The Effect of Heat Treatment on the Structure and Fracture Behavior of VST5553 Titanium Alloy

Wednesday, May 13, 2015: 2:00 PM
Room 201B (Long Beach Convention and Entertainment Center)
Prof. Sergey Demakov , Ural Federal University named after the First President of Russia B.N. Yeltsin, Yekaterinburg, Russia
Prof. Dmitry Gadeev , Ural Federal University named after the First President of Russia B.N. Yeltsin, Yekaterinburg, Russia
Prof. Anatoly Illarionov , Ural Federal University named after the First President of Russia B.N. Yeltsin, Yekaterinburg, Russia
The BASCA (Beta Annealed, Slow Cooled, Aged) heat treatment route developed by BOEING is known to be the most advanced processing route for large sized titanium parts of airplanes for now if high level of fracture toughness without sensitive strength level degradation is demanded.

The structure composition and the mechanical properties of large sized semi-product made of BASCA treated VST5553 (Russian version of Ti-5553 alloy) titanium alloy have been considered in the study.

Three-point bend and slow deformation mechanical tests revealed that fracture of the specimens occurs mainly through grain boundaries and interlamellar beta phase layers. The BASCA treated alloy has been found to be characterized by coarse beta grains with continuous grain boundary alpha phase precipitations. The grain body consists of primary and secondary lamellar alpha precipitates. Large amount of precipitation free beta areas at grain and phase boundaries has been discovered. By means of fractographic analysis it has been proved that fracture of the alloy during mechanical testing develops via these participation free beta areas.

To eliminate the presence of continuous untransformed beta areas in the structure additional heat treatment has been developed. The heat treatment includes another high temperature double step annealing at 770…790 °Ñ followed by second aging at 550…600 °Ñ.

The use of the treatment resulted in increase of the ultimate bend stress up to 1.32 times, the fracture toughness up to 1.12 times and ductility – up to 1.5 times.

See more of: Titanium Alloy Technology II
See more of: Titanium Alloy Technology