PSI - Issue 19

Masanori Nakatani et al. / Procedia Structural Integrity 19 (2019) 294–301 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

297

4

Fig. 2. Shape and dimensions (mm) of rotating bending fatigue test specimen.

Table 2. Surface roughness of as-built specimen.

S a

S z

R Sm

AM process

Max.

Ave.

Max.

Ave.

Max.

Ave.

EBM

45 20

32 12

320 128

211

978 907

696 535

DMLS

88

Fig. 3. SEM images of surface of as-built specimens.

3. Results and discussion

3.1. Surface roughness and morphology

Table 2 summarizes the average and maximum values of measured surface roughness. Here, the surface roughness of as-built specimen with/without HIP was not distinguished because HIP does not affect the surface morphology. The S a value of as-built EBM specimen is 2 times higher than that of as-built DMLS specimen. The S z values have also the same tendency. The difference of particle size and building layer thickness influence the surface roughness of as-built specimen. Figures 3 and 4 show SEM images and bird-eye height images of as-built specimen respectively. It can be seen that many unfused particles remain on surface. The existence of unfused particles enlarges the scatter of surface roughness value. The as-built surface has not only periodic but also three-dimensionally complex surface morphology.

3.2. S-N curves

Figure 5 shows S-N curves for EBM and DMLS specimens. The dotted lines in Fig. 5 indicate the ideal fatigue limits for EBM and DMLS specimens with HIP. It is well known that there is a very good correlation between