Modelling precipitation hardening in an A356+0.5 wt%Cu cast aluminum alloy

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Solvent grain boundary diffusion in binary solid solutions : a new approach to evaluate solute grain boundary segregation

International audienceA new method to estimate solute grain boundary (GB) segregation from solvent GB diffusion measurements in binary solid solutions is proposed for the systems with restricted solubility and intermediate stoichiometric phases. The method is based on the model of complex formation: solvent atoms (A) interact with solute ones (B) at GB with the formation of AB chemical bond. A description of solvent GB diffusion is then given. Using such an approach, a new equation for the dependence of solvent GB diffusion coefficient on solute bulk concentration is derived for the systems with simple atomic attraction with AB complex formation in GB. Theoretical results predict non-linear dependence of solvent GB diffusion coefficient on solute bulk content, which is in agreement with earlier published experimental data regarding the ease of grain boundary diffusion in alloys of different chemical compositions. More importantly, the equation deduced permits to evaluate, on one hand, the characteristics of solute GB segregation from solvent GB diffusion measurements and, one the other hand, GB diffusion coefficient in pure solvent. Such a numerical data analysis for Fe–Sn system is in agreement with experimental results. In special cases, such an analysis can be done analytically

Experimental and thermodynamic analysis of differences in phase transformation of Pt-modified nickel aluminide coating during isothermal and cyclic oxidation

International audiencePhase transformation of Pt-modified nickel aluminide coating β-(Ni,Pt)Al into γ′ phase was studied during isothermal and cyclic oxidation at 1100 °C. The transformation occurred with homogeneous β and γ′ phases with chemical compositions depending on oxidation conditions. Cyclic oxidation led to a higher volume fraction of topologically close-packed (TCP) phases formed in the interdiffusion zone and the chemical composition of TCP phases was found to vary with oxidation conditions. This difference in TCP precipitation in the interdiffusion zone for isothermal and cyclic oxidation was suggested to be responsible for different β and γ′ compositions. The experimental observations were discussed using thermodynamic calculations by Thermo-Calc software, and some explanations were given

Atomic transport in B2-ordered Al(Fe,Ni) alloys: Tracer-interdiffusion couple approach

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Concentration-dependent atomic mobilities in FCC CoCrFeMnNi high-entropy alloys

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Precipitation-hardness map for Al–Cu–Mg alloy (AA2024-T3)

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Grain boundary diffusion of 59Fe in high-purity copper

International audienceGrain boundary diffusion of iron in high purity polycrystalline copper is measured using the radiotracer technique and applying the 59Fe isotope. At lower temperatures, K, the measurements are performed under Harrison's C-type kinetic regime and the grain boundary diffusion coefficient of Fe in Cu. Unconventional penetration profiles are measured for Fe grain boundary diffusion in Cu at higher temperatures ( 949 K) under the intended B-type kinetic regime, in fact formal C-type profiles are systematically observed instead. Molecular dynamics simulation with the literature Finnis-Sinclair type interatomic potentials [Ackland et al., Phil. Mag. A, 1997] discovered an unexpected response of Cu grain boundaries on a partial Fe coverage at temperatures above 900 K. A model of Fe penetration in polycrystalline Cu in such conditions is proposed, which explains the untypical shape of the penetration profiles. The combination of the B- and C-type grain boundary diffusion measurements predict a strong segregation of Fe in Cu with a low segregation enthalpy

Experimental evidence for anomalous grain boundary diffusion of Fe in Cu and Cu-Fe alloys

International audienceFe grain boundary diffusion is measured in 99.995 wt.% pure Cu and the Cu-Fe alloys with iron contents of 0.18, 0.45, 0.6 and 0.8 wt. % using the radiotracer technique and applying the 59Fe isotope. A series of isothermal experiments at 1000 K reveal that the triple product of iron grain boundary diffusion is almost independent on the iron content excepting the alloy containing 0.8 wt. % of Fe where the triple product is increased by three orders of magnitude. Additional experiments at 1100, 900 and 717 K using this alloy confirm the anomaly observed at 1000 K, namely the triple product is continuously increasing following the Arrhenius dependence from 717 to 1100 K except the temperature of 1000 K, where the triple product is anomalously high. The observed experimental results are explained by the analysis of thermodynamic equilibrium and solubility of Fe and S in Cu

Short- and long-term oxidation behaviour of an advanced Ti2AlNb alloy

International audienceThe oxidation behaviour of an advanced Ti2AlNb alloy was investigated over a temperature range of 650–800 °C in lab air for short- and long-term experiments. The mass gain increased with time and temperature and oxidation kinetics was parabolic at 650 and 700 °C for durations up to 1000 h, while the parabolic oxidation rate was changed at 800 °C between 500 and 1000 h. Long-term oxidation experiments revealed oxide scales composed of alternating TiO2 and AlNbO4 layers. Results showed an improvement of the oxidation behaviour of the present alloy as compared to other titanium base alloys, including Ti2AlNb alloys