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1

Phase Transformations in Ti-15Mo Investigated by in situ Electrical Resistance

100%

Zháňal P., Harcuba P., Šmilauerová J., Stráský J., Janeček M., Smola B., Hájek M.

Acta Physica Polonica A

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2015

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vol. 128

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issue 4

779-782

EN

In this study phase transformations in metastable beta Ti-15Mo alloy were investigated by an in situ electrical resistance measurement in a wide range of temperatures from -196°C to 850°C. Different temperature ranges of the evolution of electrical resistance were correlated with underlying phase transformations. In the low temperature range, stage I (from -196°C to 220°C) the decrease of electrical resistance with increasing temperature is caused by the dissolution of ω_{ath} (formed during quenching by athermal shuffle transformation) which is accompanied by the relaxation of lattice strain, while the diffusional assisted growth of ω_{iso} in the range from 220°C to 380°C (stage II) is the main mechanism causing the increase of resistance. Another decrease of the resistance in the range from 380°C to 550°C (stage III) is explained by the dissolution or transformation of ω_{iso}. The increase of resistance above 550°C (stage IV) is related to the growth of α-phase particles. The fully reversible character of ω_{ath} growth and dissolution during heating and cooling in the stage I up to 100°C was confirmed by temperature cycling during repeated in situ resistance runs from RT. Pre-ageing of samples at 300°C promotes the formation of ω_{iso} particles. Subsequently, ω_{ath} particles are not created, which is fully consistent with electrical resistance measurements. The presence of ω_{ath} and the orientation relationship between ω and β were identified by the electron diffraction.

2

Microstructural Characteristic of Hypereutectoid Iron Alloys Melted in ArcMelter Furnace

63%

Frocisz Ł., Krawczyk J., Kozieł T., Goły M., Tokarski T., Wieczerzak K.

Acta Physica Polonica A

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2016

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vol. 130

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issue 4

939-941

EN

ArcMelter furnace is commonly used as a method for synthesis of amorphous and nanocrystalline materials. Due to easy and precise chemical composition control, also short time of whole process, this method was used to synthesis of new model hypereutectoid iron alloys. Material for the investigation was 90CrV6 steel. The chemical composition of this steel was modified to obtain the increase of carbides volume fraction with preserving the same chemical composition and mechanical properties of the matrix. The melt was conducted at sub atmospheric pressure of argon. The obtained materials were chemically analyzed by the use of optical emission spectrometer. The metallographic analysis was performed by the use of microscope. Phase composition in cast state was analyzed by X-ray diffraction. Chemical composition of the ingots differed from the previously established compositions in the range of 0.08 mass percentage. The high cooling rate resulted in dendritic character of the obtained microstructures. The microstructure of modified tool materials was plate martensite with large amount of retained austenite. The stress induced martensitic transformation in the crack area was observed. Retained austenite destabilization was initiated by the stress relaxation related with material cracking.

3

Properties of Biodegradable Alloys Usable for Medical Purposes

63%

Kubásek J., Vojtěch D., Čapek J.

Acta Physica Polonica A

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2012

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vol. 122

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issue 3

520-523

EN

Magnesium alloys are promising materials for production of biodegradable implants that may be used for fixation of fractured bones. Magnesium itself is an essential element that plays important roles in many biological processes. However, some common alloying elements of magnesium alloys such as aluminium or copper may cause health problems to the organism. A major problem is the high corrosion rate of magnesium and its alloys in physiological environment that contains chloride anions. Currently, the research focuses on alloys doped by rare-earth elements and zinc. All these elements affect corrosion resistance and mechanical properties of magnesium alloys. This work was dealing with the study of Mg-Gd binary alloy and Mg-Gd-Y, Mg-Gd-Zn ternary alloys that were prepared from pure metals by melting in induction furnace. Various alloy compositions were tested. Corrosion behaviours in 9 M NaCl saline environments (exposure tests, potentiodynamic measurements) were studied on alloys in the cast state. Good corrosion resistance and uniform corrosion were observed in the case of binary Mg-Gd alloy. The influence of the addition of Y or Zn to the Mg-Gd system is discussed.

4

Nanoquasicrystalline Phase in Mechanically Alloyed and Heat-Treated Al_{73}Cu_{11}Cr_{16}

51%

Sviridova T., Shevchukov A., Shelekhov E., Diakonov D., Gorshenkov M., Kaloshkin S., Tcherdyntsev V., Li Z., Fan G.

Acta Physica Polonica A

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2014

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vol. 126

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issue 2

599-602

EN

X-ray diffraction analysis, scanning and transmission electron microscopy, thermal analysis and measurement of chemical composition were implemented to determine structure, thermal stability and chemical composition of the decagonal quasicrystal in Al_{73}Cu_{11}Cr_{16} alloy produced by long-term mechanical alloying of elemental powders followed by annealing at 700°C. According to the TEM investigation such a technique permits to produce a single-phase nanostructural quasicrystal with grain size about 60 nm. Differential thermal analysis revealed that the decagonal phase does not exist above 923°C and undergoes incongruent two-stage melting coming to the end at 1100°C.

5

Thermal Stability and Mechanism of Thermally Induced Crystallization of Fe_{73.5}Cu₁Nb₃Si_{15.5}B₇ Amorphous Alloy

51%

Vasić M., Minić D., Blagojević V., Žák T., Pizúrová N., David B., Minić D.

Acta Physica Polonica A

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2015

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vol. 128

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issue 4

657-660

EN

Investigation of thermal stability of the alloy revealed stepwise crystallization process, manifested by two distinct complex exothermic peaks in differential scanning calorimetry curves. Kinetic parameters of individual crystallization steps were found using the Kissinger and Vyazovkin methods. Structural characterization of thermally treated samples showed formation of different iron-based phases including α-Fe(Si), Fe₂B, Fe₁₆Nb₆Si₇ and Fe₂Si and some metastable intermediary species. Morphology characterization of the surface and cross-section of the thermally treated samples showed granulated structure composed of several different phases and indicated occurrence of impingement effects during crystal growth. Value of estimated lifetime suggested very high stability against crystallization at room temperature and abrupt decrease of lifetime with temperature increase.

6

Atom Probe Tomography Investigations of Modified Early Stage Clustering in Si-Containing Aluminum Alloys

51%

Pogatscher S., Gerstl S., Löffler J., Uggowitzer P.

Acta Physica Polonica A

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2015

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vol. 128

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issue 4

643-646

EN

In this paper atom probe tomography is used to explore early stage clustering in aluminum alloys. Two novel concepts for a modification of clustering are discussed. Control of early stage clustering is welcome from an application point of view since clustering deteriorates strength evolution during the industrial heat treatment of the important class of Al-Mg-Si precipitation-hardenable alloys. Nanoscale early stage clusters are very difficult to observe and atom probe tomography is the best technique to visualize and chemically measure Si or Mg-containing clusters in aluminum alloys. Restrictions remain in achieving the ultimate quantification of such small solute aggregates by atom probe tomography, such as detection efficiency, local magnification effects, surface migration of solute atoms, and unresolved issues with the reconstruction procedure. Here we investigate one of these restricting effects, namely the migration of solute atoms during atom probe tomography measurements. In particular Si is found to be preferentially localized or absent at certain crystallographic poles in aluminum, which derogates the experimental results gained from atom probe tomography studies of clustering in Si-containing aluminum alloys. This artifact is investigated for different specimen temperatures, detection rates and pulse fractions during atom probe tomography measurements. Optimal strategies to analyze small-scale solute clusters in Si-containing aluminum alloys are presented.

7

Powder Metallurgy Preparation of Co-Based Alloys for Biomedical Applications

51%

Marek I., Novák P., Mlynár J., Vojtěch D., Kubatík T., Málek J.

Acta Physica Polonica A

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2015

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vol. 128

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issue 4

597-601

EN

Co-based alloys represent very important group of materials used for medical applications. Currently, fabrication of these materials is preferentially done by casting or forming. Production by powder metallurgy techniques is less common. However, powder metallurgy fabrication of these alloys brings advantages such as reduced machining, possibility of alloying by high-melting elements, preparation of nanocrystalline materials with enhanced mechanical properties or producing of porous alloys with improved ability to integrate into issues. In this work, our attention was focused on fundamental preparation of an CoCrMo alloy by two methods of powder metallurgy. In the first method, pure metallic powders were mixed, pressed and sintered in vacuum furnace. The second applied technology consisted of mechanical alloying using planetary ball mill and compaction by spark plasma sintering technique. A series of samples was prepared under various conditions by these procedures. Dependence of microstructure, phase composition and mechanical properties of prepared samples on fabrication conditions (milling parameters, sintering temperature etc.) was studied. Obtained results were compared with properties of commercial cast cobalt alloy used for medical applications.

Refine search results

Phase Transformations in Ti-15Mo Investigated by in situ Electrical Resistance

Microstructural Characteristic of Hypereutectoid Iron Alloys Melted in ArcMelter Furnace

Properties of Biodegradable Alloys Usable for Medical Purposes

Nanoquasicrystalline Phase in Mechanically Alloyed and Heat-Treated Al_{73}Cu_{11}Cr_{16}

Thermal Stability and Mechanism of Thermally Induced Crystallization of Fe_{73.5}Cu₁Nb₃Si_{15.5}B₇ Amorphous Alloy

Atom Probe Tomography Investigations of Modified Early Stage Clustering in Si-Containing Aluminum Alloys

Powder Metallurgy Preparation of Co-Based Alloys for Biomedical Applications