Powder Additive Manufacturing Research Articles

Influence of powder surface chemistry on the defect formation in AlSi10Mg alloy processed via laser powder bed fusion additive manufacturing

In laser powder bed fusion(LPBF) additive manufacturing(AM) of Al alloys, surface chemistry and dissolved gas composition(oxygen/oxides/hydroxides, hydrogen and moisture) of AM powders is a major influencing factor for porosity formation. Therefore, in the present investigation, this aspect is addressed using two sets of virgin AM AlSi10Mg powders, namely, Hi-Ox (2770 ppm oxygen) and Lo-Ox (660 ppm oxygen), to assess the printability under various processing parameters and defect formation in printed parts. Comprehensive and in-depth metallurgical analysis of both powders utilizing multiple characterisation techniques established the presence of various types of oxides/hydroxides with different complex chemistries on the powders’ surface. Enhanced spherical gas porosity and oxide inclusions were witnessed in Hi-Ox print coupons in contrast to the least defects in Lo-Ox coupons rationalized due to surface chemistry difference between the virgin powders. Consequently, the mechanical properties of the Hi-Ox print coupons, even with minimum defect density, are significantly inferior to Lo-Ox specimens. These observations suggest a competing influence of surface chemistry/dissolved gas composition and laser parameters for the processing of both powders. Overall, by correlating the microstructures with processing conditions and oxide concentration, defects morphology, the probable melt pool formation mechanism in LPBF of AlSi10Mg alloy (for high and low oxygen concentration) is elucidated.

Gas atomization of AA2017 aluminum alloy: Effect of process parameters in the physical properties of powders for additive manufacturing

Close-coupled gas atomization (CCGA) uses pressurized gas jets to atomize molten metals, producing powders suitable for additive manufacturing (AM). Optimization of processing parameters is crucial to achieve powders with good fluidity and high apparent density for laser powder bed fusion (L-PBF) and increase production yield. This study evaluated the influence of melt feed nozzle diameter, superheating temperature, and atomization pressure on AA2017 aluminum alloy powders' physical properties. Parameters variation poorly affected the median particle diameter (d50), while significantly altering the particle size distribution curves width (IDR = d90-d10). Suitable powders for AM/L-PBF were produced using a specific set of parameters (d0= 1.5 mm; ΔT= 150 °C; PG= 20 Bar), presenting appropriate fluidity and apparent density due to an optimal granulometric distribution and morphological characteristics. Mathematical analysis showed a good correlation between experimental and calculated mean particle size, suggesting an equation to predict percentile d90 based on previous correlations.

Powder characterisation and the impact on part performance in electron beam melted Ti6Al4V

Metallic powder for Additive Manufacturing (AM) typically varies between different batches, while being supplied to achieve the same customer specification. In order to reduce this variation and minimise waste, batches are often mixed together in both their virgin and used form. However, the properties of bulk components must have limited variance in order to be reliably used in an industrial setting. This manuscript is focused on the analysis of Grade 5 Ti6Al4V powders (3 virgin, plus 2 blends) and the associated mechanical properties of Electron Beam Melted (EBM) AM specimens. Measurements were performed in accordance with the principles defined in the MMPDS Handbook, ESDU database, and ASTM F2924. The tensile, and fatigue properties of the EBM specimens were found to be superior when compared with Ti6Al4V properties within these standards. This demonstrated that these powders are suitable for a wide range of commercial applications, and that these blended powders (including used powders) are able to achieve these requirements. Additionally, the results provide a systematic route for powder verification and highlight the importance of adhering to standardised principles and specifications to ensure quality and reliability in metallic AM materials.

Corrosion behaviour of Ti6Al4VxCryNi alloys fabricated by μ-plasma arc powder additive manufacturing process

This manuscript examines development of noble corrosion-resistant Ti6Al4VxCryNi alloys by μ-plasma arc powder additive manufacturing (μ-PAPAM) process for chemical, shipbuilding, and aerospace industries. Inclusion of chromium and/or nickel to Ti6Al4V alloy decreased corrosion rate and corrosion current density and increased corrosion potential and polarisation resistance, implying increased corrosion resistance. The EIS findings indicated that the values of polarization resistance and layer thickness of oxides increased with the addition of chromium and/or nickel to Ti6Al4V alloy. Smaller size pits were observed on the corroded surfaces of developed Ti6Al4VxCryNi alloys due to the formation of relatively more stable layer of Cr2O3 and NiO enabled by the inclusion of chromium and/or nickel to Ti6Al4V alloy. It improved the surface finish of the developed alloys, indicating less damage by their corrosion and the appearance of small-size pits due to layer formation of Cr2O3 and NiO. As compared to Ti6Al4V alloy, Ti6Al4V5Cr alloy has maximum corrosion resistance followed by Ti6Al4V2.5Cr2.5Ni and Ti6Al4V5Ni alloy.

New insights into the mechanism of ultrasonic atomization for the production of metal powders in additive manufacturing

Ultrasonic atomization is one of the promising technologies for producing metal powders for additive manufacturing, where precise control of particle size and morphology is essential. In this study, we coupled an ultrasonic transducer with a carbon fiber plate and atomized liquid droplets and films under different vibration amplitudes. Water, glycerol, and pure aluminum melt were used to study the atomization mechanism and the resulting droplet/powder characteristics, respectively. High-speed optical and ultrafast synchrotron X-ray imaging were used to study in situ the ultrasonic atomization dynamics, including pulsation and clustering of cavities inside the liquid layer/films, development of capillary waves, and formation of liquid droplets. For the first time, we observed and captured the occurrence of cavitation during the atomization of resting drops, films and impact droplets. The inertial cavitation events interfered with the capillary waves across the interphase boundary, puncturing and breaking the boundary to produce atomized mist. The in situ observation revealed the intricate dynamics of ultrasonic atomization and underscored the pivotal role of cavitation events throughout the entire atomization process. We also conducted experiments on ultrasonic atomization of liquid aluminum, producing particles of perfectly spherical shape. The particle size tended to decrease with reduced vibration amplitude Our work has demonstrated the important processing strategies on how to tailor the particle size while ensuring consistent particle shape and morphology, which is the key processing capability for producing high quality powders for additive manufacturing applications.

Inorganic Fullerene-Like WS2 Reinforced Polyamide Powders for Improved Mechanical Properties in Laser Sintered Nanocomposite Parts

Polyamide (PA) is a widely utilized engineering polymer, and its thermal and mechanical properties can be further improved by adding nanofillers. However, adding inorganic fullerene-like tungsten disulfide (IF-WS2) nanoparticles (NPs) to PA to produce composite precursor powders for additive manufacturing is challenging. Here, we report a novel and cost-effective method for fabricating PA-12 based nanocomposite (NC) powders with fixed/partially encapsulated IF-WS2 nanoparticulate fillers utilizing an advanced mixing technique because simple wet mixing (WM) can only attach fillers weakly to the powder surfaces when compared to the proposed method. The resulting nanocomposite powders maintained nearly the original particle size distribution of PA-12. They also exhibited improved rheological properties, melting, and crystallization behaviors compared with those prepared by the WM method. The laser-sintered PA-12 nanocomposite specimens revealed enhanced powder thermal stability and higher tensile strengths than pristine PA-12, validating the advantages of the novel technique for the fabrication of polyamide nanocomposite powders and their suitability for utilization in laser sintering additive manufacturing. These results demonstrate that high-performance engineered PA-12 nanocomposite components can be directly laser sintered, and this technique can potentially be extended to fabricate other engineered polymeric nanocomposite powders.

Assessing the mechanical properties of out-of-specification additive manufacturing Ti-6Al-4V powder recycled through field-assisted sintering technology (FAST)

A gas atomised Ti-6Al-4V powder, classified as out-of-specification for additive manufacturing (AM), was consolidated via Field-Assisted Sintering Technology (FAST). Fully dense 250 mm diameter discs with lamellar or bimodal microstructures were produced by FAST processing either above or below the β-transus temperature. Static and dynamic mechanical properties were assessed by testing full-size specimens in the ‘as-FAST’ condition. Material from both processing conditions exceeded the ASTM Ti-6Al-4V powder metallurgy requirements for yield/tensile strength and elongation. Furthermore, material from the edge of the disc processed below the β-transus temperature meets ASTM requirements for wrought Ti-6Al-4V. Fatigue performance also compared favourably with conventionally processed Ti-6Al-4V. This work establishes that surplus AM powders can be successfully recycled via the one-step FAST process and provides confidence that this ASTM-grade material can be used in a range of applications under both static and dynamic loading, which will improve the sustainability credentials of the AM sector.

Solid-state production of uniform metal powders for additive manufacturing by ultrasonic vibration machining

This work presents a new technique to generate uniform and micron-sized metal powders for additive manufacturing. By collecting discrete chips resulting from ultrasonic vibration machining, we demonstrate the feasibility of all solid-state production consistent powders with tight dimensional tolerance, the ability to control powder geometry, and good efficiency. The technique offers a new route for sustainable and low-cost manufacturing of high-quality metal powders. The powder generation mechanism is analyzed with a special tool path design to ensure consistent dimensions over multiple cuts. An analytical model to predict the dimensions of produced powders under different cutting parameters is introduced. Aluminum and brass powders of different dimensions are produced, and the overall shear ratio that governs the deformation during the machining process is calibrated with the experimental results. The morphology consistency of produced powders is investigated over multiple hours of production, illuminating the role of tool wear on final powder shape. A high-efficiency powder collection system and a scalable solution for parallel production are proposed for the introduced technique. Additive manufacturing experiments (laser powder bed fusion) are conducted using produced A356 aluminum powders, demonstrating the printability of produced powders in additive manufacturing. The microhardness of the printed parts for five different process parameters is measured to be 45% higher than the raw material on average.

Characteristics and health risks of the inhalable fraction of metal additive manufacturing powders

AbstractMetal additive manufacturing (AM) is gaining traction but raises worker health concerns due to micron‐sized powders, including fine inhalable particles. This study explored particle and surface characteristics, electrochemical properties, metal release in artificial lysosomal fluid (ALF), and potential toxicity of virgin and sieved virgin Fe‐based powders, stainless steel (316L), Fe, and two tooling steels. Virgin particles ranged in size from 1 to 100 µm, while sieved particles were within the respirable size range (<5–10 µm). Surface oxide composition differed from bulk composition. The Fe powder showed low corrosion resistance and high metal release due to a lack of protective surface oxide. Sieved particles of 316L, Fe, and one tooling steel released more metals into ALF than virgin particles, with the opposite was observed for the other tooling steel. Sieved particles had no notable impact on cell viability or micronuclei formation in human bronchial epithelial cells. Inflammatory response in human macrophages was generally low, except for the Fe powder and one tooling steel, which induced increased interleukin‐8 (IL‐8/CXCL‐8) and monocyte chemoattractant protein‐1 (MCP‐1/CCL‐2) secretion. This study underscores distinctions between virgin and sieved Fe‐based powders and suggests relatively low acute toxicity.

Fabrication of spherical W–ZrC powder for additive manufacturing by spray granulation combined with plasma spheroidization

In this study, a W–1%ZrC spherical powder for additive manufacturing was successfully fabricated by spray granulation combined with radio frequency (RF) plasma spheroidization. 3 μm tungsten powder and the nano-sized ZrC powder were spray granulated into a porous agglomerated powder and then spheroidized to form a dense spherical powder by RF plasma. Spherical W–ZrC powder with a narrow particle size distribution and a uniform distribution of Zr element was obtained, whose flowability and apparent density was 7.5 s/50g and 9.36 g/cm3, respectively. Furthermore, ZrC enters the tungsten grains after plasma spheroidization, which causes dislocations in the tungsten grain. The spherical W–ZrC composite powder is expected to suppress the crack formation of W parts during the laser powder bed fusion process.

Microwave Characterization of Metal Powder in Additive Manufacturing (AM)

Microwave Characterization of Metal Powder in Additive Manufacturing (AM)

HIGH-SPEED VIDEO IMAGE ANALYSIS OF LIQUID METAL ATOMIZATION PROCESS

Gas-assisted atomization is used to produce metal powders for additive manufacturing. In these systems the primary atomization governs the powder size distribution, but it is experimentally challenging to investigate. In this study, the primary atomization of a molten metal spray was monitored with a calibrated high-speed camera and digital image processing. The technique enabled the generation of spatio-temporal maps at different distances from the nozzle. Among the characteristics of the spray, mean values and standard deviation of the spray width along the spraying direction, and the frequency of the oscillation of the spray boundaries are presented. Statistically relevant spray asymmetries were identified, which can be caused by faulty spray operation in form of a localized metal solidification at the pouring nozzle. By systematically varying the gas temperature and the gas atomization pressure, it is shown that heating of the gas up to 573 K stabilizes the spraying process and enhances the liquid dispersion in the recirculation zone.

Development of high strength and lightweight Ti6Al4V5Cr alloy: Microstructure and mechanical characteristics

This article explains development of high strength and lightweight Ti6Al4V5Cr alloy by μ-plasma powder additive manufacturing (μ-PPAM) process for automotive, aerospace, military, dies and moulds, and other similar applications. Microstructure, formation of phases, porosity, microhardness, tensile properties, abrasion resistance, and fracture toughness of multi-layer deposition of Ti6Al4V5Cr alloy are studied and compared with Ti6Al4V alloy. Results reveal that the presence of chromium in Ti6Al4V5Cr alloy refined the grains of its β-Ti and α-Ti phases, increased volume % of β-Ti phase, and promoted formation of its equiaxed grains. It also increased tensile strength, microhardness, abrasion resistance, and fracture toughness of Ti6Al4V5Cr alloy. It enhanced solid solution strengthening and formed higher hardness imparting intermetallic Cr2Ti phase and changed fracture mode to mixed ductile and brittle mode with larger size dimples, cleavage facets, and micropores. But it decreased formation temperature of β-Ti phase and % elongation as compared to Ti6Al4V alloy. Chromium and vanadium content in β-Ti phase of Ti6Al4V5Cr alloy is 7 % and 2.1 % more than its α-Ti phase. This study demonstrates that inclusion of limited amount of chromium content to Ti6Al4V5Cr alloy by μ-PPAM process is very beneficial to enhance microstructure, mechanical properties, crack propagation resistance, and abrasive wear resistance of the Ti6Al4V5Cr alloy. It makes Ti6Al4V5Cr alloy very useful in many commercial applications that require higher strength than Ti6Al4V alloy along with lightweight requirement.

Sustainable Recovery of Titanium Alloy: From Waste to Feedstock for Additive Manufacturing

Titanium and its alloys are widely employed in the aerospace industry, and their use will increase in the future. At present, titanium is mainly produced by the Kroll method, but this is expensive and energy-intensive. Therefore, the research of efficient and sustainable methods for its production has become relevant. The present review provides a description of the titanium recycling methods used to produce mostly aeronautical components by additive manufacturing, offering an overview of the actual state of the art in the field. More specifically, this paper illustrates that ilmenite is the main source of titanium and details different metallurgic processes for producing titanium and titanium alloys. The energy consumption required for each production step is also illustrated. An overview of additive manufacturing techniques is provided, along with an analysis of their relative challenges. The main focus of the review is on the current technologies employed for the recycling of swarf. Literature suggests that the most promising ways are the technologies based on severe plastic deformation, such as equal-channel angular pressing, solid-state field-assisted sintering technology-forge, and the Conform process. The latter is becoming established in the field and can replace the actual production of conventional titanium wire. Titanium-recycled powder for additive manufacturing is mainly produced using gas atomization techniques.

Simulation of, Optimization of, and Experimentation with Small Heat Pipes Produced Using Selective Laser Melting Technology

With the development of microsatellite technology, the heat generated by onboard components is increasing, leading to a growing demand for improved thermal dissipation in small satellites. Metal powder additive manufacturing technology offers the possibility of customizing and miniaturizing heat pipes to meet the specific requirements of small satellites. This article introduces a small-scale heat pipe designed using selective laser melting (SLM) technology. The heat pipe’s material, structure, and internal working fluid were determined based on mission requirements. Subsequently, the SolidWorks 2021 software was used for heat pipe modeling, and the ANSYS 2021R2 finite element analysis software was employed to simulate the heat transfer performance of the designed heat pipe, confirming its feasibility. The heat pipe’s structure was optimized using multi-objective regression analysis, considering various structural parameters, such as the channel diameter, vapor chamber height, and narrow gap width. The simulation results demonstrate that the optimized heat pipe achieved a 10.5% reduction in thermal resistance and an 11.6% increase in equivalent thermal conductivity compared to the original heat pipe. Furthermore, compared to conventional metal heat-conducting rods, the optimized heat pipe showed a 38.5% decrease in thermal resistance and a 62.19% increase in equivalent thermal conductivity. The heat pipe was then fabricated using a 3D printer (EOS M280), and a vacuum experimental system was established to investigate its heat transfer characteristics. The experimental results show that the heat pipe operated most efficiently at a heating power of 20 W, reached its maximum heat transfer capacity at 22 W, and had an optimal fill ratio of 30%. These results highlight the excellent performance of the heat pipe and the promising application prospects for SLM technology in the field of small satellites.

Explosion Risk of Metal Powder Used in Additive Manufacturing

The explosive characteristic parameters of additive manufacturing (AM) dust were systematically studied. A systematic experimental study was performed on the characteristic parameters of dust explosions fueled by metal powder for AM, to obtain the distribution pattern of those parameters for four types of AM dust samples. Based on experimental data, the dust-explosive severity was classified via two-dimensional matrix analysis in terms of Pmax and Kst, and the dust-explosive sensitivity was classified via three-dimensional matrix analyses of the MIE, MIT, and MEC. Finally, a dust-explosive risk assessment model of AM metal powder was established based on comprehensive considerations of the dust-explosive severity and sensitivity, and four types of AM dust sample were applied empirically. The risk assessment method can provide a scientifically credible and effective basis for assessing and improving the AM process based on powder spreading.

Friction stir powder additive manufacturing of Al 6061/FeCoNi and Al 6061/Ni metal matrix composites: Reinforcement distribution, microstructure, residual stresses, and mechanical properties

Fusion based additive manufacturing (FBAM) of second, sixth, and seventh series Al alloys and their metal matrix composites (MMC) is difficult due to their higher thermal conductivity and solidification related problems namely porosity, cracks, thermal distortion, and formation of undesired phases. This paper presents friction stir powder additive manufacturing (FSPAM) process as a promising alternative to overcome these problems in producing multi-layer depositions of Al 6061 based MMCs namely Al 6061/6 wt%FeCoNi and Al 6061/6 wt%Ni. Their microstructure, distribution and elemental mapping of reinforcement particles, phase analysis, residual stresses of the MMCs and their correlation with microhardness, tensile strength, and fretting wear characteristics are investigated. Material accumulation on their advancing side was minimized by changing tool rotation direction in consecutive layers which produced smoother surfaces on both sides of their deposition. FSPAM made multi-layer depositions of Al 6061/FeCoNi and Al 6061/Ni MMCs have uniform distribution of reinforcement particles, good bonding between layers without cracks and defects, refined and equiaxed grains facilitated by dynamic recrystallization and pinning effect of reinforcement particles, compressive residual stresses of 39 and 48 MPa, no formation of deleterious intermetallic compounds due to absence of melting of matrix and reinforcement, and bowl-shaped substrate-deposition interface. Microhardness and ultimate tensile strength of the MMCs improved by 11.3% and 22.3%, and 30.5% and 31.5% respectively than Al 6061 alloy depositions, their wear resistance enhanced significantly, but % elongation reduced. This study proves FSPAM to be a potential alternative to FBAM processes for better quality multi-layer deposition of Al alloy-based MMCs.

Effects of powder surface conditions on the rheological behavior of Ti–6Al–4 V alloy powders for additive manufacturing

Laser powder-bed fusion (L-PBF) is a promising manufacturing process for fabricating metallic parts with tailored architectures. A feedstock powder with good flowability is required to homogeneously deposit the powder on the building substrate and obtain reliable and high-quality L-PBF products. Although the effects of powder morphology and particle size on flowability have been widely investigated, the relationship between powder surface conditions and rheological behaviors is not well established. Therefore, in this study, the surface conditions of Ti–6Al–4 V alloy powders were intentionally adjusted through conventional heat treatments under different gas atmospheres. The morphology and particle size distribution of the Ti–6Al–4 V powder heat treated at 773 K in air (Air773) and Ar (Ar773) atmospheres remained unchanged compared to those of the untreated powder. However, the quantity of surface oxides on the Air773 powder increased, enhancing the decoration of surface hydroxyl groups, as illustrated by water wettability tests. By contrast, the oxide layer of the Ar773 powder decomposed and dissolved into the matrix, resulting in the generation of fresh metallic surfaces. Consequently, the flowability of the Air773 powder increased, whereas that of the Ar773 powder tended to decrease, thereby deteriorating the quality of powder beds during the recoating process. The results prove that the cohesive strength of Ti–6Al–4 V powder is more strongly determined by metallic TiTi interactions than by hydrogen bonds. Thus, the effective approach for adjusting the powder surface conditions presented in this study offers new insights into the potential for economically developing high-performance Ti alloy components by controlling the powder properties and L-PBF process.

Predicting the element loss in aluminum (AA2195) powder produced by gas atomization with a numerical model

Gas atomization (GA) is commonly used for making metal powders for additive manufacturing due to its efficiency and cost-effectiveness. However, the process results in the loss of low-boiling temperature elements like magnesium and lithium. These can negatively impact the performance of lightweight components of AA2195. To understand and address this issue, we used Inductively Coupled Plasma to compare the composition of ingots and powders produced by GA. The results showed a loss of around 20% of magnesium and lithium during the process. To investigated this symptom scientifically, we developed a numerical model based on evaporation theory. The simulation findings indicated that the loss of elements took place nearby the nozzle. Furthermore, it was observed that the utilization of powder with larger particle sizes resulted in a higher degree of element loss. Based on the results of simulation, we optimized the GA parameters and produced new powders that meet design criteria.

Friction Stir Powder Additive Manufacturing of Multi-track Depositions of Al 6061 Alloy for Cladding and 3D Printing Applications

Friction Stir Powder Additive Manufacturing of Multi-track Depositions of Al 6061 Alloy for Cladding and 3D Printing Applications