Akademik Məlumat İdarəetmə Sistemi
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, vol.53, no.5, pp.1859-1872, 2022 (SCI-Expanded, Scopus)
In the design and development of next-generation Ni-based superalloys, the addition of refractory impurity elements not only induces better degree of bonding strengthening, but also helps in maintaining structural stability of the constituent γ and γ′ phases. Therefore, in this study, the potential contributions of X = Mo or W atoms to the electronic properties of coherent γ/γ′ interfaces as well as their effects on size, volume fraction, and shape features of γ′ intermetallics in model Ni80Al15X5 alloys are extensively examined. Accordingly, it is argued that bigger atomic size X = W impurities, which are more prone to occupy Al sites of γ′ phase, would further increase the precipitate volume fraction. Correspondingly, a greater amount of directional (i.e., covalent-like) bondings formed via p–d and d–d type hybridizations would enhance the mechanical strength of ternary Ni–Al–W superalloys a bit more, although X = Mo atoms seem to cause relatively strong bonding interactions within both γ and γ′ phases. Furthermore, the better bonding stability effect of slow-diffusing X = W atoms in γ matrix and at γ/γ′ interface would lead to a remarkable delay on precipitate coarsening. In γ′ intermetallics, the ability of X = W atoms to create much stronger and stable bondings with Al atoms compared to Al–Al pairs would prevent the dissolution of this vital phase at longer aging durations by hindering Al diffusion toward γ matrix. The shape of γ′ precipitates, which itself is not considered as a primary parameter for the mechanical strength, appears to govern the degree of strength worsening upon γ′ coarsening, i.e., while regular-shaped (e.g., cubic) γ′-Ni3Al-Mo(W) precipitates can prohibit extreme strength degradations, alternative transition X impurity additions (i.e., X = Co, Ti, Nb, or Ta) causing irregular-shaped (e.g., elongated or agglomerated) γ′ intermetallics would accelerate the strength losses.