Phase Transformation Textures in Hot-Rolled Binary Ti-Nb Alloys
- PDF / 1,915,410 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 14 Downloads / 220 Views
TITANIUM and its alloys have grown as commercially important materials during the last four decades for a wide range of applications in aerospace, automotive, chemical, and biomedical industries. A large number of components used in these applications is in plate, sheet, or extruded rod forms, which are produced by thermomechanical processing/treatments. This involves hot and/or cold deformation (forging and rolling) and heat treatments of alloys at various temperatures. Thermomechanical treatments are likely to give rise to a characteristic texture at different stages of processing. Therefore, the texture present in the alloy depends on the nature of processing and heat treatments. The heat treatment consists of both the recrystallization and the phase transformations. Phase transformations in titanium and its alloys have generally been studied by heat treatments in b and a + b phase fields followed by different cooling rates. A typical heat treatment of near a and a + b type titanium alloys in b phase field follows a fi bfi a¢ and a fi b fi a during water quenching (WQ) and furnace cooling (FC), respectively. The effect of crystallographic texture of high-temperature b phase on its transformation product a phase (closed-packed hexagonal [cph]) in near a and a + b type alloys has been largely documented.[1–11] The comparison between initial and final texture has been explained based on a fi b fi a transformation seS. BANUMATHY and A.K. SINGH, Scientists, are with the Defense Metallurgical Research Laboratory, Hyderabad 500 058, India. Contact e-mail: singh_ashok3@rediffmail.com R.K. MANDAL, Professor, is with the Centre of Advanced Study, Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India. Manuscript submitted November 21, 2011. Article published online February 12, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
quences. It has been observed that the final texture evolves during a fi b fi a transformation at the scale of a grain either during a fi b transformation on heating or (and) during b fi a transformation on cooling. The texture present in the a phase is also strongly dependent on the b fi a cooling rate.[12] The change in a phase texture after b fi a transformation has been documented well in the literature.[1–11] However, the a fi b transformation during heating has been studied by a few investigators.[13–15] Bhattacharyya et al.[15] have investigated a fi b transformation using a high-temperature neutron diffraction technique. This study has been aimed to address issues related to a fi b transformation, which occur either by growth of the b phase preexisting at room temperature or by fresh nucleation. It is known that only the latter case follows Burgers orientation relation (OR). It has been observed that texture of b phase strengthens on heating, and both the b and a phases do not follow OR.[15] They have produced convincing evidence that a fi b transformation occurs by the growth of preexisting b phase and not by the fresh nucleation of b in the a phase. It has
Data Loading...
