Abstract
Additive manufacturing (AM) of brittle materials remains challenging, as they are prone to cracking due to the steep thermal gradients present during melting and cooling after laser exposition. Silicon is an ideal brittle material for study since most of the physical properties of single-element materials can be found in the literature and high-purity silicon powders are readily available. Direct laser melting (DLM) of silicon powder was performed to establish the conditions under which cracks occur and to understand how the solidification front impacts the final microstructure. Through careful control of process conditions, paying special attention to thermal gradients and the growth velocity, epitaxial pillars free of cracks could be grown to a length of several millimeters.
Highlights
Powder bed laser scanning, selective laser melting (SLM) and selective laser sintering (SLS), are among the most widespread additive manufacturing techniques
Detachment of the pillar from the substrate occurred when the substrate was at room temperature transported(Figure with2a,c), a commercial pulsed powder transport system
Detachment of the pillar from the substrate occurred when the substrate was at room temperature (Figure 2a,c), crack formation occurred in the case of a preheated substrate at 50 Hz/405 mJ (Figure 2b) and crack-free attachment was obtained for 200 Hz/160 mJ when the substrate was preheated to 730 ◦ C
Summary
Selective laser melting (SLM) and selective laser sintering (SLS), are among the most widespread additive manufacturing techniques. Two main drawbacks of SLM and SLS are the time-consuming powder bed preparation and the need to recover and recycle unused powder Both of these disadvantages can be overcome by forgoing the powder bed and, instead, adding material in powder or wire form directly to the melt pool. This approach is closely related to laser cladding and includes laser metal deposition (LMD), laser engineered net shaping (LENS) and direct energy deposition (DED), among others. It is even possible to successfully repair or modify existing parts, overcoming the big challenge of avoiding solidification shrinkage and hot cracking for high-performance alloys
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