Effect of different point-defect energetics in Ni80X20 (X = Fe, Pd) on contrasting vacancy cluster formation from atomistic simulations

Recent irradiation experiments have shown that smaller vacancy clusters are observed in Ni80Pd20 compared to Ni80Fe20. Using atomistic calculations, we find that the vacancy energetics are significantly different between the two alloys. Ni80Pd20 has lower vacancy migration barriers and lower vacancy-vacancy binding energies than Ni80Fe20. The consequence of these energetic differences is observed in molecular dynamics (MD) simulations, where despite higher vacancy diffusivity that would help in cluster formation, significantly reduced vacancy clusters are observed in Ni80Pd20 than Ni80Fe20. Calculations show that binding energy decreases and formation energy increases with increasing Ni-Ni bond lengths, and larger Ni-Ni bond lengths are observed in Ni80Pd20 than Ni80Fe20. Thus, the reduced vacancy vacancy binding and higher formation energy due to longer Ni-Ni bonds in Ni80Pd20 are possibly the underlying reasons for smaller vacancy clusters in Ni-80-Pd-20 than Ni80Fe20. This study illustrates the unique effects of alloying elements on defect energetics and microstructural evolution in random alloys.

Automated summary

Recent irradiation experiments have shown that smaller vacancy clusters are observed in Ni80Pd20 compared to Ni80Fe20. Atomistic calculations reveal that the vacancy energetics are significantly different between the two alloys, with Ni80Pd20 having lower vacancy migration barriers and lower vacancy-vacancy binding energies than Ni80Fe20. This leads to the observation of reduced vacancy clusters in Ni80Pd20 in molecular dynamics simulations, despite higher vacancy diffusivity, possibly due to longer Ni-Ni bond lengths and reduced vacancy vacancy binding energies in Ni80Pd20.