Jana Šmilauerová

Ordered array of ω particles in β-Ti matrix studied by small-angle X-ray scattering

Abstract Nanosized particles of ω phase in a β -Ti alloy were investigated by small-angle X-ray scattering using synchrotron radiation. We demonstrated that the particles are spontaneously weakly ordered in a three-dimensional cubic array along the 〈 1 0 0 〉 -directions in the β -Ti matrix. The small-angle scattering data fit well to a three-dimensional short-range-order model; from the fit we determined the evolution of the mean particle size and mean distance between particles during ageing. The self-ordering of the particles is explained by elastic interaction between the particles, since the relative positions of the particles coincide with local minima of the interaction energy. We performed numerical Monte Carlo simulation of the particle ordering and we obtained a good agreement with the experimental data.

Growth kinetics of ω particles in β-Ti matrix studied by in situ small-angle X-ray scattering

Nucleation and growth kinetics of nanoparticles of hexagonal ω phase in a body-centered cubic β titanium matrix in single crystals of β-Ti alloys were investigated by small-angle x-ray scattering measured in-situ during ageing at various temperatures up to 450 °C. The experimental data were compared with numerical simulations based on a three-dimensional short-range order model of nanoparticle self-ordering. The x-ray contrast of the particles is caused by an inhomogeneous distribution of impurity atoms (Mo, Fe and Al), whose density profile around growing nanoparticles was simulated by solving the corresponding diffusion equation with moving boundary conditions. From the analysis of the experimental data we determined the mean distance and size of the nanoparticles and confirmed the validity of the ∝ t1/3 growth law following from the Lifshitz-Slyozov-Wagner theory. From a detailed comparison of the experimental data with simulations we also assessed the diffusion coefficient of the impurity atoms and its activation energy.

Evaluation of anisotropic small-angle neutron scattering data from metastable β-Ti alloy

ABSTRACT Small-angle neutron scattering (SANS) data from single-crystal metastable β-Ti alloys exhibit an anisotropic character with interparticle interference maxima due to ordering of the dense system of ω particles. For an evaluation of such data, the program NOC (previously used for evaluation of data from dense ordered γ′ precipitate system in single-crystal nickel-based superalloys) was well suited. Nevertheless, an improvement of this evaluation program was necessary in its model-forming part. A further change of the evaluation program concerned the mode in which the size distribution was calculated. This upgrade is presented. The improved NOC program was employed for the evaluation of SANS data of annealed metastable single-crystal β-Ti alloy containing ω particles. 3D fit in reciprocal space was successfully used. A model of ellipsoids did not lead to a better fit than a model of particles with the spherical shape. The microstructural parameters of ω particles were determined.

On the completeness of the β→ω transformation in metastable β titanium alloys

The completeness of the β→ω transformation in ω particles in a Ti–8 at.%Mo (Ti–15 wt%Mo) single crystal was investigated by measuring the X-ray diffraction maximum 20{\overline 2}2, which is forbidden in both the pure body-centred cubic β phase and the hexagonal ω phase, and also the diffraction maxima 0001, 0002 and 10{\overline 1}1, which are forbidden in the β phase and allowed in ω. From a comparison of the integrated intensities and widths of the diffraction peaks with simulations, the effective (mean) degree of the transformation was determined and the radial profile of the transformation degree in an ω particle was estimated.

Characterization of Phase Transitions Occurring in Solution Treated Ti-15Mo during Heating by Thermal Expansion and Electrical Resistance Measurements

Metastable β titanium alloy Ti-15Mo was investigated in this study. In-situ electrical resistance and thermal expansion measurements conducted on solution treated material revealed influence of ongoing phase transitions on measured properties. The monotonicity of the dependence of electrical resistance on temperature changes at 225, 365 and 560 °C The thermal expansion deviates from linearity between 305 and 580 °C.