Solute Segregation to Grain Boundaries in Al: A First-Principles Evaluation

Solute-induced grain boundary (GB) strengthening is effective in improving the toughness and tensile strength of polycrystalline alloys. In this work, GB segregation behaviors of solute elements in Al alloys and their potential effects on GB binding have been systematically investigated from first-principles energetics. The low-energy sigma 3(111) and sigma 11(113) are immune to vacancy segregation, while high-energy Al GBs, such as sigma 13(320), sigma 9(221), sigma 5(210), and sigma 5(310), can attract both vacancies and solutes. Under-sized elements (Ni, Fe, Co, Cu) and similar-sized elements (Si, Zn, Ag, and Ti) prefer interstitial or vacancy sites at the GB interface, while over-sized elements (Mg, Zr, Sc, Er) tend to substitute Al or vacancy-neighboring sites at the GB interface. Segregated vacancies weaken GBs. Under-sized Ni, Co, Cu, similar-sized Ti, and over-sized Zr, Er, can directly enhance Al GBs, while similar-sized Ag and over-sized Mg reduce the GB binding strength. Solute strengthening or weakening effects tend to be always mitigated, more or less, by GB-segregated vacancies.