Manufacturability of AlSi10Mg overhang structures fabricated by laser powder bed fusion

Setchi

et al. 2019

Additive Manufacturing

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Laser powder bed fusion (LPBF) is a proven additive manufacturing (AM) technology for producing metallic components with complex shapes using layer-by-layer manufacture principle. However, the fabrication of crack-free high-performance Nibased superalloys such as Hastelloy X (HX) using LPBF technology remains a challenge because of these materials' susceptibility to hot cracking. This paper addresses the above problem by proposing a novel method of introducing 1 wt.% titanium carbide (TiC) nanoparticles. The findings reveal that the addition of TiC nanoparticles results in the elimination of microcracks in the LPBF-fabricated enhanced HX samples; i.e. the 0.65% microcracks that were formed in the asfabricated original HX were eliminated in the as-fabricated enhanced HX, despite the 0.14% residual pores formed. It also contributes to a 21.8% increase in low-angle grain boundaries (LAGBs) and a 98 MPa increase in yield strength. The study revealed that segregated carbides were unable to trigger hot cracking without sufficient thermal residual stresses; the significantly increased subgrains and lowangle grain boundaries played a key role in the hot cracking elimination. These findings offer a new perspective on the elimination of hot cracking of nickel-based superalloys and other industrially relevant crack-susceptible alloys. The findings also have significant implications for the design of new alloys, particularly for hightemperature industrial applications.

Section: Introductionmentioning

confidence: 99%

Additive manufacturing of high-strength crack-free Ni-based Hastelloy X superalloy

Setchi

et al. 2019

Additive Manufacturing

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“…Aluminium and its alloys are increasingly applied within the aerospace and automotive industries because of these materials' lightweight and high specific strength [1][2][3][4]. Among such alloys, AlSi10Mg is a traditional cast alloy that is widely used for die-casting.…”

Section: Introductionmentioning

confidence: 99%

Effect of heat treatment and laser surface remelting on AlSi10Mg alloy fabricated by selective laser melting

Int J Adv Manuf Technol

Jiao

2019

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The selective laser melting (SLM) of aluminium alloys is of interest to researchers because of these alloys' potential applications in the aerospace and automotive domains. Post-processing is generally required in order to enhance the mechanical properties of devices that involve moving parts, where surface mechanical properties are significant factors. This paper describes a preliminary study that was conducted to investigate the effect of post-processing on the microstructure and mechanical properties of SLM fabricated AlSi10Mg alloy, with an emphasis on the laser surface remelting (LSR) process. The experimental results demonstrate that the heat treatment degraded tensile strength while improving ductility by achieving grain growth and residual stress release. The yield strength obtained in the experiment was reduced from 200 to 100 MPa, whereas the elongation increased from 6 to 22%. The LSR process was found to contribute to an improvement in surface finish. The surface roughness indicator R a was determined to be 0.93 μm in the LSR post-processed sample, compared to a fairly high value of 19.3 μm in the as-fabricated samples. The LSR process also enhanced the microhardness by refining the microstructure; the Si eutectic dendritic structure that formed was found to be finer than that of the as-fabricated samples. Compared to the as-fabricated samples, the LSR process contributed to a 19.5% increase in microhardness. The findings suggest that the microstructure and mechanical properties of SLM-fabricated AlSi10Mg parts could be tailored by suitable post-processing such as heat treatment and LSR. The significance of this research is its proposal of a novel technique to enhance surface hardness using LSR, which is a significant step towards the combination of SLM and LSR processes to manufacture customised aluminium components for the automotive and aerospace sectors.

“…Laser additive manufacturing (AM) is an established technology for the direct fabrication of metal components with complex geometries using layer-by-layer powder deposition and a high-power laser [1] [2] [3]. A wide range of metallic materials can be successfully processed using laser AM, including steel [4], titanium [5] [6], aluminium [7][8] [9], nickel [10] [11] and various composites. A variety of powder bed characteristics are critical to achieving a quality process because they affect the dimensional accuracy and structural integrity of the fabricated parts.…”

Section: Introductionmentioning

confidence: 99%

Discrete element simulation of powder layer thickness in laser additive manufacturing

Setchi

2019

Powder Technology

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The optimisation of the laser additive manufacturing (AM) process is a challenging task when a new material is considered. Compared to the selection of other process parameters such as laser power, scanning speed and hatch spacing, optimisation of powder layer thickness is much more time-consuming and costly because a new run is normally needed when the layer thickness value is changed. In practice, the layer thickness is fixed to a value that is slightly higher than the average particle size. This paper introduces a systematic approach to layer thickness optimisation based on a theoretical model of the interactions between the particles, the wiper and the build plate during the powder deposition. The focus is on a systematic theoretical and experimental investigation of the effect of powder layer thickness on various powder bed characteristics during single-layer and multi-layer powder deposition. The theoretical model was tested experimentally using Hastelloy X (HX) with an average particle size of 34.4 µm. The experimental results validated the simulation model, which predicted a uniform powder bed deposition when employing a 40 µm layer thickness value. Lower (30 µm) and higher (50 µm) layer thickness values resulted in large voids and short-feed defects, respectively. The subsequent optimisation of the scanning speed and hatch spacing parameters was executed using a 40 µm layer thickness. The optimum process parameters were then used to examine the microstructure and tensile performance of the as-fabricated HX. This study provides an improved understanding of the powder deposition process and offers insights into the selection of suitable powder layer thicknesses in laser AM.