Papers by Author: Henryk Morawiec

Abstract: Series of the near stoichiometric two phase (martensite + , parent + ) Co2NiGa alloys were studied. Different thermal treatments changing the microstructure were applied. After annealing for 20 h at 9000C large  precipitates were dispersed, they decorated mainly the grain boundaries. For the alloys quenched from the 11000C modulated structures were observed. Furthermore, during aging at the 3500C ' precipitation process occured in the matrix.

Abstract: 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.

Abstract: A polycrystalline ferromagnetic Ni2MnGa alloy with chemical composition of 49.13 at % Ni, 27.48 at % Mn and 23.39 at % Ga was hot rolled at 10000C causing deformation of 27%, 57% or 69%. The influence of the rolling process on the structure and texture of the parent phase were analyzed by EBSD and by X-ray powder diffraction methods. All samples revealed presence of the reversible martensitic transformation. During the solidification process columnar grains were formed with the <110>B2 texture. Sample deformation done by hot-rolling caused texture evolution from the <110> via <100> to the complete random distribution.

Abstract: 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.

Abstract: The Ni-Mn-Ga alloys extruded at high temperature with a relatively large reduction rate were the subject of the studies. The microscopic observations of the transient zone in the extruded rods revealed rotation of the columnar grains in the ingot along the rod axis - giving the preferred <001> orientations. Comparison of the texture, magnetization and magneto-crystalline anisotropy constant for samples cut out from the columnar grain zone and these cut from the extruded rods was carried out for two alloys which differ in chemical composition and Ms temperature. Both alloys have the 5M martensitic structure at room temperature. The samples cut out of the ingot and the extruded rods have shown the axial <001> orientation, similar magnetization curves and magnetocrystalline anisotropy constant Ku = 1.5-1.6 J/m3•105.

Abstract: 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.

Abstract: The nearly-equiatomic NiTi (50.6 at.%Ni, Af = 10°C) alloy was nitrided at 1073 K using glow discharge technique. Additionally, at the end of the nitriding some amount of oxygen was added. Phase identification and thickness of the nitrided/oxided layer was done using electron microscopy method and the X-ray reflectivity measurements. The chemical composition of the layers was determined using energy dispersive spectrometer. Combination of nitriding and oxidation of the NiTi surface produces nitride/oxide complex layer of a nanocrystalline structure. The average thickness of the obtained layer was about 0,5 μm. The potentiodynamical studies in Tyrod’s solution reveal good corrosion resistance of obtained nitrided/oxidized NiTi surface proving its high quality.

Abstract: In order to increase corrosion resistance, the NiTi shape memory alloy was covered by protection layers using glow discharge method. Samples were nitrided with some oxygen addition at temperatures: 350, 380, 400 and 800°C. Microstructure and sequence of obtained layers were studied applying X-ray diffraction technique as well as electron microscopy. Low temperature process produces a layers which consist of Ti3O5, TiN and Ni2Ti4O. Intermediate Ni3Ti layer was between Ni2Ti4O and NiTi matrix. High temperature process forms TiO2 and TiN with interlayer Ti2Ni. Surface does not contain phase with Ni, which is considered as toxic element.

Abstract: In the present paper the effect of heat treatment on microstructure, martensitic transformation temperatures and magnetic properties behavior of Co-Ni-Ga pollycrystal was discussed in detail. Microscopic observations revealed two types of two phase polycrystalline alloys: i) martensite with γ-precipitates and ii) parent phase with γ-precipitates. Making use of Xray and electron diffraction methods the crystal structure of martensite phase was identified as bct structure (with co/ao about 1.2). Annealing of Co-Ni-Ga alloy at 1223K/40 min causes a separation of martensitic and magnetic transformation and an increase of the Curie temperature by about 70K, after this annealing any significant structural changes in the parent (martensitic) and γ phase are not observed.