Jiri Bursik

Microstructural development during high temperature creep of 9% Cr steel

The modified 9% Cr steel Type P91 is one of the materials presently employed in power plant pipework components. The detailed microstructural analysis of a trial melt produced by Vitkovice Steel, Ostrava is reported in the present work. The microstructural evolution during creep at 873 K was investigated by means of transmission electron microscopy and computer image analysis. Two main microstructural elements of tempered martensite ferritic steels, namely subgrains and secondary phase particles, are studied quantitatively. The influence of stress free ageing and the influence of stress under creep conditions on particle coarsening and subgrain growth is determined.

Surface modification of polyethylene and polypropylene in atmospheric pressure glow discharge

An atmospheric pressure glow discharge (APGD) was used for surface modification of polyethylene (PE) and polypropylene (PP). The discharge was generated between two planar metal electrodes, with the top electrode covered by a glass and the bottom electrode covered by the treated polymer sample. The discharge burned in pure nitrogen or in nitrogen–hydrogen or nitrogen–ammonia mixtures. The surface properties of both treated and untreated polymers were characterized by scanning electron microscopy, atomic force microscopy, surface free energy measurements and x-ray photoelectron spectroscopy. The influence of treatment time and power input to the discharge on the surface properties of the polymers was studied. The ageing of the treated samples was investigated as well. The surface of polymers treated in an APGD was homogeneous and it had less roughness in comparison with polymer surfaces treated in a filamentary discharge. The surface free energy of treated PE obtained under optimum conditions was 54 mJ m−2 and the corresponding contact angle of water was 40°; the surface free energy of treated PP obtained under optimum conditions was 53 mJ m−2 and the contact angle of water 42°. The maximum decrease in the surface free energy during the ageing was about 10%.

On the microstructural development of the tempered martensitic Cr-steel P 91 during long-term creep—a comparison of data

Abstract Microstructural data for creep of the tempered martensitic 9 wt.%CrMoV steel P 91 at 873 K were analyzed. It was found that the variation of the subgrain size with strain conforms to an exponential change from the initial to the stress dependent steady-state value. Analysis of the size distributions of precipitated particles confirmed the previous result that in P 91 there is a superposition of growth of particles with the dynamic precipitation of new particles mostly of type MX. From the distributions the numerical fractions of two types of particles, a predominating population of M 23 C 6 carbides and a population of fine particles representing mostly carbonitrides of type MX, and their sizes could be deduced. The variation of the creep rate with strain is in qualitative agreement with these microstructural changes.

Ordering of Substoichiometric δ‐TiCx Phase in Ti–V–C Alloys

Several Ti-V-C alloys have been studied by transmission electron microscopy (TEM) after cooling from the melt, with special attention paid to ordering processes taking place in the highly substoichiometric (Ti,V)C x phase. The effects of both short and long range ordering in the carbon sublattice are observed in selected area electron diffraction patterns. The Warren-Cowley short range order parameters have been evaluated from the intensity distribution in reciprocal space. More complex models for the intensity distribution are then developed and the effects on the predicted short range order parameters are discussed.

Theoretical and experimental study of the γ and γ' equilibrium in Ni-based superalloys

Abstract Ni-based superalloys with aluminium belong to systems with order–disorder transition for the γ and γ′ structures. Because of the complexity of these alloys, quaternary systems can be taken as suitable and sufficiently representative model systems for a theoretical study of their phase equilibria. In recent years several assessments including various model descriptions of ordered phases and ordering based on the CALPHAD formalism have been made with the aim to describe phase diagrams of relevant binary, ternary and some quaternary systems. For our study, the Ni–Al–Cr–Co system was chosen and phase boundaries of γ and γ′ phase equilibrium were calculated based on the data for lower-order systems. The calculations were performed by means of the software ‘Thermo-Calc’. Values obtained were compared with experimentally determined phase information for five alloys with constant Ni content (70 at.%) after long-term annealing at 900°C. The experiments were realized by means of energy-dispercive microanalysis in scanning transmission electron microscopy. For better agreement of theory with experiment, an thermodynamic optimization was performed.

Creep behaviour of leaded brass

Abstract The creep behaviour of Cu–36wt.% Zn alloys containing 2.5 wt.% of lead has been investigated. Constant tensile stress creep experiments were carried out in the temperature range from 523 to 823 K and under constant stresses from 5 to 250 MPa. Scanning electron microscopy and energy dispersive X-ray analysis were performed on crept as well as uncrept parts of the specimens in order to examine the mechanisms of creep deformation in leaded brass. Attention has been paid to the role of lead on the creep behaviour of brass, the influence of temperature on creep curves, the stress sensitivity parameter and apparent activation energy of creep. The creep data obtained are examined by several methods of conventional analysis of steady-state creep.

Experimental Study of the Sb-Sn-Zn Alloy System

The Sb-Sn-Zn alloy was prepared and researched by experimental methods, which allow obtaining information on the thermodynamic stability of the coexisting phases. Thermal analysis was used to determine the phase transition temperatures of experimental alloys. Equilibrium composition of coexisting phases after long-term temperature equilibration was determined by electron microscopy. The existence of one ternary stoichiometric phase Sb2SnZn was experimentally confirmed by diffraction technique. The CALPHAD method for prediction of the phase diagram of the Sb-Sn-Zn system from binary subsystems was used in this work.

Mesoporous SnO2–SiO2 and Sn–silica–carbon nanocomposites by novel non-hydrolytic templated sol–gel synthesis

A novel non-hydrolytic sol–gel (NHSG) synthesis of mesoporous tin silicate xerogels is presented. The polycondensation between silicon tetraacetate, Si(OAc)4, and tetrakis(diethylamido)tin, Sn(NEt2)4, resulting in acetamide elimination leads to tin silicate xerogels containing Si–O–Sn linkages. The addition of Pluronic P123 or F127 templates provides homogeneous stiff gels that are, after template removal by calcination at 500 °C in air, converted to stable mesoporous silica xerogels with large surface areas (476 m2 g−1) and dispersed SnO2 nanoparticles (6–7 nm). Heat treatment of the as-prepared tin silicate gels in an inert N2 atmosphere leads to reduction and transformation to Sn nanoparticles (70–150 nm) embedded in a silica–carbon matrix. The composition and morphology of the xerogels, volatile reaction byproducts, and thermal transformations were followed by elemental analyses, IR spectroscopy, thermal analysis TG-DSC, nitrogen adsorption measurements, solid-state NMR spectroscopy, DRUV-vis spectroscopy, electron microscopy, and HT powder XRD. The SnO2–SiO2 xerogels were tested as potential catalysts for aminolysis of styrene oxide with aniline and for the Meerwein–Ponndorf–Verley reduction of 4-tert-butylcyclohexanone. The resulting reaction systems displayed good activity and selectivity.

Transformation of the β-(Ti, V) phase in Ti-V-C alloys

The importance of Ti and V compounds with C and/or N, e.g. in precipitation strengthened steels, hard coatings, cutting tools, fuel cladding materials and in electronics, has stimulated extensive experimental work resulting in several isothermal sections of the Ti-V-C equilibrium phase diagram. The present paper reports on a study of the transformation of the {beta} phase in Ti-V-C alloys. The microstructure was studied by means of analytical TEM and HREM. Special attention was paid to the {beta} to {omega} transition and to a qualitative description of the influence of carbon on this process.

Experimental investigation and modeling of diffusion in the InP/(In,Ga)As heterostructures

The interdiffusion of lattice-matched InP/(In,Ga)As superlattice structures (nominally undoped, p-doped and n-doped) has been studied by analytical electron microscopy (x-ray analysis) using a field emission gun, scanning transmission electron microscope. The point-spread function of the electron beam was used to correct the experimental data (obtained as x-ray maps, 50×50 nm in area) in order to derive diffusion profiles of the group V elements (As, P) after annealing. The results, showing a marked asymmetry in the As profiles after annealing, are interpreted using a model based on the coherent diffusion of the group III and V elements on their own sublattices, each of which is treated as a regular solution. A mathematical procedure, based on the minimization of the difference between the measured and predicted concentration profiles, is employed to compute the two lattice-specific composition-dependent velocities from the experimental diffusion profiles. A good agreement is found between the experimenta...