Design and development of high temperature nickel-based superalloys

Eriş, Rasim
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-thermodynamical theory of ordering and electronic theory of alloys in the pseudopotential approximation. Simulations have shown that, all ternary alloying element atoms (except Pt) tend to occupy Al sublattice sites of Ni3Al intermetallics, whereas Pt atoms prefer to substitute for Ni sublattice sites. However, in contrast to other X elements, sublattice site occupancy characteristics of Re atoms seem to be both composition and temperature dependent. Distribution of Re atoms at both Al and Ni sublattice sites above critical temperatures, Tc, may lead to localized supersaturation of the parent Ni3Al phase and makes possible formation of topologically close-packed (TCP) phases. In order to validate these results, site occupancy tendencies of afore mentioned alloying X elements have also been determined by performing first-principles ab initio calculations at 0 Kelvin and similar results have been obtained. Furthermore, by making use of charge density difference (CDD), electron localization function (ELF) and density of states (DOS) methods, the effects of alloying X elements on the bonding nature of Ni3Al-X phases have been simulated. Superior mechanical properties of nickel-based superalloys strongly depend on microstructural characteristics of these materials (i.e. γ' volume fraction, size & size distribution, orientation and shape). For this purpose, Ni80Al15X5 alloy systems (X = Al, Co, Cr, Hf, Mo, Nb, Ta, Ti and W, respectively) have been produced and characterized by various techniques. In the light of all theoretical and experimental data, it has been concluded that better micro-hardness properties of nickel-based superalloys can be obtained by appropriate alloying element additions and heat treatment procedures which lead to γ' precipitates having higher lattice parameter, higher volume fraction, smaller size and correspondingly optimum δ parameter.  


Design and development of iron aluminium intermetallic compounds for structural applications at high temperatures
Yıldırım, Mehmet; Akdeniz, Mahmut Vedat; Mekhrabov, Amdulla O.; Department of Metallurgical and Materials Engineering (2014)
Fe-Al based intermetallic compounds are considered as suitable candidates for structural applications at high temperatures due to their outstanding oxidation and corrosion resistance, good intermediate temperature strength, low density, low cost and relatively high melting point. These outstanding physical and mechanical properties are mainly attributed to their long-range ordered superlattices, deviation from stochiometry and ternary alloying additions. However, poor ductility at ambient temperatures signi...
Investigation of microstructure inhomogeneity in SiCp-reinforced aluminum matrix composites
Gacsi, Zoltan; Gür, Cemil Hakan; Makszimus, Andrea; Pieczonka, Tadeusz (2007-01-01)
The type, volume fraction, size, shape and arrangement of embedded particles influence the mechanical properties of the particle reinforced metal matrix composites. This presents the investigation of the SiC particle and porosity distributions in various aluminum matrix composites produced by cold- and hot-pressing. The inicrostructures were characterized by optical microscopy and stereological parameters. SiC and porosity volume fractions, and the anisotropy distribution function were measured to establish...
Numerical investigation of coupled heat and mass transfer inside the adsorbent bed of an adsorption cooling unit
Solmus, Ismail; Rees, D. Andrew S.; Yamali, Cemil; Baker, Derek Keıth; KAFTANOĞLU, BİLGİN (2012-05-01)
In this study, the influence of several design parameters on the transient distributions of temperature, pressure and amount adsorbed in the radial direction of a cylindrical adsorbent bed of an adsorption cooling unit using silica gel/water have been investigated numerically. For this purpose, a transient one-dimensional local thermal non-equilibrium model that accounts for both internal and external mass transfer resistances has been developed using the local volume averaging method. For the conditions in...
Selçuk, Nevin (1988-05-01)
Exact expressions for the distributions of the components of radiative flux density and the radiative energy source term in terms of wall and medium temperature distributions have been formulated for an emitting absorbing medium of constant properties bounded by black walls of a cylindrical enclosure. The accuracy of numerical solutions has been tested on an idealized enclosure for which exact analytical solution of the expressions is possible and shown to have six‐figure accuracy. The exact expressions hav...
Investigation of structural, electronic, magnetic and lattice dynamical properties for XCoBi (X: Ti, Zr, Hf) Half-Heusler compounds
Surucu, Gokhan; IŞIK, MEHMET; CANDAN, ABDULLAH; Wang, Xiaotian; Güllü, Hasan Hüseyin (Elsevier BV, 2020-06-15)
Structural, electronic, magnetic, mechanical and lattice dynamical properties of XCoBi (X: Ti, Zr, Hf) Half-Heusler compounds have been investigated according to density functional theory and generalized gradient approximation. Among alpha, beta and gamma structural phases, gamma-phase structure has been found as the most stability characteristics depending on the calculated formation enthalpies, energy-volume dependencies and Cauchy pressures. Energy-volume plots of possible magnetic orders of gamma-phase ...
Citation Formats
R. Eriş, “Design and development of high temperature nickel-based superalloys,” M.S. - Master of Science, Middle East Technical University, 2017.