Optimizing 3D Printing for High-Performance Parts.

In the rapidly evolving field of additive manufacturing (AM), particularly with the use of Laser Powder Bed Fusion (LPBF), achieving defect-free components with superior mechanical properties remains a significant challenge. Researchers Mr. Ranjith Kumar Ilangovan , Dr. Hariharan Krishnaswamy , Dr. Saravana Kumar Gurunathan , Dr. Murugaiyan Amirthalingam , Dr. Ravi Sankar Kottada from Indian Institute of Technology, Madras (IIT Madras), Chennai, India and Dr. Koundinya N.T.B.N , from Max Planck Institute for Sustainable Materials , Düsseldorf, Germany tackles this issue head-on, exploring the crucial role of powder surface chemistry in defect formation within AlSi10Mg alloy.

The primary aim of the study was to understand how variations in powder surface chemistry affect defect formation and overall mechanical properties of AlSi10Mg alloy parts produced through LPBF. By investigating two types of AlSi10Mg powders—Hi-Ox (high oxygen content, 2770 ppm oxygen) and Lo-Ox (low oxygen content, 660 ppm oxygen) sought to uncover the mechanisms driving defect formation and to propose strategies for optimizing powder properties to enhance component quality.

Understanding and controlling the surface chemistry of AM powders is pivotal for the production of high-quality components, especially in industries like aerospace and automotive where material integrity and performance are critical. The findings provide valuable insights that can lead to more reliable and efficient AM processes, ultimately pushing the boundaries of what is achievable with LPBF technology.

The researchers’ experimental approach involved a comprehensive analysis of Hi-Ox and Lo-Ox AlSi10Mg powders. They conducted a series of LPBF trials using the state-of-the-art iFusion 150 (formerly known as iFusion SF1) LPBF 3D printer from Intech Additive Solutions Pvt Ltd, Bengaluru, India. The iFusion 150, known for its precision and reliability, was integral to their experiments. They systematically varied processing parameters and examined the resulting microstructures and mechanical properties of the printed parts. Advanced characterization techniques, including Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), were employed to assess defect types.

Researchers revealed that Hi-Ox powders, characterized by higher levels of oxides and hydroxides, led to increased porosity and defect density in printed parts compared to Lo-Ox powders. This was visually evident in Figure 1 and Figure 2, which shows the comparative porosity levels in parts produced from Hi-Ox and Lo-Ox powders.

Figure 1 - Optical micrographs taken from the blocks printed with Hi-Ox powders using various processing parameters (i.e., laser power and scan speed). The relative density (%) obtained using cross sectional microstructures is also shown in each micrograph. The red arrows indicate the circular smooth-walled pores attributed to gas porosity.

Figure 2 - Optical micrographs taken from the blocks printed with Lo-Ox powders using various processing parameters (i.e., laser power and scan speed). The relative density (%) obtained using cross sectional microstructures is also shown in each micrograph. Red arrows indicate a lack of fusion porosity under some processing conditions.

Despite the higher defect density, parts produced with Hi-Ox powders exhibited inferior mechanical properties. Figure 3 illustrates the tensile strength and elongation at break for parts made with both types of powders, clearly showing the superior performance of parts printed with Lo-Ox powders.

Figure 3 - Uniaxial tensile flow curves of the LPBF-AlSi10Mg specimens printed with Hi-Ox and Lo-Ox powders a) Engineering stress - engineering strain for Hi-Ox and Lo-Ox specimens, b)True stress - true strain curves of Hi-Ox and Lo-Ox specimens.

To understand the role played by the microstructural difference on the mechanical properties, fractography of the tensile fractured specimens was done using SEM on both Hi-Ox and Lo-Ox specimens, and corresponding fractographs are shown in Figure 4. The fractographs revealed thick oxide layers and larger pores in Hi-Ox specimens, which acted as crack initiation sites during tensile deformation.

Figure 4 - Fractographs of the tensile fractured specimens of Hi-Ox and Lo-Ox specimens showing porosity differences and oxide layers. a) The fractograph of Hi-Ox specimens shows a larger number of pores and a thicker oxide layer, and b) The fractograph of Lo-Ox specimens shows smaller and fewer pores besides the thin visible oxide layer.

The researchers also provided critical insights into the melt pool dynamics influenced by the surface chemistry of the powders. Hi-Ox powders altered the melt pool behavior, promoting keyhole formation and increased porosity. In contrast, Lo-Ox powders facilitated a more stable melt pool, resulting in fewer defects and more consistent mechanical properties.

?The research underscores the importance of controlling the surface chemistry of AM powders to minimize defects and optimize the mechanical properties of printed components. By demonstrating the detrimental effects of high oxygen content on defect formation and mechanical performance, they highlight the need for stringent powder handling and storage practices.

The researchers acknowledge the critical inputs at various stages from Mr. Revanth Metla , Team Lead of New Product Development, and Mr. Steevan Lester Baptist , Lead Application Engineer of Intech Additive Solutions , Bengaluru, India. Their expertise and support were critical in maximizing the capabilities of the iFusion 150 LPBF equipment.

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This article is based on the Research Paper, accepted by 爱思唯尔 : Ilangovan, R.K., Koundinya, N.T.B.N., Krishnaswamy, H., Kumar, S., Amirthalingam, M. and Kottada, R.S., 2024. Influence of powder surface chemistry on the defect formation in AlSi10Mg alloy processed via laser powder bed fusion additive manufacturing.