Wyniki wyszukiwania - Biblioteka Nauki

1

Solute redistribution after back-diffusion in cellular and dendritic growth of binary alloys

100%

Wołczyński W. , Kloch J.

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tom Vol. 46, nr 3

277-288

EN

A modification of the Brody-Flemings model for microsegregation is worked out to describe a solute redistribution for oriented cells and dendrites. An improved equation for the liquid concentration is introduced into the presented model. The solute redistribution satisfies mass balance at each stage of directional growth of binary alloys. The back-diffusion into the solid is also included to analysis of the behaviour of the solute concentration in both liquid and solid. The limitation and physical justification for the alfa-back diffusion parameter are considered. The limitation determines both extremal values of alfa-back diffusion parameter; 0 <=alfa<=1. The alfa-parameter is defined as the ratio of solidification time to diffusion time. The presented model is reducible to the Scheil model for alfa = 0 and to the equilibrium solidification for alfa = 1.

2

Solid-liquid interface morphology of white carbide eutectic during directional solidification

100%

Trepczyńska-Łent M.

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tom Vol. 62, iss. 1

365--368

EN

In this paper the analysis of solid-liquid interface morphology in white carbide eutectic was made. In a vacuum Bridgman-type furnace, under an argon atmosphere, directionally solidified sample of Fe - C alloy was produced. The pulling rate was v = 125 μm/s (450 mm/h) and constant temperature gradient G = 33.5 K/mm. The microstructure of the sample was frozen. The microstructure of the sample was examined on the longitudinal section using an light microscope and scanning electron microscope.

3

Characteristics of the Growth of the Directionally Solidified Fe-4.25% C Eutectic Alloy

100%

Trepczyńska-Łent M.

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2021

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tom Vol. 66, iss. 4

1179--1186

EN

The current work is dedicated to the mathematical description of a protrusion of the leading phase (cementite) over the wetting phase (austenite) observed during the author’s experiments in previous articles. A cementite protrusion is confirmed in the directionally solidified Fe-4.25% C eutectic alloy. The protrusion is defined due to the mass balance fulfilment. A coordinate system is attached to the solid/liquid interface, which is moving with the constant growth rate v.

4

High Temperature Oxidation Property of Ni Based Superalloy CM247LC Produced Via Selective Laser Melting Process

88%

Lee J.-U. , Kim Y.-K. , Seo S.-M. , Lee K.-A.

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tom Vol. 68, iss. 1

107--112

EN

CM247LC alloy was manufactured by using selective laser melting (SLM) process, one of the laser powder bed fusion (L-PBF) methods. The hot isostatic pressing (HIP) process was additionally conducted on the SLM-built CM247LC to control its microstructures and defects. The high temperature oxidation property was investigated, and it was compared with conventional DS247LC sample (reference) prepared via the directional solidification process. The L-PBF HIP sample showed blocky-type MC carbides generated along the grain boundary with average size of about 200 nm. A semi-spherical primary γ' phase of size 0.4-1.0 μm was also observed inside the grains. Moreover, the DS247LC sample displayed a coarse eutectic γ' phase and many script-type MC carbides. Furthermore, cuboidal-type γ' with an average size of about 0.5 μm was detected. High-temperature oxidation tests were conducted at 1000°C and 1100°C for 24 hours. The results at 1100°C oxidation temperature showed that the measured oxidation weight gains for HIP and DS247LC were 1.96 mg/cm2 and 2.26 mg/cm2, respectively, indicating the superior high-temperature oxidation resistance of the L-PBF HIP sample. Based on the above results, a high-temperature oxidation mechanism of the CM247LC alloys manufactured by the SLM process and the directional solidification process has been proposed.

5

X-ray Diffraction Study of Directional Solidification Ledeburite

75%

Trepczyńska-Łent M. , Szykowny T.

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tom Vol. 15, iss. 3

71--76

EN

Directionally solidified sample of Fe-Fe3C eutectic alloy were produced under an argon atmosphere in a vacuum Bridgman-type furnace to study the eutectic growth with v = 167 μm/s pulling rate and constant temperature gradient G = 33.5 K/mm. Since how the growth texture of eutectic cementite is related to its growth morphology remains unclear, the current study aims to examine this relationship. The technique such as X-ray diffraction, have been used for the crystallographic analysis of carbide particles in white cast irons.

6

Mathematical and numerical model of directional solidification including initial and terminal transients of the process

75%

Kapturkiewicz W. , Burbelko A. A. , Fraś E.

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tom Vol. 8, iss. 4

65-70

EN

The, developed in this study, simple model and numerical solution of diffusion growth of the solid phase under the conditions of directional solidification allow for the effect of constituent diffusion in both liquid and solid phase and assume the process run in which (like in reality) the preset parameter is the velocity of sample (pulling velocity) at a preset temperature gradient. The solid/liquid interface velocity is not the process parameter (like it is in numerous other solutions proposed so far) but a function of this process. The effect of convection outside the diffusion layer has been included in mass balance under the assumption that in the zone of convection the mixing is complete. The above assumptions enabled solving the kinetics of growth of the solid phase (along with the diffusion field in solid and liquid phase) under the conditions of diffusion well reflecting the process run starting with the initial transient state, going through the steady state period in central part of the casting, and ending in a terminal transient state. In the numerical solution obtained by the finite difference method with variable grid dimensions, the error of the mass control balance over the whole process range was 1- 2%.

7

Preparation of Twinned Dendrites of Al-Zn Alloy with High Zn Content

75%

Gao K. , Song W. , Fan L. , Ding Y. , Guo X. , Zhang R.

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nr 4

8

Identification and evaluation of freckles in directionally solidified casting made of PWA 1426 nickel-based superalloy

75%

Chmiela B. , Sozańska M. , Cwajna J.

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tom Vol. 57, iss. 2

559-564

EN

Manufacturing of modern aero engine turbine blades made of nickel-based superalloys is very complex and expensive. The thrust and performance of new engines must address constantly more demanding requirements. Therefore, turbine blades must be characterised by very good mechanical properties, which is possible only if the blades are free of casting defects. An important innovation has been the launching of directionally solidified (DS) and single crystal (SX) turbine blades. But, manufacturing procedures and the chemical composition of many superalloys promote the formation of casting defects that are characteristic only for directional solidification. One of these defects is freckles. Freckles are small equiaxed grains in the form of long chains parallel to the solidification direction and are located on the surface of the casting. Freckles decrease the mechanical properties of DS and SX blades; therefore, they should be always unambiguously identified to improve the manufacturing process. This work presents the possibilities of identifying and evaluating freckles in DS casting made of PWA 1426 superalloy by combining the scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and electron backscatter diffraction (EBSD) techniques.

PL

Wytwarzanie łopatek turbin nowoczesnych silników lotniczych jest bardzo złożone i kosztowne. Stale rosną też wymagania dotyczące ciągu i sprawności nowych silników. Dlatego łopatki turbin musza charakteryzować się bardzo dobrymi właściwościami mechanicznymi. Jest to możliwe tylko wtedy, gdy łopatki nie wykazują wad odlewniczych. Ważną innowacją w wytwarzaniu łopatek było wprowadzenie łopatek kierunkowo krystalizowanych (DS) i monokrystalicznych (SX). Skład chemiczny wielu nadstopów i proces wytwarzania łopatek stanowią czasem czynniki sprzyjające powstawaniu wad odlewniczych, charakterystycznych tylko dla procesu kierunkowej krystalizacji. Przykładem takiej wady są frekle. Wada ta ma postać małych, równoosiowych ziaren tworzących łańcuchy, przeważnie równoległe do kierunku krystalizacji. Wada ta znacznie obniża właściwości mechaniczne łopatek DS i SX, dlatego powinna być zawsze jednoznacznie identyfikowana w celu usprawnienia procesu ich wytwarzania. W pracy przedstawiono możliwości identyfikacji i oceny wady frekle w kierunkowo krystalizowanym odlewie z nadstopu niklu PWA 1426 przy użyciu elektronowej mikroskopii skaningowej (SEM), mikroanalizy rentgenowskiej (EPMA) i dyfrakcji elektronów wstecznie rozproszonych (EBSD).

9

Anisotropic in Situ Metal Matrix Composite Reinforced with VC Carbide Fibres

63%

Kawalec M. , Górny M. , Sikora G.

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tom Vol. 15, iss. 1

21--24

EN

A eutectic reaction is a basic liquid-solid transformation, which can be used in the fabrication of high-strength in situ composites. In this study an attempt was made to ensure directional solidification of Fe-C-V alloy with hypereutectic microstructure. In this alloy, the crystallisation of regular fibrous eutectic and primary carbides with the shape of non-faceted dendrites takes place. According to the data given in technical literature, this type of eutectic is suitable for the fabrication of in-situ composites, owing to the fact that a flat solidification front is formed accompanied by the presence of two phases, where one of the phases can crystallise in the form of elongated fibres. In the present study an attempt was also made to produce directionally solidifying vanadium eutectic using an apparatus with a very high temperature gradient amounting to 380 W/cm at a rate of 3 mm/h. Alloy microstructure was examined in both the initial state and after directional solidification. It was demonstrated that the resulting microstructure is of a non-homogeneous character, and the process of directional solidification leads to an oriented arrangement of both the eutectic fibres and primary carbides.

10

Modelling the composition of carbides in nickel-based superalloys of directional crystallization

51%

Glotka O. A.

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2020

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tom Vol. 102, nr 1

5--15

EN

Purpose: The specifics of the influence of alloying elements on the chemical composition of various types of carbides, their topology and morphology for a multicomponent system of the type Ni-5Cr-9Co-6Al-1Ti-11.7W-1.1Mo-1.6Nb-0.15C using the calculation method CALPHAD. It is shown that the obtained dependences closely correlate with thermodynamic processes occurring in the system. Design/methodology/approach: This work presents the results of studies of the distribution of chemical elements in the composition of carbides, depending on their content in the system. Findings: It was found that the influence of alloying elements on the composition of carbides is complex and is described by complex. Research limitations/implications: An essential problem is the prediction of the structure and properties of heat-resistant alloys without or with a minimum number of experiments. Practical implications: The obtained dependences can be used both for designing new heat-resistant alloys and for improving the compositions of industrial alloys. Originality/value: The value of this work is that the obtained dependences of the influence of alloying elements on the dissolution (precipitation) temperatures and the distribution of elements in carbides in the alloy of the Ni-5Cr-9Co-6Al-1Ti-11.7W-1.1Mo-1.6Nb-0.15C.