Abstract
Aging of metastable beta-Ti alloys leads to the precipitation of omega phase, resulting in a significant loss in ductility (omega brittleness). This presentation reports the results of 3D observations of isothermal omega phase by an orthogonal FIB/SEM system. It was revealed that the shape of omega phase particles varies with the particle size. By serial sectioning, it was possible to obtain a 3D image for the volume of several micrometer cube containing numerous omega particles. The volume fraction of omega phase was qualitatively determined. The value was much lower than the previous investigation by X-ray diffraction by Hickman in 1969. The SEM and TEM revealed the formation of shear bands in the cold rolled samples, where the shearing of omega phase and transformation into beta phase while maintaining the depletion of Mo was found. After the HPT deformation, white etching layers are formed near the median plane of the disc, where the omega phase particles were absent and exhibit significantly lower hardness values. These findings may help to clarify the cause of brittleness in beta Ti alloys with isothermal omega phase.
Highlights
Isothermal aging of metastable beta-Ti alloys leads to the dense precipitation of so-called “isothermal omega phase”, resulting in increase in hardness accompanied by a significant loss in ductility
An ingot of Ti-12wt%Mo were prepared by cold-crucible levitation melting (CCLM)
In metastable beta Ti alloys containing isothermal omega phase particles, the deformation localizes into shear bands since the omega-to-beta transformation occurs by the motion of partial dislocation leading to significant softening
Summary
Isothermal aging of metastable beta-Ti alloys leads to the dense precipitation of so-called “isothermal omega phase”, resulting in increase in hardness accompanied by a significant loss in ductility (omega brittleness). Due to their small size and high number density, the observation method of omega phase has been limited to transmission electron microscopy (TEM) and 3DAP. Chen et al studied the omega embrittlement in Ti-20Mo alloy. They have related to the extent of omega collapse to the change in the dislocation activity in beta phase from homogeneous slips to heterogeneous ones[2]. The present investigation asses the mechanism of omega embrittlement by microstructural observation of the samples subjected to cold-rolling and high-pressure torsion deformation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
