Józef Lelątko

Structure and properties of melt-spun Cu–Al–Ni shape memory alloys

Abstract Increase of the wheel speed causes the grain refinement, rise of a columnar morphology of grains and the DO 3 fibre texture in the melt-spun ribbons of the studied alloys. This influences their tensile strength, yield stress and shape recovery under load. Additional possibilities of influencing the structure and hence the properties of the ribbons open up for the alloys containing Ti+Mn by presence of particles of the X -phase as well as by recrystallisation. The ribbons of the studied alloys melt-spun with the wheel speed up to 20 m/s exhibit a relatively high transformation temperature.

Structure and Properties of the 32CrMoV12-28 Steel Alloyed with WC Powder Using HPDL Laser

This paper presents the investigation results of laser alloying and the influence on structure and properties of the surface of the 32CrMoV12-28 hot work steel, carried out using the high power diode laser (HPDL). Structure changes were determined in the work, especially structure fragmentation. Also hardness investigation of the different remelting areas was performed. The reason of this work was also to determine the laser treatment parameters, particularly the laser power, to achieve good work stability and to make the tool surface more resistant for work extremal conditions. Based on microstructural examinations of the obtained material, the distribution of the reinforcing ceramic particles in the hot work tool steel was revealed. Tungsten carbide WC powder was used for alloying. The remelted layers which were formed on the surface of the investigated hot work steel were examined metallographically and analyzed using a hardness testing machine.

TEM study of the interface in ceramic-reinforced aluminum-based composites

Abstract The microstructure and interfaces of aluminum matrix composites were studied using conventional and high-resolution transmission electron microscopy (HREM). Also convergent-beam electron diffraction (CBED) was used. Two kinds of Al-based ceramic-reinforced composites (Al–TiC and Al–TiB 2 ) were studied. Transmission electron microscopy (TEM) revealed the presence of a relatively high dislocation density in the matrix of both kinds of investigated composites. The dislocation density is higher near the interface region than inside the matrix. The local strength of the matrix was determined near the reinforcing particles, using TEM at CBED. Analysis of the higher-order Laue zone (HOLZ) lines allowed a determination of the changes in the lattice constant versus the distance from the interface.

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.

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.

Structure of Multi-Layers Deposited on NiTi Shape Memory Alloy

In order to improve a biocompatibility of a NiTi shape memory alloys used as a long-term implant, surface was covered by protective multi-layers coating. First, alloy was passivated in autoclave, and then hydroxyapatite was deposited using electrophoresis at room temperature. In result of that multi-layer was formed on the top of the surface consisted of titanium oxide and hydroxyapatite. Phase identification done with use of grazing incidence beam X-ray diffraction proved sequence of obtained coatings. Applied procedure for multi-layer deposition allowed avoiding of the B2 parent phase decomposition. Moreover, the martensitic transformation occurs in two-steps.

Application of EIS to Study the Corrosion Resistance of Passivated NiTi Shape Memory Alloy in Simulated Body Fluid

The NiTi shape memory alloy passivated for 90 min by autoclaving has been studied towards corrosion performance in the Tyrode’s simulated body fluid using open circuit potential and EIS measurements. The surface morphology and thickness of the oxide layer was determined by XRR. The HREM was used to observe the cross-section of the thin foil and to confirm the amorphous state of the TiO2 layer and its thickness. Electrochemical measurements revealed a good corrosion resistance at the beginning of long-term (20 days) immersion. It was found that with the increase of immersion time, the corrosion resistance of the surface deteriorated after nearly 1 day of immersion due to occurence of pitting corrosion. The EIS method was used to detailed study on the electrolyte | passive layer interfacial properties. Equivalent electrical circuit for the pitting corrosion on the passivated NiTi alloy has been applied.

Influence of Alloying Additions on Enhancement of Soft Magnetic Properties Effect and Crystallization in FeXSiB (X=Cu, V, Co, Zr, Nb) Amorphous Alloys

The crystallization and optimization of magnetic properties effects in FeXSiB (X=Cu, V, Co, Zr, Nb) amorphous alloys were studied by applying X-ray diffraction methods, high resolution transmission electron microscopy (HRTEM), resistometric and magnetic measurements. The temperatures of the first and the second stage of crystallization, the 1h optimization annealing temperature and the Curie temperature were determined for different amorphous alloys. Activation energies of crystallization process were obtained by applying the Kissinger method. The influence of alloy additions on optimization effect and crystallization processes was carefully examined.

Hot Extrusion of Ni-Based Polycrystalline Ferromagnetic Shape Memory Alloys

Two Ni-based (Ni-Mn-Ga and Ni-Mn-Co-In) ferromagnetic nonstoichiometric shape memory alloys were studied in order to determine the influence of hot extrusion process on macro, microstructure and texture of the studied alloys. The microstructure of the alloys in the as cast state and after extrusion was analyzed by electron backscatter diffraction technique. Typical microstructure of the as cast alloys consisted of radially oriented columnar grains elongated perpendicularly to the casting axis. For the alloys Ni-Mn-Ga and Ni-Mn-Co-In alloys the 10M and 14M modulated martensite were observed, respectively. After extrusion Ni-Mn-Ga samples revealed high density of fibre texture parallel to the extrusion axis. In spite of applying different extrusion parameters it was not possible to avoid cracks and overcome the brittleness of the Ni-Mn-Co-In alloys.