PSI - Issue 17

Thomas Simson et al. / Procedia Structural Integrity 17 (2019) 843–849

845

Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Table 1. Chemical composition provided by producer of “ new ” MAR 300 powder. Material (wt-%) Fe Co Ni Mo Ti Al Cu Cr Mn Si C P S New Balance 8.76 18.25 4.80 0.64 0.06 0.03 0.12 0.06 0.02 0.01 <0.01 0.01

Table 2. Process parameters for different pattern. Pattern Laser power (W)

Scan speed (mm/s)

Hatch spacing (mm)

Layer thickness (mm)

In Fill

285 153 145

960 600

0.11 0.11 0.11

0.04 0.12 0.16

UpDown DownSkin

2400

2.2. Characterizations

The mechanical properties were evaluated by hardness measurements, tensile and notch impact resistance tests. As the manufacturing process results in a rough sample surface, they must be post-processed by grinding processes before being examined. The post-processing took place on a surface grinding machine, up to a roughness of Rz 4.8 μm. The hardness of the samples was measured by a Frankoskop Vickers hardness tester according to the 98 N loaded HV10 scale and is represented by an average value from ten measured points. The tensile properties were evaluated by an UTS Eurotest 250 universal material testing machine (according to ASTM E8 (2013)) with the speed of 5 mm/min. The ultimate tensile strength ( Rm ), yield strength ( Rp 0.2 ) and elongation at failure ( ε tot ) of the LPBF samples were determined as an average value from three measured samples. The size of the standard samples was 140 x 25 x 3 mm ( G 40 mm, W 12 mm). The notch impact test is used to determine material toughness by hitting a test sample with a hammer, mounted at the end of a pendulum according to ASTM E-23-96. The sample is broken by a single blow from the pendulum that hits the middle of the unnotched side. The difference between height of fall and height of rise gives the amount of energy absorption involved in deforming and breaking the sample. A V-shaped notch is generally used in the impact sample in order to control the fracture process by concentrating stress in the area of minimum cross-section. The size of the standard sample is 10 x 10 x 55 mm with a notch as defined in the same standard (Fig. 1). An Amsler RKP 450 with pendulum construction is used. This tester is particularly suitable for quick test runs (under 5 s) and ASTM E 23 tests on tempered and cooled samples. The samples were tested at three different temperatures, 20 °C, -20 °C and -50 °C. The pendulum hammer (300 J) with a mass of 22 kg strikes the samples at a velocity of 5.23 m/s from a 150° angle of attack and a resonant circle radius of 0.748 m. A test setup for ball joints with an LPBF built support frame was tested for frequency response at hydro-pulse testing lab. The test simulated an external frequency from 5 to 50Hz with constant amplitude. A vibration actuator TIRA TV 52110 with the power amplifier BAA120 was used for this application. The acceleration response was measured by laser-Doppler accelerometer OMETRON VH 1000-D. The measurement of the speed signal of the laser vibrometer was performed with the NI 9233 AD card with USB interface. As a signal source of sinus signal the function generator MATRIX MFG 2110A is used.

Fig. 1. Horizontal and vertical samples for mechanical tests.

3. Results and discussion

3.1. Powder characteristics

For the LPBF process performance, the quality of the feedstock powder is an essential factor. The process relies on the melting of thin powder layers, which are selectively melted for producing the massive metallic component. Consequently, basic powder properties such as particle size range, particle morphology, apparent density, flowability and surface oxide are of great importance. Since the powders are used multiple times (not compacted powder from the space between the built parts in mixtures with fresh powder), powder properties can change by ageing effects. Fig. 2 shows the morphology of “ new ” (fresh), “ used ” (after sieving)