On the Optimization of the Microstructural and Mechanical Properties of Model Ni-Based Superalloys Through the Alloying Effects of Refractory Mo and W Elements


Eriş R. , Akdeniz M. V. , Mekhrabov A.

METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, vol.53, no.5, pp.1859-1872, 2022 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 53 Issue: 5
  • Publication Date: 2022
  • Doi Number: 10.1007/s11661-022-06642-0
  • Title of Journal : METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
  • Page Numbers: pp.1859-1872

Abstract

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 gamma and gamma ' phases. Therefore, in this study, the potential contributions of X = Mo or W atoms to the electronic properties of coherent gamma/gamma ' interfaces as well as their effects on size, volume fraction, and shape features of gamma ' 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 gamma ' 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 gamma and gamma ' phases. Furthermore, the better bonding stability effect of slow-diffusing X = W atoms in gamma matrix and at gamma/gamma ' interface would lead to a remarkable delay on precipitate coarsening. In gamma ' 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 gamma matrix. The shape of gamma ' precipitates, which itself is not considered as a primary parameter for the mechanical strength, appears to govern the degree of strength worsening upon gamma ' coarsening, i.e., while regular-shaped (e.g., cubic) gamma '-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) gamma ' intermetallics would accelerate the strength losses.