PSI - Issue 7

88 R.D. Xu et al. / Procedia Structural Integrity 7 (2017) 84–91 R. D. Xu, et al. / Structural Integrity Procedia 00 (2017) 000–000 5 SLM K536 X-orientation specimens are found to have high and 0 . 2 values at every temperature in contrast with those of Z-orientation specimens. The b value of X-orientation specimens is 800 MPa at room temperature, which is 3.13 percent higher than it of Z-orientation specimens what is 775MPa; and at 400 º C, 500 º C, 600 º C, and 700 º C, the percent is between 1.98~4.10. The 0 . 2 value of X-orientation specimens is 338 MPa at room temperature, which is 3.85 percent higher than it of Z-orientation specimens what is 325 MPa; and at 400 º C, 500 º C, 600 º C, and 700 º C, the percent is between 1.88~6.14. There is a regular difference of monotonic tensile properties between the X-orientation and Z-orientation specimens that may be caused by the lack of fusion between layers due to adverse laser penetration. Compared to the data of wrought K536 alloy, SLM K536 alloy exhibit higher monotonic properties value at most points what are shown in Fig. 3. This means that the monotonic tensile strength of SLM K536 is pretty good. The main difference is at 600 º C , where there is a skyrocket in the wrought K536 curves as a slow-fall phase in the SLM K536 curves. It needs further research. 3.2. Fatigue behavior The results of the fatigue tests are shown in Fig. 4, in terms of the S-N plot of maximum stress vs. log number of cycle to failure. The target fatigue lifetime was set at 1 x 10 7 cycles, as the “run-out” samples marked by arrowheads. The stress-life curves are acquire by using three-parameter exponential function [9], which is simple in form and applicable to describe the relationship between maximum stress and fatigue life at a settled stress radio, R . The function is: ( ) f max m n N C σ σ − = (1) This equation can be rewritten in the form ( ) f 1 2 max 3 log log N B B B σ = + − (2) where: 1 ， 2 ， 3 are material constants, 1 = log ， 2 = − ， 3 = 0 . Computation value of 1 ， 2 ， 3 of each S-N curve are listed in Table. 2. Table 2 Coefficients of the fitting formula of the S-N curve of SLM K536 at different temperatures in two building orientations

orientation

R

B 1

B 2

B 3

r

T, ºC

K t

400

1

0.1

77.24

-25.90

-

0.852

X

600

1

0.1

30.82

-10.16

196.02

0.936

400

1

0.1

17.81

-5.70

429.20

0.884

Z

600

1

0.1

65.70

-22.24

-

0.947