Dariusz Zasada

Synthesis of Fe-Al-Ti Based Intermetallics with the Use of Laser Engineered Net Shaping (LENS)

The Laser Engineered Net Shaping (LENS) technique was combined with direct synthesis to fabricate L21-ordered Fe-Al-Ti based intermetallic alloys. It was found that ternary Fe-Al-Ti alloys can be synthesized using the LENS technique from a feedstock composed of a pre-alloyed Fe-Al powder and elemental Ti powder. The obtained average compositions of the ternary alloys after the laser deposition and subsequent annealing were quite close to the nominal compositions, but the distributions of the elements in the annealed samples recorded over a large area were inhomogeneous. No traces of pure Ti were observed in the deposited alloys. Macroscopic cracking and porosity were observed in all investigated alloys. The amount of porosity in the samples was less than 1.2 vol. %. It seems that the porosity originates from the porous pre-alloyed Fe-Al powders. Single-phase (L21), two-phase (L21-C14) and multiphase (L21-A2-C14) Fe-Al-Ti intermetallic alloys were obtained from the direct laser synthesis and annealing process. The most prominent feature of the ternary Fe-Al-Ti intermetallics synthesized by the LENS method is their fine-grained structure. The grain size is in the range of 3–5 μm, indicating grain refinement effect through the highly rapid cooling of the LENS process. The Fe-Al-Ti alloys synthesized by LENS and annealed at 1000 °C in the single-phase B2 region were prone to an essential grain growth. In contrast, the alloys annealed at 1000 °C in the two-phase L21-C14 region exhibited almost constant grain size values after the high-temperature annealing.

Systematic Study on Morphology of Anodic Alumina Produced by Hard Anodization in the Electrolytes Modified with Ethylene Glycol

The morphology of anodic aluminum oxide (AAO) produced by hard anodization (HA) in oxalic acid electrolyte modified with various amount of ethylene glycol (EG) was investigated. The EG induces a considerable changes in the AAO morphology. The AAO transforms from continuous nanoporous film to separated AAO nanotubes upon addition of increasing amount of EG. In the sample II (4:1 v/v water to EG mixture) well separated nanotubes with variable wall thickness are produced. In the sample III (1:1 v/v water to EG solution) the nanotubes “imprisoned” in a partially dissolved cell skeleton with regularly spaced apertures along the cell are formed. In the electrolyte with the highest amount of EG (1:4 v/v water to EG mixture) an irregular AAO consisted of formless oxide and the oxide in a form of separated tubes of thick walls and small pores is fabricated. Based on the data obtained in this work it is concluded that the C containing ionic species originating from the EG dissociation along with the high electric field (E) operating during the HA were responsible for the separation phenomena. These ions, driven by the high E, were transported from the electrolyte to the pore base, where they were being embedded into the AAO framework generating strong mechanical stresses at cell boundaries and initiating the cell cleavage process. Moreover, some of these charged particles were ionized under the high E providing additional electrons to the overall current flow and giving rise to a sudden current density boost in the samples II and III.

Synthesis and characterization of noble metal–titania core–shell nanostructures with tunable shell thickness

Core–shell nanostructures have found applications in many fields, including surface enhanced spectroscopy, catalysis and solar cells. Titania-coated noble metal nanoparticles, which combine the surface plasmon resonance properties of the core and the photoactivity of the shell, have great potential for these applications. However, the controllable synthesis of such nanostructures remains a challenge due to the high reactivity of titania precursors. Hence, a simple titania coating method that would allow better control over the shell formation is desired. A sol–gel based titania coating method, which allows control over the shell thickness, was developed and applied to the synthesis of Ag@TiO2 and Au@TiO2 with various shell thicknesses. The morphology of the synthesized structures was investigated using scanning electron microscopy (SEM). Their sizes and shell thicknesses were determined using tunable resistive pulse sensing (TRPS) technique. The optical properties of the synthesized structures were characterized using UV–vis spectroscopy. Ag@TiO2 and Au@TiO2 structures with shell thickness in the range of ≈40–70 nm and 90 nm, for the Ag and Au nanostructures respectively, were prepared using a method we developed and adapted, consisting of a change in the titania precursor concentration. The synthesized nanostructures exhibited significant absorption in the UV–vis range. The TRPS technique was shown to be a very useful tool for the characterization of metal–metal oxide core–shell nanostructures.

The Evaluation of the Cavitational Damage in MgAl2Si Alloy Using Various Laboratory Stands

Evaluation of cavitation erosion resistance of is carried out by using various testing stands, that differ by the way of cavitation excitation and its intensity. These various testing conditions have led to a standardization of some part of laboratory stands, that in turn allows a direct comparison of results obtained in different laboratories. The aim of this study was to determine the course of cavitational destruction of MgAl2Si alloy samples tested on three different laboratory stands. The research was conducted on a vibration stand according to ASTM G32, where cavitation is forced by the vibrating element; in the cavitation tunnel reflecting actual flow conditions, and on a jet impact stand- simulating the impact microjet in the final phase of the cavitational bubbles implosion. Each laboratory stand has given a different course of cavitational destruction.

Cavitation Wear of CuZn10 Alloy in As-Cast State and after Plastic Working and Annealing

Copper alloys due to their very good corrosion properties are often used to a fabrication of components that are subjected to both a cavitational destruction and a corrosive action of an environment, e.g.. ships’ propellers, sliding elements, pump parts etc. The course of cavitational destruction depends mainly on a material’s structure (a grain size, a type of inclusions, morphology and phase distribution, etc.) but also on the load distribution, and a possible activity of chemical, electrochemical and thermal processes near cavitation bubbles. Properties of a material that is subjected to the cavitational damage are strongly affected by its structure formed upon manufacturing or applied processing. In the present paper, results of the cavitational resistance analysis of CuZn10 alloy in the as cast state (the grain size of 200 μm) and after thermomechanical processing (the grain size of 10 or 200 μm) evaluated on vibrational laboratory stand in accordance with ASTM G-32 standard, are shown.

The Destruction Mechanism of Titanium Subjected to Cavitation Erosion

A cavitation erosion is the process based on an impact of pressure pulses on a material’s surface caused by the phenomenon of cavitation. The term cavitation is defined as a phenomenon of formation, growth and disappearance (implosion) of bubbles due to cyclic pressure variations in a liquid. The cavitation initiators are embryos (cavitation nuclei with a size up to 50 μm), located in the water or on wetted surfaces that lead to decreasing of the liquid ability to transfer tensile stresses. The role of embryos is played by micro gas bubbles, fine solid particles, micro-organisms or gas-filled pores on a surface of solid body embedded in a liquid. A rapid pressure drop occurring within the liquid and a presence of cavitational kernel causes rupture the continuity of the liquid and thus lead to the formation of steam-gas mixture areas, a so called cavitation bubbles. A cavitation bubble may be filled with a gas, a vapor or a steam/gas mixture.A course of cavitation depends on a cavitation type. In thepresent work, a mechanism of cavitiational destruction of 99,7 % titaniumtested on vibrational and jet-impact valaboratory stands, is analyzed. Results of thecavitational resistance evaluation of Ti99.7 titanium carried out onvibrational and jet-impact stands have revealed different mechanisms of acavitation destruction caused by various forms of cavitation. It was found thata surface of titanium samples tested on the vibratory stand was covered by verylarge number of microcracks which in a later stage of the research leads to theerosion of the material. The cavitational destruction of Ti samples on the jet-impact stand is initiatedby a plastic straining of subsurface area, which in the further stage leads toan erosion represented by the detachment of whole grains anda formation of deep pits on the material’s surface. Additionally, results of conducted studies have confirmed the fatigue character of the cavitationaldestruction process.

Structure and Mechanical Properties of 1.4539 Austenic Steel Joints Made by TIG and Laser-Beam Welding

This paper presents the analysis of structural research, micro-hardness and fatigue properties of the base material which is 1.4539 steel and joints made with CO2 laser beam and TIG method. Theoretical and experimental analysis of low cycle fatigue based on deformation criterion was presented. Safe fatigue estimation consistent with the results of experiments was obtained during calculations.

Analysis of the Effect of the Wearing Type on Surface Structural Changes of Ni3Al-Based Intermetallic Alloy

Results of an analysis of effect of wearing type on surface structural changes of a Ni3Al intermetallic alloy, are shown in the present paper. A microstructure evaluation was carried out by Quanta 3D FEG field emission gun scanning electron microscope (FEG SEM) equipped with an integrated EDS/WDS/EBSD system. The Ni3Al-based intermetallic alloy with an addition of boron, zirconium and chromium was examined. The investigated material had γ’ single-phase, ordered solid solution structure with 20 μm grain size. An electron backscatter diffraction (EBSD) method was applied to visualize surface structural changes upon an abrasive, a cavitational and a tribological wearing of the material.An observation of surface layer after the abrasive wear was carried out on samples examined in loose abradant by T-07 tester and according to GOST 23.2008-79 norm. An analysis of cavitational wear on changes in the near surface area of Ni3Al-based alloy was performed on an impact-jet stand. Observed structural changes were described based on results of the SEM/EBSD complex structural examination and hardness measurements. It was found, that the EBSD is an effective and sensitive method that allows estimating surface strain introduced during analyzed wearing types.

Cavitation Erosion and Corrosion of Pearlitic Gray Cast Iron in Non-Standardized Cavitation Conditions

A results of test of erosion and corrosion resistance of pearlitic gray cast iron (grade EN GJ 400) are showed. The NaCl solutions and of ethylene glycol solutions were used as the test environment. Examination were performed at varying cavitation load, in the range 2,8 ÷ 20 W/cm2.

The Effect of Aluminum Content on the Microstructure and Cavitation Wear of Feal Intermetallic Alloys

Abstract Intermetallic-based alloys (so called intermetallics) of the Fe-Al binary system are modern construction materials, which in recent decades have found application in many branches of the power, chemical and automotive industries. High resistance of FeAl based alloys to cavitational erosion results first of all from their high hardness in the as-cast state, large compressive stresses in the material, as well as homogeneous structure. In the present paper, the effect of aluminum content on the microstructure, texture and strain implemented upon cavitation wear of FeAl intermetallic alloys, have been analyzed by field emission gun scanning electron microscopy (FEG SEM) and electron backscatter diffraction (EBSD) analysis. Obtained results of structural characterization indicates that with increasing aluminium content effects of orientation randomization (weakening of <100>//ND casting texture), grain refinement and rising of mechanical strenght (and so cavitational resistance) take place.