Wojciech Gurdziel

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.

Crystallization of CoSi2-Si Eutectic Composites

The subject of the study is the composite material of CoSi2-Si eutectic composition. The influence of crystallization speed on microstructure was examined. The ingots were obtained using Bridgman method. Three different pulling down speeds of crucibles with melted charges were applied. The prepared samples were subjected to metallographic, X-ray, TEM techniques and mechanical examinations in order to characterize the properties of the studied composite material. It was shown that the favourable crucible pulling down speed to obtain CoSi2-Si fibrous eutectic microstructure was 3mm/h.

Morphology of Tungsten Growth Forms in Quasicrystalline Al65Cu20Fe14W Alloys

The growth morphology and arrangement of tungsten and β-phase (Al (Fe, Cu)) in Al‑Cu‑Fe‑W alloy were analyzed. The composition of Al65Cu20Fe14W1 (at.%) was used for preparation of ingots containing the icosahedral quasicrystalline phase.The ingots were obtained in a two-stage process. At the first stage the induction melting of the elements and preliminary homogenization by mechanical mixing were carried out. The second stage was realized by vertical Bridgman technique of directional crystallization. The X-ray phase analysis, optical and scanning electron microscopy (SEM) observations and chemical analysis were performed. It was stated that the whiskers of tungsten were irregularly distributed in the volume of ingots. They often form a clump-like agglomerations. The whiskers have different diameters and length. Minimal diameter of the whiskers was about 10 – 100 nm and maximal – several dozen micrometers. The whiskers of tungsten formed a clump-like frames on which the membrane form of β-phase was stretched out or a non-planar oval forms.

The Microstructure of Quasicrystalline Al-Cu-Fe Alloys Doped with Tungsten

The microstructure of Al65Cu20Fe14 (numbers indicate at.%) alloy doped with 1 at.% of W was studied. The selected alloy composition should allow to obtain the quasicrystalline icosahedral phase after solidification process. The bulk samples were obtained in two stages. At first, the synthesis of alloy through premelting of component elements in induction furnace and then, the directional solidification by the Bridgman method were performed. The morphology of selected areas of the samples were studied using Scanning Electron Microscope equipped with energy dispersive X-ray spectroscope, which was used to examine chemical compositions of each analysed areas. Additionally the X-ray powder diffraction was used to identify the phases present in the alloys. It was stated that the filaments of tungsten were present in the alloys. The filaments have thickness ranged from 0.01 to 2.5 μm. As a result of investigation, the arrangement of filaments in the material was determined.

Crystallization and Microstructure of Co0.75Ni0.25Si2 Solid Solution

The microstructure of Co0.75Ni0.25Si2 solid solution, obtained by two different techniques was studied. The solidification processes were conducted using Bridgman and Czochralski methods. The processes were conducted under atmospheric pressure and in the helium atmosphere. Various pulling down (Bridgman method) and pulling up (Czochralski method) rates were applied for ingots and boules preparation. The obtained Co0.75Ni0.25Si2 ingots and boules were subjected to the metallographic observations and chemical microanalysis, mainly used Scanning Electron Microscopy techniques. They were studied using X-ray phase analysis too. Comparing the investigation results it was found that the ingots obtained by the Bridgman method and boules obtained by the Czochralski method were single crystalline. The boules, obtained using the Czochralski method, possess better structural quality than ingots obtained by the Bridgman method.

Characterization of Al65.0Cu32.9Co2.1 Alloy Containing Nanofibres

Microstructure of terminal area of Al65Cu32.9Co2.1 ingots (numbers indicate at.%), obtained via directional solidification was studied. Scanning Electron Microscopy, Transmission Electron Microscopy and X-ray powder diffraction were applied. Point microanalysis by Scanning Electron Microscope was used for examination of chemical compositions of alloy phases. It was found that tetragonal θ phase of Al2Cu stoichiometric formula was the dominate phase (matrix). Additionally the alloy contained orthogonal set of nanofibres of Al7Cu2Co T phase with the average diameter of 50-500 nm and oval areas of hexagonal Al3(Cu,Co)2 H-phase, surrounded by monoclinic AlCu η1 phase rim. Inside some areas of H-phase cores of decagonal quasicrystalline D phase were observed.

Microstructure and Lattice Parameter Studies of Constituent Phases in CoSi2-Si Eutectic Composite

The subject of the study was an examination of the lattice parameter variations of the constituent phases in CoSi2-Si eutectic composite according to the vertical axes of samples. A preparation of samples has been conducted using Bridgman and Czochralski techniques. The aim of the study was to establish an influence of applied preparation method on a stability of appropriate lattice parameters. It was shown that the constituent phases of the CoSi2-Si eutectic samples obtained via Czochralski technique are distinguished by a higher stability of the lattice parameter than samples obtained using Bridgman technique.

Temperature influence on stress-strain relationship of Al-Cu-Fe crystal-quasicrystal composites

The columnar composites obtained “in situ” through solidification of Al61Cu27Fe12 alloy by the Bridgman method were studied. It has been verified that the matrix consisted of cubic single crystal β phase and the reinforcement of icosahedral quasicrystal ψ phase and monoclinic crystal λ phase, which have the form of rods. This kind of composites will be named the Al-Cu-Fe crystal-quasicrystal (CQ) composites. The effect of heating from a temperature of about 100°C to about 650°C on the stress-strain relationships σ(ε) of parallel samples was studied. Additionally, the σ(ε) relationship was defined in cyclic load-unload tests at different temperatures. The composites were examined by powder X-ray diffraction and scanning electron microscope.

Preparation of Co1-xFexSi2 Solid Solution Crystals

The main goal of paper was obtaining of solid solution Co1-xFexSi2 crystals from liquid phase by Bridgman method. There are presented features and quality parameters of obtained ingots. It was found that the substitutional solid solution Co1-xFexSi2 crystals can be obtained only for x = 1at.% Fe.