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Metals 2016,6, 218
Analysis of the fracture surfaces of broken tensile specimens clearly showed that fracture of
the as-built sampleswas basedon aductile-type failuremechanismconsisting in voidnucleation,
growth and their coalescence. Larger voids mainly originated from pre-existing defects, such as
unmeltedpowderparticles(seesphericalparticlesinFigure11a),splats(largerremeltedparticlesthatare
blownawayfromthemoltenpoolandarethenengulfedintothefollowinglayers),cavitiesoriginatedby
incompletemeltingbetweenadjacent tracks. Peakagedsamples (Figure11b) featuredsimilar fracture
nucleation sites but the development of crackswasmainly ruled by a quasi-cleavage decohesion
mechanism,presumablyacross themartensiteblocks (compareFigures5and11b).
Figure 11. Fracture surfaces of broken tensile specimens: (a) as-built sample; and (b) 460 ◦C
peak-agedsample.
Additional informationaboutdevelopmentofcracksunder tensioncanbedrawnbyobserving
longitudinally-sectioned specimens close to the fracture line, as shown in Figure 12. The low
magnification image(Figure12a)allowsonetohighlight thegrowthof relatively largecracksstarting
fromboundaries of adjacent laser tracks,whereas, fromhighermagnification views (Figure 12b),
it canbesuggestedthat thepresenceof reversedaustenite locatedatboundariesofcellsdoesnotplay
acrucial roleonfractureprocess.
Figure12.Low-magnificationviewsof longitudinally-sectionedbrokentensile specimensclose to the
fracture line. (a)As-built sample,optical image;and(b) 460 ◦Cpeak-agedsample,SEMimage.
4.Discussion
Wrought maraging steels are usually aged after a solution treatment carried out at high
temperature to homogenize the microstructure inherited from previous operations and to fully
transform it intomartensite on cooling. Even though it is stated thatmartensite can form even
aftermoderatecoolingrates, inpublishedresearchworkseitherwatercooling[2,4]orair cooling[5,8]
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book 3D Printing of Metals"
3D Printing of Metals
- Title
- 3D Printing of Metals
- Author
- Manoj Gupta
- Editor
- MDPI
- Location
- Basel
- Date
- 2017
- Language
- English
- License
- CC BY-NC-ND 4.0
- ISBN
- 978-3-03842-592-2
- Size
- 17.0 x 24.4 cm
- Pages
- 170
- Keywords
- 3D printing, additive manufacturing, electron beam melting, selective laser melting, laser metal deposition, aluminum, titanium, magnesium, composites
- Categories
- Naturwissenschaften Chemie