PSI - Issue 7

Z.H. Jiao et al. / Procedia Structural Integrity 7 (2017) 124–132 Z.H. Jiao et Al./ Structural Integrity Procedia 00 (2017) 000–000

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tensile strength of SLM produced Ti6Al4V alloy at RT and 400 ℃ is significantly affected by building orientation, nevertheless, the ductility has nothing to do with building orientation. Compared with the tensile properties at RT and 400 ℃ of conventionally manufactured Ti6Al4V alloys, shown in Table 2, the UTS and YS of horizontal orientation specimens of SLM produced Ti6Al4V are superior to that of all the conventionally manufactured specimens concerned. However, the UTS and YS of vertical orientation are inferior to some kinds of conventional alloys. The ductility of SLM produced Ti6Al4V is in accordance with forging and bar alloys and superior to casting alloy obviously.

Table 2 Tensile properties of SLM and conventionally manufactured Ti6Al4V alloys.

UTS (MPa)

YS (MPa)

Elongation (%)

Reduction of area (%)

Alloys

Temperature ( ℃ )

Orientation

Vertical

988

871 962 545 619 860 495 920 555 935 575 885 420

14 15 16 15 15 17 13 15 16 17 11 11

48 52 65 62 44 56 44 61 43 56 23 36

RT

Horizontal

1041

Ti6Al4V (SLM)

Vertical

688 742 910 605 980 670 705 970 505

400

Horizontal

RT 400 RT 400 RT 400 RT 400

/ / / / / / / /

Ti6Al4V (1# forging)

Ti6Al4V (2# forging)

1000

Ti6Al4V (bar)

Ti6Al4V (casting)

3.2. Crack propagation The d a /d N - △ K curves of SLM produced Ti6Al4V specimens are shown in Fig. 5. Fig. 5(a) and (b) display the effect of stress ratio as well as specimen orientation for each experiment temperature, whereas Fig. 5(c) and (d) show the effect of experiment temperature as well as specimen orientation for each stress ratio. It must be noted that the experimental work did not include the determination of the threshold △ K values. The d a /d N - △ K curves of different specimen orientations (XY, YZ and ZX) are in accordance with each other. It seems no anisotropy on FCG resistance of SLM produced Ti6Al4V. For each experiment temperature, the alloy shows higher FCGR under the stress ratio of 0.5 than 0.1, which conforms to the basic rule that metal materials exhibit a faster FCGR under a higher stress ratio. However, the d a /d N - △ K curves of stress ratio of 0.1 and 0.5 for RT and 400 ℃ show close to each other, furthermore, the tendency becomes more and more obvious with △ K increasing. The Paris equation d a /d N =CΔ K m fitting curves of FCG experiment results are also present in Fig. 5. The equation parameters are listed in Table 3. There is intersection point between d a /d N - △ K curves of RT and 400℃ , shown in Fig. 5(c) and (d). For stress ratio of 0.1, the two temperatures curves intersect at △ K of 25.4MPa·m 1/2 and FCGR of 3.49 × 10 -4 mm/cycle. For stress ratio of 0.5, the curves intersect at △ K of 18.8MPa·m 1/2 and FCGR of 1.97 × 10 -4 mm/cycle. The steady stage FCGR at 400 ℃ shows faster than RT in the △ K region below the intersection point and slower than RT in the △ K region above the intersection point. It demonstrates that the steady stage FCGR at RT is slower than 400 ℃ in the earlier stage, but grows faster with the increase of △ K value. When △ K exceeds the intersection point, The FCGR at RT becomes faster than 400 ℃ . The d a /d N - △ K curves of SLM and conventionally manufactured Ti6Al4V under the stress ratio of 0.1 and experimental temperature of RT and 400 ℃ are shown in Fig. 6. For RT, the FCGR of SLM produced Ti6Al4V is slower than bar alloy and basically consistent with forging and casting alloys, but it shows faster than forging and casting alloys in the lower △ K region. For 400 ℃ , the FCGR of SLM produced Ti6Al4V is slower than bar and 1#