PhD Thesis Colloquium: Vivek Kumar Chandravanshi (27/07/23)
Thesis title:
Hot deformation behavior of some β titanium alloys in two-phase conditions
Faculty advisor(s):
Prof. Satyam Suwas
When?
27th July, 2023 (Thursday), 03:00 PM (India Standard Time)
Where
KI Vasu Auditorium, Department of Materials Engineering
Abstract:
Near b and metastable b-titanium alloys are difficult to process due to narrow processing window. Lower processing temperature causes difficulty in recrystallization of these alloys especially in two-phase conditions. However, processing in this regime is important for achieving microstructural control for the desired mechanical properties. Furthermore, most of the studies in this field are either in single phase b or about the globularization behavior of mostly a-laths in the (a+b) regions. Hence, there is dearth of information on the microstructural state and role of the b-phase during deformation in these conditions. Therefore, aim of the present investigation is to address the gaps in literature pertaining to recrystallization behavior of a and b phases during hot deformation of near b - and metastable β- titanium alloys in (a+b) phase field.
To achieve the above-mentioned goals in the present work, a metastable b titanium alloy, Ti10V-2Fe-3Al, and a near b titanium alloy, SP-700, both with lamellar starting microstructure, have been subjected to uniaxial compression tests in (a+b) regions as function of temperature and strain rate to optimize the primary processing conditions. Subsequently, the alloys were hot rolled up to 90 pct. in the (a+b) region followed by static annealing as a function of temperature and time to elucidate the microstructural and textural evolution in finally processed condition. In these conditions, the most relevant properties were evaluated for the two alloys, namely, fatigue crack growth (FCG) for Ti-10-2-3 alloy and, superplastic behaviour for the SP-700 alloy.
While kinking and bending is the dominat mechanism in globularization of a phase; grains are formed through CDRX mechanism in the b-phase for both the alloys at lower temperature and at lower strain rate. The best processing conditions were identified that led to DRX of a and b phases through the strain rate sensitivity maps, for both the alloys. Signatures of the deformation texture were observed in the a and b phases of both the alloys in all the annealed conditions. Grain boundary sliding was found to be one of the dominant deformation mechanisms during superplastic testing of the SP-700 alloy.