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F. Warchomicka, C. Poletti, M. Stockinger, H.P. Degischer:
"Microstructural evolution of titanium base materials during hot deformation";
Talk: Materials Science and Engineering, Darmstadt - Germany; 08-24-2010 - 08-26-2010.

Titanium alloys are attractive for structural applications in the aerospace industry due to their high specific strength in comparison with other engineering materials. These properties are strongly related to the microstructure obtained during thermo-mechanical processes. The influence of the processing parameters on the microstructure is investigated to prepare criteria for the control of these processes. The studied alloys: near beta Ti-10V-2Fe-3Al (Ti1023) and Ti-5Al-5Mo-5V-3Cr-1Zr (Ti55531) and alpha-beta Ti-6Al-4V (Ti64) are used in landing gears and other structural parts in aircrafts. The hot compression behavior near the beta transus temperature of these alloys is investigated by means of a Gleeble 1500 and a TMTS servotest machine, analyzing the flow curves and the microstructure evolution for different strains and strain rates. The local strain within the compressed samples is determined by finite element methods and correlated to the microstructure observed.
In the alpha-beta field, the flow curves show a continuous softening at 0.1 and 1/s and steady flow at 0.01/s of strain rate. A steady flow for all the strain rates is observed above beta transus temperature.
The use of EBSD measurements help to determine the restoration mechanism involved during the deformation. Deformation within the alpha-beta region is accompanied by continuous dynamic recrystallization for all the alloys: the alpha grains of Ti64 and the beta grains of the near beta alloys show an increment of the cumulative crystallographic misorientation by reaching the grain boundary and the formation of new grains. The same mechanism is observed in Ti55531 deformed within the beta field. Dynamic recrystallization in Ti64 during deformation above beta transus is determined by light optical microscopy, denoting a dependence of the degree of recrystallization with the initial grain size and the strain rate applied.

titanium alloys, EBSD, hot deformation