2.2 Experimental procedure
Cylindrical specimens with a gauge diameter of 5 mm and a gauge length
of 25 mm were used in this study. All fatigue test specimens were cut
from the same turbine disc. These specimens were polished with fine
abrasive paper and then electropolished to minimize the effect of
residual stress on the surface.
Fatigue tests were stress-controlled and conducted on a Zwick Roell
resonance testing system. The loading frequency is 80Hz in the test. In
order to simulate turbine disc operation conditions, the maximum
stresses of high and low amplitude loads were designed to be the same
value, i.e., 1200 MPa, as shown in Fig 1. The test temperature was 600℃,
and the test was conducted in the air environment. It should be noted
that the entire test time is very short. It is known from the materials
handbook that creep deformation and creep damage caused by the mean
stress are very limited. Therefore, the creep effect in this test can be
neglected. The detailed test matrix is listed in Table 2.