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The effect of the processing parameters (beam current, beam scanning frequency, feed rate, etc.) on the capability to produce 3D-printed parts with precise geometry and uniformity made of commercially pure titanium and Ti-6Al-4V alloy by electron beam additive manufacturing was studied. The best quality and uniformity of the 3D-printed samples was found to be obtained at the low movement speed in the XY plane (3.5 mm/s) in combination with the high beam scanning frequency (500 Hz). The microstructure, phase composition and mechanical properties of the 3D-printed commercially pure titanium and Ti-6Al-4V alloy samples were investigated by optical microscopy, X-ray diffraction and nanoindentation. [ABSTRACT FROM AUTHOR]

Microstructure and phase composition in fusion zone, heat affected zone and base metal of Ti–6Al–4V samples, produced by Selective Laser Melting (SLM) and Electron Beam Free-Form Fabrication (EBF³) methods were studied. Metallographic analysis was performed to compare sizes of prior columnar β grains and acicular α′ phase formed in the weld of Ti–6Al–4V samples obtained by different additive manufacturing methods. X-ray diffraction analysis revealed a change of β phase volume fraction in the weld of 3D printing Ti–6Al–4V samples. Distribution of Vickers microhardness of weld joint cross section specimens was under study. [ABSTRACT FROM AUTHOR]

Changes of the microstructure and phase composition of selective laser melting Ti-6Al-4V titanium alloy samples during ultrasonic impact post-processing were investigated by optical, transmission microscopy, and X-ray analysis. Significant refinement of the microstructure in the thin surface layer was observed as a result of ultrasonic impact treatment. This causes an increase in microhardness and strength characteristics of the surface layer of selective laser melting samples under uniaxial tension. [ABSTRACT FROM AUTHOR]

Failure mechanisms of yttria-stabilized zirconia (YSZ) and CeO2 thermal barrier coatings on titanium substrates subjected to thermal cycling are studied. Deposition of a Ni-Al bond coat is shown to result in substantial enhancement of thermal cycling resistance of YSZ coatings; however, this layer has a negligible effect on the thermal cycling resistance of CeO2 coatings. The latter is due to the high sintering rate of CeO2 coatings at elevated temperatures, which induces their densification during thermal cycling and, consequently, prevents inward oxygen diffusion. [ABSTRACT FROM AUTHOR]

A microstructure-based model for polycrystalline titanium is constructed and implemented in finite-element calculations of uniaxial tension. The grain structure is considered explicitly, with grain orientations being given by a set of local coordinate systems related to the crystal lattice. Elastic-plastic anisotropy on the grain scale is described using generalized Hooke's law and the crystal plasticity theory. It has been found that the plastic deformation of grains is accompanied by crystal lattice rotations within and near localized shear bands and along grain boundaries. A correlation between plastic strains and Schmid factors of grains is discussed. [ABSTRACT FROM AUTHOR]

Micro- and mesoscale surface roughening in as-received and rolled aluminum alloys under uniaxial tension is investigated experimentally and numerically. Experiments were conducted on the evolution of the surface roughness in as-received alloys and those produced from a rolled sheet cut across and along the rolling direction. Three-dimensional polycrystalline models of equiaxed and elongated grain structures were developed and implemented in finite-element and finite-difference calculations. Constitutive models of grains were constructed using anisotropic elasticity and crystal plasticity theory. The roughness patterns have been found to vary with the microstructure and texture of the materials and with loading conditions, even though all test specimens have certain features in common. The mesoscale surface undulations observed are shown to be much more pronounced in the rolled specimens, whereas the microscale surface relief attributed to intragranular strains is well-defined in the as-received non-textured polycrystals. [ABSTRACT FROM AUTHOR]

A numerical simulation is performed to investigate the mesoscale stress-strain localization in a surfacemodified commercial titanium alloy (VT1-0 according to Russian classification). The calculated crystalline microstructure corresponds to that observed experimentally and is explicitly accounted for as initial conditions of a dynamic boundary-value problem. The latter is formulated in terms of plane strain developing in a microstructure subjected to tension and is solved numerically by the finite-difference method. Elastic-plastic constitutive models are built to describe the experimental mechanical responses both of the substrate and of the modified layer. The plastic strain localization is found to depend on the grain yield stress. [ABSTRACT FROM AUTHOR]