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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phase grain boundaries which are filled with very fine needles of acicular αʹ -martensite and α+β lamellar structure. 60% portion grains are full of fine αʹ -martensite while 40% portion grains are full of α+β lamellar structure. Part prior β g rain boundaries are marked by α layer s. The tensile specimens and the compact tension C (T) specimens were machined respectively from the cylindrical rods and rectangular blocks. The geometry and dimensions of the two kinds of specimens are shown in Fig. 4. The thickness of the C (T) specimen is 10mm. The orientations of the tensile specimens are parallel and perpendicular to the build direction Z axis, in line with the direction of cylindrical rods shown in Fig. 1. The orientations of the C (T) specimens shown in Fig. 1 are labelled according to ASTM E399 standard: axis direction perpendicular to the notch plane followed by the axis direction in which the crack is expected to propagate. Consequently, three different specimen geometries arise, namely XY, YZ and ZX. Tensile and FCG performance of four kinds of conventionally manufactured Ti6Al4V alloys (casting, bar and two forging alloys with different heat treatment) are concerned in this study to compare with SLM produced Ti6Al4V. Same geometry and dimensions tensile and C (T) specimens of these conventional alloys were machined under equipment condition and criterion in accordance with SLM produced Ti6Al4V to ensure all the specimens are in same state before testing.

Building direction

YZ

ZX

XY

Fig. 1. Layout of the tensile and C(T) specimen blocks on Fig. 2. Ti6Al4V powder particles used to fabricate the build platform with the standard AM axis system. the SLM samples in this study. Table 1 Norm and actual chemical composition of the powder. Al(%) V(%) Fe(%) O(%) C(%) N(%) H(%) Y(%) Si(%)

Ti (%)

Norm value

5.6~6.5

3.4~4.5

≤0.25

0.08~0.13

≤0.05

≤0.03

≤0.0125

≤0.005

≤0.1

Balance

Actual value

6.29

3.99

0.2

0.12

0.009

0.02

0.002

<0.005

0.031

Balance

(a)

(b)

Z

Z

X

Y