The use of non-spherical powder particles in Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) generally involves the use of near-spherical powders due to their smooth morphology and enhanced flowability that allow for easier powder layering and laser processing. Non-spherical powders, on the other hand, are more cost-efficient to manufacture, however, the underlying mechanisms of their movement and interparticle interaction on the powder bed are still unclear. Thus, this study reports on the use of irregular iron-based powder material in LPBF, with a specific focus on particle motion and interaction behavior on the powder bed. The powder morphology, sphericity and particle size were analysed using X-ray computed microtomography and scanning electron microscopy. Based on the acquired data and by using a simplified analytical calculation, the influence of the particle shape/size on the particle movement in LPBF was established. High-speed imaging was employed to investigate the particle flow dynamics in the process zone, as well as the powder entrainment phenomenon. Particle entrainment and entrainment distances along the scanning direction were measured for near-spherical and non-spherical powders. The obtained results were compared between the powders, revealing a dissimilar particle transfer behavior. Non-spherical powder had a shorter entrainment distance partly attributed to the weaker drag force acting on these particles.

Коррозионностойкие стали в аддитивном производстве

This review discusses the main methods for producing spherical powder particles of corrosion-resistant steels as a material widely used in all industries. Also the examples of products made by modern additive methods are described. Currently, spherical powder particles of corrosion-resistant steels are used in the following additive methods: selective laser melting, selective laser sintering, direct laser sintering, and electron beam melting. Each of these methods has its own requirements for the characteristics of spherical powder particles of corrosion-resistant steels. The review provides a brief description of the principles of operation of each method and the requirements for spherical powder particles of corrosion-resistant steels. It also considers a detailed description of each method of additive manufacturing with a description of the principle of operation and specific examples of obtaining spherical particles of corrosion-resistant steel powders with indication of their properties (morphology, structural features, chemical composition, fluidity, bulk density). A comparative analysis was carried out with a description of disadvantages and advantages of each method. Examples of the use of spherical particles of corrosion-resistant steel powders for the manufacture of products by various additive methods (including post-processing) are given with description of the final products characteristics. Based on the data presented, a conclusion was made about the preferred methods for obtaining spherical particles of corrosion-resistant steel powders for specific additive methods used in modern industry. The review considers the following methods for producing spherical powder particles: water atomization (atomization of liquid metal with a jet of water under pressure); gas atomization (atomization of the melt with a jet of inert gas (argon or nitrogen) under pressure); centrifugal atomization (atomization of molten metal with a high-speed rotating disc); ultrasonic atomization (atomization of liquid metal by ultrasound); non-contact atomization (atomization of liquid metal with a powerful pulse of electric current); plasma wire spraying; plasma spraying of a rotating electrode; plasma spheroidization.

Structure Evolution of Ni36Al27Co37 Alloy in the Process of Mechanical Alloying and Plasma Spheroidization

In this paper, a novel approach to obtain a ferromagnetic material for smart applications was implied. A combination of mechanical alloying (MA) and plasma spheroidization (PS) was applied to produce Ni36Al27Co37 spherical powder. Then its structure was systematically studied. It was shown that homogenization of the structure occurs due to mechanism of layered structure formation. The dependence of the lamella thickness on the energy dose input at MA was defined. It was found that 14.7 W⋅h/g is sufficient to obtain lamella thickness of 1 μm and less. The low-energy mode of a planetary mill with rotation speeds of the main disk/bowl of 150/−300 rpm makes it possible to achieve a uniform element distribution upon a minimal amount of impurity. During MA in an attritor Ni3Al-type intermetallic compounds are formed that result in more intensive degradation in particle size. Plasma spheroidization of the powder after MA allowed obtaining Ni36Al27Co37 spherical powder. The powder had a fine β + γ-structure. The particle size distribution remains almost unchanged compared to the MA stage. Coercivity of the powder is 79 Oe. The powder obtained meets the requirements of selective laser melting technology, but also can be utilized as a functional filler in various magnetic composites.

Influences of powder characteristics and recoating conditions on surface morphology of powder bed in metal additive manufacturing

Metal additive manufacturing technology requires a real-time monitoring and feedback control system to assure the quality of the final products. In particular, it is essential to reveal the phenomena of recoating and melting-solidification processes in laser powder bed fusion using a real-time monitoring system because they influence strongly the occurrence of defects. This study was conducted to elucidate the correlation among the powder characteristics, recoating conditions, and surface morphology of a powder bed in the recoating process to determine the relationship between the surface morphology of the powder bed and the final product quality. To this end, a surface morphology measurement system composed of a powder recoating test bench and a layer surface morphology measurement apparatus was first designed and fabricated. Then, it was used to quantify the surface morphology of the powder bed. Specifically, the influences of the different powder characteristics and the recoating parameters of the powder supply ratio and recoating speed on the surface morphology of the powder bed were investigated using various powders of Al-10Si-0.4Mg (AlSi10Mg) alloy and Inconel 718 (IN718) alloy. The surface morphology of the powder bed was measured as the value of 2σ at a resolution of 30 μm in height. It was found that the angle of repose and the basic flow energy of the bulk powder are promising parameters for evaluating the surface morphology. The surface morphology was significantly affected by the powder characteristics and recoating speed. The value of 2σ for the AlSi10Mg powder increased rapidly over a recoating speed of 50 mm/s for all powders. The value of 2σ for the irregularly shaped AlSi10Mg powder was approximately 19 μm, and the 2σ values for the other powders were approximately 17 μm at a recoating speed of 15 mm/s. However, at a recoating speed greater than 300 mm/s, the irregularly shaped powder exhibited better surface morphology than did the spherical powder. The recycling process deteriorated the flowability of the new powder. However, the surface morphology of the spherical recycled powder was similar to that of the spherical powder. Consequently, the correlation among the powder characteristics, recoating conditions, and surface morphology of the powder bed was revealed by employing the surface morphology measurement system. Quantification of the surface morphology of the powder bed using the monitoring system facilitates control of the recoating process to prevent the occurrence of defects.

Progress of Flake Powder Metallurgy Research

This paper reviewed several recent progresses of the new powder metallurgy technology known as flake powder metallurgy (FPM) including different processing routes, conventional FPM (C-FPM), slurry blending (SB), shift-speed ball milling (SSBM), and high-shear pre-dispersion and SSBM (HSPD/SSBM). The name of FPM was derived from the use of flake metal powders obtained by low-speed ball milling (LSBM) from spherical powder. In this case, the uniformity of reinforcement distribution leads to increased strength and ductility. Powder is the basic unit in PM, especially advanced PM, and its control is key to various new PM technologies. The FPM is a typical method for finely controlling the powder shape through low-energy ball milling (LEBM) to realize the preparation of advanced material structures. The present paper represents a review of the main results of research on FPM and indicates the potential for future studies devoted to the optimization of this processing route.

Karakterisasi Serbuk Timah dari Sistem Atomisasi Gas Argon Panas - Sub Sistem Gas Alir Tabung Gas

<p class="Abstract">The tin powder was used in some applications and technology such as for part manufacture through alloying, pressing, and sintering process, mixing material for the pyrotechnic application, the main material for solder pasta, mixing material on tin chemical, and others. Therefore, the demand for tin powder with a small size, spherical shape, and high purity is increasing severely. Indonesia (PT. Timah Tbk.) is one of the world’s largest producers of tin raw materials. This raw material can be processed be as powder by the atomization method. In this research, hot argon gas atomization system was used to generated tin powder. Raw tin was melted in a melting chamber with temperature variations of 600, 700, 800, and 900 °C. This experiment generates powder with a dominant size of 37 – 150 mm. Meanwhile, for size powder of 0 – 30 mm, dominated by size range of 0 – 10 mm. Furthermore, the size powder of 0 – 30 mm is composed of tin phase, without tin oxide. The tin powder of melting chamber temperature of 900 °C produces the largest tin powder with a size of 0 – 10 mm and spherical powder.</p>

A Coupled DEM/SPH Computational Model to Simulate Microstructure Evolution in Ti-6Al-4V Laser Powder Bed Fusion Processes

A new multi-stage three-dimensional transient computational model to simulate powder bed fusion (L-PBF) additive manufacturing (AM) processes is presented. The model uses the discrete element method (DEM) for powder flow simulation, an extended smoothed particle hydrodynamics (SPH) for melt pool dynamics and a semi-empirical microstructure evolution strategy to simulate the evolving temperature and microstructure of non-spherical Ti-6Al-4V powder grains undergoing L-PBF. The highly novel use of both DEM and SPH means that varied physics such as collisions between non-spherical powder grains during the coating process and heat transfer, melting, solidification and microstructure evolution during the laser fusion process can be simulated. The new capability is demonstrated by applying a complex representative laser scan pattern to a single-layer Ti-6Al-4V powder bed. It is found that the fast cooling rate primarily leads to a transition between the β and α martensitic phases. A minimal production of the α Widmanstatten phase at the outer edge of the laser is also noted due to an in situ heat treatment effect of the martensitic grains near the laser. This work demonstrates the potential of the coupled DEM/SPH computational model as a realistic tool to investigate the effect of process parameters such as powder morphology, laser scan speed and power characteristics on the Ti-6Al-4V powder bed microstructure.

Selective Laser Melting AlSi12 Alloy by Utilizing of Non-Spherical Air-Atomized Powder

AlSi12 alloy is one of the most widely used materials in selective laser melting. Selective laser melting (SLM) of AlSi12 alloy has been well studied in recent years. Researchers typically use very expensive spherical powders atomized in an inert atmosphere. For this paper, we studied SLM of air-atomized non-spherical powder to determine its printability. Nine specimens were fabricated using different SLM process parameters. The lowest porosity that was achieved was 1.3%.