The single line tracks used by the Swiss team to identify the optimal 3D printing parameter set. Image via the Applied Materials Today journal.
Optimized precious metal printing
Initially, using single line tracks, the researchers were able to determine the ideal parameters for their experiments, which turned out to be at a laser power level of 40-60W, with anything higher than 80W resulting in print deceleration. Having identified the optimal set up, the team proceeded to fabricate twelve samples each measuring 5 x 5 x 1mm3 , but early prototypes exhibited highly-irregular shapes.
To correct this distortion, the researchers introduced a one-second wait between the printing of each layer, giving the samples time to cool between successive laser tracks. Interestingly, upon later dissection, each of the test specimens featured an amorphous in structure, but the part produced at 60W proved to have the widest processing window, validating the team’s earlier hypothesis.
Leveraging their final parameter set, the engineers wrapped up their tests by 3D printing a 3mm x 4mm cylinder, which exhibited a porosity volume of just 0.4%. However, the team did concede that their results could be affected by the resolution of their μCT scan, and that the specimen’s compressive strength was 14% less than casted alternatives, proving the need for further process optimization.
What’s more, summary kinetic analysis revealed that the researchers’ parts crystallized more slowly than they could be processed, suggesting that cross-contamination and powder atomization may have impacted on their findings, thus the issue warrants investigation before such BMGs can be deployed as an end-use precious metal substitute.
“Despite the good glass-forming ability of Pd-based BMGs, the critical aspects in LPBF fabrication for avoiding crystallization are not so much the thermal conditions, but the absence of impurities,” concluded the team in their paper. “[Our] work illustrates how the combination of precious metals, amorphous state and AM can lead to promising applications, especially in the jewellery and watch industries.”