Papers by Keyword: Two-Phase Alloy

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Authors: Hye Youn Lee, Masahiko Demura, Y. Xu, Dang Moon Wee, Toshiyuki Hirano
Abstract: Evolution of surface morphology in Ni(γ)/Ni3Al(γ´) two-phase foil of binary Ni-18 at.%Al was examined during the electrochemically selective etching in the electrolyte of distilled water including 1 wt.% (NH4)2SO4 and 1 wt.% citric acid. In the early stage (0.5 h), only the γ matrix was etched and the outmost γ´ particles were protected by a preexisting surface product. As the γ matrix was etched more, the side surfaces of the outmost γ´ particles and the γ´ particles that were located inside were exposed in the electrolyte. They were dissolved, and had a high density of fine dimples. However, the dissolution rate of the γ´ particles was slower than that of the γ matrix and thus the selective etching was retained in this stage. Finally, at 5h, more γ´ particles were exposed and the flat and smooth surfaces of the outmost γ´ particles were completely eliminated by the dissolution on the side surfaces. From these observations plus the saturation of the current density observed in the electrochemical test, we concluded that the change in the surface morphology was finished at this stage. Thus, the surface became more rough and irregular, which resulted from the original two-phase microstructure and the fine dimple structure by transpassivation.
Authors: Marcelo de Castro-Rebello, Jorge Alberto Soares Tenório, Stephan Wolynec
Authors: Jacques Stolarz
Abstract: Low cycle fatigue of porosity free Al-Si alloys containing between 11 and 18 wt.% Si and produced through directed solidification has been investigated. All alloys contain acicular Al-Si eutectic as the principal element of microstructure, completed by different amounts of primary (Al) and (Si) phases. Crack initiation and propagation modes have been determined for all alloys: crack initiation is always associated with brittle Si particles while propagation takes place across layers of the ductile aluminium which act as effective microstructural barriers. A simple energetic model allows a semi-quantitative interpretation of experimental results concerning damage evolution at the surface: single or multiple cracking. LCF data are analysed both on the basis of Coffin-Manson relation and taking into account the effect of the maximal stress on the fatigue life. The second approach gives a coherent and complete interpretation of experimental results in all investigated materials. The fatigue life of two phase Al-Si model alloys is determined by a combination of the macroscopic response of alloys to cyclic straining which depends on the overall microstructure, including phases which do not participate directly in fatigue, and of local parameters which act at the level of short crack propagation. Since the damage mechanisms at the microstructure size scale are the same in all investigated alloys, the parameter which really determines the fatigue life is the maximal stress. Concerning the effect of microstructure, it is emphasized that it is necessary to take into account both extreme and average values of parameters associated with microstructure elements which effectively play a role in fatigue. Finally, it is shown that the conclusions of the present work can be easily generalised to the fatigue of various single and two phase materials, the unifying element being the physical nature and the resistance of microstructural barriers to the propagation of short cracks.
Authors: Rafael Schouwenaars, H. A. Cortéz, V. H. Jacobo, A. Ortiz
Abstract: The effects of strain, annealing time and temperature during the processing of an Al-Sn-based triboalloy were researched by response surface analysis. A second-degree polynomial in strain-time-temperature space was compared to a formulation based on generally accepted physical models for recrystallisation, recovery and grain growth, using the rule of mixtures for a microstructure consisting of recovered, recrystallised and second-phase grains. The polynomial approach provides interesting information on the role of rolling reduction in the optimisation of the alloy. The mechanism-based approach yields higher precision with less fitting parameters and provides insight into the relative importance of the physical phenomena involved in the processing of an alloy which has rarely been studied from the viewpoint of physical metallurgy.
Authors: Masahiko Demura, Ya Xu, Toshiyuki Hirano
Abstract: Texture evolution during recrystallization and grain growth was examined for a Ni3Al/Ni two-phase single crystal (binary Ni-18 at.% Al) 83% cold-rolled, then compared with that for a Ni3Al single-phase single crystal (Ni-24 at.% Al). The cold-rolled single crystal had a sharp {110}<001> (Goss) texture. When it was recrystallized at 873K, the texture changed into a complicated one consisting of several components. Most of them had a special rotation relationship to the original Goss texture, i.e. 40˚ about <111>, which special relationship was similarly observed in the single-phase case. The 40˚<111> texture became shaper with no quantitative change as the grain growth proceeded. This high stability of the recrystallized texture contrasted with the single-phase case in which the authors previously found that the texture returned to the original Goss texture. The difference was discussed based on the orientation analysis by an electron backscattered diffraction method.
Authors: Hirotake Honda, R. Matubara, N. Ashie, K. Nakamura, Sei Miura
Authors: Yan Niu, Anne Marie Huntz, F. Gesmundo, P. Castello
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