAl polycrystals have been deformed in compression at room temperature under 0.4 GPa confining pressure at a strain rate of about 10 −4 s −1 . The strength of the samples depends on the preferred orientation with respect to the compression axis, with 〈100〉 being much harder than those with 〈110〉 and 〈111〉. Similarly, the frequency of intercrystalline microcracking shows the same tendency. The orientation distribution of the microcracks indicates that they mainly result from internal stresses released after unloading. The plastic anisotropy at elevated strains correlates with the Taylor energy calculated. The deviation from axially symmetric deformation is due to the tendency of minimizing the Taylor energy.

Microstructure and Texture Development during Recrystallization of Rolled Molybdenum Sheets

Recrystallization is an important tool to adjust the grain size and texture of polycrystalline materials in order to optimize their properties. In the present work recrystallization and the related changes of texture have been studied on rolled molybdenum sheets as a function of temperature and time. The microstructure was investigated by orientation contrast in a scanning electron microscope. The kinetics of recrystallization displayed in a JMAK plot yields Avrami coefficients decreasing with temperature from 2.5 to 1.1. The activation energy amounts to 5 eV, which agrees well with the volume self-diffusion coefficient. The textures of the sheet surface and central layer were measured by X-ray diffraction. The rolling texture in the centre of the sheets is characterized by a strong a-fibre with the rotated cube component {100}<110> dominating. Besides that, there exists a weak g-fibre. In contrast, the surface layer is characterized by a weak cube component. During recrystallization changes in texture are insignificant. With long annealing times all texture components tend to degrade. Conclusions regarding the deep-drawability are drawn.

Influence of texture and hydrostatic pressure on the room temperature compression of NiAl polycrystals

Abstract Compression of NiAl polycrystals was carried out at room temperature under atmospheric as well as 0.4 GPa confining pressure at constant strain rate. The stress–strain curves show that the strength as well as the work-hardening rate is generally higher when deformed under hydrostatic pressure. Moreover, there is a strong plastic anisotropy, that is, samples having a 〈100〉 crystallographic preferred orientation parallel to the compression axis are much harder than those having 〈110〉 and 〈111〉. Similarly, the frequency of microcracking shows the same tendency. It seems that the microcracks in the samples deformed under confining pressure mainly result from internal stresses released after unloading. The strength of the differently textured samples at elevated strains correlates with the Taylor energy calculated. These calculations also explain for certain textures the deviation from a homogeneous shape change during compression towards plane–strain deformation. The textural changes produced by deformation are simulated with the Taylor model.

Plastic anisotropy of textured ODS nickel-base alloy PM 1000

Abstract Strongly textured ODS nickel-base alloy PM 1000 with a pancake grain structure has been deformed in axisymmetric and plane strain compression at 1000°C and a true strain rate of 10 −4 s −1 . The texture has been measured by neutron diffraction. Based on the texture, Taylor factors have been calculated for the different deformation modes. The linear dependence of the strength on the Taylor factor indicates that the plastic anisotropy observed is due to the texture and not to the anisotropy of the grain structure.

Development of microstructure and texture in extruded NiAl

Abstract High temperature extrusion of polycrystalline NiAl yields a 〈111〉〈110〉 double fibre texture. Electron back-scattering diffraction (EBSD) analysis of the partially recrystallized microstructure shows that the 〈111〉 fibre is due to recrystallization. The 〈110〉 deformation fibre can be simulated with the full constraints Taylor model using the known high temperature slip systems 110〈100〉 and 110〈110〉. Relaxing the constraints yields the 〈111〉 fibre which may represent the nuclei for recrystallization. The recrystallization is most probably dynamic by subgrain rotation and preferred subgrain growth in a grain core/mantle strain and orientation gradient.

Deformation and Recrystallization Textures in Iron Aluminides

Iron aluminides of different composition were deformed at high temperatures by extrusion through a round and rectangular die, approximating tension and plane strain deformation, respectively. Depending on temperature and composition dynamic recrystallization takes place. To investigate post-deformational recrystallization annealing treatments have been applied. Global and local textures were measured by neutron and electron back scatter diffraction (EBSD), respectively. The EBSD method allows the separation of deformation and recrystallization texture components. Moreover, the texture development is correlated with the microstructure evolution derived from EBSD mappings. The development of the deformation and recrystallization textures is discussed by means of different models on polycrystal deformation and recrystallization, respectively. Conclusions concerning the anisotropy of the elastic and plastic properties are drawn.