Characterizing nanoscale precipitation in a titanium alloy by laser-assisted atom probe tomography

Abstract

Atom-probe tomography was performed on the metastable -Ti alloy, Ti-5Al-5Mo-5V-3Cr wt.% (Ti-5553), aged at 300 °C for 0 to 8 h, to precipitate the embrittling isothermal  phase. A dependency of precipitate quantification laser pulse energy is found by comparing measurements. Ultraviolet laser pulse energies above ~30 pJ result in significant complex molecular ion formation during field-evaporation, causing mass spectral peak overlaps that inherently complicate data analyses. Observations and accurate quantification of the phase under such conditions are difficult. The effect is minimized or eliminated by using smaller laser pulse energies. With a small laser pulse energy, Ti-rich and solute depleted precipitates of the isothermal  phase with an oxygen enriched interface are observed as early as after 1 h aging time utilizing the LEAP 5000X S (77% detection efficiency). We note that these precipitates were not detected below a 2 h ageing time with the LEAP 4000X Si (58% detection efficiency). The results correct the archival literature and the discrepancies are rationalized. The Al concentration in the matrix/precipitate interfacial region increases during aging. Nucleation of the -phase at longer aging times may be facilitated by the O and Al enrichment at the matrix/precipitate interface (both strong -stabilisers). The kinetics and compositional trajectory of the -phase with aging time are quantified, facilitating direct correlation of the APT data to previously published mechanical testing.

A review of the metastable omega phase in beta titanium alloys: the phase transformation mechanisms and its effect on mechanical properties

“…For example, in a binary Ti-9.9Mo (at%) alloy, the ellipsoidal ω phase was found to have a Mo concentration near 2 atomic % [20,93]. More complex alloys have also been studied using APT, showing that ω iso is depleted of both βand α-stabilizing elements [22,27,30,71,80,82,83,87,94,95].…”

Atomic-scale 3D imaging of individual dopant atoms in an oxide semiconductor

“…We note that we restrict the analysis to TiO 2 + as this peak in the mass spectrum gives the best signal-to-noise ratio and, in contrast to the TiO 2+ species, does not show substantial overlap with other peaks. As a consequence, and because the evaporation of Ti produces the same single or molecular ions independent of the host material and its lattice position [34][35][36][37] , this restriction improves the reliability of the SDMs without restricting the generality of our conclusions (see also Supplementary Fig. 11).…”

Recent Advances in the Design of Novel β‐Titanium Alloys Using Integrated Theory, Computer Simulation, and Advanced Characterization

“…[ 36 ] The isothermal ω phase tends to be solute‐free, which rejects not only β stabilizers (such as Mo in the Ti–Mo system and V in the Ti–V system), but also α stabilizers (such as Al, in the Ti‐5553 system) into the adjacent β matrix. [ 18,37–43 ] Thus, the elemental partitioning between the α and ω phases leads to a continuous variation in the degree of plane collapse across the β/ω interphase. Depending on the degree of β/ω misfit, the morphology of ω precipitates can be described in two ways.…”