PSI - Issue 7

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

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

(c)

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Fig. 3. Morphologies of SLM produced Ti6Al4V alloy. (a) Morphology of XZ plane; (b) Morphology of YZ plane; (c) Morphology of XY plane; (d) Magnification morphology of XY plane.

(a) (b) Fig. 4. Geometry and dimensions of the tensile and C(T) specimens. (a) Tensile specimen; (b) C(T) specimen.

2.2. Mechanical testing Tensile and FCG experiments were performed for the respective SLM and conventionally manufactured Ti6Al4V alloys. Tensile tests were performed on INSTRON electromechanical static testing systems according to ASTM E8/E8M standard at room temperature (RT) and ASTM E21 at 400 ℃ . Three specimens were tested in each experimental condition. The FCG tests were carried out on MTS servo-hydraulic machines according to ASTM E647 at RT and 400 ℃ . The FCG was determined using a sine wave cyclic load in tension ( R = 0.1and 0.5) with a fixed amplitude △ P and a fixed cycle frequency of 10 Hz. The crack propagation was monitored visually using a camera system and the raw data was translated to a crack length ( a ) versus number of cycles ( N ) curve. The d a /d N ratios were then calculated using increasing local polynomial fitting derivation method and △ K values were determined. The fracture morphology of FCG specimens was investigated using Leica DMS 1000 stereoscopic microscope and FEI nano Field emission SEM to clarify the fracture mechanism of SLM produced Ti6Al4V alloy. 3. Results 3.1. Tensile testing The average tensile mechanical properties at RT and 400 ℃ of SLM and conventionally manufactured Ti6Al4V specimens are listed in Table 2. Significant difference is observed between vertical and horizontal orientation specimens on the platform. For RT, the ultimate tensile strength (UTS) of horizontal orientation specimen shows 53MPa higher than vertical orientation as well as the yield strength (YS) exhibits 91MPa higher than vertical orientation, whereas the two orientation specimens owns identical tensile ductility. For 400 ℃ , the tensile strength and ductility of vertical and horizontal orientation specimens have similar regularity with RT. It demonstrates that