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Národní úložiště šedé literatury Nalezeno 2 záznamů.  Hledání trvalo 0.01 vteřin. 
AN INTERPLAY BETWEEN HEAT TREATMENT CONDITIONS AND B2 <-> B19 ' TRANSFORMATION IN Ni-Ti SHAPE MEMORY ALLOYS
 Kuběnová, Monika ; Zálešák, Jakub ; Čermák, Jiří ; Dlouhý, Antonín
This study investigates the influence of a heat treatment atmosphere on multistage martensitic transformations in a Ti-50.9at% Ni shape memory alloy. Evacuated quartz tubes were filled with hydrogen while the hydrogen partial pressure was carefully controlled in each experiment. The encapsulated specimens were subjected to heat treatments consisting of annealing and aging. After the heat treatment, the path of martensitic transformation was investigated using differential scanning calorimetry (DSC). On cooling, martensite initial temperatures decrease with the increasing partial pressure of hydrogen applied during the heat treatment. Moreover, the formation of martensite phase may not take place for partial pressures that exceed a certain limit. On the other hand, two-and multiple-step B2/R/B19' martensitic transformations are observed in specimens heat treated at lower hydrogen pressures. Results obtained using transmission electron microscopy (TEM) clearly show that the size of Ni4Ti3 precipitates becomes smaller in alloys that were heat treated at higher hydrogen pressures. The results are discussed in terms of a chain of events. It is suggested that diffusion of hydrogen into the specimen during the annealing step first influences the nucleation of the Ni4Ti3 phase. The sizes and distribution of the Ni4Ti3 precipitates than control the characteristics of B2/B19' transformation.
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THE INFLUENCE OF INITIAL DEFORMATION ON STRUCTURE AND MECHANICAL PROPERTIES OF P92 STEEL
 Svobodová, M. ; Čmakal, J. ; Horváth, L. ; Chmela, T. ; Sklenička, Václav
The paper deals with materials properties of steel bends. Tubes and pipes, respectively, of P92 steel were hot and/or cold bended. Moreover, the various combinations of tubes/pipes dimensions were chosen. Then, as-bended steel was exposed to a long-term temperature and/or mechanical loading. Investigating the materials behaviour, some structure and mechanical tests on as-exposed bends were carried out. So, this paper summarizes recent results of performed tests including numerical simulations by FEM.
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