Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Materialien/Werkstoffe Poster: Do., 13:00–15:30 D-P389
Phase distribution and texture analysis over a gamma-TAB/Ti64 friction
weld
Seung-Jun Jin 1 , Heinz-Guenter Brokmeier 1,2 , Sabine Lenser 1 , Volker
Ventzke 3 , Mustafa Kocak 3 , Jens Homeyer 4
1 Institute of Materials Science and Engineering, Clausthal University of Technology,
Germany – 2 GKSS Research Center, Department WFN, Geesthacht, Germany
– 3 GKSS Research Center, Department WMF, Geesthacht, Germany – 4 Hasylab at
DESY, Hamburg, Germany
Titanium alloys are widely used for structural application, especially where high specific
stiffness is required at elevated temperature. In the present investigation the friction
welding process between two rods of Ti6Al4V alloy and of γ- TAB with 24.5mm φ and
80mm length are of basic interest. TiAl-based alloys have a high melting temperature,
a good oxidation resistance and good strength at high temperatures. Ti6Al4V is one
of the standard Ti-alloys, relatively cheap but limited in high temperature application
up to 600 ◦ C. The microstructure of nominally γ-TAB can be single phase γ-TiAl,
or in slightly leaner compositions, two-phased composition of tetragonal γ-TiAl and
of hexagonal α2-Ti3Al. γ-TAB alloy had been developed at GKSS-Research Center
Geesthacht for application in turbine construction was available for investigations. The
Ti6Al4V alloy which is also two-phased, hexagonal α-Ti and cubic β-Ti, was available
in addition. Among others the phase distribution in the weld and in the heat affected
zone, describing the joining process is of great importance for the quality. High energy
X-rays of 100keV were used to scan over the welding seam in order to investigate the
phase composition. The measurements were carried out at the high energy beam line
BW5 at HASYLAB with local resolution of 1x1mm slits and an overlapping z-scan of
steps in 0.5mm. Two problems occur by this experiment: Firstly, the welded seam is
smaller than 0.5mm and secondly the γ-TAB is rather coarse grained. The used Mar345
image plate detector covers a set of complete Debye-Scherrer ring able to calculate
integrated sum diffraction pattern. The data analyses were carried out on MAUD
(Material Analysis Using Diffraction) program doing phase analyses. Due to the sum
diffraction pattern, the texture influence on quantitative phase analysis was reduced.
In the basic material we have a two-phased system of hexagonal α-Ti (P 63/mmc, about
82wt.%) and of cubic β-Ti (I m3m, about 18 wt.%) for Ti6Al4V and tetragonal γ-TiAl
(P 4/mmm, about 98.2 wt.%) and hexagonal α2-Ti3Al (P 63/mmc, about 1.8 wt.%)
for γ-TAB. Inside the weld a small region of at least three crystallographic phases
were observed. In addition crystallographic textures were measured using neutron
synchrotron diffraction.