Perspectives on Titanium Science and Technology

The relationship between grain boundary characteristics and the formation of grain boundary carbides in AISI 304 stainless steel have been investigated by using the electron backscattered diffraction (EBSD) technique. It was observed that an increase in the misorientation between two adjacent grains resulted in a change in the carbide morphology from a plate-like to an acute triangular form, where carbides preferentially maintained coherency with the grain for which the {111} planes made the smallest angle with the grain boundary plane. The carbides grew into the other grain at a later stage, having the lowest interfacial energy, which subsequently resulted in the triangular carbide morphology. After low cycle fatigue with a hold time at tensile peak strains, it was observed that cavity formation was more pronounced at random boundaries than at coincidence site lattice (CSL) boundaries. This result provides a good explanation that acute triangular carbides, which predominantly precipitate at random boundaries, are more likely to lead to cavity nucleation than the plate-like carbides precipitate at CSL boundaries.

Correlation of the M23C6 precipitation morphology with grain boundary characteristics in austenitic stainless steel

Crystallographic and morphological relationships between β phase and the Widmanstätten and allotriomorphic α phase at special β grain boundaries in an α/β titanium alloy

Effects of boron on microstructure in cast titanium alloys

Variant selection during α precipitation in Ti–6Al–4V under the influence of local stress – A simulation study

The crystallography of α(hcp) precipitates formed on the β(bcc) matrix grain boundaries has been studied with transmission electron microscopy (TEM) in a Ti-15V-3Cr-3Sn-3Al alloy. The α precipitates have a near-Burgers orientation relationship with respect to at least one of the adjacent β grains. Among the possible 12 variants in this orientation relationship, the variant that [11•20]α is parallel to the 〈111〉β closest to the grain boundary plane tends to be preferred by the α precipitates. Additionally, further variant selections are made so as to minimize the deviation of orientation relationship with respect to the “opposite“ β grain from the Burgers one. Such rules in variant selection often result in the formation of precipitates with a single variant at a planar grain boundary. Prior small deformation of β matrix changes the variant of α precipitates at the deformed portion of grain boundary. It is considered that the stress field of dislocations in the slip bands intersecting with the boundary strongly affects the variants of α precipitates. Discussion of these results is based upon a classical nucleation theory.

Crystallography of grain boundary α precipitates in a β titanium alloy

The crystallography of {alpha}(hcp) precipitates formed on the {beta}(bcc) matrix grain boundaries has been studied with transmission electron microscopy (TEM) in a Ti-15V-3Cr-3Sn-3Al alloy. The {alpha} precipitates have a near-Burgers orientation relationship with respect to at least one of the adjacent {beta} grains. Among the possible 12 variants in this orientation relationship, the variant that [11{bar 2}0]{sub {alpha}} is parallel to the {sub {beta}} closest to the grain boundary plane tends to be preferred by the {alpha} precipitates. Additionally, further variant selections are made so as to minimize the deviation of orientation relationship with respect to the ``opposite`` {beta} grain from the Burgers one. Such rules in variant selection often result in the formation of precipitates with a single variant at a planar grain boundary. Prior small deformation of {beta} matrix changes the variant of {alpha} precipitates at the deformed portion of grain boundary. It is considered that the stress field of dislocations in the slip bands intersecting with the boundary strongly affects the variants of {alpha} precipitates. Discussion of these results is based upon a classical nucleation theory.

H. Watanabe

Papers

Crystallography of grain boundary α precipitates in a β titanium alloy

Crystallography of grain boundary {alpha} precipitates in a {beta} titanium alloy