TEM and XRD characterisation of commercially pure α-Ti made by powder metallurgy and casting

The hcp-structured α-Ti is one of the two basic phases (α-Ti and β-Ti) in Ti materials. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to analyse the α-Ti phase in both as-sintered and as-cast α-Ti materials. The structure factor of the (0001) plane of the α-Ti phase is 0. No diffraction should thus occur from the (0001) plane of the α-Ti phase when characterised by either x-ray diffraction or electron diffraction. However, electron diffraction of the as-sintered α-Ti materials recorded unambiguous diffraction from the (0001) plane as well as (000 l) where l = 2n + 1 (n   is integer). A detailed analysis has clarified that this is a result of double diffraction arising from the two strong neighbouring (101¯0) and (1¯011) diffraction planes. The same phenomenon also occurred to the characterisation of as-cast α-Ti materials.

► As-sintered and as-cast α-Ti studied by electron diffraction and x-ray diffraction.
► The (0001) plane of α-Ti not detectable by x-ray diffraction.
► Electron diffraction from the (0001) plane revealed by TEM unambiguously.
► Double diffraction phenomenon responsible for these contradictory observations.