CIFICEN   24414
CENTRO DE INVESTIGACIONES EN FISICA E INGENIERIA DEL CENTRO DE LA PROVINCIA DE BUENOS AIRES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The joint use of PAS and Monte Carlo kinetic simulations to describe the vacancy-assisted solute transport mechanism associated with the first stage of precipitation hardening in Al-Cu-based alloys
Autor/es:
C. MACCHI; M. A. O QUIROGA; A. SOMOZA
Lugar:
Helsinki
Reunión:
Conferencia; 19th International Conference on Positron Annihilation; 2022
Institución organizadora:
ICPA
Resumen:
In this plenary talk, results obtained using PAS joined with kinetic Monte Carlo (kMC)simulations to study the fundamental mechanisms responsible for the solute-vacancyinteraction and solute atoms diffusion mediated by vacancies during the first stages of theprecipitation kinetics at room temperature in the ternary Al-1.74Cu-0.35Mg (in at.%) age-hardenable alloy are presented. Here, I only present a particular case of a larger experimentalinvestigation carried out in our Laboratory during the last 25 years on the vacancy-assistedmechanisms involved in the precipitation hardening process of different Al-Cu(-Mg,-Ag)alloys prepared by PALS and CDBS, complemented with results obtained through differentconventional experimental techniques (Vickers hardness, TEM, HREM and/or mechanicalproperties). We have focused our investigations on the study of Al-based alloys aged forvariable times at moderate temperatures (RTTaging343 K), low enough to avoid the formationof more stable nanostructures, or at higher temperatures (373 K<Taging< 473 K) in which as theartificial aging times increase, a progressive structural evolution of the alloys corresponding tothe different stages of the precipitation kinetics is induced From the experimental PAS resultsobtained on the prepared Al-Cu(-Mg,-Ag) alloys, it was possible to conclude that quenched-invacancies not only act as a carrier of solute atoms, but they are also responsible for theformation and growth of solute clusters. Furthermore, specific information on the vacancy-typedefects and, through them, on their chemical environments of the species of atoms belongingto the alloy studied was reported. However, after PAS analysis, there was still an open questionto be responding on how vacancies assist to the solute cluster formations during the very earlystages of the precipitation kinetics. We were recently able to give a satisfactory response to thisquestion with the results obtained by kMC simulations. To exhaustively describe the soluteatom transport assisted by a single vacancy in the crystal lattice, kMC simulations were carriedout using an ad-hoc developed code. One of the key points that allowed us to associateexperimental data with the calculated ones was to establish a relationship that would correlatethe MC steps with the physical times that each atom species belonging to the alloys studied(Al, Cu or Mg atoms, in our case) spends in contact with the vacancy. The kMC results obtainedfor the Al-1.74Cu-0.35Mg (in at.%) at two different temperatures (293 K and 342 K) indicatethat the vacancy remain bonded to Cu and/or Mg atoms forming solute-vacancy clusters. Wealso found that when aging proceeds, solute atoms transported by the vacancy progressivelyform Cu-Mg co-clusters containing different amounts of non-mixed Cu or Mg solute atoms.In summary, the PAS and kMC results presented for Al-1.74Cu-0.35Mg (in % at.) aged at asingle temperature (RT) are representative enough to show the full capability of this novelapproach to study the most important vacancy-assisted mechanisms operating during theprecipitation hardening process. These results made it possible to comprehend that the vacancynot only acts as a carrier of solute atoms, but it is also responsible for the formation of Cuand/or Mg solute clusters and Cu-Mg solute co-clusters, fulfilling the vacancy pump model.