Interface characteristics in an α+β titanium alloy

Abstract

The α/β interface in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) is investigated via centre of symmetry analysis, both as-grown and after 10% cold work. Semi-coherent interface steps are observed at a spacing of 4.5 ±1.13 atoms in the as-grown condition, in good agreement with theory prediction (4.32 and 4.25 atoms). Lattice accommodation is observed, with elongation along [1210] α and contraction along [1010] α . Deformed α exhibited larger, less coherent steps with slip bands lying in {110} β . This indicates dislocation pile-up at the grain boundary, a precursor to globularisation, offering insight into the effect of deformation processing on the interface, which is important for titanium alloy processing route design.

A cracking oxygen story: A new view of stress corrosion cracking in titanium alloys

“…A compositional analysis from the core of this segregated region, (c), revealed almost 12 at.% 18 O, but no D. There was also a slight increase in the H and 16 O signals, which can be attributed to the changes in the field evaporation behaviour at the linear defect. Zr excess was also observed in the interface, (b) & (d), believed to be associated with Zr segregation to interface (misfit) dislocations, which is also present in the undeformed sample 25 . No D or 18 O excess was observed at the / interface.…”

“…This presupposes that H is in fact present from corrosion, which has not been observed directly. Parallels are often drawn with (single phase 𝛼 or near-𝛼) zirconium alloys, in which the delayed hydride cracking phenomenon is a result of hydrogen migration to regions of high hydrostatic stress, which results in the precipitation of brittle hydrides that cause crack advance, even in static loading conditions at room temperature 25 . This is of concern, for example for the dry storage of spent nuclear fuel, where the hydrogen results from corrosion under elevated temperature operating conditions, where the solubility for H is elevated compared to room temperature.…”

Study of Microstructural Morphology of Ti-6Al-4V Alloy by Crystallographic Analysis and Phase Field Simulation

“…However, it is very close to 1, thus, the twinned regions of two variants with small volume fraction of one twinned variant exist in the microstructure. Moreover, different dislocations and structural ledges have been observed in the interface between α variant and β matrix [ 29 , 31 ], which produce a semi-coherent zigzag interface. Therefore, the generally accepted {3 3 4} habit planes only refer to a semi-coherent interface, which would be the main source of the small angular deviation for the PTMT and micro-elasticity theory calculation.…”

“…Another geometrical method is the topological model (TM) constructed by Pond and Hirth [ 29 ]. Unlike the PTMT theory, the habit plane and orientation relationship between parent and product phase are predicted based on the interfacial defects, but without High Resolution TEM the crystallographic geometry of interfacial disconnections is difficult to confirm [ 30 , 31 ]. Due to the simple calculation and highly accurate physical results from the PTMT theory, it has been employed widely to obtain the crystallographic features of alloys during martensitic transformation [ 21 , 32 , 33 , 34 , 35 , 36 ].…”

Coherent and semicoherent α/β interfaces in titanium: structure, thermodynamics, migration

“…5. According to the phenomenological theory of martensite crystallography [35][36][37] , the semicoherent α/β interface plane should be a habit plane determined by geometry, as follows. Take the coherent interface with the BOR as a reference (i.e., the misorientation angle θ and the inclination angle ϕ of the coherent interface are defined to be zero).…”