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APPLICATION OF SMALL PUNCH TECHNIQUE FOR EVALUATION OF MECHANICAL PROPERTIES OF ADVANCED METALLIC MATERIALS
Milička, Karel ; Dobeš, Ferdinand
Results of an application of small punch tests on non-steel advanced materials are presented with the aim to show several possibilities of this techique. As representative, three materials were selected: an aluminium alloy 2124Al reinforced with 20 vol.% SiC particulates, a composite of alloy AZ91 with Saffil fibres and an intermetallic alloy based on Fe3Al compound. It is shown that there are some close relationships between the results of the small punch technique and results of creep tests using massive specimens. Advantages of the small punch tests under specific conditions, e.g., if a small amount of testing materials is at disposal, are discussed.
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Creep of intermetallic alloy TiAl at very low strain rates
Mareček, P. ; Kloc, Luboš ; Fiala, J.
Intermetallic alloys are very advanced materials for high-temperature applications. There are series of attractive properties exceed coventional up to now used creep resistance steels. The creep behaviour of TiAl alloy was investigated under an applied stress lower than 100 MPa at temperatures 700-850 °C. The strain rate was lower than 10-9 s-1 under testing conditions, which have importance for technical applications. In relation to results, the creep behavior of intermetallic alloy TiAl shows a transition to a mechanism with low stress exponent in the range of minimum strain rates, similar to creep resistance steels with evidence change of deformation mechanism under strain rate 10-10 s-1 . However, this transition in TiAl alloys is not as clear as in creep resistant steels.
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Vliv zatěžovací historie na creep 9% chromové oceli
Kloc, Luboš ; Sklenička, Václav
The creep life assessment is currently based on the phenomenological models mostly derived from the constant stress or constant load creep experiments. Since the loading history of the parts in industry used to be complicated and frequently unknown, the model data can be invalid. Stress change creep experiments were done on the P-91 type creep resistant steel at loading conditions corresponding to the low stress creep regime. The experiment was interrupted, that is cooled down and heated up again several times. The interrupts were done during the ``quasi-steady state'' when the creep rate is stabilized. The effect of both stress changes and temperature cycles on creep properties was analyzed. While the temperature cycle introduce some additional creep strain, the stress changes reduce the creep rate considerably. Taking into account the proportionality between the creep strain and creep damage nucleation, it is possible to conclude that small stress changes during primary stage can improve the creep strength of the steel, while the temperature changes have opposite effect.
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MECHANISMY CREEPOVÉ DEFORMACE U UTRAJEMNOZRNNÉHO HLINÍKU PŘIPRAVENÉHO METODOU ECAP
Dvořák, Jiří ; Sklenička, Václav ; Král, Petr
Extremely coarse-grained aluminium (99,99%) was subjected to severe plastic deformation (ECAP)for obtain an ultrafine-grained microstructure. Creep tensile and compression tests were conducted on such material and for comparison reasons also on coarse-grained aluminium. The results indicate an increased creep resistant of ultrafine-grained aluminium compared to its coarse-grained state. It was proposed, that creep of ultrafine-grained aluminium is probably control by the same creep mechanisms as coarse-grained one. However, the role of grain boundary sliding in creep considerably differs in both ECAP and coarse-grained materials
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