Visual guide to the most common defects in powder bed fusion technology

Pores [1]

Gas pores
May arise from powder surface chemistry modification and/or trapped gas in particles that are released during melting and locked in during solidification
May also be due to key-hole effect for deep melt pools.

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Elongated, non spherical pores [1]
processed induced, due to an inefficient melting regime - either insufficient melting (too little energy input with respect to hatching distance or layer thickness) or spatter and fumes ejection (too much energy input)

Unmelted powder particles

Unfused powder
Processed induced – insufficient melting or overlap between successive layers or adjacent melted tracks

Balling effect [1]

Balling
solidification of melted material into spheres – due to lack of wettability with previous layer, driven by surface tension and directly related to melt pool characteristics [4]

​Cracking [2, 3]
Due to solidification cracking or grain boundary cracking or other macroscopic effects (macroscopic defects, residual stress, surface roughness, … )

warping schematic [7]

Warping
Can occur between 2 layers or at the boundary between support and part layer (curling)
May occur when the build is stopped and re-started or at the boundary between substrate and first layers
fect for deep melt pools.

Delamination [1]

Delamination
separation of successive layers
due to inappropriate melting overlap with previous underlying solidified powder or incomplete paticles melting.
Macroscopic effects and cannot be repaired by post-processing [5]

Swelling

Swelling
similar to the humping phenomenon in welding
occurs due to surface tension effects related to the melt pool geometry [6]

References
[1] W. J. Sames, F. A. List, S. Pannala, R. R. Dehoff & S. S. Babu (2016): The metallurgy and processing science of metal additive manufacturing, International Materials Reviews http://dx.doi.org/10.1080/09506608.2015.1116649
[2] L. N. Carter, M. M. Attallah and R. C. Reed: ‘Laser powder bed fabrication of nickel-base superalloys: influence of parameters; characterisation, quantification and mitigation ofcracking’, in ‘Superalloys 2012’, (ed. Eric S. Huron et al.), 577– 586; 2012, Champion, PA, John Wiley & Sons, Inc.
[3] TWI. What is hot cracking (solidification cracking)?, 2015. Available at http://www.twi-global.com/technical-knowledge/faqs/material-faqs/faq-what-is-hot-cracking-solidification-cracking/
[4] K. Kempen, L. Thijs, B. Vrancken, S. Buls, J. Van Humbeeck and J.-P. Kruth: ‘Producing, crack-free, high density M2 HSS parts by selective laser melting: pre-heating the baseplate’, in ‘Solid freeform fabrication symposium’, Austin, TX, 2013.
[5] K. Kempen, L. Thijs, B. Vrancken, S. Buls, J. Van Humbeeck and J.-P. Kruth: ‘Producing, crack-free, high density M2 HSS parts by selective laser melting: pre-heating the baseplate’, in ‘Solid freeform fabrication symposium’, Austin, TX, 2013.
[6] J. A. Manriquez-Frayre and D. L. Bourell: ‘Selective laser sintering of binary metallic powder’, in ‘Solid freeform fabrication symposium’, Austin, TX, 1990, 99–106.
[7] Di Wang, Yongqiang Yang, Ziheng Yi, Xubin Su, Research on the fabricating quality optimization of the overhanging surface in SLM process, The International Journal of Advanced Manufacturing Technology April 2013, Volume 65, Issue 9, pp 1471-1484