Fig. 7: Dependences of the cavity number density ρ after 10
cycles in (a) and the cavitated GB area fraction f in (b) on the
tensile and compressive hold times of t t andt c
3.4 Effect of stress magnitude in tensile and compressive
holds
Fig. 8a presents the effect of Δσ t on finalρ (i.e. calculated after 10 cycles); the values of
Δσ t and t t are varied for
this purpose. Other input parameters are kept the same as those listed
in Table 2. A positive correlation is found between ρ and
Δσ t for both t t=100 s and
60 s, suggesting that a higher tensile stress promotes a higher cavity
nucleation rate. However, the breakdown of this correlation occurs when
Δσ t is lower than ~145 MPa under
the condition of t t=60 s. This sharp decrease in
final ρ is related to the effect of compression phase on cavity
sintering. When the tensile stress reduces to lower level, the
associated σ n under a fixedt t does not allow the nucleated cavities to grow
large enough to be survived from the following compression phase where
the sintering would occur. As shown in the enlarged view of Fig. 8a,
such a threshold Δσ t appears at the stress level
of ~105 MPa under the condition oft t=100 s. This means that the threshold value for
Δσ t to generate the cavitation is inversely
proportional to t t (i.e. 145 MPa fort t=60 s as compared with 105 MPa fort t=100 s)