•Al3Y precipitated firstly and then became nuclei for Al3Zr during aging of Al-Zr-Y.•Al3(Zr,Y) precipitates do not have the typical “Al3Y core-Al3Zr shell” structure.•Strong binding between Y and Zr led to the co-precipitation of Y and Zr atoms.Structural and compositional evolution of Al3(Zr,Y) precipitates in aged Al-Zr-Y alloy was investigated through atom probe tomography (APT) and transmission electron microscope (TEM) analysis and first principles calculations. The results show that short-bar-shaped D019-Al3Y with some Zr atoms dissolved in precipitated at the very beginning of decomposition and worked as heterogeneous nuclei for L12-Al3Zr with spherical morphology after being aged at 400 °C for 2 h. Quasi-static coarsening happened as the aging treatment lasted from 2 h to 200 h. However, distribution of Zr and Y atoms in Al3(Zr,Y) is nearly uniform and Al3(Zr,Y) do not have the typical “Al3RE core-Al3Zr shell” structure which observed in other RE containing Al-Zr-RE alloys with L12-Al3RE as nuclei. First principles calculations revealed that binding energy between Y and Zr is strong during the growth of Al3(Zr,Y), which led to the co-precipitation of Y and Zr atoms and attribute to the evolution of Al3(Zr,Y).

•Fe diffusion in Cu systems effect by allay elements have been computed.•The five frequency model was employed to determine impurity diffusion coefficients.•The eight frequency model was employed to investigate the Fe diffusivities.Iron diffusion in face-centered cubic (fcc) copper affected by a third element have been computed from first principles using density-functional theory (DFT). The five frequency model was employed to determine impurity diffusion coefficients through atomistic structure calculations. The self-diffusion coefficient of Cu and impurity diffusion coefficients in Cu agreed well with experimental measurements available. Specifically, an eight frequency model was built based on the five frequency model to investigate the changes in Fe diffusivities, both the diffusion pre-factor D0 and the activation energy after adding the third element were calculated. The results showed that 9 potential elements may accelerate significantly iron diffusion in copper.

•Solute–vacancy binding is a key quantity in understanding diffusion kinetics.•A large database of solute–vacancy binding energies in Cu from first-principles calculations based on density functional theory was presented in the paper.•The trends in the binding energies in terms of super cell size, solutes size and magnetic moments were analyzed.Solute–vacancy binding is a key quantity in understanding diffusion kinetics, and may also have a considerable impact on the hardening response in Cu alloys. However, the binding energies between solute atoms and vacancies in Cu are largely unknown and difficult to measure accurately. A large database of solute–vacancy binding energies in Cu from first-principles calculations based on density functional theory was presented in the paper. The trends in the binding energies in terms of super cell size, solutes size and magnetic moments are analyzed. The calculated binding energies agree well with experimental measurements available.

•The effect of Ag addition on the diffusion mechanisms of aging precipitation processed Cu–Fe alloys was investigated.•Activation energy for diffusion calculations revealed that Ag atom significantly reduced the diffusion barrier and diffusion activation energy of Fe.•The calculation gives way to find other suitable alloying elements for preparation of high strength and high conductivity Cu–Fe alloys.The effect of Ag addition on the diffusion mechanisms of aging precipitation processed Cu–Fe alloys were investigated by first-principles calculations. The calculation of solute–solute binding energies accurately revealed an attractive binding for the Fe–Fe at the first NN site, and Ag–Ag at the first NN site as well as the second NN site, however the Fe–Ag interactions are repulsive both at the first NN and the second NN distance. The investigation of binding energy between X and V (X represents Fe or Ag and V a vacancy) showed that vacancy is more likely to be in the proximity of the solute Ag atom, and the addition of Ag to dilute Cu–Fe system will increase the local vacancy concentration close to a Ag–Fe dimer. The calculated migration energy for an X–V exchange indicated that the Ag atom diffused more easily in Cu than Fe atom; and the addition of Ag decreased the energy of the transition state, thereby significantly reduced the migration energy of Fe. The results agree well with the available experimental observation. The calculation gives way to find other suitable alloying elements for preparation of high strength and high conductivity Cu–Fe alloys or in situ composites.

•Additions of Y obviously accelerate the precipitation kinetics of Al3Zr in Al–Zr–Y.•High density and small radius of Al3(Zr,Y) (L12) are obtained in Al–Zr–Y.•The coarsening rate of Al3(Zr,Y) is slower than that of Al3Zr at 500 °C.•Additions of Y increase the recrystallization temperature of Al–Zr alloys by 50 °C.The effects of Y on the precipitation evolution and recrystallization of Al–Zr alloys were investigated. The results show that the addition of Y obviously accelerates the precipitation kinetics of Al3Zr with L12 structure in Al–Zr–Y alloys. The number density of Al3(Zr,Y) precipitates is nearly one order of magnitude larger than that of Al3Zr. Smaller Al3(Zr,Y) precipitates near grain boundaries keep relatively high number density in Al–0.30Zr–0.08Y, whereas Al3Zr precipitates show decreased number density and larger radius towards the grain boundaries in Al–0.30Zr. Precipitate free regions adjacent to grain boundaries in Al–0.30Zr–0.08Y are much narrower than that in Al–0.30Zr. The Al3(Zr,Y) precipitates exhibit slower coarsening kinetics at 500 °C as compared with Al3Zr. The recrystallization temperature of Al–Zr–Y alloys is about 50 °C higher than that of Al–Zr alloys.

A novel in-situ synthesized Fe-Ti-N master alloy was employed as a grain refiner for refining of the 409L ferritic stainless steel solidification structure. Two groups of experiments have been carried out to test the grain refinement performance of the Fe-Ti-N master alloy. In one group, 2 wt% of the Fe-Ti-N master alloy has been added into 409L ferritic stainless steel melts with various temperatures just before casting. In the other group, 409L ferritic stainless steel melts with 2 wt% Fe-Ti-N master alloy added at 1803K were held for various times before casting. It was found that high melt temperature resulted in a lower proportion of equiaxed grains and coarser structures. As the holding time increased, the proportion of the equiaxed grain zone decreased quickly. However, the proportion of the equiaxed grain zone re-increased when the holding time was extended longer than extreme points. The mechanisms of these experimental phenomena have been analyzed in terms of thermodynamics.