Dj. Simbi et Jc. Scully, ASPECTS OF FRACTURE MORPHOLOGY EXHIBITED IN THE STRESS-CORROSION BEHAVIOR OF TI-155 IN METHANOL HYDROCHLORIC-ACID SOLUTION, Corrosion, 53(4), 1997, pp. 298-305
Stress corrosion cracking (SCC) of Ti-155 (UNS R50400) was investigate
d in methanol-hydrochloric acid (MeOH-HCl) solution in preexposure and
anodic polarization experiments using specimens with tensile axis in
the parallel or transverse orientation to the rolling direction. Inter
granular penetration data showed a dependence of the intergranular cor
rosion process on preexposure time. Susceptibility to SCC, as indicate
d by the elongation to failure index (epsilon(m)/epsilon(a)) increased
with increasing preexposure time and applied anodic current density.
Fractographic analysis by scanning electron microscope (SEM) of fractu
red specimen surfaces in preexposure and anodic polarization experimen
ts showed a fracture morphology comprised of intergranular at the expo
sed surface edge, an intermediate transgranular cleavage zone, and a t
erminal ductile region. The transgranular cleavage and associated flut
ings were more pronounced in Specimens tested with the tensile axis in
the transverse orientation than those tested with their tensile axis
parallel to the rolling direction. These observations supported the vi
ew that intergranular fracture and transgranular cleavage occuring dur
ing SCC of titanium in MeOH-HCl solution is caused by mechanisms relat
ed to anodic dissolution and hydrogen embrittlement (HE), respectively
. A mechanism to describe the simultaneous Occurrence of dissolution a
nd NE at the grain boundary was suggested. In anodic polarization expe
riments, outer grains of the intergranular zone exhibited ''sliced pat
terns.'' me extent of slicing, which was prominent in specimens tested
in the parallel orientation increased with increasing anodic current
density. In many cases, the sliced patterns were aligned in what appea
red to be crystallographic planes. The occurrence of slicing, which ha
s been related to formation of a hydride phase, was considered to be m
echanical in origin At applied current densities greater than or equal
to 40 mA/mm(2), the slicing effect was extensive, with some slices di
sintegrating. me disintegration product of the sliced layer was analyz
ed by x-ray diffraction and confirmed to be titanium hydride (TiH1.9).