Jiří Buršík

Effect of Heat Treatment on the Microstructure and Creep Behavior of Mg-Sn-Ca Alloys

The development of new Mg-Sn based alloys that have shown improved corrosion resistance needs further investigations to develop standard alloys for industrial use. In the present study, the influence of heat treatment was investigated by examining the creep resistance of Mg-Sn and Mg-Sn-Ca alloys at 85 MPa under 135 °C identify the best conditions to improve the mechanical properties of such alloys. Additionally, the changes in microstructure of these alloys were studied and analysed by light microscopy, X-ray diffraction and scanning electron microscopy. It was found that the heat treatments can affect the microstructure of the binary alloy while no apparent change in the microstructure was found in the Mg-Sn-Ca alloys, indicating that the second phase CaMgSn is thermal stable in this alloy. Based on the obtained results, the relationship between the microstructure and creep behaviour are discussed.

Ag-Cu colloid synthesis: bimetallic nanoparticle characterisation and thermal treatment

The Ag-Cu bimetallic colloidal nanoparticles (NPs) were prepared by solvothermal synthesis from metalloorganic precursors in a mixture of organic solvents. The nanoparticles were characterized by dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). The properties of metallic core and organic shell of the nanoparticles were studied by direct inlet probe mass spectrometry (DIP/MS), Knudsen effusion mass spectrometry (KEMS), double-pulse laser-induced breakdown spectroscopy (DPLIBS), and differential scanning calorimetry (DSC). The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used for particle characterization before and after thermal analysis. The experiment yielded results that were for AgCu nanoparticles for the first time. The detected liquidus temperature has been compared with the prediction obtained from calculation of the phase diagram of Ag-Cu nanoalloy. The experimental results show that of near-eutectic composition AgCu nanoparticles possess the fcc crystal lattice. Surprisingly, spinodal decomposition was not observed inside the AgCu nanoparticles at temperatures up to 230°C. The depression of the eutectic AgCu melting point was calculated but not observed. The eutectic AgCu microparticles are formed before melting.

Atmospheric pressure microwave torch for synthesis of carbon nanotubes

The microwave (mw) plasma torch at atmospheric pressure has been studied for carbon nanotube (CNT) synthesis. The depositions were carried out on silicon substrates with 515 nm thin iron catalytic overlayers from the mixture of argon, hydrogen and methane. The optical emission spectroscopy of the torch showed the presence of C2 and CH radicals as well as carbon and hydrogen excited atoms. The vicinity of the substrate influenced the relative intensities and increased the emission of C2. For fixed mw power, the temperature of the substrate strongly depended on its position with respect to the nozzle electrode and on the gas mixture, particularly the amount of H2. The speed of the substrate heating during an early deposition phase had a significant effect on the CNT synthesis. An abrupt increase of the temperature at the beginning increased the efficiency of theCNTsynthesis. Areas of dense straight standing CNTs, 30 nm in average diameter, with approximately the same sized iron nanoparticles on their tops were found in accordance with the model of growth by plasma enhanced chemical vapour deposition. However, the deposit was not uniform and a place with only several nanometres thick CNTs grown on much larger iron particles was also found. Here, taking into account the gas temperature in the torch, 31003900 K, we can see similarities with the dissolutionprecipitation model of the CNT growth by high temperature methods, arc or laser ablation.

Deformation due to migration of faceted twin boundaries in magnesium and cobalt

Recent experimental observations show that twin boundaries in hexagonal close-packed (hcp) metals are frequently faceted. The objective of this paper is to investigate the influence of this faceting on the strain produced by twinning. We show that basal–prismatic (BP) facets are terminated by opposite disclinations and the migration of these facets along a straight twin boundary produces ordinary twinning shear. On the other hand, joining conjugate twins gives rise to BP facets terminated on the parent twin boundaries by identical disclinations. In this case, the strain produced by the migration of BP facets is an average between the strains produced by the individual conjugate twins. These theoretical studies are complemented by two EBSD measurements on cobalt that is closely related to magnesium. The misorientation profiles measured across two conjugate twin boundaries yield a misfit of approx. 7° consistent with the theoretical prediction that the corner of a twin embryo is terminated by two identical disclinations, each accommodating a misfit of 3.7°.

Mechanical and microwave absorbing properties of carbon-filled polyurethane.

Polyurethane (PU) matrix composites were prepared with various carbon fillers at different filler contents in order to investigate their structure, mechanical and microwave absorbing properties. As fillers, flat carbon microparticles, carbon microfibers and multiwalled carbon nanotubes (MWNT) were used. The microstructure of the composite was examined by scanning electron microscopy and transmission electron microscopy. Mechanical properties, namely universal hardness, plastic hardness, elastic modulus and creep were assessed by means of depth sensing indentation test. Mechanical properties of PU composite filled with different fillers were investigated and the composite always exhibited higher hardness, elastic modulus and creep resistance than un-filled PU. Influence of filler shape, content and dispersion was also investigated.

Microstructural and phase equilibria study in the Ni-Al-Cr-W system at 1173 and 1273 K

Abstract Several alloys of the Ni–Al–Cr–W quaternary system were prepared and their microstructure was studied quantitatively after long-term annealing at 1173 and 1273 K using scanning and transmission electron microscopy with energy-dispersive X-ray analysis. Thermodynamic modelling of the system was done by means of the Thermo-Calc software package. The thermodynamic parameters for the calculations were taken from commercial database for Ni-base superalloys. Two sections of quaternary phase diagrams at 1173 and 1273 K with constant Ni level of 71 and 76 at.% were discussed. Based on the comparison of our new experimental data with the results of thermodynamic modelling, a necessity of adjustment of some thermodynamic parameters was stated. Two of the interaction parameters describing the Ni–Al–W ternary subsystem were adjusted and better agreement of calculations with experiments was attained.

The existence of P phase and Ni2Cr superstructure in Ni-Al-Cr-Mo system

The knowledge of the long term microstructural stability has fundamental importance for understanding the properties and for further development of structural materials. This work is aimed towards the description of the influence of chemical composition and the temperature of long term annealing on the microstructure of Ni-Al-Cr-Mo alloys using transmission electron microscopy (TEM). The quaternary system was selected for this study as relatively simple yet sufficiently representative model system for advanced Ni-based superalloys. Two annealing temperatures were used, the lower one inside the expected temperature region of Ni{sub 3}Al-type + Ni{sub 2}Cr-type LRO coexistence.

Effect of Nickel Purity on Self-Diffusion along High-Diffusivity Paths

In the temperature range 600–1000 °C, the effect of material purity on self-diffusion along grain boundaries has been studied in both the pure (Puratronic 99.9945%) and the technical (99.5%) nickel. The penetration profiles were measured by the serial sectioning method using the 63Ni radiotracer. The extensive electron backscatter diffraction (EBSD) analysis was performed on the same samples in order to reveal possible differences in microstructure induced by the impurity content. The obtained microstructure characteristics were further interpreted in terms of the coincidence site lattice (CSL) model.

Analytical electron microscopy of InP/(In, Ga)As heterogeneous structures

Abstract Aspects of processing raw analytical data to correct for a finite probe size and beam−specimen interactions are discussed and demonstrated for the case of interdiffusion in lattice-matched InP/(In, Ga)As heterostructures. At first, the probe size of the microscope was evaluated following the method of Michael and Williams. Then the two principal factors, affecting the results of composition profile measurement, were taken into account, namely the sample drift during prolonged data acquisition and the beam broadening by elastic scattering inside the foil. A method of quantification of the sample drift effect was proposed, as well as a method of final scaling of the composition profiles. Using this approach, we can get closer to measuring the true changes of composition profiles caused by interdiffusion at the nanometre level.

On the relationship between and conjugate twins and double extension twins in rolled pure Mg

Abstract The paper presents a new type of twin-like objects observed in rolled pure magnesium. They have and habit planes and their misorientations to the matrix are close to 56° and 63° about axis, respectively. The ad hoc performed theoretical analysis and atomic simulations allow to interpret the objects as double twins formed by the simultaneous action of two twinning shears with completely re-twinned volume of primary twin. The observed inclinations from the ideal misorientations for such double twins can be explained by the compliance of the strain invariant condition in the twin boundary. It seems plausible that, once the double twin is formed, its twin boundaries are hard to move by glide of twinning disconnections. If so, these twins represent obstacles for the motion of crystal dislocations increasing the hardness of the metal.