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Interaction between TiAl metl and coated ceramic crucibles
Dočekalová, Kateřina ; Dlouhý, Antonín ; Zemčík, L. ; Fiala, J.
The present work focused on interactions between TiAl melt and coated oxide refractories. Melting experiments were performed in vacuum induction furnace (VIM technology). The attention is given mainly to reaction interfaces between the melt and ceramics, however, the microstructure of the cast alloy is also taken into account. The analysis is performed using scanning electron microscopy (SEM) and EDAX. Experimental results were compared with results of thermodynamic calculations that estimated a probability of chemical reactions at the melt-refractory interface. The results indicate that there is an influence of ceramic coatings on the cast microstructure. The detailed composition of the reaction interface and the explanation of reaction mechanisms based on thermodynamic calculations is presented.
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Heat treatment conditions and their influence on precipitation of Ni4Ti3 phase in Ni-rich NiTi shape memory alloys
Dlouhý, Antonín ; Bojda, Ondřej ; Fiala, J.
The present work deals with a quantitative analysis of Ni4Ti3 precipitates after solution annealing (850°C/30min) and ageing (450°C/1hod) in air or inert argon atmosphere. The attention is given not only to the size of precipitates in the vicinity of grain boundaries and in the grain volume and to the corresponding Ni4Ti3 volume fractions, but also to subsequent martensitic transformations B2-(R)-B19’. Quantitative analysis of transmission electron microscopy micrographs is based on the automatic image processing by means of the Adaptive Contrast Control programme. Martensitic transformations were documented using differential scanning calorimetry. Results indicate a homogeneous precipitation of Ni4Ti3 with the heterogeneous distribution of crystallographic particle variants. A possible influence of the heat treatment environment on Ni4Ti3 precipitation and martensitic transformations is discussed in this work.
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Diffusion of C and Mn in steel weldment Fe-0.3C-5Mn/Fe-0.3C-15Mn
Král, Lubomír ; Million, Bořivoj ; Čermák, Jiří
In this paper, the results of measurements of chemical diffusion of Mn and C in weldments of alloys Fe-0,3%C-5%Mn / Fe-0,3%C-15%Mn are reported. Alloys were cast in induction furnace under protective Ar atmosphere. They were hot-forged to rods of diameter 15mm and cut into pieces of 4mm thickness. These cylindrical samples were metalographical polished. Diffusion couples, welded by electrical impulse, were sealed together with Ti-chips, into evacuated silica ampoules. After that, they were annealed at 1100-800 °C for 1.5-96 hours respectively. Measurement of C redistribution was done in a normal direction to welding interface using electron-scanning microscope Philips SEM-505WDS equipped with Microspec WDX-2A. Diffusion coefficients of C and Mn were obtained and the relations between them were found.
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Fatigue behaviour of nickel base superalloy Inconel 713LC at high temperature
Juliš, M. ; Obrtlík, Karel ; Podrábský, T. ; Petrenec, Martin
Total strain controlled tests have been performed on cylindrical specimens of Inconel 713 LC polycrystals at 800 °C. Cyclic hardening-softening, cyclic stress-strain and fatigue life curves were obtained. Fracture surface was studied using scanning electron microscopy. High amplitude cycling results in early pronounced hardening followed by softening. Low amplitude cycling is characterized by the stable stress response. Manson-Coffin and Basquin laws can reasonably approximate the fatigue life data. Fatigue crack initiation at casting defects is documented.
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Effect of Number of ECAP Passes on Creep Behaviour and Microstructure of Pure Aluminium and Al-Sc Alloy
Král, Petr ; Dvořák, Jiří ; Kvapilová, Marie ; Svoboda, Milan ; Sklenička, Václav
Experiments were conducted to determine an effect of equal-channel angular pressing (ECAP) on the creep behaviour and the microstructure of pure aluminium and an Al-Sc alloy. The coarse-grained materials in their as-received states were subjected to ECAP at room temperature using a die, which had a 90° angle between the channels. Experiments show that ECAP reduced the average grain sizes of ~1µm and ~0.3µm for pure Al and Al-Sc. The grain sizes after 8 ECAP passes and subsequent creep exposure are ~12µm and ~2µm for Al and Al-Sc alloy, respectively. The fracture analysis and morphology of creep fracture surfaces of an Al-Sc alloy revealed the formation of shear bands which were orientated along the direction of the last ECAP pass. The application of ECAP method causes a substantial continuous decrease in the creep resistance of Al and Al-Sc alloy with increasing numbers of ECAP passes which can be explained by increasing contribution of grain boundary sliding to the total creep strain.
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