C. L. Fu

Bio: C. L. Fu is an academic researcher from Oak Ridge National Laboratory. The author has contributed to research in topics: Dislocation. The author has an hindex of 1, co-authored 1 publications receiving 180 citations.

Elastic constants, fault energies, and dislocation reactions in TiAl: A first-principles total-energy investigation

Abstract: First-principles total-energy calculations of the elastic constants and shear fault energies of TiAl are presented. We find a large elastic-shear anisotropy along the [011] direction, and high antiphase-boundary energies due to the strong cohesion between Ti and A1 layers as well as the formation of directional d bonds in the Ti layer. Shear faults of intrinsic type, extrinsic type and twin boundary type are predicted to be prevalent owing to their low energies. The anomalous temperature dependence of the flow stress is explained by the cross-slip-pinning and fault-dragging mechanisms. The intrinsic brittleness of TiAl is discussed in terms of these results.

Density functional theory for calculation of elastic properties of orthorhombic crystals: Application to TiSi2

Abstract: A theoretical formalism to calculate the single crystal elastic constants for orthorhombic crystals from first principle calculations is described. This is applied for TiSi2 and we calculate the elastic constants using a full potential linear muffin-tin orbital method using the local density approximation (LDA) and generalized gradient approximation (GGA). The calculated values compare favorably with recent experimental results. An expression to calculate the bulk modulus along crystallographic axes of single crystals, using elastic constants, has been derived. From this the calculated linear bulk moduli are found to be in good agreement with the experiments. The shear modulus, Young’s modulus, and Poisson’s ratio for ideal polycrystalline TiSi2 are also calculated and compared with corresponding experimental values. The directional bulk modulus and the Young’s modulus for single crystal TiSi2 are estimated from the elastic constants obtained from LDA as well as GGA calculations and are compared with the ...

Microstructure and deformation of two-phase γ-titanium aluminides

Abstract: During the past decade considerable research efforts have been directed towards achieving balanced engineering properties of two-phase γ-titanium aluminide alloys for future applications as structural materials. For optimization of mechanical properties such as yield and creep strengths, tensile ductility and fracture resistance, a basic understanding of the temperature dependent micromechanisms of plasticity and fracture, and their interplay with various microstructural constituents is required. In this review article, the current knowledge on dislocation types and slip systems, the development of deformation substructures, factors controlling the mobility and multiplication of dislocations, interface related plasticity, solid solution and precipitate strengthening mechanisms as well as microscopic aspects of creep and fracture will be addressed. These topics will be related to specific microstructures and associated engineering properties.

Interatomic potentials for atomistic simulations of the Ti-Al system

Abstract: Semiempirical interatomic potentials have been developed for Al, $\ensuremath{\alpha}\ensuremath{-}\mathrm{Ti},$ and $\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}$ within the embedded atom method (EAM) formalism by fitting to a large database of experimental as well as ab initio data. The ab initio calculations were performed by the linearized augmented plane wave (LAPW) method within the density functional theory to obtain the equations of state for a number of crystal structures of the Ti-Al system. Some of the calculated LAPW energies were used for fitting the potentials while others for examining their quality. The potentials correctly predict the equilibrium crystal structures of the phases and accurately reproduce their basic lattice properties. The potentials are applied to calculate the energies of point defects, surfaces, and planar faults in the equilibrium structures. Unlike earlier EAM potentials for the Ti-Al system, the proposed potentials provide a reasonable description of the lattice thermal expansion, demonstrating their usefulness for molecular-dynamics and Monte Carlo simulations at high temperatures. The energy along the tetragonal deformation path (Bain transformation) in $\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}$ calculated with the EAM potential is in fairly good agreement with LAPW calculations. Equilibrium point defect concentrations in $\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}$ are studied using the EAM potential. It is found that antisite defects strongly dominate over vacancies at all compositions around stoichiometry, indicating that $\ensuremath{\gamma}\ensuremath{-}\mathrm{TiAl}$ is an antisite disorder compound, in agreement with experimental data.

Room-temperature tensile deformation of polysynthetically twinned (PST) crystals of TiAl

Abstract: Tensile deformation behavior of polysynthetically twinned (PST) crystals of TiAl with a nearly stoichiometric composition was investigated as a function of the angle o between the lamellar boundaries and tensile axis at room temperature. Tensile elongation to fracture strongly depends on the angle o but its dependence on the angle o is not symmetrical with respect to o = 45°. A tensile elongation as large as 20%, which is far larger than any other reported values on TiAl-based compounds, has been obtained for o = 31°. The yield stress also strongly depends on the angle o but any particularly significant tension-compression asymmetry in yield stress has not been observed. Fracture has been found to occur in a brittle manner without showing any local contraction even after deformation to more than 10%. When the tensile axis is perpendicular or inclined to the lamellar boundaries, fracture occurs in a cleavage-like mode with a habit plane parallel to the lamellar boundaries while fracture occurs in a zigzag across the lamellar boundaries when the tensile axis is parallel to the lamellar boundaries.