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Abstract

In this study, the combined effect of Zr and Si on isothermal oxidation of Ti for 25 and 50 h at 820°C, which is the temperature related to exhaust valves operation, was investigated. Si addition into Ti-5mass%Zr alloy led to a distribution of silicide Ti5Si3 phase formed by a eutectic reaction. The Ti sample containing only Zr showed more retarded oxidation rate than Ti-6Al-4V, the most prevalent Ti alloy, at the same condition. However, while a simultaneous addition of Zr and Si resulted in greater increase of oxidation resistance. The oxide layer formed after the addition of Zr and Si comprised TiO2, ZrO2, and SiO2.

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Authors and Affiliations

S.-H. Ha
B.-H. Kim
Y.-O. Yoon
H.-K. Lim
S.K. Kim
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Abstract

In this paper, thermal oxidation resistance of silicide-coated niobium substrates was tested in a temperature range of 1300–1450°C using an HVOF burner. Pure niobium specimens were coated using the pack cementation CVD method. Three different silicide thickness coatings were deposited. Thermal oxidation resistance of the coated niobium substrates was tested in a temperature range of 1300–1450°C using an HVOF burner. All samples that passed the test showed their ability to stabilize the temperature over a time of 30 s during the thermal test. The rise time of substrate temperature takes about 10 s, following which it keeps constant values. In order to assess the quality of the Nb-Si coatings before and after the thermal test, light microscopy, scanning electron microscopy (SEM) along with chemical analysis (EDS), X-ray diffraction XRD and Vickers hardness test investigation were performed. Results confirmed the presence of substrate Nb compounds as well as Si addition. The oxygen compounds are a result of high temperature intense oxidizing environment that causes the generation of SiO phase in the form of quartz and cristobalite during thermal testing. Except for one specimen, all substrate surfaces pass the high temperature oxidation test with no damages.
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Authors and Affiliations

Radosław Szklarek
1 2 3
Tomasz Tański
1
ORCID: ORCID
Bogusław Mendala
1
Marcin Staszuk
1
ORCID: ORCID
Łukasz Krzemiński
1
Paweł Nuckowski
1
Kamil Sobczak
3

  1. Silesian University of Technology, ul. Akademicka 2A, 44-100 Gliwice, Poland
  2. Spinex Spinkiewicz Company, Klimontowska 19, 04-672 Warsaw, Poland
  3. Łukasiewicz Research Network – Institute of Aviation, al. Krakowska 110/114, 02-256 Warsaw, Poland
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Abstract

AM50/Mg2Si composites containing 5.7 wt. % and 9.9 wt. %. of Mg2Si reinforcing phase were prepared successfully by casting method. The microstructure of the cast AM50/Mg2Si magnesium matrix composites was investigated by light microscopy and X-ray diffractometry (XRD). The microstructure of these composites was characterized by the presence of α-phase (a solid solution of aluminium in magnesium), Mg17Al12 (γ-phase), Al8Mn5 and Mg2Si. It was demonstrated that the Mg2Si phase was formed mainly as primary dendrites and eutectic.

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Authors and Affiliations

M.A. Malik
K. Majchrzak
K.N. Braszczyńska-Malik
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Abstract

Doping is one of the possible ways to significantly increase the thermoelectric properties of many different materials. It has been confirmed that by introducing bismuth atoms into Mg sites in the Mg2Si compound, it is possible to increase career concentration and intensify the effect of phonon scattering, which results in remarkable enhancement in the figure of merit (ZT) value. Magnesium silicide has gained scientists’ attention due to its nontoxicity, low density, and inexpensiveness. This paper reports on our latest attempt to employ ultrafast selfpropagating high-temperature synthesis (SHS) followed by the spark plasma sintering (SPS) as a synthesis process of doped Mg2Si. Materials with varied bismuth doping were fabricated and then thoroughly analyzed with the laser flash method (LFA), X-ray diffraction (XRD), scanning electron microscopy (SEM) with an integrated energy-dispersive spectrometer (EDS). For density measurement, the Archimedes method was used. The electrical conductivity was measured using a standard four-probe method. The Seebeck coefficient was calculated from measured Seebeck voltage in the sample subjected to a temperature gradient. The structural analyses showed the Mg2Si phase as dominant and Bi2Mg3 located at grain boundaries. Bismuth doping enhanced ZT for every dopant concentration. ZT = 0:44 and ZT=0.38 were obtained for 3wt% and 2wt% at 770 K, respectively.
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Authors and Affiliations

Bartosz Bucholc
1
ORCID: ORCID
Kamil Kaszyca
1
ORCID: ORCID
Piotr Śpiewak
2
ORCID: ORCID
Krzysztof Mars
3
ORCID: ORCID
Mirosław J. Kruszewski
2
ORCID: ORCID
Łukasz Ciupiński
2
ORCID: ORCID
Krystian Kowiorski
1
ORCID: ORCID
Rafał Zybała
1 2
ORCID: ORCID

  1. Łukasiewicz Research Network - Institute of Microelectronics and Photonics, Aleja Lotników 32/46, 02-668 Warsaw, Poland
  2. Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland
  3. Faculty of Materials Science and Ceramic, AGH University of Science and Technology, Kraków, Al. Mickiewicza 30, 30-059, Poland
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Abstract

Wider application of silicon carbide (SiC) is anticipated for increasing the durability of various structural facilities. For this study, SiC was fabricated with decreased electrical resistivity for precision electrical discharge machining. Two-step reaction sintering by infiltration of molten Fe-Si alloy was applied for SiC fabrication. The procedure included first sintering at 973 K in Ar gas atmosphere and second sintering by spontaneous infiltration of molten Fe-75%Si alloy at 1693 K in vacuum. The sintered structure porosity became very low, forming 3C-type SiC. Results confirmed that molten Fe-75%Si alloy infiltration occurred because of reaction sintering. The electrical resistivity of the sintered SiC infiltrated by molten Fe-75%Si alloy can be improved to be two orders of magnitude lower than that by molten Si, consequently maintaining the high performance of SiC.

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Authors and Affiliations

Yoshitsugu Hanada
Yang Xiao
Akio Sonoda
Hyo-Gyoung Kang
Hideaki Nagayoshi
Atsuo Yamamoto
Tatsuya Tokunaga

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