Intrinsic defects induced structural transitions and the improvement of cohesive properties at Ni3Al grain boundaries: A first-principles study

It is known that grain boundaries play a vital role in the mechanical properties of materials. Most investigations focus on the effect of the GBs with alloying elements on the cohesive properties of alloys. However, one seldom pays attention to the GBs with intrinsic defects and the interaction between them. In this work, using the first-principles method, we have studied the formation tendency of vacancies, anti-site and self-interstitial atoms (SIAs) at the Ni 3 Al GBs and their effect on the GB structure and properties. It is found that it is easier for Ni vacancy and Al anti-site defects to appear at the GBs than in the bulk. Vacancies tend to form near the GB plane, not in the GB plane. SIA defects can form easily in pure Ni layers and prefer to stay the interstitials in the GB hole to form more Ni–Al bonds due to stronger Ni–Al interaction. Vacancies can induce the structural transitions of the GBs. This transition changes the disorder degree of GB structures. It is found that SIA defects have almost no strengthening effect on the GBs. The strengthening effect of anti-site defects is related to the types of GBs. Ni Al anti-site defects can strengthen the GBs, but Al Ni anti-site defects only strengthen high energy GBs such as Σ5(210) GBs. Our investigations show clear evidence to change GB structures and their properties via intrinsic defects. • Compared to bulk Ni 3 Al, Ni vacancies and Al Ni anti-site defects are more likely to form at Ni 3 Al GBs. This is determined by the sparsity of the GBs and the difference in atomic radii. • Both Ni and Al Self interstitial atom defects preferentially form more heterogeneous Ni–Al bonds, rather than homogeneous Ni–Ni and Al–Al bonds at the GBs. • Vacancy defects can induce structural transitions of the GBs. This transition increases the disorder of the GB structure. • Self interstitial atom defects have almost no strengthening effect on the GBs. Ni Al anti-site defects can strengthen the GBs, but Al Ni anti-site defects can only enhance cohesive properties of Σ5(210) GBs.