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Vysokocyklová únava ložiskové oceli
Kunz, Ludvík ; Činčala, M.
S-N curve of 14109 bearing steel was experimentally determined in symmetrical tension-compression in the interval of 10 to 5 to 10 to 8 cycles to fracture. Continuous increase of the number of cycles to fracture with decreasing stress amplitude was observed. Large scatter of experimental data is related to the initiation of fatigue cracks on internal defects of Al2O3 and TiN type.
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Study of transition layers in a gamma TiAl - CaO - Al2O3 SYSTEM
Dočekalová, Kateřina ; Dlouhý, Antonín ; Zemčík, L. ; Fiala, J.
The main attention in the present study focuses on the reactions between a ceramic crucible and the molten intermetallic alloy. The qualitative and quantitative metallographic analysis investigates the transition layers which are built during the melting process on the CaO-coated surface of the Al2O3 crucible. Preliminary results suggest that relevant chemical reactions are limited to a boundary layer with a characteristic thickness of 200 mm. In this layer, the high-temperature diffusion contributes to the nucleation and growth of complex phases the origin of which could result in an enrichment of the melt by oxygen.
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Quantitative image analysis of precipitates in Ni-rich NiTi shape memory alloys
Bojda, Ondřej ; Dlouhý, Antonín ; Fiala, J.
A microstructure of a Ti-50.7at%Ni shape memory alloy resulting from solution annealing and subsequent aging at 500°C/3.6ks/8MPa is quantitatively analysed. The TEM study is assisted by Adaptive Contrast Control (ACC) routines embedded in a recent image processing system. The assessment focuses on the number density, size and distribution of crystallographic variants of Ni4Ti3 precipitates. It was found that the distribution of crystallographic particle variants in the microstructure is inhomogeneous. The influence of the heterogeneous Ni4Ti3 precipitation on the characteristics of the martensitic transformation B2®B19´ is briefly discussed.
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Fracture behaviour of welds made of pearlitic and bainitic steel
Dlouhý, Ivo ; Holzmann, Miloslav ; Zbořil, J.
The paper is focused on microstructure evaluations, hardness and fracture behaviour analyses of welded joint made from newly developed cast bainitic Lo8CrNiMo steel and pearlitic rail steel of the type UIC 900A. Dynamic fracture toughness was evaluated based on data from precracked Charpy type specimens loaded by means of instrumented impact tester. The lowest dynamic fracture toughness values and consequently the higher risk of brittle fracture possesses the pearlitic steel UIC 900A and its HAZ. At application temperature range this steel is on lower shelf of ductile to brittle transition, the tempering in HAZ didnŽt affect the toughness substantially. The cast bainitic steel in joint is typical by two times higher toughness values comparing to pearlitic one, in HAZ further toughness increase may be expected. The weld zone itself is characterised by high scatter of toughness data, nevertheless, all the values are above the scatter band characterising the pearlitic steel.
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