Deposition-Based Additive Manufacturing Research Articles

Multi-material structures of Ti6Al4V and Ti6Al4V-B4C through directed energy deposition-based additive manufacturing

The demand for advanced materials has driven innovation in titanium alloy design, particularly in the aerospace, automotive, and biomedical sectors. Additive manufacturing (AM) enables the construction of multi-material structures, offering potential improvements in mechanical properties such as wear resistance and high-temperature capabilities, thus extending the service life of components such as Ti6Al4V. Directed energy deposition (DED)-based metal AM was used to manufacture radial multi-material structures with a Ti6Al4V (Ti64) core and a Ti6Al4V-5 wt.% B4C composite outer layer. X-ray diffraction analysis and microstructural observation suggest that distinct B4C particles are strongly attached to the Ti6Al4V matrix. The addition of B4C increased the average hardness from 313 HV for Ti6Al4V to 538 HV for the composites. The addition of 5 wt.% B4C in Ti6Al4V increased the average compressive yield strength (YS) to 1440 MPa from 972 MPa for the control Ti6Al4V, i.e., >48% increase without any significant change in the elastic modulus. The radial multi-material structures did not exhibit any changes in the compressive modulus compared to Ti6Al4V but displayed an increase in the average compressive YS to 1422 MPa, i.e., >45% higher compared to Ti6Al4V. Microstructural characterization revealed a smooth transition from the pure Ti6Al4V at the core to the Ti64-B4C composite outer layer. No interfacial failure was observed during compressive deformation, indicating a strong metallurgical bonding during multi-material radial composite processing. Our results demonstrated that a significant improvement in mechanical properties can be achieved in one AM build operation through designing innovative multi-material structures using DED-based AM.

End-to-end path planning for homogeneous temperature fields in additive manufacturing

This study explores a novel approach to path planning in deposition-based additive manufacturing, integrating the frequently overlooked process-induced temperature fields. Currently, existing approaches either ignore temperature effects entirely or only consider them in small-scale problems due to the high computational cost involved in predicting them and the combinatorial nature of path planning optimization. To address these challenges, the present work proposes an optimization pipeline that involves deriving a reduced order model from a finite volume method model with balanced truncation, using an analytical function to model the heat input and, calculating the steady-state response of the system to an arbitrary path using the Laplace transformation. Then, the optimization is transformed into a sequential decision-making problem and approximated with Monte Carlo tree search. The pipeline is validated through computational and experimental results, demonstrating its efficiency in managing large and complex geometries, as well as its resilience in overcoming the challenges posed by the simulation to reality gap.

Assessing crack susceptibility in blended copper-stainless steel compositions during laser directed energy deposition-based additive manufacturing

This study investigates the effect of composition and process parameters on the crack susceptibility of the Cu -SS304L system during laser directed energy deposition (LDED). The microstructure of LDED deposits is analysed aiming at elemental distribution and crack susceptibility. The trapping behaviour of Cu changes with Cu concentration. The crack susceptibility reduces with Cu concentration and escalates with an increase in laser power and scan speed, irrespective of composition. The mode of solidification cracking varied from the rupture of Cu film to crack-assisted porosity. Furthermore, the critical solidification cooling rate is estimated for LDED of different blended Cu -SS for crack-free deposition. The above findings offer insights into cracking behaviour and provide processing guidelines for LDED of Cu -SS.

Environmental drawbacks of lightweight design algorithms in material extrusion additive manufacturing: a case study

Lightweight design is often assumed to be the leading strategy to improve the sustainability of parts produced by additive manufacturing. The present study confutes such an assumption by a cradle-to-gate life cycle assessment of different lightweight strategies applied to a specific case study in the medical field. In particular, a patient-specific finger splint made of polyamide is redesigned by means of generative design, topology optimization and lattice structures. The analysis investigates two markedly different deposition processes, namely Arburg plastic freeforming and fused filament fabrication. The former is carried out on an industrial-grade machine, while a desktop printer is used for the latter. This allows for observing the impact of the redesign in two quite distinct scenarios. Findings demonstrate that, since environmental impacts are mainly driven by building time, the adoption of automated design algorithms can be detrimental to the sustainability of the process. On the other hand, relevant benefits on environmental impacts were achieved by reducing the infill percentage of parts. The results of this work highlight the most relevant aspects which must be considered to limit environmental impacts when designing parts for deposition-based additive manufacturing. This information can be used by designers to drive weight reduction towards sustainability.

Radial bimetallic structures via wire arc directed energy deposition-based additive manufacturing

Bimetallic wire arc additive manufacturing (AM) has traditionally been limited to depositions characterized by single planar interfaces. This study demonstrates a more complex radial interface concept, with in situ mechanical interlocking and as-built properties suggesting a prestressed compressive effect. A 308 L stainless core is surrounded by a mild steel casing, incrementally maintaining the interface throughout the Z-direction. A small difference in the thermal expansion coefficient between these steels creates residual stresses at their interface. X-ray diffraction analysis confirms phase purity and microstructural characterization reveals columnar grain growth independent of layer transitions. Hardness values are consistent with thermal dissipation characteristics, and the compressive strength of the bimetallic structures shows a 33% to 42% improvement over monolithic controls. Our results demonstrate that biomimetic radial bimetallic variation is feasible with improved mechanical response over monolithic compositions, providing a basis for advanced structural design and implementation using arc-based metal AM.

Laser Directed Energy Deposition-Based Additive Manufacturing of Fe20Cr5.5AlY from Single Tracks to Bulk Structures: Statistical Analysis, Process Optimization, and Characterization

Laser directed energy deposition (LDED) can be deployed for depositing high-performance materials for various engineering applications. Alumina-forming steel is a high-performance material that possesses excellent corrosion and oxidation resistance, finding application in the power generation sector. In the present work, LDED using powder feeding (LDED-PF) was used to deposit Fe20Cr5.5AlY alloy using single-track, multi-track, and multi-layer deposition on SS 316L substrate. Response surface methodology (RSM)-based optimization was used to optimize the single-track deposition. The relationship between the track geometry parameters and the build rate with the LDED-PF processing parameters was studied. Further, the nonlinear relationship among the major process parameters was developed and an analysis of variance (ANOVA) was utilized to find significant parameters. The multi-track deposition yielded densely clad layers with a columnar grain structure. The presence of complex oxide slag of Y, Al, and Zr on the clad layer was detected. A micro-hardness of 240–285 HV was observed in the clad layer, with a hardness of 1088–1276 HV at the slag layer. The multi-layered structures showed a relative density of 99.7% with columnar growth and an average microhardness of 242 HV. The study paves the way for the deposition of dense alumina-forming steel structures for building components for power generation applications.

Robotic laser directed energy deposition-based additive manufacturing of tubular components with variable overhang angles: Adaptive trajectory planning and characterization

The present work reports on an adaptive trajectory planning to build tubular components with variable overhang angles using a robotic Laser Directed Energy Deposition (LDED) based Additive Manufacturing process without utilizing support structures. The proposed technique uses a non-parallel slicing methodology to build complex components (e.g., bent pipes) and deploys adaptively varying scanning speed and tool orientation. The variation in scanning speed aids in having point-to-point variable layer height enabling non-parallel deposition while changing the tool orientation during deposition permits the manufacturing of support-free bent pipe parts. The bent pipes with 45° and 90° bents were built using an in-house developed LDED system and the built parts are characterized for geometry, density, microstructure, and microhardness. The geometrical analysis indicates a deviation in the range of + 0.5 mm to − 0.5 mm, with minimal roundness deviation at different sections. The density analysis of the segments extracted from the bent pipe reveals a density > 98%, with the presence of a few lack of fusion pores and gas pores at isolated locations. The microstructure and microhardness studies show that regions built with higher scanning speeds have a finer grain structure and higher average hardness. The study paves a path to build defect-free and dimensionally stable complex-shaped components with varying overhang angles using LDED.

Inconel 718-CoCrMo bimetallic structures through directed energy deposition-based additive manufacturing

Bimetallic structures and coatings through additive manufacturing (AM) have demonstrated a high degree of freedom for tailoring properties depending on the application. In this study, Inconel 718 and CoCrMo were used as both are common alloys and exhibit unique properties, such as high-temperature oxidation, wear, and fatigue resistance. Using directed energy deposition-based metal AM, bimetallic structures containing these two alloys were manufactured, and the resulting structures exhibited no intermetallic phase formation, cracking, or porosity. Scanning electron microscopy and energy dispersive spectroscopy revealed a smooth elemental transition between the two compositions. Hardness testing showed a linear transition in the interfacial zone, validating no brittle intermetallic phase formation. Compression testing and fracture surface analysis revealed that the failures were not dependent on the interface properties. High-temperature oxidation showed no distinct effect on the interface, a firmly attached chromium oxide layer on the Inconel 718 side and a loosely attached chromium oxide layer on the CoCrMo side. There was also evidence of pit formation on the Inconel 718 surface, but not on the CoCrMo. These findings confirm a stable bimetallic system in which one of the two alloys can be used on the other material to improve the structure’s high-temperature oxidation or wear/corrosion resistance.

Air-to-Liquid Heat Exchanger Fabricated Using Deposition-Based Additive Manufacturing Processes

Abstract This work describes the use of deposition-based additive manufacturing (AM) techniques to fabricate air-cooled, two-fluid heat exchangers. The project focused on a Heating, Ventilation and Air Conditioning application and used an industry-standard copper/aluminum heat exchanger manufactured with conventional technology as the basis for assessing performance. The manufacturing constraints associated with using deposition-based AM technology for this application include the need for a continuous tool path within each build layer that allows uninterrupted extrusion and therefore defect-free water channel walls that correspond to a reliably leak-tight heat exchanger. A geometry that respects these constraints was developed, simulated, optimized and finally manufactured and tested. The material used was a composite of polymer filled with conductive flakes in order to provide high conductivity in the direction that heat must flow in this heat exchanger, across the wall separating the fluids. The measured performance for several test coupons matched the predicted performance and the test coupons exhibited performance that approach and in some cases exceeds conventional technology

Origami-inspired infill pattern for additive manufacturing

Infill patterns determine the interior structure of additively manufactured parts and significantly affect the part’s print time, strength, and weight. In this research, a new origami-inspired structure is proposed as an infill pattern for material deposition-based additive manufacturing applications. Origami techniques derived from antique paper folding arts have been applied to solve engineering problems such as space-saving structures and rapid deployment for their foldability. Recently, origami techniques have also shown another potential in mechanical reinforcement for structural designs. Studies have shown that the mechanical behavior can be significantly improved by combining origami patterns to tubular or box structures. This paper applies a Kresling-inspired structure as the infill pattern for additive manufacturing (AM) to achieve a better lateral compression performance. Fused filament fabrication (FFF) is selected as the testbed for the origami-inspired infill patterns. Results showed that the samples with origami infills had higher ultimate compressive strength, stiffness, and energy absorption than samples with grid or honeycomb infill patterns. This novel structural reinforcement method can be expanded to crash-worthy structures, functional structures, and the design of lightweight, high-strength parts.

Inconel 718-W7Ni3Fe bimetallic structures using directed energy deposition-based additive manufacturing

ABSTRACT Bimetallic structures produced via additive manufacturing (AM) have demonstrated outstanding potential for improving the properties of high-temperature structures. To this end, it was hypothesised in this study that using a tungsten alloy would increase the thermal conductivity of the bimetallic structure compared to pure Inconel 718. Bimetallic structures of Inconel 718 and W7Ni3Fe were manufactured using directed energy deposition (DED)-based AM. Hardness, thermal analysis by diffusivity measurement, and compression testing were done to evaluate the effect of tungsten alloy deposition on Inconel 718's thermal and mechanical properties. Bimetallic structures of Inconel 718-W alloy containing a 50–50 volume % of each displayed a 100% improvement in thermal diffusivity compared to pure Inconel 718, with extensive mixing and remelting due to laser processing. Furthermore, the bimetallic compression samples showed a 100% increase in yield strength combined with a 50% reduction in modulus of elasticity compared to Inconel 718.

Designing high-temperature oxidation-resistant titanium matrix composites via directed energy deposition-based additive manufacturing

Composite material development via laser-based additive manufacturing offers many exciting advantages to manufacturers; however, a significant challenge exists in our understanding of process-property relationships for these novel materials. Herein we investigate the effect of input processing parameters towards designing an oxidation-resistant titanium matrix composite. By adjusting the linear input energy density, a composite feedstock of titanium-boron carbide-boron nitride (5 wt% overall reinforcement) resulted in a highly reinforced microstructure composed of borides and carbides and nitrides, with variable properties depending on the overall input energy. Crack-free titanium-matrix composites with hardness as high as 700 ± 17 HV0.2/15 and 99.1% relative density were achieved, with as high as a 33% decrease in oxidation mass gain in the air relative to commercially pure titanium at 700 °C for 50 h. Single-tracks and bulk samples were fabricated to understand the processing characteristics and in situ reactions during processing. Our results indicate that input processing parameters can play a significant role in the oxidation resistance of titanium matrix composites and can be exploited by manufacturers for improving component performance and high temperature designs.

Effect of scan pattern on Hastelloy-X wall structures built by laser-directed energy deposition-based additive manufacturing

This article systematically analyzes the effect of scan pattern on the geometry and material properties of wall structures built using laser-directed energy deposition (LDED)-based additive manufacturing. Hastelloy-X (Hast-X), a nickel superalloy, is deposited using an indigenously developed 2-kW fiber laser–based LDED system. The wall structures are built using unidirectional and bidirectional scan patterns with the same LDED process parameters and effect of scan pattern on the geometry, microstructural and mechanical characteristics of Hast-X wall structures built using LDED. The wall width is higher for samples deposited with the bidirectional pattern at the starting and ending points as compared to walls built with the unidirectional pattern. Further, the range of width value is higher for walls built with bidirectional strategy as compared to walls built with unidirectional strategy. Wall height is more uniform with unidirectional deposition at the central region, with the range and standard deviation for walls built using bidirectional deposition at 3 and 2.5 times more than unidirectional deposition, respectively. The deposition rate for bidirectional deposition is two times that of unidirectional deposition. The microstructure of the built walls is cellular/dendritic, with bidirectional deposition showing a finer grain structure. Elemental mapping shows the presence of elemental segregation of Mo, C and Si, confirming the formation of Mo-rich carbides. Micro-hardness and ball indentation studies reveal higher mechanical strength for samples built using the bidirectional pattern, with unidirectional samples showing strength lower than the conventional wrought Hast-X samples (197 HV). This study paves a way to understand the effect of scan pattern on LDED built wall structures for building intricate thin-walled components.

IFAC IMS 2019 special issue: process planning solution strategies for fabrication of thin-wall domes using directed energy deposition

ABSTRACT Although multi-axis bead deposition-based additive manufacturing processes have been investigated in many aspects in the literature, a general process planning approach to address collision detection and prevention still needs to be developed to fabricate complex thin-wall geometries in a supportless fashion. In this research, an algorithm is presented that partitions the surfaces of the part and finds the appropriate tool orientation for each partition to avoid collisions.1 This algorithm is applied to segment the surface of a thin-wall hemisphere dome and fabricate it without the need of support structures. Two main fabrication strategies are developed: wedge-shaped partitioning, and a rotary toolpath. A five-axis toolpath and a 2 + 1 + 1-axis toolpath is introduced to fabricate the partitioned build scenarios. A rotary (1 + 3-axis) toolpath is also developed. Tool paths are developed, and the domes built using a directed energy deposition process. The built geometry aligns well with the process planning solutions, but material build up is observed at the partition interfaces. Planar slicing is used to generate toolpaths. However, it is concluded that planar slicing brings limitations to reduce the number of partitions that can be modified by a constant-step-over toolpath.

Understanding the corrosion behaviour of laser directed energy deposition-based additive manufacturing built Inconel 718 under acidic environments

Understanding the corrosion behaviour of laser directed energy deposition-based additive manufacturing built Inconel 718 under acidic environments

Titanium-Silicon on CoCr Alloy for Load-Bearing Implants Using Directed Energy Deposition-Based Additive Manufacturing.

Cobalt-chromium (CoCr) alloys offer outstanding wear resistance when compared to other biocompatible metallic materials and are extensively used in articulating surfaces of total hip and knee arthroplasty. However, CoCr alloys' biocompatibility is known to be inferior to titanium (Ti). Wear- and corrosion-induced metal-ion release from CoCr alloys has been reported to cause cancer and negative physiological impacts. In this study, CoCr alloy was coated with commercially pure Ti (CpTi) and CpTi-Silicon (CoCrTi-Si) with the specific objective of reducing Co and Cr ion release during articulation, without degrading the excellent wear resistance of the CoCr alloy. Directed energy deposition (DED), a blown powder-based laser additive manufacturing technique, was utilized to process CpTi- and CpTi-Si-based coatings on Stellite 6B commercial CoCr alloy. Scanning electron microscopy (SEM), X-ray diffraction (XRD) analyses, and hardness testing found that refined carbides and titanium silicides increased the hardness from 321 ± 13 to 758 ± 48 HV0.5. Tribological studies determined a comparable wear rate between Stellite 6B alloy and CoCrTi-Si in DI water but a statistically significant reduction in Dulbecco's Modified Eagle Medium (DMEM). The wear rates for Stellite 6B were 8.5 ± 0.8 × 10-5 and 12.9 ± 0.4 × 10-5 mm3/Nm in DI water and DMEM, respectively. While the wear rates for CoCrTi-Si were 9.1 ± 0.5 × 10-5 and 8.9 ± 0.8 × 10-5 mm3/Nm in DI water and DMEM, respectively. Contact resistance acquisition displayed the presence of a passive film formation during tribological testing. ICP-MS results for Stellite 6B and CoCrTi-Si concluded a reduction of Co ions release in DI water from 149.8 ± 66.7 to 17.5 ± 0.7 ppb and a reduction in Cr ions release from 66.7 ± 32.4 to 18.0 ± 0.5 ppb, respectively. In DMEM media, Co ion release for Stellite 6B and CoCrTi-Si reduced from 10.1 ± 1.4 to 4.1 ± 0.2 ppb and Cr ion release for Stellite 6B and CoCrTi-Si reduced from 8.7 ± 0.2 to 5.0 ± 0.7 ppb, respectively. The current study revealed a new mode of manufacturing for CoCr alloy-based load-bearing implants that can reduce toxic metal ions release due to wear- and corrosion-induced damages.

Characterizing Novel Honeycomb Infill Pattern for Additive Manufacturing

Abstract Prismatic closed cells, i.e., honeycomb structures, are often used as infill in additive manufacturing (AM) for providing physical stability to the skin and mechanical integrity to the object. These cells are periodic in nature and uniform in density. In this research, a new fabrication pattern for honeycomb infill is proposed for material deposition-based additive manufacturing applications. The proposed pattern uniformly distributes the material within the cell and can accommodate a controllable variational honeycomb infill while maintaining continuity with relative ease. First, the honeycomb unit cell geometry is defined for uniform and non-uniform voxel sizes. A continuous toolpath scheme is then designed to achieve the honeycomb structure with uniform wall thickness. Unlike traditional honeycomb cells, the aspect ratio of the proposed cell type is not restricted, which helps to introduce variational honeycomb architecture in the infill. Additionally, the proposed cell type is four-time smaller than the traditional cell, which increases the unit cell packing density for the same R3 space. The proposed infill structures are fabricated with both uniform and variational patterns, which are then compared with the traditional honeycomb pattern with compression testing. In comparison to the traditional samples, the proposed uniform and variational infill patterns have achieved higher elastic modulus, collapse strength, and absorbed more specific energy along the X-direction. However, the values measured for both proposed patterns are lower along the Y-direction. Similar results are achieved for two different materials (PLA and TPU), which indicates the consistency of our findings.

Microstructure and Mechanical Properties of AISI 316L Produced by Directed Energy Deposition-Based Additive Manufacturing: A Review

Directed energy deposition (DED) as a metal additive manufacturing technology can be used to produce or repair complex shape parts in a layer-wise process using powder or wire. Thanks to its advantages in the fabrication of net-shape and functionally graded components, DED could attract significant interest in the production of high-value parts for different engineering applications. Nevertheless, the industrialization of this technology remains challenging, mainly because of the lack of knowledge regarding the microstructure and mechanical characteristics of as-built parts, as well as the trustworthiness/durability of engineering parts produced by the DED process. Hence, this paper reviews the published data about the microstructure and mechanical performance of DED AISI 316L stainless steel. The data show that building conditions play key roles in the determination of the microstructure and mechanical characteristics of the final components produced via DED. Moreover, this review article sheds light on the major advancements and challenges in the production of AISI 316L parts by the DED process. In addition, it is found that in spite of different investigations carried out on the optimization of process parameters, further research efforts into the production of AISI 316L components via DED technology is required.

Mechanical Properties of 3D Nanostructures Obtained by Focused Electron/Ion Beam-Induced Deposition: A Review.

This article reviews the state-of-the -art of mechanical material properties and measurement methods of nanostructures obtained by two nanoscale additive manufacturing methods: gas-assisted focused electron and focused ion beam-induced deposition using volatile organic and organometallic precursors. Gas-assisted focused electron and ion beam-induced deposition-based additive manufacturing technologies enable the direct-write fabrication of complex 3D nanostructures with feature dimensions below 50 nm, pore-free and nanometer-smooth high-fidelity surfaces, and an increasing flexibility in choice of materials via novel precursors. We discuss the principles, possibilities, and literature proven examples related to the mechanical properties of such 3D nanoobjects. Most materials fabricated via these approaches reveal a metal matrix composition with metallic nanograins embedded in a carbonaceous matrix. By that, specific material functionalities, such as magnetic, electrical, or optical can be largely independently tuned with respect to mechanical properties governed mostly by the matrix. The carbonaceous matrix can be precisely tuned via electron and/or ion beam irradiation with respect to the carbon network, carbon hybridization, and volatile element content and thus take mechanical properties ranging from polymeric-like over amorphous-like toward diamond-like behavior. Such metal matrix nanostructures open up entirely new applications, which exploit their full potential in combination with the unique 3D additive manufacturing capabilities at the nanoscale.

Application of Directed Energy Deposition-Based Additive Manufacturing in Repair

In the circular economy, products, components, and materials are aimed to be kept at the utility and value all the lifetime. For this purpose, repair and remanufacturing are highly considered as proper techniques to return the value of the product during its life. Directed Energy Deposition (DED) is a very flexible type of additive manufacturing (AM), and among the AM techniques, it is most suitable for repairing and remanufacturing automotive and aerospace components. Its application allows damaged component to be repaired, and material lost in service to be replaced to restore the part to its original shape. In the past, tungsten inert gas welding was used as the main repair method. However, its heat affected zone is larger, and the quality is inferior. In comparison with the conventional welding processes, repair via DED has more advantages, including lower heat input, warpage and distortion, higher cooling rate, lower dilution rate, excellent metallurgical bonding between the deposited layers, high precision, and suitability for full automation. Hence, the proposed repairing method based on DED appears to be a capable method of repairing. Therefore, the focus of this study was to present an overview of the DED process and its role in the repairing of metallic components. The outcomes of this study confirm the significant capability of DED process as a repair and remanufacturing technology.