Anomalous Dilatometric Response of Hot-Worked Ti-5Al-5Mo-5V-3Cr Alloy: In Terms of Evolution of Microstructure, Texture
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INTRODUCTION
ULTRA-HIGH-STRENGTH steels have been replaced by high-strength b titanium alloys in several aerospace structural applications because of the high strength-to-weight ratio. b Titanium alloy Ti-10V-2Fe-3Al (Ti-10-2-3) components have been used in the Boeing 777 for the last few decades, but most recently a new b titanium alloy, Ti-5Al-5V-5Mo-3Cr (Ti-5553), has been introduced as a material for the truck beam
MAINAK SEN, SUJOY KUMAR KAR, TRIDEEP BANERJEE, and AMLAN DUTTA are with the Metallurgical and Materials Engineering Department, Indian Institute of Technology Kharagpur, 721302, India. Contact e-mails: [email protected], [email protected] AMIT BHATTACHARJEE is with the Defence Metallurgical Research Laboratory, DRDO, Hyderabad, 500058, India. SRIKUMAR BANERJEE is with the Bhabha Atomic Research Centre, Mumbai, 400085, India. Manuscript submitted September 15, 2019. Article published online March 12, 2020 METALLURGICAL AND MATERIALS TRANSACTIONS A
component of the landing gear of the Boeing 7E7 and Airbus A-380.[1,2] Ti-5553 exhibits excellent hardenability and superior strength combined with high fracture toughness and excellent high cycle fatigue behavior compared with Ti-6Al-4V and Ti-10-2-3. There are several processing advantages of using Ti-5553 over Ti-10-2-3.[3] To retain the large volume fraction of metastable b phase, Ti-5553 can be air cooled after solution treatment without property deterioration, whereas Ti-10-2-3 components have to be water quenched, limiting their thickness to 76 mm as opposed to the 152 mm possible for Ti-5553.[2] Ti-10-2-3 also suffers from the formation of b flecks during ingot production. More extensive use of Ti-5553 in aircraft structural components calls for better understanding of the influence of the factors that influence the evolution of the microstructure, which in turn controls its mechanical properties. Moreover, the thermal distortion of an aircraft component, resulting from processes such
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as phase transformations and removal of residual stress, is of major concern. The use of dilatometric investigations of Ti alloys dates back to 1963. Borok et al.[4] looked into dilatometric responses in various binary Ti alloys (Ti-Fe, Ti-Cr, Ti-Co and Ti-Mo) and noted contraction due to x phase formation and expansion due to the reverse transformation, b+ x fi b + a. An anomalous dilatometric response of another Ti alloy (Ti-6242) was observed earlier by Carvalho et al.[5] They rationalized the observed contraction in terms of out-gassing of the interstitials and solute redistribution. Lin et al.[6] investigated hydrogen diffusion in a Ti alloy using dilatometry based on the fact that a linear relationship exists between the lattice parameter of b phase and the hydrogen concentration in it. Bonisch et al.[7] used dilatometry to observe contraction/expansion phenomena due to isothermal x formation and the reverse reaction, x fi b, respectively. Nakai et al.[8] studied the thermal expansion of cold-rolled Ti-29Nb-13Ta-4.6Zr alloy (T
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