PSI - Issue 5

Author name / Structural Integrity Procedia 00 (2017) 000 – 000

6

Marcin Wachowski et al. / Procedia Structural Integrity 5 (2017) 422–429

427

Fig. 5. Fatigue curves obtained for smooth samples

Similar considerations for smooth samples are presented in Fig. 5, therefore the marks in this figure are the same as in Fig. 4. It is interesting to note that in the case of this shape of samples positive impact of the heat treatment is visible for the whole range limited durability. At the highest level of maximum stress of 350 MPa, the fatigue life of the samples after the heat treatment is even more than twice higher in comparison to the base material. The number of cycles to failure for the samples after the heat treatment is higher by about 30 % in relation to basic material at the level of  max =300 MPa and decreases to 20% at the level of  max =250 MPa. Positive effect of heat treatment disappears at a level of 175 MPa. As might be expected the intersection of the regression line in this case was at the maximum stress level of 175 MPa. Additional benefit of heat treatment was an increase in the endurance limit for these samples. The fatigue limit value increased from Sf = 153 for basic material to Sf = 163 for smooth samples after heat treatment (Fig. 5). Macro and microfractographic research results revealed character of fatigue fracture surface of the developed structure. Fatigue fracture surfaces of samples without cracking initiators are shown in Fig. 6-7. Scanning electron microscope observation of samples topography showed the presence of multiple fracture characteristic eg. smooth fracture surface (Fig. 6) in the border zone Ti6Al4V/AA1050.