THESIS
2022
1 online resource (xvi, 169 pages) : illustrations (some color)
Abstract
Cu is a fundamental material for a large variety of industries including electrical power
system and electronic industry. Laser processing of pure Cu is challenging because of Cu’s very
low absorptivity to most laser beams, and this difficulty is applicable to the recently developed
laser powder bed fusion (LPBF) additive manufacturing (AM) as well. How to realize high-quality
LPBF forming is urgently pursued in order to maximize its advanced manufacturing
potential in directly making various Cu parts.
In this thesis, theoretical analysis of laser absorptivity was given. Based on the analysis,
three possible routes to enhance the laser absorptivity of highly reflectivity materials were
proposed, i.e., powder alloying, powder surface modification and using short-wavelength laser.
Accordi...[
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Cu is a fundamental material for a large variety of industries including electrical power
system and electronic industry. Laser processing of pure Cu is challenging because of Cu’s very
low absorptivity to most laser beams, and this difficulty is applicable to the recently developed
laser powder bed fusion (LPBF) additive manufacturing (AM) as well. How to realize high-quality
LPBF forming is urgently pursued in order to maximize its advanced manufacturing
potential in directly making various Cu parts.
In this thesis, theoretical analysis of laser absorptivity was given. Based on the analysis,
three possible routes to enhance the laser absorptivity of highly reflectivity materials were
proposed, i.e., powder alloying, powder surface modification and using short-wavelength laser.
According to the first two routes, selective laser melting (SLM) of Cu-10Sn-0.4P pre-alloyed
powder and surface-oxidized powder was conducted respectively. Residual stress of the as-printed
Cu-10Sn-0.4P was measured and relieved via heat treatment. Microstructure and
mechanical properties were investigated, too, according to which the effect of trace amount of
P element was confirmed. During the SLM of surface-oxidized Cu powder, laser remelting was
adopted to counter the high thermal conductivity of Cu and provide extra liquid phase for better
densification. Various research means were used to investigate mechanical performances,
microstructural details, and electrical performance of the as-printed Cu. Furthermore,
femtosecond laser was used to modify the surface of the SLM-manufactured Cu-10Sn-0.4P.
The laser-modified samples exhibited an increased microhardness, and their surface wettability
and optical properties were also changed due to the laser-induced periodic surface structure.
Finally, several typical applications of laser-based 3D printing of Cu and Cu alloys such as
jewelry, copper sheathing, heat exchanger and metamaterials were demonstrated, and the
related properties such as density and surface roughness were characterized to verify the good
printability of Cu and Cu alloys.
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