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M. Dikovits, C. Poletti, F. Warchomicka:
"Hot deformation and processing maps of a β-Ti alloy";
Poster: Euromat 2011, Montpellier; 09-12-2011 - 09-15-2011.

In this work the hot formability of a near-β-Ti alloy is studied by the use of processing maps. Compression tests of Ti-5Al-5Mo-5V-3Cr-1Zr are carried out using a Gleeble® 1500 device in the range of temperature between 763-843 °C and strain rates between 0.001-10 s-1. A strong dependence of the strain rate on the flow behaviour is observed. Processing maps are calculated at 0.3, 0.4, 0.5 and 0.6 of logarithmic strain using the modified dynamic material model developed by Murty and Rao. The use of light optical microscopy and EBSD measurements help to correlate the processing maps with the microstructure and thus to determine which mechanisms of restoration are activated during deformation. Three areas are recognized in the processing maps: at low strain rates the flow is stable and the η-values are strongly dependent on the temperature and on the strain. Dynamic recovery takes place in the β-phase where subgrain formation is detected. Continuous geometric dynamic recrystallization along the grain boundaries is determined for larger deformation values and it is more pronounced at high temperatures. For moderate strain rate values, the η-values show nearly no dependence on the temperature. At highest strain rates, the flow instabilities take place in the whole range of temperatures. The EBSD measurements show a strong misorientation along the beta grains without visible formation of subgrains. Continuous dynamic recrystallization occurs by lattice rotation at the β-grain boundaries with increasing strain. The processing maps can also be divided into an α and β and a β-field. In the two phases range, there is a stronger dependence of the flow behaviour on the strain rate than in the β-field.

hot deformation, titanium alloys, processing maps, EBSD

http://publik.tuwien.ac.at/files/PubDat_201657.pdf