In situ TEM observations on the structural evolution of a nanocrystalline W-Ti alloy at elevated temperatures

• Published in: Journal of alloys and compounds 2018-06, Vol.749, p.1000-1008
• Main Authors: Callisti, M., Tichelaar, F.D., Polcar, T.
• Format: Article
• Language: English
• Subjects: Alloys; Annealing; Chemical vapor deposition; Cooling; Evolution; Grain boundaries; Heating; High temperature; High-temperature alloys; In situ TEM heating; Nanocrystals; Phases separation; Physical vapour deposition (PVD); Segregations; Solid solutions; Structural stability; Structuralism; Thermal stability; Titanium; Tungsten base alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2018.03.335

The thermal stability and nanoscale structural evolution at elevated temperatures of a sputter deposited W-Ti alloy thin film were studied by a combination of ex situ and in situ techniques. XRD, FIB, SEM-EDX and STEM-EDX were used to characterise the film annealed ex situ in vacuum at 1373 K for 48 h. In situ TEM heating experiments were conducted at various temperatures up to 923 K to capture transitional phenomena occurring in the alloy upon heating and cooling. At a microscopic level, the alloy annealed at 1373 K for 48 h transformed from a single-phase β-(WTi) solid solution into a two-phase alloy consisting of Ti-rich grains in equilibrium with Ti-depleted β-(WTi) solid solution grains. In situ TEM observations revealed initial Ti segregations along columnar grain boundaries at T ∼ 423–573 K, followed by Ti-rich clusters formation in the grains interior at T ∼ 573–773 K. The microstructure observed at 923 K remained stable upon cooling to room temperature and consisted of Ti-rich segregations along the columnar grain boundaries and of alternate Ti-rich and Ti-depleted nanoscale domains in the grains interior, which formed a stable dual-phase nanocrystalline structure. •High temperature structural changes in W-Ti alloys are studied by in situ TEM.•β-(WTi) solid solution transforms macroscopically into a two-phase alloy.•Ti-rich segregations form along grain boundaries upon heating.•Alternate Ti-rich/Ti-depleted nanoscale domains form in the grains interior.•A stable dual-phase nanocrystalline structure forms after in situ heating.