PSI - Issue 53

Mariana Cunha et al. / Procedia Structural Integrity 53 (2024) 386–396 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

391

6

The results of microhardness measurements of the original AISI P20+Ni metal chips and the powder particles produced by PND 1, via disc milling in size range 38-212 µm are presented in Table 5.

Table 5- Microhardness of the chips and powder particles.

Sample

Microhardness

AISI P20+Ni Metal Chips Powder Produced by PND 1 (38

532 ± 31 HV 0.01 532 ± 26 HV 0.01

The powder produced by disc milling (PND 1) exhibits a comparable Vickers microhardness to that of AISI P20+Ni metal chips. This similarity is due to the insufficient plastic deformation during both the chip production and milling processes, which did not induce significant work-hardening in these samples. 3.3 Printings through Direct Energy Deposition Table 6 outlines the parameters applied for the eleven lines, considering the process variables like energy density and powder deposition density. Figure 4 illustrates the cross-sectional views of each line, such as bead, dilution and heat affected zone (HAZ) and Table 7 presents the relevant measurements corresponding to each line's characteristics made using the Image J software.

Table 6- Printing parameters combined considering the Taguchi L9

Scanning Speed [mm/s]

Powder Feed Rate [g/min]

Global Energy Density [J/mm 2 ]

Powder Deposition Density [g/mm 2 ]

Line

Laser Power [W]

1 2 3 4 5 6 7 8 9

500 900 500 900

14.2 14.2

8 3 6 8 6 4 3 8 3 3 8

17 30 32 57 61

0.004 0.002 0.006 0.008 0.003 0.004 0.012 0.011 0.006 0.012 0.011

7.5 7.5 8.0 2.0 6.0 4.0 2.0 6.0

1800 1800

14.2

107 119 143

500

1800

500 900 900

60

10 11

214

71

Thus, it becomes apparent that lines 1, 2, 3, 4, 7, 9, 10 and 11 exhibit a noticeable absence of dilution. These specific lines correspond to the deposition parameters with the lowest laser power, namely 500 W and 900 W. It appears that employing lower power is ineffective in facilitating dilution and establishing a bond between the printed and substrate materials. due to insufficient energy. Consequently, the parameters associated with these lines are excluded. Unlike lines 6 and 8, line 5 exhibits a small bead height despite displaying dilution. This could be attributed to the combination of a high scanning speed and a low powder feed rate, resulting in a lower density of powder deposition. Upon comparing line 6 and line 8, both exhibit interesting cross-section characteristics. Line 8 demonstrates a higher overall energy density compared to line 6, because despite having the same laser power, the scanning speed for line 8 is slightly lower. Consequently, more energy is available to melt the substrate, as evidenced by the greater depth observed in Figure 4 and Table 6. Furthermore, line 8 displays a slightly greater height in comparison to line 6. Additionally, the AR, representing the ratio between height and width, is higher for line 8. Considering these factors collectively, it was determined that the parameters from line 8 would be adopted for further investigation in the study. For deciding the overlapping, single layer printing was performed, and it was concluded that using the combination of parameters from line 8 with the sole modification of laser power being set at 1900 W, an overlapping of 60% would lead to less defects.