PSI - Issue 53

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

389

4

2.5 Microstructural and Mechanical Characterization

To study the characteristics of the powder and metal chips and the final microstructure of the printed samples via L-DED, the samples were prepared metallographically. This preparation was initiated with the cutting of cross section aided by Mecatome T260 cutting machine. Afterwards, all cut samples were cold mounted in epoxy resin and ground usnig SiC abrasive papers to 4000 grit sequentially, and finally polishing them using diamond suspension of 6 and 1µm respectively. Nital 2% was used as an etchant to reveal microstructure. To conduct metallographic observations, digital microscope Leica DVM6 A and optical microscope (OM) Leica DM4000 M was utilized. A scanning electron microscope (SEM) (FEI Quanta 400 FEG (ESEM, Hillsboro, USA) equipment, using secondary electron (SE) and backscattered electron (BSE) modes) equipped with energy-dispersive X-ray spectroscopy (EDS) (EDAX Genesis X4M, Oxford Instrument, Oxfordshire, UK) was utilized to perform comprehensive microscopic analysis as well as semi-quantitative chemical analyses. Mechanical characterization was performed through Vickers hardness tests following ISO 6507-1:2023 standard (ISO 2023). Metal chips and powder specimens underwent 10 indentations with 25 gf (HV0.025) indentation load, while L-DED manufactured samples had indentations with 10 and 100 gf (HV 0.01 and HV 0.1) indentation loads. Microhardness tester FALCON 300 was used to perform these tests. 3. Results and Discussion 3.1 Chemical Composition The chemical analysis enables a comparison of the semi-quantitative and qualitative chemical composition of the material, both before and after the milling process. Table 3 presents the chemical compositions obtained via SEM EDS analysis for initial metal chips and the powders produced in the current study. In this manner, it is feasible to state that the chemical composition of the milled particles is similar to that of the chips, the slight differences is attributed to characteristics of EDS analysis that is a semi-quantitative technique performed only on a specific-tiny volume of the sample excited by the energy source.

Table 3- Semi-quantitative chemical composition (wt. %) of metal chips and powder particles (except C and S)

C

S

Si

Mo 0.38 0.83 0.56

Cr

Mn 1.73 1.93 1.87

Ni

Fe

Metal Chips Powder Particle PND 1 (38 µm

0.51 - -

<0.0055 - -

0.77 0.71 0.65

2.11 2.33 2.14

0.79 0.91 0.90

Rem.

3.2 Powder Production for L-DED Since the goal was to obtain the maximum amount of powder particles in the size range of 38-212 µm from the metal chips. The weight % powder yield (in size ranges of interest) of each milling procedure was calculated after sieving analysis (Figure 2). With this analysis it is possible to conclude that PND 1 is a potentially suitable procedure. PND 1 only needs 75 minutes of milling time to obtain 63 wt.% yield of powder particles in size range of 38-212 µm. Consuming only 56% of the milling time of that of PND 2, PND 1 can achieve almost same yield as of PND 2 for the metal powder in 38-212 µm range. Consequently, PND 1 showcased lower energy consumption and economic viability while yielding comparable results. Approximately 1500 grams of powder was produced using PND 1. A total 18 hours of total milling time was required to produce this powder, accounting for nearly 57 hours including break times (a 10-minute pause after every 5 minutes of milling and a 30-minute pause after every 30 minutes of milling). Therefore, on average, it takes approximately 38 hours, including break times, to produce 1 kilogram of powder.