PSI - Issue 13

5

Wenbo Sun et al. / Procedia Structural Integrity 13 (2018) 1020–1025 Author name / Structural Integrity Procedia 00 (2018) 000–000

1024

According to Paris law   m da dN C K   , the constants , C and m can be obtained. The calculated values are summarized in Table 2. The constant m represents the slope of the scatter in Fig 5, and the larger value represents high fatigue crack growth rate.

Table 2. Paris constants of different building directions Building Directions C

m

0 °

1.89187e-10 1.66546e-10 3.59138e-11

2.22344 2.21466 2.72869

45 ° 90 °

4.2. Fracture Surface The fracture surfaces were taken by the digital microscope QM413T. Fig 6 (a), (b) and (c) are for the 0°, 45° and 90°specimens separately. Fracture surface can be divided into three regions according the fatigue crack growth rate. For the 0° building direction specimen, the macroscopic fracture surface is relatively flat, and small intersecting grooves can be clearly seen. Some inclusions can be observed in Region II, which is due to the fact that the particle powders are not fully melted when the laser beam runs fast. In the Region III, the specimen was fractured under the static load, so the section is rough. For 45° and 90°specimens, more inclusions and pores can be observed, and 90° specimen is rougher. The deposition layer can be observed in 90° specimen, and fatigue striations are not clear.

a

b

c

90°

0°

45°

Inclusion

Figure 6. Fracture surfaces of specimens with different building directions

5. Conclusions In this paper, the fatigue crack propagation behavior of Ti-6Al-4V with three different building directions manufactured by selective laser melting is studied, and da dN K   curves are obtained. The fracture morphologies of different building direction specimens were taken and analyzed. The conclusions are as follows: 1. The fatigue crack growth life of 45° specimen is 1.49 times longer and 1.46 times longer than of that of 90°and 0°specimen separately. 2. The fatigue crack growth rate of 45° specimen is slow, and the fatigue crack growth rate of 0° and 90° specimen is close. 3. The macroscopic fracture surface of 0° building direction specimen is relatively flat, and small intersecting grooves can be seen. More inclusions and pores can be observed in 45 ° and 90 ° specimen, and 90° specimen is rougher. The deposition layer can be observed in 90° specimen, and fatigue striations are not clear.