Atomic size effect of alloying elements on the formation, evolution and strengthening of gamma'-Ni3Al precipitates in Ni-based superalloys

2019-06-01
Mechanical properties of Ni-based superalloys strongly depend on phase and site preferences of alloying elements which influence bonding strength within gamma'-Ni3Al precipitates and microstructural characteristics of these unique class of materials. In the current work, therefore, besides disclosure of the phase partitioning behaviours of alloying X elements (i.e. X = Co, Cr, Nb, Ta or Ti) among gamma' and gamma phases, their site occupancy tendencies in gamma' precipitates (determined via first-principles ab initio calculations at 0 K) and effects on the microstructural evolution of Ni80Al15X5 alloy systems (exposed to aging at 800 degrees C for 4, 16, 64 and 256 h, respectively) have been examined. Bonding features of Ni-Al, Ni-X and Al-X atomic pairs within Ni3Al-X intermetallics have been simulated by utilizing charge density difference (CDD) method, which reveals site preferences of alloying X elements as well. Present theoretical and experimental investigations have shown that mechanical strength of Nibased superalloys is predominantly affected by bonding properties within precipitates. As atomic radii of alloying X elements become closer to that of Al atom, energy change parameter, E-Ni -> Al(X) values decrease and more Al sublattice sites are preferentially occupied in gamma' precipitates. Correspondingly, bonding strength of Ni-X atomic pairs along < 110 > directions of Ni3Al-X phases and micro-hardness properties of both as-cast and pre aged Ni80Al15X5 alloy systems enhance in the order of X = Co < Cr < Ti < Nb < Ta additions. Nevertheless, with increasing aging time, mechanical strength of alloys weakens in parallel with increasing size of gamma' precipitates simultaneously evolved from near-spherical to irregular forms.

Suggestions

Magnetic monitoring approach to kinetics of phase transformations in multicomponent alloy systems
Duman, Nagehan; Mekhrabov, O. Mekhrabov; Akdeniz, Mahmut Vedat; Department of Metallurgical and Materials Engineering (2012)
It is of great importance for a materials scientist both from fundamental and applicability aspects to have better understanding of solid-state phase transformations and its kinetics responsible for micro-/nano-structure development in alloys and corresponding physical and mechanical properties. Transformation kinetics can be analyzed by various experimental techniques such as thermal analysis, laborious electron microscopy combined with extensive image analysis or by measuring changes in electrical resisti...
Molecular dynamics study of random and ordered metals and metal alloys
Kart, Hasan Hüseyin; Tomak, Mehmet; Department of Physics (2004)
The solid, liquid, and solidification properties of Pd, Ag pure metals and especially PdxAg1-x alloys are studied by using the molecular dynamics simulation. The effects of temperature and concentration on the physical properties of PdxÞAg1-x are analyzed. Sutton-Chen (SC) and Quantum Sutton-Chen (Q-SC) many-body potentials are used as interatomic interactions which enable one to investigate the thermodynamic, static, and dynamical properties of transition metals. The simulation results such as cohesive ene...
Design and development of high temperature nickel-based superalloys
Eriş, Rasim; Akdeniz, Mahmut Vedat; Mekhrabov, Amdulla O.; Department of Metallurgical and Materials Engineering (2017)
Remarkable high temperature mechanical properties of nickel-based superalloys are related with the arrangement of ternary alloying elements in L12-type ordered γ'-Ni3Al intermetallics. Therefore, in this thesis, high temperature site occupancy preference and energetic-structural characteristics of atomic short range ordering of ternary alloying X elements (X = Co, Cr, Hf, Mo, Nb, Pt, Re, Ru, Ta and W, respectively) in Ni75Al21.875X3.125 alloy systems have been studied by combining the statistico-thermodynam...
Electronic properties of transition metal oxides
Mete, Ersen; Ellialtıoğlu, Süleyman Şinasi; Department of Physics (2003)
Transition metal oxides constitute a large class of materials with variety of very interesting properties and important technological utility. A subset with perovskite structure has been the subject matter of the current theoretical investigation with an emphasis on their electronic and structural behavior. An analytical and a computational method are used to calculate physical entities like lattice parameters, bulk moduli, band structures, density of electronic states and charge density distributions for v...
Flame retardancy of polymer nanocomposites
Işıtman, Nihat Ali; Kaynak, Cevdet; Department of Metallurgical and Materials Engineering (2012)
This thesis is aimed to understand the role of nanofiller type, nanofiller dispersion, nanofiller geometry, and, presence of reinforcing fibers in flame retardancy of polymer nanocomposites. For this purpose, montmorillonite nanoclays, multi-walled carbon nanotubes, halloysite clay nanotubes and silica nanoparticles were used as nanofillers in polymeric matrices of poly (methyl methacrylate) (PMMA), high-impact polystyrene (HIPS), polylactide (PLA) and polyamide-6 (PA6) containing certain conventional flame...
Citation Formats
R. Eriş, M. V. Akdeniz, and A. Mehrabov, “Atomic size effect of alloying elements on the formation, evolution and strengthening of gamma’-Ni3Al precipitates in Ni-based superalloys,” INTERMETALLICS, pp. 37–47, 2019, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/33117.