Texture and micromechanics of Forged Ti-10V-2Fe-3AI

• Main Author: Raghunathan, Seema L.
• Published: Imperial College London 2007
• Subjects: 620.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485552

Ti-lOV-2Fe-3AI is a near-p titanium alloy· primarily used in the landing gear of aircraft. Such components are normally produced by isothermal forging but the sensitivity of the microstructure to temperature makes forging optimisation difficult and therefore, an empirical approach is usually applied. To reduce the resultant high processing costs, it is essential for the industry to accurately l:ffiderstand and predict microstructural evolution and properties with respect to the isothennal forging variables. This thesis considers the evolution of macrotexture and microtexture in Ti-l0V..2Fe-3AI during and after forging. The aim of this research is to improve our understanding of the micromechanics ofthis alloy. t· The effect of aging on the lattice strain behaviour of Ti-l0V-2Fe-3Al was investigated. In-situ synchrotron diffraction was performed while the as-forged condition and the forged and aged were undergoing tensile loading at room temperature. The behaviour ofboth conditions was modelled using a two-phase elastic-plastic self consistent (EPSC) scheme in an attempt to rationalise the material behaviour. It was found that the constrained p phase stiffuess, Ezoo, increased from 45GPa in the asforged condition to 88GPa in the forged and aged material. The model results showed that ell -CIZ increased from 12GPa in the forged condition to 47GPa in the forged and aged material. This can be attributed to an increase in p-stabiliser content and is in agreement with atomistic predictions. The EPSC models, while reasonably successful at reproducing the observed behaviour, do not provide a complete description of the micromechanics of these materials due to the complexity of the microstructures. The macrotexture and microtex-ture were investigated during a.+p forging of Ti-l0V-2Fe-3Al and were characterised using a combination of neutron, in-situ synchrotron X-ray and ex-situ electron backscatter -diffraction (EBSD). The EBSD analysis showed that the measured misorientation distributions at a strain of 0.8 and strain rates of 0.ls-1 and O.Ols-· were similar, with an average misorientation of 2.2°. It was. found that during forging, the moderate cube macrotexture inherited from the parent material evolved into a moderate fibre texture, with the major change occurring between strains of 0.4 and 0.6. The synchrotron diffraction studies allowed the orientation evolution of individual grains to be characterised. At the highest strain rate of 0.15-·, this indicated a change in behaviour from dispersion of the crystal mosaic (peak angular spread) at low strains, to convergence of the crystal mosaic at larger strains. At lower strain rates, only convergence of the crystal mosaic was observed. It is suggested that these results indicate a change in mechanism between deformationcontrolled behaviour during the early stages of deformation and a strain rate of 0.1 s-· and diffusional, recovery-controlled behaviour lower strain rates and higher strains.