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Characterization of the β Phase Decomposition in Ti-5Al-5Mo-5V-3Cr at Slow Heating Rates

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DOI: 10.4236/ojmetal.2011.11001    5,437 Downloads   13,643 Views   Citations

ABSTRACT

The influence of slow heating rates: 2, 5, 10 and 30?C/min (0.033, 0.083, 0.166 and 0.50℃/s) on the β phase decomposition of Ti-5Al-5Mo-5V-3Cr (Ti-5553) during continuous heating were characterized by differential scanning calorimetry (DSC) analysis, light microscopy, scanning electron microscopy, X-ray diffraction and hardness testing. Starting microstructure was the β phase obtained by heating the Ti-5553 above the Tβ temperature and a water quench. Results show that heating rate has a significant impact on the precipitation mechanisms and on the β→α transformation in this range of heating rates. The main formation of α precipitates occurs between 500 and 600℃at all heating rates tested.A heating at 2℃/min produces very fine and homogeneously distributed α plate precipitates which have nucleated on the nanometer size ωiso precipitates. The ωiso precipitates between 350 and 400℃. At higher heating rates 10, 15 or 30℃/min, the amount of precipitation of ωiso is lower so an additional formation of nanometer size precipitates occurs between 450 and 500℃ It is supposed that both precipitates act as nucleation sites for α phase precipitation. The resultant microstructure consists in a fine intragranular distribution of α precipitates and a coarser precipitation of α at the grain boundaries. It is shown that the precipitation of ωiso phase retards or prevents the precipitation of nanometer size precipitates occurring between 450 and 500℃. This cannot be generalized to all the β-metastable titanium alloys since Ti-LCB does not exhibit the same heating rate dependence on DSC curves.

Conflicts of Interest

The authors declare no conflicts of interest.

Cite this paper

Q. Contrepois, M. Carton and J. Lecomte-Beckers, "Characterization of the β Phase Decomposition in Ti-5Al-5Mo-5V-3Cr at Slow Heating Rates," Open Journal of Metal, Vol. 1 No. 1, 2011, pp. 1-11. doi: 10.4236/ojmetal.2011.11001.

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