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1

Transient Liquid Phase bonding of γTiAl using Al films and SPS method

Szastak K., Matsuura K., Kata D., Ohno M.

Journal of Achievements in Materials and Manufacturing Engineering

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2014

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Vol. 67, nr 1

5--13

EN

Purpose: Investigation of joining γ-titanium aluminides using Al interlayers. Design/methodology/approach: : In order to achieve a proper joining of TiAl elements, a method known as Transient Liquid Phase (TLP) bonding was combined with Spark Plasma Sintering (SPS). All the experiments were performed under a uniaxial pressure of 7.4 MPa in a vacuum to prevent possible oxidation of liquid Al in the interlayer. The study analyzed the difference in microstructure of joints achieved with Al film thicknesses of 50, 100, 200 and 300 μm, as well as two different bonding temperatures of 900 and 1100°C. After bonding the samples were cross-sectioned, polished using 220-1200 mesh SiC paper, and 1/4 μm diamond dispersion, and analyzed using OM, SEM, EDS and EBSD, while Vickers hardness tests were performed to compare the hardness of the joint to that of the base material. Findings: The analysis of the microstructures revealed that a joint has been created between the two starting γTiAl elements. The bond consisted of TixAly phases, with some presence of Ti2AlC and TiC. The Vicker’s hardness tests reviled in some cases similar results to those of base material. Research limitations/implications: Presence of carbon rich phases within the joint, are the result of graphite mold and filling what react with molten Aluminum. This can be counteracted by replacing graphite with prefabricated TiAl powder after SHS. That however results in increasing the amount of phases such as Ti3Al, TiAl2 and TiAl3, different from the original γTiAl within the joint. An increase in bonding time and temperature could allow for faster homogenization in the joint, but would make the process more expensive and time-consuming. Practical implications: The process allows for creation of strong joints, showing signs of homogenization. Low temperature and short time makes it a possible candidate for joining γTiAl elements. Originality/value: The use of Al instead of commonly used Cu or Ni, allows minimalization of introduce impurities into the joint, while Al is still cheap and common and thus doesn’t increase the cost of the process.

2

Determination of the flow stress model of AZ80 Mg alloy

Tokunaga T., Kuziak R., Matsuura K.

Computer Methods in Materials Science

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2014

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Vol. 14, No. 2

123--130

EN

The flow stress model of AZ80 Mg alloy, whose grain size is approximately 30 μm, is created by interpreting the experimental results with the inverse analysis. Compression tests were conducted at temperatures of 523, 573 and 623 K and at strain rates of 0.01, 0.1 and 1 s"'. On the basis of the test results, the flow stress model of the Mg alloy was determined. As candidates of the flow stress model, three equations were selected and the coefficients in those equations were determined by using the inverse analysis and optimization process. In the optimization process, the measured and calculated loads were compared and the difference between them was minimized as objective functions. Consequently, the flow stress equation was chosen and the coefficients were determined. Reasonably good agreements of measured and calculated results were obtained with the equation which can be taken into account not only the softening but also the saturation of the flow stress due to the dynamic recrystallization.

PL

Model naprężenia dla stopu magnezu AZ80 o wielkość ziarna około 30 μm opracowano na podstawie interpretacji: danych doświadczalnych za pomocą rozwiązania odwrotnego. Próby ściskania próbek osiowosymetrycznych przeprowadzone w temperaturach 523, 573 i 623 K z prędkościami odkształcenia 0.01, 0.1 i 1 s'. Uzyskane wyniki posłużyły do opracowania modelu. Przy budowie modelu wybrano trzy równania i współczynniki w tych równaniach wyznaczono za pomocą rozwiązania odwrotnego. W procedurze optymalizacyjnej porównywane zmierzone i obliczone siły a różnica między nimi była minimalizowana jako funkcja celu. W konsekwencji wybrano równanie najlepiej opisujące zachowanie się materiału i wyznaczono współczynniki w tym równaniu. Równanie to uwzględnia zarówno umocnienie materiału jak i mięknięcie w wyniku dynamicznej rekrystalizacji oraz stan ustalony przy większych odkształceniach. Uzyskano dobrą zgodność między obliczonymi i zmierzonymi siłami w próbie ściskania.

3

Otrzymywanie kompozytów W/WxC metodą SPS

Macherzyńska B., Matsuura K.

Materiały Ceramiczne

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2007

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R. 59, nr 3

118-120

PL

Artykuł opisuje zastosowanie metody SPS (Spark Plasma Sintering) do otrzymywania spieków z proszków roztworów stałych w układzie W-C otrzymanych metodą spalania. W celu zbadania podstaw wytwarzania materiałów gradientowych (FGM) w tym układzie, przygotowano próbki o zawartości węgla zmieniającej się od 10 do 60% at. Strukturę i właściwości otrzymanych materiałów badano za pomocą mikroskopii optycznej i skaningowej, dyfrakcji rentgenowskiej oraz pomiarów twardości Vickersa. Znaleziono korelacje pomiędzy udziałem węgla w wyjściowej mieszaninie substratów, a składem fazowym, twardością i mikrostrukturą otrzymanych tworzyw. Ponadto, wytworzono materiały gradientowe o zawartości węgla 10, 30 i 50 % at. Właściwości mechaniczne materiałów gradientowych zmieniały się z udziałem węgla. Wytworzono materiał, w którym ziarna węglika wolframu o zmiennym składzie były wiązane wolframem metalicznym.

EN

For combustion-synthesizing of W-C hard alloys from the elemental powders, the spark plasma sintering (SPS) method was used. To establish a fundamental base of processing of functionally graded materials (FGM), samples with different atomic fraction of carbon, from 10 at% up to 60 at%, were produced. The structure and properties were systematically characterized by optical microscopy, scanning electron microscopy, X-ray diffraction analysis, and Vickers hardness measurement. Interestingly, a correlation between atomic fraction of carbon in the elemental powder mixture and hardness, microstructure and constituting phases after the synthesis has been found. Successively, the FGM samples with a graded carbon fraction of 10, 30 and 50 at% were produced. The mechanical properties of these FGM samples changed with the carbon fraction. Finally a graded material tungsten carbide was bonded with pure tungsten metal.