The origin of striation in the metastable β phase of titanium alloys observed by transmission electron microscopy

Abstract

For the phase of Ti-5553-type metastable -Ti alloys, striations in transmission electron microscopy (TEM) bright-and dark-field images have been frequently observed but their origin has not been sufficiently investigated. In the present work, this phenomenon is studied in depth from the macroscopic scale by neutron diffraction to the atomic scale by high-resolution TEM. The results reveal that the phase contains homogeneously distributed modulated structures, intermediate between that of the phase (cubic) and that of the phase or the ! phase (hexagonal), giving rise to the appearance of additional diffraction spots at 1/2, 1/3 and 2/3 diffraction positions. The intermediate structure between and is formed by the atomic displacements on each second {110} plane in the h110i direction, whereas that between and ! is formed by atomic displacements on each second and third {112} plane in the opposite h111i direction. Because of these atomic displacements, the {110} and {112} planes become faulted, resulting in the streaking of diffraction spots and the formation of extinction fringes in TEM bright-and dark-field images, the commonly observed striations. The present work reveals the origin of the striations and the intrinsic correlation with the additional electron reflections of the phase.

Formation of slip bands and microstructure evolution of Ti-5Al-5Mo-5V-3Cr-0.5Fe alloy during warm deformation process

“…Metastable β titanium alloys are important structural materials for aeronautical applications due to their high strength to density ratio, superior strength and ductility combination and good workability [1,2,3,4]. Thereupon enormous work and effort in resolving the complex microstructural evolution related to thermomechanical process (TMP) and their correlations with the resultant mechanical properties have been done in the past decades [5,6,7,8]. Various alloy compositions and microstructures of titanium alloys are related to the different deformation mechanisms.…”

STRAIN INDUCED PHASE TRANSFORMATION IN Ti-15Mo β ALLOY

“…There were no other phases iden fied by electron diffrac on. The matrix and the Mo-depleted par cles are likely β and β‫,׳‬ which are formed through a bimodal chemical decomposi on of the matrix β-phase [26][27][28]. The forma on of Moenriched β-phase and Mo-depleted β‫-׳‬phase were reported in β tanium.…”

“…It has been reported as twins, composi on varia on of the β-phase and ar facts, etc. [26,41] . From the SAD pa�ern in Fig.…”

“…The phase transforma on of β-Ti to α-Ti through a series of β + β‫׳‬ and ω, α‫׳‬ or α‫״‬ etc. is further complicated by a recently reported O‫׳‬ metastable phase [26][27][28][29][30].…”

Effect of secondary annealing and deep cryogenic treatment on microstructure and mechanical properties of TC27 titanium alloy

“…The total peaks of the α phases also tend to rise. This phenomenon suggests that after annealing, the βphase is largely transformed into the α-phase [11 .…”