Stretchability of Commercial Purity Titanium Sheet
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TITANIUM and its alloys are widely used in aerospace, chemical processing, defense, medical, and electronics industries owing to their high strength to weight ratio and excellent corrosion resistance. A significant amount of sheet metal of commercial purity (CP) titanium produced is used for the manufacture of components employing forming operations—gas bottles and propeller tanks for the aerospace industry being two examples. Since titanium has a hexagonal-close-packed (hcp) structure, its intrinsic ductility is limited and characterization of sheet formability is crucial to successful part production. The work reported here is a
TEENA MOUNI CHINAPAREDDYGARI and SHAJU K. ALBERT are with the Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India, and also with the Homi Bhabha National Institute, Anushakthi Nagar, Mumbai 400094, India. CHANDRASEKARAN RAVISHANKAR and UTPAL BORAH are with the Metallurgy and Materials Group, Indira Gandhi Centre for Atomic Research. Contact email: [email protected] KARTHIKEYAN THANGARAJ is with the El Forge Limited, 1A Sriperumbudur High Road, Appur, Kanchipuram 603204, India. ANIL KUMAR VESANGI and ROHIT KUMAR GUPTA are with the Materials and Mechanical Entity, Vikram Sarabhai Space Centre, Trivandrum 695022, India. Manuscript submitted March 25, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
study of the stretchability of Grade 4 CP titanium sheet manufactured by M/s MIDHANI from the titanium sponge produced by Kerala Metals and Minerals Limited at the Titanium Sponge Plant set up by the Vikram Sarabhai Space Centre (VSSC), Trivandrum. Stretchability of sheet material is described quantitatively by the forming limit diagram (FLD), originally proposed by Keeler and Backofen[1] and Goodwin.[2] FLD is a map in the principal strain space that separates the safe strain combinations from the more severe combinations that result in failure. In these tests, sheet is stretched at a fixed strain ratio until failure (which is usually the appearance of a localized neck), the limit strains being the principal strains at the onset of failure. The complete FLD is obtained by varying the strain ratio from that of pure shear to equibiaxial tension.[1, 2] The FLD is strongly dependent on the strain hardening ability and texture of the material. Large strain hardening ability is known to enhance formability, while large r values (which reflect the crystallographic texture) are known to suppress stretchability for positive strain ratios while improving limit strains in the negative strain region.[3–5] CP titanium is comprised of the a phase at room temperature and has an hcp crystal structure. CP titanium sheets are known to develop strong texture during rolling and recrystallization processes with the basal plane in the plane of the sheet with a spread of
± 40 deg from sheet normal toward the transverse direction.[6] Since the close packed plane is the basal plane and the deformation occurs on this plane along the direction parallel to edges of the cell with
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