Intergranular Strain Evolution in Titanium During Tensile Loading: Neutron Diffraction and Polycrystalline Model
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NTRODUCTION
TITANIUM and its alloys are technologically important. With applications in various areas such as aerospace, naval, and biomedical, the superior specific strength and excellent corrosion resistance of these materials is making them more and more popular. Pure titanium (a-Ti) has a hexagonal close-packed (hcp) crystal structure. These alloys are known to exhibit strong mechanical anisotropy at the grain and macroscopic levels due to crystallographic texture and the wide variety of deformation mechanisms.[1,2] It is generally reported[1,3–7] that there are four types of slip systems on three glide planes in this hcp system: hai on the prismatic plane f10:0gh11:0i, hai on the basal plane f00:2gh11:0i, hai on the pyramidal plane f10:1gh11:0i , and hc+ai on the pyramidal plane f10:1gh11:3i. Prismatic glide is reported to be the main active deformation mode. In addition to slip, several experimental studies also reported occurrence of two main deformation twinning modes in a-Ti.[8–10] Twinning of f10:2g and f11:1g types are expected in extension along the hci axis, whereas twinning of f11:2g and f10:1g types are expected in compression along the hci axis. Plastic deformation of titanium alloys is accommodated by a complex mixture of crystallographic slip and DAVID GLOAGUEN, Professor, GUY OUM, PostDoc Position, VINCENT LEGRAND, JAMAL FAJOUI, Associate Professors, and MARIE-JOSE´ MOYA, Engineer, are with the Institut de Recherche en Ge´nie Civil et Me´canique (UMR CNRS 6183), Universite´ de Nantes - Centrale Nantes, 58 rue Michel Ange - BP 420 44606 SaintNazaire cedex, France. Contact e-mail: [email protected] THILO PIRLING, Instrument Scientist, is with the Institut Laue Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble, France. WINFRIED KOCKELMANN, Instrument Scientist, is with the ISIS, STFC Rutherford Appleton Laboratory, Chilton Didcot, Oxfordshire OX11 0QX, U.K. Manuscript submitted October 7, 2014. Article published online July 28, 2015 5038—VOLUME 46A, NOVEMBER 2015
deformation twinning. It is difficult to identify the role played by the different deformation mechanisms on the overall behavior. It is necessary to know both texture and deformation mechanisms to be able to model these mechanical properties. This requires, in particular, a proper knowledge of deformation mechanisms with their corresponding critical resolved shear stresses (CRSS). Only few data are available about CRSS in the literature. Moreover, CRSS generally depend significantly on the contents of alloying elements. It is still unclear which deformation systems are actually activated in a polycrystal during straining. It is important to understand the fundamentals of deformation mechanisms in these alloys. These mechanisms are responsible for the creation and evolution of internal stresses which have an important influence on the mechanical performance and lifetime of the material. Over the last decades, many micromechanical approaches like the self-consistent scheme or the Taylor model were used for the evaluation of the effec
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