The Effect of Phase Constitution and Morphology on Room Temperature Deformation Behavior of Binary Titanium Alloys

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Wyatt, Zane W.
Ankem, Sreeramamurthy
Currently, titanium alloys are used in a variety of applications, including defense, aerospace, biomedicine, and even common consumer products such as bicycles and golf clubs. In many applications such as the landing gear of aircraft and geothermal energy production, titanium components may be subjected to stresses for extended periods of time. It has long been known that single-phase &alpha; (HCP), single-phase &beta; (BCC), and two-phase &alpha; + &beta; Ti alloys can creep at low temperatures (<0.25Tm). For this reason, creep is an important factor to consider when designing titanium alloys for various applications. The first part of this investigation is concerned with single-phase &alpha;-Ti alloys. It was found that the twin size (lamellar thickness) decreases with an increase in strain rate. This behavior is unexpected based on the classical understanding of instantaneous twinning. This investigation was able to for the first time demonstrate a time-dependent twinning phenomenon during high strain rate tensile deformation. The second part of this investigation is concerned with experimentally and theoretically studying low-temperature creep deformation behavior of two-phase &alpha; + &beta; Ti alloys. Deformation mechanisms were seen in two-phase &alpha; + &beta; Ti alloys that are not present during creep of the respective single-phase alloys with compositions equivalent to the individual phases. To investigate the possible interphase interaction stresses, 3D anisotropic Finite element modeling (FEM) was used. These simulations revealed that due to the Burgers orientation relationship between the two phases, deformation such as slip or twinning in the &alpha; phase can create very high additional shear stresses on different slip systems in the &beta; phase. This work also revealed that the interfacial stresses that develop between the two phases during elastic deformation will often be much greater than the applied stress. These results were used to help explain the additional deformation mechanisms seen in two-phase alloys that are not seen in the respective single-phase alloys during creep. This work was supported by the National Science Foundation under Grant Number DMR-0906994.