Indian Institute of Science
Nair, Shanoob Balachandran.
Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys.
Degree: PhD, Faculty of Engineering, 2017, Indian Institute of Science
The properties of titanium alloys are based on alloy compositions and microstructures that consist of mixtures of the two allotropic modifications of titanium, the low temperature α (hcp) and the high temperature β (bcc) phases. This thesis deals with the hot working behaviour of three commercial titanium alloy compositions designated IMI834, Ti17 and Ti5553 with a focus and detailed analysis of the Ti5553 alloy. These alloys represent the differing uses of titanium alloys in the aerospace industry. IMI834 is a near α alloy used in high temperature creep resistant applications as compressor discs and blades in aeroengines. Ti17 is a high strength alloy α+β used at intermediate temperatures in fan and compressor discs of aeroengines, while Ti5553 is a high strength-high toughness metastable β alloy used in the undercarriages of aircraft. The three alloys have widely differing β transus temperatures (related to α phase stability) and compositions. Titanium alloys are vacuum arc melted and thermomechanically processed. This process involves ingot breakdown in β (bcc) phase, and subsequent thermomechanical processing in two-phase α+β (hcp+bcc) region at temperatures that typically involve volume fractions of α in lath or plate form ranging from 15% to about 30%. The thermomechanical processing breaks down lath α to spheroidal particles, a process known as globularisation. Chapter I of this thesis reviews the current understanding of the hot working of titanium alloys and microstructure evolution during the hot working process. Chapter II summarises the main experimental techniques used: the hot compression test, and subsequent microstructure and microtexture analysis by scanning electron microscopy and related electron back scattered diffraction techniques (EBSD), transmission electron microscopy and related precession electron diffraction techniques (PED) for orientation imaging.
The starting structure in the α+β domain of hot work is generally not a random distribution of the 12 variant Burgers Orientation Relationship (BOR) between the α and β phases, (11̅0)β || (0001)α and <111>β || <112̅0>α . A variety of morphologies and distributions ranging from the typical colony structures of near α and α+β alloys to the fine distributions of variants arranged in a triangular fashion are observed with specific growth directions and habit planes. Chapter III describes a quantitative evaluation of α distribution that are typical of some of the starting structures for the hot working conditions used in this thesis, specifically in the Ti5553 alloy. For this purpose, a Matlab based script has been developed to measure the spatially correlated misorientation distribution. It was found that experimental spatially correlated misorientation distribution varies significantly from a random frequency for both pair and triplet wise distribution of α laths. The analysis of these structures by established techniques of analysis of self-accommodated structures based on strain energy minimisation shows that the observed variant…
Advisors/Committee Members: Banerjee, Dipankar (advisor).
Subjects/Keywords: Titanium Alloys; Titanium Alloys Microstructure; Titanium Alloys Microtexture; Microstructure Evolution; Ti5553 Alloy; Materials Engineering
to Zotero / EndNote / Reference
APA (6th Edition):
Nair, S. B. (2017). Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/2678
Chicago Manual of Style (16th Edition):
Nair, Shanoob Balachandran. “Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys.” 2017. Doctoral Dissertation, Indian Institute of Science. Accessed January 16, 2021.
MLA Handbook (7th Edition):
Nair, Shanoob Balachandran. “Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys.” 2017. Web. 16 Jan 2021.
Nair SB. Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2017. [cited 2021 Jan 16].
Available from: http://etd.iisc.ac.in/handle/2005/2678.
Council of Science Editors:
Nair SB. Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys. [Doctoral Dissertation]. Indian Institute of Science; 2017. Available from: http://etd.iisc.ac.in/handle/2005/2678