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)