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1
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Microstructure, Thermal and Mechanical Properties of Non-Isothermally Annealed Al-Sc-Zr and Al-Mn-Sc-Zr Alloys Prepared by Powder Metallurgy

100%
Vlach M., Stulíková I., Smola B., Císařová H., Piešová J., Daniš S., Gemma R., Tanprayoon D., Neubert V.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
439-443
EN
This paper reports results of a study aimed at understanding the precipitation processes occurring during the annealing of two Al-Sc-Zr-based alloys with and without Mn prepared by powder metallurgy with subsequent hot extrusion at 350°C. Samples were isochronally annealed up to ≈ 570°C. Precipitation behaviour was studied by electrical resistometry and differential scanning calorimetry. Mechanical properties were monitored by microhardness HV1 measurements. Transmission electron microscopy examinations and X-ray diffraction of specimens quenched from temperatures of significant resistivity changes helped to identify the microstructural processes responsible for these changes. Fine (sub)grain structure develops and fine coherent Al_3Sc and/or Al_3(Sc,Zr) particles precipitate during extrusion in both alloys. The distinct changes in resistivity (at temperatures above ≈ 330°C) of the Al-Mn-Sc-Zr alloy are mainly caused by precipitation of Mn-containing particles. The easier diffusion of Mn atoms along the (sub)grain boundaries is responsible for the precipitation of the Al_6Mn and/or Al_6(Mn,Fe) particles at relatively lower temperatures compared to the temperature range of precipitation of these particles in the classical mould-cast Al-Mn-Sc-Zr alloys The apparent activation energy for precipitation of the Al_3Sc and Al_6Mn particles in the Al-Mn-Sc-Zr alloy was determined as (106 ± 10) kJ mol^{-1} and (152 ± 33) kJ mol^{-1}, respectively.
2
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Defects in Decomposing Copper Alloys Studied by Positrons

100%
Mikhalenkov V., de Lima A., Lopes Gil C.
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vol. 95
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issue 4
615-622
EN
The evolution of defect structure during isochronal annealing of water-quenched Cu-4.83 at.% In and Cu-4.94 at.% Sn alloys was studied by measuring positron lifetime and Doppler broadening of annihilation line. The behaviour of annihilation parameters in both alloys is found to be analogous. In as-quenched alloys one component of about 180 ps is detected in the lifetime spectra. It remains intact up to the annealing temperature of 450 K and is attributed to positron annihilation at quenched-in vacancies associated with alloying atoms. When going above this temperature, the short component appears in the lifetime spectra, while intensity of the long component starts to drop giving evidence to the reduction of defect concentration. This process is observed to develop up to 550 K; thereafter all annihilation parameters level off. After crossing the phase separation temperature they begin to vary again since the defect structure comes into dependence on cooling conditions. The obtained results are discussed in terms of defect structure evolution in the course of precipitate formation.
3
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Effect of Deformation on Positron Annihilation in Decomposing Copper Alloys

80%
Mikhalenkov V. S., Hautojärvi P., Vehanen A.
Acta Physica Polonica A
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1995
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vol. 88
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issue 1
199-204
EN
Positron lifetime spectra were measured in the quenched or slowly cooled Cu-3.93 at.% Ag alloy, subjected to subsequent cold rolling, as a function of isochronal annealing temperature. The results were compared with the formerly obtained data for quenched, but not deformed, C͟u-Ag alloy and for deformed C͟u-Ge solid solution. All lifetime spectra, after background and source corrections, are single exponential with the lifetimes which exceed those in well-annealed Cu solid solutions. This gives evidence to positron annihilation from a trapped state. One-component spectra may then testify to existence of a set of different traps with too weak distinction in the individual positron lifetime to be resolved as separate components. At low annealing temperatures the stage arisen from continuous decomposition is not revealed, being masked by the removal of deformation defects. The stages of discontinuous decomposition and of subsequent precipitates coagulation turn out to depend on the sample history. The role of deformation defects in the decomposition of supersaturated solid solutions is attempted to be accounted for in a wide range of annealing temperatures.
4
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Phase Identification of Nanometric Precipitates in AlSi9Cu Alloy after Remelting by Laser Beam

80%
Pawlyta M., Labisz K., Matus K.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
827-829
EN
The aim of presented paper is an investigation of the structure changes in AlSi9Cu alloy after remelting by a laser beam. Scanning transmission electron microscopy was applied for structure characterization and precipitates phase identification. In the raw material, precipitates were larger and during remelting such precipitates were dissolved and very fast crystallization came next. Observed precipitates are generally uniform: in size, shape, and chemical composition. Generally, after remelting precipitates are not uniformly distributed in the whole sample but areas with dense, nanometric precipitates are common. Numerous volumes with elongated Ti precipitates, identified as Ti(Al_{1-x}Si_{x})₃, were found. Observed precipitate can strongly affect material properties (even in a case of law Ti concentration) because it may act as a crystal nucleus for other phases.
5
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Phase Transformation and Sintering of Algeria Clay Powder

80%
Beddiar L., Sahnoune F., Heraiz M., Redaoui D.
Acta Physica Polonica A
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2017
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vol. 131
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issue 3
566-568
EN
Clay is one of the most used natural materials in the ceramic industry with various applications such as pottery, tiles, cement and bricks. The latter are used as a building material because of their excellent thermal and mechanical properties. In the present study, Algerian clay from Al-maathed area, M'sila district, was used to prepare bricks. The chemical composition of the clay was determined using X-ray fluorescence. Firing of clay was carried out in the temperature range 20-1000°C, at different heating rates. The present phases and their transformations, the activation energy, and the sintering mechanism were evaluated using X-ray diffraction, differential thermal analysis, thermogravimetric analysis and dilatometry. The activation energy for the sintering mechanism obtained from non-isothermal treatments is 420 kJ/mol. The value of the Avrami exponent, n, is determined from the shape of the crystallization exothermic dependence. It is related to m parameter (a numerical factor which depends on the dimensionality of crystal growth) obtained by Matusita method. Both of which are about 1.2 for clay sintering. These values indicate that bulk nucleation is dominant in clay sintering by three-dimensional growth, with polyhedron-like morphology controlled by interface reaction.
6
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Creep Deformation of Intermetallic TiAl-Based Alloy

80%
Lapin J., Staneková H.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
453-456
EN
In the present work, the creep deformation behaviour of a new cast intermetallic Ti-46Al-8Ta [at.%] alloy is analysed. Constant load tensile creep tests were performed at initial applied stresses ranging from 200 to 400 MPa in the temperature range from 973 to 1073 K. The measured creep deformation curves are analysed and the observed deviations from calculated curves are discussed based on microstructural changes observed in the studied alloy during creep. The kinetics of creep deformation are evaluated in terms of the true activation energy for creep and the stress exponent. Creep damage initiation and propagation leading to the fracture of the creep specimens are characterized as functions of the applied stress and temperature.
7
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Small-Angle Scattering of Synchrotron Radiation for Studying Solid State and Biological Systems

80%
Fratzl P.
Acta Physica Polonica A
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1992
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vol. 82
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issue 1
121-136
EN
The principles of small-angle X-ray scattering are briefly reviewed with emphasis on the particular advantages of the use of synchrotron radiation. The application of the technique is illustrated by several examples concerning precipitates in alloys, internal oxidation, porous materials, as well as the structure of bone.
8
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The Influence of Silicon Content on Recrystallization of Twin-Roll Cast Aluminum Alloys for Heat Exchangers

80%
Poková M., Cieslar M., Lacaze J.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
625-629
EN
Thin foils of aluminum alloys are commonly used in automotive industry for manufacturing heat exchangers. Use of twin-roll casting instead of direct-chill casting requires modifications in the manufacturing process and use of improved materials. In the present study, the evolution in microstructure and mechanical properties during isochronal annealing of two AW3003-based alloys differing in silicon content was monitored. The silicon influenced both the microhardness and precipitation kinetics during annealing, but not the recrystallization temperature. Precipitation of cubic α-Al_{15}(Mn,Fe)_3Si_2 phase occurred in two steps in the material with higher Si content, while mainly precipitates of Al_6(Mn,Fe) phase formed in the second material in a broad temperature interval, preferentially at grain boundaries.
9
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Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu-Based Alloys

80%
Melichova O., Vostrý P., Procházka I., Cieslar M., Stulíková I., Faltus J.
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vol. 95
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issue 4
627-631
EN
The improved workability of the commercial automatic machine designed alloy Al-Cu-Bi-Pb is guaranteed by the presence of Pb. Nevertheless, the toxic element Pb reduces some of the alloy properties. Therefore new Pb-free machinable Al-based alloys are developed. The Al-Cu-Bi-Sn alloy belongs to these non-traditional materials. The contribution deals with the investigation of precipitation effects in Al-Cu-Bi-Sn alloy during step-by-step isochronal annealing up to 500°C after previous solution heat treatment by means of positron annihilation spectroscopy completed with electrical resistivity measurements and results of independent transmission electron microscopy studies. The used combination of experimental methods gives the possibility to detect separately the redistribution of Sn and Cu atoms in the matrix and to study the influence of vacancies on this process.
10
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Investigation of Sulphur Nanoclusters in Ageing Ni-S System after Irradiation and Thermal Treatment by Positron Annihilation

80%
Perminov D., Druzhkov A., Arbuzov V., Danilov S.
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vol. 125
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issue 3
729-732
EN
The pure Ni and Ni-S ageing systems, thermally aged and also irradiated by 5 MeV electrons at 270 K with subsequent annealing, are studied by means of positron annihilation spectroscopy. The formation of ultrafine S-rich precipitates (clusters) is observed in Ni-S during thermal ageing at about 650 K. It is assumed that these clusters do not contain vacancy-type defects and they are coherent to the Ni matrix. The positrons localize in sulphur clusters that is due to affinity-induced confinement. In irradiated Ni-S system, the mobile vacancy-S atom complexes are formed at post-irradiation annealing above 350 K (stage III). These complexes form the three-dimensional vacancy clusters (nanovoids) decorated with S atoms. The radiation induced nucleation of S-rich clusters occurs when nanovoids dissociate.
11
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Mechanism and Kinetics of Precipitation and Dissolution of GP Zone and Metastable Phase in Al-3wt% Cu Alloy

80%
Khamel B., Sahnoune F., Fatmi M., Brihi N.
Acta Physica Polonica A
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2017
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vol. 131
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issue 1
133-135
EN
Thermal analysis techniques remain important tools amongst the large variety of methods used for analysis of the precipitation and dissolution of the Guinier-Preston zone and metastable phase θ' in Al-3wt% Cu. In the present study, the kinetics of precipitation and dissolution of the Guinier-Preston zone and metastable phase θ' in Al-3wt% Cu was investigated using differential scanning calorimetry carried out between room temperature and 430°C at heating rates of 20, 25, and 30°C min¯¹. The activation energies evaluated through isothermal differential scanning calorimetry treatment using the Johnson-Mehl-Avrami theory were 25, 100, and 80 kJ mol¯¹ for the Guinier-Preston zone precipitation, formation of θ'/θ and dissolution of θ', respectively. The Avrami constant n obtained by the Ligero method was about 1.5 for the formation of θ'/θ indicating that bulk nucleation is dominant in θ'/θ formation controlled by diffusion from a constant number of nuclei.
12
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PSG Method for Simulating Agglomeration of Al₂O₃ Inclusions in Liquid Steel

80%
Kalisz D., Żak P.
Acta Physica Polonica A
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2016
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vol. 130
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issue 1
157-159
EN
A quantitative description of the non-metallic inclusions removal from liquid steel is the most important element of secondary metallurgy. Authors made an attempt at calculating balance of Al₂O₃ particles during turbulent flow, which represents the steel refining conditions. For this purpose a special program was worked out. The agglomeration of non-metallic inclusions in liquid steel was modeled with the particle grouping method. Calculations were performed for steel with 300 and 500 ppm oxygen content. Then the quantity of generated aluminum oxide was calculated. Various mixing rates of the melt, corresponding to the actual conditions in the ladle, were applied. Simulations were performed for 6 groups of particles for the initial size of inclusions 1, 3, and 5 μ m. The size interval for each group was predefined very strictly. The diameter increase and particle number reduction of the successive groups were graphically presented in plots. In the initial phase the rate of particle removal was very high, especially when high mixing energies were involved. This calculation procedure realistically describes the agglomeration and elimination of non-metallic inclusions in the secondary metallurgical processes and can be implemented for modeling this type of processes.
13
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Mechanism and Kinetic Parameters of the Thermal Decomposition of Gibbsite Al(OH)₃ by Thermogravimetric Analysis

70%
Redaoui D., Sahnoune F., Heraiz M., Raghdi A.
Acta Physica Polonica A
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2017
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vol. 131
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issue 3
562-565
EN
In this study, the mechanism and the kinetic parameters of the thermal decomposition of gibbsite Al(OH)₃ were studied by differential thermogravimetry technique under non-isothermal conditions, between room temperature and 1200 K at heating rates of 5, 10, 15 and 20°C min¯¹. The obtained differential thermogravimetry curves show clearly three distinct peaks. The first peak is due to the partial dehydroxylation of gibbsite. Among the 32 types of differential equations of non-isothermal kinetics, we have found that the most suitable mechanism is (A_{3/2}: g(x)=[-ln(1-x)]^{2/3}) also called Avrami-Erofeev equation of order 2/3. The values of the activation energy E_{A} and of the pre-exponential factor K are 157 kJ mol¯¹ and 7.58×10¹⁵ s¯¹, respectively. The second peak corresponds to the decomposition of gibbsite to boehmite. Decomposition is controlled by the rate of second-order reaction (F₂: g(x)=(1-x)¯¹-1), under the applied conditions. The activation energy E_{A} and pre-exponential factor K correspond to 243 kJ mol¯¹ and 3.73×10²² s¯¹, respectively. The third peak is due to transformation of boehmite to alumina. However the mechanism for such transformation is better described by the 3/2 rate order reaction (F_{3/2}: g(x)=(1-x)^{-1/2}-1). In addition, the values of E_{A} and K were determined to be around 296 kJ mol¯¹ and 1.82×10¹⁹ s¯¹, respectively. The results of differential thermogravimetry were supplemented by the differential thermal analysis. X-ray powder diffraction analysis was carried out for samples of gibbsite treated at different temperatures between 200 and 1200°C in 200°C steps.
14
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Controlling Mechanisms of Creep Deformation of New Air-Hardenable TiAl-Based Alloy

70%
Staneková H., Lapin J., Pelachová T.
Acta Physica Polonica A
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2012
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vol. 122
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issue 3
512-515
EN
In the present work, controlling mechanisms of creep deformation of a new cast air-hardenable Ti-46Al-8Ta [at.%] alloy was studied. Long-term constant load tensile creep tests combined with an abrupt change of the applied stress were performed at 700°C. The response of the alloy to a stress reduction is analyzed. Transient behaviour with zero creep before recommencing creep at a reduced load is related to possible creep deformation mechanisms. The dislocation microstructures are analysed for creep strains corresponding to the minimum creep rate by transmission electron microscopy. The controlling mechanisms of creep deformation are identified from the transient creep behaviour of the alloy during stress reduction, the stress exponent and dislocation microstructures observed after creep testing.
15
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The Effect of σ-Phase Formation on Long-Term Durability of Welding Joints in SUPER 304H Steels

70%
Horváth J., Král P., Janovec J.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
960-962
EN
Article presents results on the analysis of secondary phases formed in the medium-term static isothermal ageing welding joints of a SUPER 304H (675°C/2×10⁴ h). The investigations of the precipitates were focused on the occurrence of σ-phase because its formation leads to significant deterioration of mechanical properties. The microstructure was investigated on microscopic level by scanning/transmission electron microscopy. The distribution and quantification of brittle σ-phase were studied on macroscopic level by color etching method using light optical microscopy. The effect of microstructural changes (σ-phase formation) on the impact strength of an aged base material was investigated. For comparison impact tests on received state material were also performed. The results showed that long-term ageing led to the significant reduction of impact strength as a result of the formation of the σ-phase. It was found that the σ-phase distribution is influenced by welding process. The influence of brittle σ-phase on long-term durability of the degraded steel regarding its insufficient impact strength has been discussed.
16
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Characterization of CeO₂, ZrO₂, and CeZrO₂ Crystals on CNT

70%
Matus K., Łamacz A., Liszka B.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
966-968
EN
Carbon nanotubes are increasingly being used as a support for catalyst particles. Carbon nanotubes are also used for filtering and reduction, their widespread use due to the high surface area which allows for attachment to the surface of carbon nanotubes a large amount of metallic (Ni, Fe, Pt, etc.) or oxide particles, serving as catalysts. The use of ceria-zirconia mixed oxide deposited on the surface of the nanotubes has not yet been sufficiently examined. Scanning transmission electron microscope with high-angle annular dark-field imaging and high-resolution transmission electron microscopy imaging were used as primary research techniques. Conducted research using high-angle annular dark-field imaging allows determining that catalyst particles have a regular shape which is the best from the standpoint of catalysis. Using a fast Fourier transform: and diffraction pattern has identified the catalyst particles as CeZrO₂.
17
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The Evolution of Microstructure and Mechanical Properties of Al-Mn-Fe-Si Alloys During Isothermal Annealing

70%
Poková M., Zimina M., Cieslar M.
|
EN
Recrystallization during isothermal annealing is studied in a twin-roll cast Al-Mn-Fe-Si alloy with Zr addition. Al₃Zr precipitates, which are known to improve the recrystallization resistance by exerting the Zener drag on migrating grain boundaries, form during heat treatment at 450°C. Materials with and without Al₃Zr precipitates are subjected to 4 passes of equal channel angular pressing at room temperature and a submicrometric grain size is achieved. In the course of isothermal annealing materials recrystallize at 400°C, 425°C and 450°C. The time required for recrystallization follows an Arrhenius equation. Recrystallization kinetics is similar independently of the presence of Al₃Zr precipitates. Precipitation of α-Al(Mn,Fe)Si particles is thought to increase the recrystallization resistance in the material without Al₃Zr.
18
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Structure of the Extruded and Thermally Treated Ni_{54.3}Fe_{16.2}Ga_{29.5} Alloy

61%
Prusik K., Matyja E., Zubko M., Goryczka T.
Acta Physica Polonica A
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2016
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vol. 130
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issue 4
1020-1022
EN
Hot extrusion process was applied to Ni_{54.3}Fe_{16.2}Ga_{29.5} polycrystalline alloy. Then the rod was annealed subsequently for 1 h at 700, 800, 900, and 1100°C. In this paper the effect of annealing on the microstructure of the polycrystalline extruded Ni-Fe-Ga alloy were analyzed. The structure of the alloys was determined by the X-ray and transmission electron microscopy. The electron backscattering diffraction technique was applied to obtain the texture of the extruded rods after heat treatment.
19
Content available remote

Effect of Deformation on the Transformation Temperatures of Martensite and Bainite Structures in Cu-9.97%Al-4.62%Mn Alloy

61%
Aldirmaz E.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1
40-42
EN
At present study of Cu-9.97%Al-4.62%Mn alloy system is used. Some physical properties of martensitic and bainite phase transformatios in Cu-9.97%Al-4.62%Mn (wt%) alloy were investigated by means of scanning electron microscopy and differential scanning calorimetry. In scanning electron microscope observations of Cu-9.97%Al-4.62%Mn alloy were noted two kinds of martensitic phases. These phases were defined as β'₁ (M18R) and γ'₁ (2H) martensites structures. According to differential scanning calorimetry measurement results, the deformation induced temperature is expected to be higher than the thermally induced temperature in Cu-9.97%Al-4.62%Mn alloy for martensite and bainite structures.
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