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RISS 인기검색어
- 검색키워드
- 저자 : Pavel Strunz (검색결과 3 건)
- 무료
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Matrix Transformation in Boron Containing High-Temperature Co–Re–Cr Alloys
Pavel Strunz,Debashis Mukherji,Přemysl Beran,Ralph Gilles,Lukas Karge,Michael Hofmann,Markus Hoelzel,Joachim Rösler,Gergely Farkas 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.5
An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect ofboron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr 2 Re 3 type) phases were measuredat ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diff raction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobaltand to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that thetransformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperaturedid not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm ofboron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which bindshcp-stabilizing elements (Cr and Re). Moreover, borides were identifi ed in alloys with high boron content.
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Effect of Composition on the Matrix Transformation of the Co-Re-Cr-Ta-C Alloys
Přemysl Beran,Debashis Mukherji,Pavel Strunz,Ralph Gilles,Michael Hofmann,Lukas Karge,Oleksandr Dolotko,Joachim Rösler 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.4
Neutron diffraction measurement was performed in-situ at high temperatures on Co-Re-Ta-C alloys with and without Cr addition. This included alloys containing different C content with the C/Ta ratio varying between 0.5 and 1.0. The Co-Re-solid solution matrix of the experimental alloys is polymorphic (like in pure cobalt) and transformed from low temperature hexagonal ε phase to high temperature cubic γ phase on heating. This transformation is reversible and show hysteresis. The main alloying addition, Re, stabilizes the ε Co-phase and increases the transformation temperature to above 1273 K. The onset of the ε γ transformation during heating and cooling was found to differ depending on the alloy composition. In alloys without Cr addition the transformation was not completed on cooling and the high temperature γ phase was partly retained at room temperature in metastable state with the amount depending on the cooling rate from high temperature. The diffraction and microstructural results showed that Cr is ε stabilizer (similar as Re) but the role of Ta is not clear. The C/Ta ratio has no direct effect on the matrix phase transformation. Nevertheless, it influences indirectly by determining the amount of Ta which is freely available in the matrix.
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David Canelo‑Yubero,Radim Kocich,Charles Hervoches,Pavel Strunz,Lenka Kunčická,Ludmila Krátká 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.4
Residual stresses were studied in tungsten heavy alloy bars produced by powder metallurgy and deformed by rotary swagingat room temperature (RT) and at 900 °C. Neutron diffraction technique was used to scan the residual stresses acrossthe bars. Both tungsten particles and NiCo2W solid solution matrix were analysed. Maximum axial stresses of ~ 300 MPaand ~ 200 MPa were observed for the tungsten phase at the centre in the RT and in the high-temperature deformed samples,respectively. Compressive residual axial stresses were found close to the sample surface, showing that rotary swaging is asuitable deformation method for tungsten heavy alloys to provide an appropriate surface modification for its use in metallicparts undergoing, e.g., fatigue. Residual stresses developed in the NiCo2W-phase are larger than those found in the tungstenparticles although with a secondary role in the overall equilibrium conditions due to its lower strength and smaller volumefraction. Total stresses for each phase were separated into macro- and microstresses. Macrostresses can be mainly influencedby the incompatibility of the elliptical cross-section of the sintered sample with the head of the rotary machine while microstressesare mainly developed by the elastic mismatch between the constituent phases.
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