Time-resolved X-ray absorption spectroscopy on Al–Cu alloys – from solute copper to stable precipitates

Abstract

Although binary aluminium alloys seem to be uninteresting and well known, some aspects of their precipitation sequence -especially the early stages immediately after quenching -are still not well understood. Since the Al-Cu system is the basis for many ternary and quaternary high-strength alloys with application in the aviation sector, it is important to understand this binary system in detail. This problem is here tackled by a unique combination of differential scanning calorimetry and X-ray absorption fine structure measurements, where relaxed atomic coordinates for simulation of the spectra have been obtained by ab initio calculations. Thereby, it is possible to attribute any exo-or endothermal peak to a certain type of precipitate, even though formation and dissolution regions have a large overlap in this system. This unique combination of experimental and numerical methods allows one to determine the local atomic environment around Cu atoms, thus following the formation and growth of Guinier-Preston zones, i.e. Cu platelets on {100} planes, during the precipitation process. research papers 1340 Danny Petschke et al. Time-resolved XAFS on Al-Cu alloys

A new perspective on the precipitation sequence in a high-purity Al-1.74 at.% Cu alloy by employing positron annihilation spectroscopy: experiment and theory

“…τ 2 reaches a value of 164 ps in the temperature range 190-220 • C. Although this lifetime (164 ps) is very close to the bulk value (158 ps), the decomposition is highly reliable and τ 1 is always less than the bulk lifetime. The average positron lifetime is nearly constant in this temperature range and reaches a minimum at 200 • C. This is in good agreement with Petschke et al [72] who claim that a temperature treatment at 200 • C between 2 h and 1 d produces exclusively GP-II zones (Θ -precipitates). Since τ 2 has rapidly decreased and reaches a value of 164 ps in the temperature range 190-220 • C, this can only be interpreted in such a way that the formation of GP-II zones (Θ -phase), which are coherent with the matrix, has led to an elimination of vacancies.…”

Revisiting the crystal structure of the equilibrium S (Al2CuMg) phase in Al–Cu–Mg alloys using X-ray absorption spectroscopy (XAFS)

“…As shown by Baur & Gerold, a considerable amount of isolated Cu remains in solid solution during the formation and growth of Guiner-Preston (GP) zones in Al-Cu alloys and strongly depends on the aging temperature and Cu concentration [41]. Hence, we assume that the experimental curve, especially in the near edge region (8980-9010eV) might be rather reflected by a superposition of solute Cu atoms with the refined structures based on the model proposed by Perlitz & Westgren (see also [35]). The experimental curve could as well be matched by a superposition or distribution of various lattice parameters and/or atomic positions, where those given by Heying et al and Styles et al represent potential mean values.…”

“…The XAFS measurements were carried out on the ID24-L beamline at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, which is designed for timeresolved purposes on the millisecond scale. The spectra were recorded at the Cu-K edge (8979eV [34]) under the same conditions as described by the authors in a previous study [35].…”

Exploring the hidden world of solute atoms, clusters and vacancies in aluminium alloys

“…Column 'Vac' specifies sensitivity to (mono)vacancies, 'In-situ' whether phenomena can be followed in the same sample during ageing, 'Examples' provides some references for Al-Mg-Si alloys. (TEM) no no [25,26] X-ray absorption spectroscopy has been applied to NA in alloys such as Al-Cu [27], while for Al-Mg-Si alloys only AA has been investigated [16].…”