Toward a better understanding of the enhancing/embrittling effects of impurities in Nickel grain boundaries

Abstract

The fracture path follows grain boundaries (GB) in most metallic system under tensile test. In general, impurities, even in ppm concentration, that segregate to these boundaries can remarkably change materials mechanical properties. Predicting impurities segregation effects in Nickel super-alloys might not be seen as intuitive and perhaps more fundamental understanding is needed. We performed a density functional theory calculation to elucidate the effect of eight light elements (B, C, N, O, Al, Si, P and S) and twelve transition metal elements (Tc, Ti, V, Cr, Mn, Zr, Nb, Mo, Hf, Ta, W, Re) on Nickel ∑5(210) grain boundary formation and its Ni free surface. The effect of impurities was carefully examined by calculating different properties such as segregation, binding and cohesive energies, strengthening/embrittling potency and the theoretical tensile strength. Additionally, we employed the electron density differences and magnetic effects to explain why and how impurities such as B, S, V, Nb, Mn and W affect Nickel ∑5 GB. We used the generated data calculated on equal footing, to develop a fundamental understanding on impurity effect. A clear and strong correlation is found between difference in magnetic moment change between isolated and imbedded impurity atom on one hand and the tensile strength on the other hand. The higher the loss of the magnetic moment, the more the impurity consolidates the GB.

Solute-point defect interactions, coupled diffusion, and radiation-induced segregation in fcc nickel

“…P is known to embrittle austenitic alloys [19], but its embrittling effect on Ni is debated [17,18,20,21]. Studies regarding the behaviour of Ti in Ni alloys are scarcer; however, Ti depletion following irradiation has been observed [22], and solute-induced enhancement of theoretical strength has been reported [23]. Mn is present in all austenitic steels, as well as in Ni-based superalloys, and is also a common ingredient in fcc HEAs.…”

The Effect of Vacancies on Grain Boundary Segregation in Ferromagnetic fcc Ni

“…The calculations in Reference [2] were performed using the same exchange-correlation energy but a smaller cell with a higher concentration of impurities at the GB (impurity monolayer). In reference [8] norm-conserving pseudopotentials and local density approximation for the exchange-correlation potentials were employed. The method used in Reference [50] is based on the full-potential linearized augmented plane wave method with the generalized gradient approximation of PBE96 parametrization [29] and, again, a smaller cell with even higher concentration of impurities than in [2] (impurity monolayer at GB) is applied.…”

“…These issues have far-reaching practical implications manifested in the mechanical and magnetic properties. As an example, let us mention the strengthening/embrittling energy of segregated sp-elements from the 3rd, 4th and 5th period at the Σ5(210) grain boundary in ferromagnetic fcc nickel and cobalt [2][3][4][5][6][7][8]. Similar topics are also studied experimentally when, for example, the diffusion and segregation of silver in copper Σ5(310) grain boundary were investigated [9] or the influence of boron (segregated at the GB) on fracture resistance of Ni 3 Al [10] was analyzed.…”

Modeling the Effects of Varying the Ti Concentration on the Mechanical Properties of Cu–Ti Alloys

“…A detailed understanding of the atomistic mechanisms that improve the strength of Cu through the addition of small amounts of Ti can be achieved by using theoretical and computational modeling. Kohn–Sham , density functional theory (DFT) and other quantum mechanics-based calculation methods that provide highly accurate electronic structure measurements for alloys. , Several theoretical studies highlight the strengthening effect of metallic solutes when they are introduced into the grain boundaries (GBs) of metals, such as Cu, Ni, V, and Au . These calculations are limited to systems with only ∼100 atoms due to their computational cost .…”

“…Kohn–Sham 11 , 12 density functional theory (DFT) and other quantum mechanics-based calculation methods that provide highly accurate electronic structure measurements for alloys. 13 , 14 Several theoretical studies highlight the strengthening effect of metallic solutes when they are introduced into the grain boundaries (GBs) of metals, such as Cu, 15 Ni, 16 V, 17 and Au. 18 These calculations are limited to systems with only ∼100 atoms due to their computational cost.…”