The microstructural evolution of near beta alloy Ti-10V-2Fe-3Al during subtransus forging
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I. INTRODUCTION
TI-10V-2FE-3AL (Ti-10-2-3) is a high-strength/ toughness, deep hardenable material, developed in the 1970s to provide weight savings over high-strength steels in forged aircraft undercarriage components. The alloy possesses good hot die forgeability due to a low transus of 800 °C, almost 200 °C below the transus of the high-strength alloy Ti-6Al-4V. Thermomechanical processing (TMP) techniques such as isothermal forging (IF) (as opposed to conventional forging) are required to fabricate Ti-10-2-3 aerospace components because the microstructure is particularly sensitive to temperature, especially close to the transus. In the literature, the effect of TMP on the microstructure of Ti-10-2-3 around the transus focuses on the break up of an initial prior forged microstructure, consisting of plates and grain boundary in and around large grains. The microstructure evolves to an equiaxed grain morphology, consisting of spheroidized within a matrix, with increasing strain.[1,2] Such microstructural development imparts ductility and superplasticity into the forged product as deformation proceeds. The current cost reduction drive in the IF industry has been to accurately predict such microstructural evolution with respect to IF variables such as temperature, strain rate, and strain. Process modeling has been increasingly employed over the last decade or so to predict macroscopic forging effects and reduce forging die geometry iterations. These approaches have been successfully demonstrated for the deformation of various engineering alloys, but titanium is rather complex, due to the sensitivity of the and phases to chemistry, volume fraction, and morphology during subtransus IF. Therefore, the next step is to develop reliable constitutive models that relate IF variables to microstructure evolution. However, the effort in acquiring such data to generate inforMARTIN JACKSON, Research Lecturer, and RICHARD DASHWOOD, Senior Lecturer, are with the Department of Materials, Imperial College London, London SW7 2AZ, United Kingdom. Contact e-mail: martin-jackson@ imperial.ac.uk HARVEY FLOWER, formerly Professor of Materials Science, with the Department of Materials, Imperial College London, is deceased. LEO CHRISTODOULOU, Program Manager, is with Defense Sciences Office, DARPA/DSO, Arlington, VA. Manuscript submitted July 2, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
mation for such constitutive relationships is very laborious due to the required large test matrix of conventional uniaxial compression cylinders. In this article, a testing technique is exploited to overcome such a problem. The technique effectively captures microstructural information for a range of strains at constant temperature and near constant strain rate in a single specimen. The IF of a double truncated cone specimen (Figure 1) is simulated using finite-element (FE) software to evaluate the microstructural information with the IF variables, such that the onset of globularization or recrystallization can be cor
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