Effect of Surface Finish and Temperature on Low Cycle Fatigue Behavior
of GRCop-42
Abstract
This study investigates various surface finishes on the low cycle
fatigue properties of laser powder bed fusion GRCop-42. The surfaces
evaluated include as-built, machined, and chemical mechanical polishing
with two surface finishes (1 .0% and 2 .0%).
Additionally, the LCF life of polished GRCop-42 was assessed across a
range of temperatures, including cryogenic (−195 ◦ C ), ambient, and
elevated temperatures (200 ◦ C , 400 ◦ C , 600 ◦ C , and 800 ◦ C ), at
three fatigue strain amplitudes: 0 .7%, 1 .0%, and 2
.0%. It was found that surface finish does not significantly
affect the LCF life of the specimens since specimens with the as-printed
surface exhibited a similar fatigue life to that of machined and
polished specimens. In contrast, temperature significantly influences
the fatigue life, with the average fatigue life decreasing as
temperature increases. Furthermore, stress was examined as a function of
fatigue life at different strain levels. The surface finish shows little
effect on the cyclic hardening/softening, with all exhibiting an initial
cyclic hardening followed by progressive cyclic softening. We found that
the testing temperature from cryogenic to elevated temperature induces a
deformation transition, affecting the material’s cyclic hardening and
softening behavior. Cryogenic temperatures led to cyclic hardening
followed by cyclic stabilization, while ambient temperature and 200 ◦ C
displayed initial cyclic hardening followed by progressive cyclic
softening. Specimens tested at 400 ◦ C and above displayed cyclic
softening throughout the test. Finally, fractographic analysis
demonstrated that surface finish impacted the plastic deformation, where
specimens with the as-printed and polished surfaces had a brittle
fracture while machined specimens showed a more ductile behavior.
Moreover, specimens tested at cryogenic and ambient temperatures
exhibited brittle fractures, while specimens tested at elevated
temperatures displayed plastic deformation and secondary cracks on the
gage section. Additionally, increasing the test temperature led to
shorter and broader secondary cracks.