Tomasz Goryczka

Two-stage martensitic transformation in a deformed and annealed NiTi alloy

Deformation and subsequent annealing of NiTi alloys offers great possibilities of controlling characteristic temperatures, sequences of transformations and shape recovery. Todoroki and Tamura showed that depending on annealing temperatures, changes in transformation sequences in deformed alloys occur during both heating and cooling. They also observed that the cooling DSC (Differential Scanning Calorimetry) curves exhibit two peaks in the range of the martensitic transformation for specimens annealed at 500 C. Referring to the paper of Monasevich and Pascal they explained this effect as the formation of two types of martensite. In this paper the authors try to prove that the appearance of two peaks in the martensitic range on the DTA (Differential Thermal Analysis) cooling curves may be due to changes of dislocation configuration caused by the low-temperature annealing.

Rare earth-doped lead borate glasses and transparent glass–ceramics: Structure–property relationship

Correlation between structure and optical properties of rare earth ions in lead borate glasses and glass-ceramics was evidenced by X-ray-diffraction, Raman, FT-IR and luminescence spectroscopy. The rare earths were limited to Eu(3+) and Er(3+) ions. The observed BO(3)↔BO(4) conversion strongly depends on the relative PbO/B(2)O(3) ratios in glass composition, giving important contribution to the luminescence intensities associated to (5)D(0)-(7)F(2) and (5)D(0)-(7)F(1) transitions of Eu(3+). The near-infrared luminescence and up-conversion spectra for Er(3+) ions in lead borate glasses before and after heat treatment were measured. The more intense and narrowing luminescence lines suggest partial incorporation of Er(3+) ions into the orthorhombic PbF(2) crystalline phase, which was identified using X-ray diffraction analysis.

Ultraviolet-to-visible downconversion luminescence in solgel oxyfluoride glass ceramics containing Eu 3+ :GdF 3 nanocrystals

GdF3 nanocrystals doped with Eu3+ ions in oxyfluoride glass ceramics were prepared by a solgel method. The structural properties were examined by x-ray diffraction measurements. The effects of gadolinium codoping on europium emission in the prepared solgel glasses and glass ceramics have been studied. The emission bands originating from the 5D0 state of Eu3+ ions are enhanced under excitation of Gd3+ ions by 273 nm line. The electric dipole 5D0→7F2 transitions were dominant in the samples before heat treatment, whereas magnetic dipole 5D0→7F1 transitions had a higher probability in the samples after annealing. The luminescence lifetime for the 5D0 level of Eu3+ ions in the samples after excitation at 273 nm is long lived in comparison to excitation at 393 nm and increased to 190%. Energy transfer from Gd3+ to Eu3+ was observed.

Crystallite Size Determination of MgO Nanopowder from X-Ray Diffraction Patterns Registered in GIXD Technique

The problem of the crystallite size determination for nanomaterials from X-ray diffraction data obtained in asymmetrical GIXD geometry was analyzed. The studies were performed on nanocrystalline MgO powder prepared by sol-gel synthesis. The nanopowder was preliminary characterized from X-ray diffraction pattern registered in classical Bragg-Brentano geometry and electron microscope observation. The estimated crystallite size, calculated form Williamson-Hall method, equals to 5 nm whereas the lattice distortion is negligible (0.1%). The X-ray diffraction patterns were registered in 30-135º 2θ range using tunnel GIXD technique for the incident α angle: 0.25; 0.5; 1; 2.5 and 5 degrees, respectively. Additional broadening of diffraction lines originated from applied geometry was observed. The calculated crystallite size deviate significantly in comparison to results obtained from classical Bragg-Brentano data. Corrections for additional line broadening were determined, which should be applied for accurate crystallite size calculation in studies of thin nanocrystalline layers using GIXD technique.

Influence of silicate sol–gel host matrices and catalyst agents on the luminescent properties of Eu3+/Gd3+ under different excitation wavelengths

Sol–gel silicate glasses co-doped with Gd3+ and Eu3+ ions were successfully obtained and the pronounced effect of the matrix composition on the energy transfer process from Gd3+ to Eu3+ was confirmed. Qualitative compositions of the examined matrices were varied while the europium and gadolinium ion concentrations were kept constant. Different chemical compositions of the sol–gel matrices were clearly marked by changes in the photoluminescent properties. The effect of gadolinium ions on the visible emission of europium ions has been studied. The characteristic emission bands corresponding to the 5D0 → 7FJ (J = 0–4) transitions of Eu3+ were registered. The emission of Eu3+ ions significantly increased during indirect excitation via the energy transfer process Gd3+ → Eu3+ (λexc = 273 nm) in comparison to direct excitation of Eu3+ ions (λexc = 393 nm). The beneficial influence of the energy transfer process on the 5D0 luminescence lifetimes of Eu3+ ions was definitely stated. The structure of the prepared silica sol–gel materials was examined using X-ray diffraction measurements (XRD) and FT-IR spectroscopic techniques. The formation of GdF3 and Gd2O3 nanocrystalline phases was confirmed.

Structure of Low Temperature Nitrided/Oxidized Layer Formed on NiTi Shape Memory Alloy

Structure of the nitride-oxide surface layers, formed using glow discharge technique at low temperature (between 200 and 380°C) changing the parameters of the process, was examined applying X-ray diffraction as well as transmission electron microscopy. The phase analysis was supported by results obtained from XPS measurement. Obtained results have shown that low temperature nitriding/oxiding produced the thin layers (18 ÷ 30 nm in thickness), which consist of titanium nitride and oxide phase. Low amount of the nickel-titanium oxide was also identified in the layer produced at higher temperature. Decrease of nitriding/oxidizing temperature below 300oC cause that between nitride-oxide surface layer and NiTi alloy did not create the intermediate layer of Ni3Ti phase. The results were verified and confirmed by observation carried out using high resolution electron microscopy. The corrosion properties of such coatings were tested in the physiological Tyrod’s solution using the cyclic potentiodynamic polarization method.

Lattice and Peak Profile Parameters in GIXD Technique

Grazing incident X-ray diffraction technique was applied to determine the influence of incident beam angle (α angle) on structural parameters as well as peak profile. X-ray diffraction patterns were registered in asymmetrical geometry, in which a parallel beam was formed by Soller and divergence slits. Lowering of the α angle results in accuracy decrease of lattice parameters as well as in significant broadening of a half-width of X-ray diffraction line.

Magnetostrictive and shape memory properties of Fe-Pd alloys with Co and Pt additions

Fe?~30?at.%?Pd is well known as a ferromagnetic shape memory alloy. The influence of Co and Pt additions on the shape memory and magnetostrictive behavior of Fe?Pd has been examined in the present investigation.

Surface Structure of NiTi Alloy Passivated by Autoclaving

Sterilization of the NiTi alloy in boiling water or steam causes passivation, which results in an amorphous 3.5 nm thick TiO2 layer on the surface. Between the surface and the matrix a transition layer of Ni2O3 and NiO was observed, using the X-ray photoelectron spectroscopy. Differences in sterilization conditions affect the amount of metallic nickel on the surface.

Texture Analysis of Hot Rolled Ni-Mn-Ga Alloys

The studies were carried out on three Ni-Mn-Ga polycrystalline alloys with the 10M martensite and the L21 parent phase. The specimens were cut along the [001] and [110] directions of the columnar grains from the ingots of either round or flat shape. The samples were heated up to 10000C and rolled in one direction in several steps. The final reduction of the samples thickness was: 28%, 36%, 57% and 69%. The texture of the initial [001] orientation rolled with the highest deformation 60% shows the following orientation components: {111}<112>, {112}<011>, {111}<011> which are typical for deformed and recrystallized metals of the A2 structure. The texture of the specimen with the initial [110] orientation rolled with 69% can be described as a fibre texture scattered around the <110> direction.