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Effect of sintering temperature on microstructure and mechanical properties of AE42 magnesium alloy prepared by spark plasma sintering
Minárik, P. ; Lukáč, František ; Cinert, Jakub ; Šašek, S. ; Král, R.
Magnesium alloy AE42 was prepared by powder metallurgy technique of spark plasma sintering. The effect of sintering parameters, particularly sintering temperature, on the microstructure and mechanical strength was investigated. The gas-atomized powder was sintered at four temperatures in the temperature range of 400-550 °C. It was found that mechanical strength of the sintered samples was significantly affected by several microstructural features. Application of relatively high load during sintering caused deformation of the individual particles and consequent recrystallization depending on the processing temperature resulted in the release of internal strain and in grain growth. As a result, the evolution of the mechanical strength as a function of the sintering temperature was significantly affected by residual stress, grain size and coarsening of secondary phase particles.
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Characterization of flame sprayed abradable seal NiCrAl-bentonite coatings
Houdková, Š. ; Česánek, Z. ; Schubert, J. ; Lukáč, František ; Bystrianský, M.
The NiCrAl-21% Bentonite abradable coating, deposited by flame spraying, was exposed to 720°C / 1 hour air-annealing to evaluate its resistance against heat-induced changes. The SEM and XRD microstructure evaluation was done. After the air-annealing, the increase of HR15Y surface hardness was recorded and accompanied with decrease of abradability evaluated by Progressive Readability Hardness (PAH) test, although no demonstrable microstructural changes was recorded by SEM. XRD analyses evidenced the formation of nickel oxides and ordered Ni3Al phase during the air-annealing. Besides the abradable coating evaluation, this work brings the verification of the potential of PAH for scratch hardness testing. The measurement provides the results with low scatter, compared to usual surface hardness testing, and enables to distinguish between the depth of indentation in loaded and unloaded state, pointing out to the elastic/plastic deformation ratio.
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The effect of spark plasma sintering on the porosity and mechanical properties of Ti-15Mo alloy
Terynková, A. ; Kozlík, J. ; Bartha, K. ; Chráska, Tomáš ; Dlabáček, Zdeněk ; Stráský, J.
Metastable β-titanium alloys are receiving much interest for various applications such as aircraft industry and medicine thanks to their excellent mechanical properties and biocompatibility. The common way of preparing the titanium alloys is hindered by its production costs. Powder metallurgy (PM) approach is a promising route for cost-effective fabrication of titanium alloys due to possibility of near net shaping. In this study, binary biomedical Ti-15Mo alloy was prepared by PM. Gas atomized powder was sintered by spark plasma sintering (SPS) above the β-transus temperature of the studied alloy. The compaction of the powders was accomplished by short-time sintering. The effect of the time of sintering on the porosity and the microhardness in centre part as well as in periphery part of the sample was investigated. The samples revealed significant inhomogeneity the porosity increases with the distance from the centre of the specimen. With increasing sintering times the porosity decreases and simultaneously the microhardness increases.
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Microstructure of commercially pure titanium after cryogenic milling and spark Plasma sintering
Kozlík, J. ; Harcuba, P. ; Stráský, J. ; Chráska, Tomáš ; Janeček, M.
Commercially pure titanium was prepared by advanced powder metallurgy methods with the aim to produce the ultra-fine grained material. Cryogenic attritor milling was used as a first step to refine the microstructure at liquid argon temperatures to suppress recovery and dynamic recrystallization. Spark plasma sintering was subsequently employed to produce bulk material, exploiting its ability to achieve fully dense structure in short time and thus to reduce the grain growth. In order to understand the undergoing microstructural changes during the process, detailed investigation was performed after each preparation step. Powder morphology was changed significantly after milling, while particle fragmentation was only limited. Grain size after sintering was in micrometer scale, relatively independent of sintering conditions.
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