Net Shape Parts Research Articles

Microstructure control in additively manufactured Ti-6Al-4V during high-power laser powder bed fusion

Laser powder bed fusion (LPBF) is a premier additive manufacturing (AM) process capable of making intricate metallic parts with short lead time, but its widespread industrial acceptance is still limited due to its low build rate in producing high-quality near net-shape parts. Herein, we have demonstrated the capability of employing high laser power LPBF for the manufacture of quality Ti-6Al-4V at a much-increased build rate, combined with decent dimensional accuracy, suitable microstructure, and superior mechanical performance. Compared to LPBF under low laser power (≤ 400 W), high laser power (600 W) LPBF offers a much narrower processing window to reach a balance among dimensional accuracy, materials density, and desired microstructure. For a given high laser power, a combination of low scanning speed, small hatch spacing, and small focal offset distance imparts a thermal environment with reduced cooling rates to facilitate the formation of lamellar α+β or globular α microstructures at a much lower critical energy density than that under low power. The findings in this work advance our understanding of optimizing the LPBF process in the high-power regime towards sustainable and efficient manufacturing of quality Ti-6Al-4V components having superior mechanical performance.

Additive Manufacturing of cryogenic materials

The use of pure copper and Inconel 718 as cryogenic materials has been well known in the cryogenic materials space. Despite their potential, little is known about the use of these materials in cryogenic environments regarding their ability to withstand these conditions when manufactured using Additive Manufacturing (AM) methods. AM has emerged as a promising production method due to its ability to produce complex geometries and near net-shape parts. Copper and Inconel 718 offer a wide range of uses in cryogenic applications, as Copper being highly conductive makes it ideal for electrical applications, whilst Inconel 718 serves well as an engineering material.In this paper, we demonstrate the Coldgas Spraying (CS) of copper and the Selective Laser Melting (SLM) of Inconel 718 and Scalmalloy as the AM processes of choice for each respective material. The main distinction between both processes is that CS is useful for rapid deposition of material in the range of several kg/h whereas SLM is limited to a range of several hundred g/h. However, CS can only yield bulk structures while SLM allows the production of fine and intricate structures due to the nature of their approaches.The work presented here was performed in the framework of a research project named AdHyBau. It is funded by the German government in which several partners from industry and academia seek to jointly develop a 500 kW output power electric drive for aviation applications which employs liquid hydrogen as a propellant for a fuel cell but also for advanced cooling to obtain very high power densities in the range of above 10 kW/kg.

Additive manufacturing of defect-free TiZrNbTa refractory high-entropy alloy with enhanced elastic isotropy via in-situ alloying of elemental powders

Laser powder-bed fusion (L-PBF) additive manufacturing presents ample opportunities to produce net-shape parts. The complex laser-powder interactions result in high cooling rates that often lead to unique microstructures and excellent mechanical properties. Refractory high-entropy alloys show great potential for high-temperature applications but are notoriously difficult to process by additive processes due to their sensitivity to cracking and defects, such as un-melted powders and keyholes. Here, we present a method based on a normalized model-based processing diagram to achieve a nearly defect-free TiZrNbTa alloy via in-situ alloying of elemental powders during L-PBF. Compared to its as-cast counterpart, the as-printed TiZrNbTa exhibits comparable mechanical properties but with enhanced elastic isotropy. This method has good potential for other refractory alloy systems based on in-situ alloying of elemental powders, thereby creating new opportunities to rapidly expand the collection of processable refractory materials via L-PBF.

A roadmap for tailoring the microstructure and mechanical properties of additively manufactured commercially-pure titanium

In recent years there has been a growing interest in using additive manufacturing to produce near net-shape parts from titanium alloys. Most of these studies have focused on the fabrication of various high-strength alloys such as Ti5553 and Ti–6Al–4V, but there is also a desire to produce parts out of lower-strength and higher elasticity alloys such as commercially pure titanium (CP–Ti). In this work, we have shown the effects on various properties of CP-Ti Grade 2 produced via the Laser Powder Bed Fusion (L-PBF) manufacturing process and subsequent heat treatments. Samples with 99.98 % density were produced. Microstructure and phase evolution was characterized by X-ray and electron backscatter diffraction and polarized light microscopy. Oxygen was found to be incorporated during manufacture and processing by Inert Gas Fusion (IGF). Heat-treatment of the samples resulted in recrystallization of the acicular microstructure. By testing the mechanical properties throughout the recrystallization temperatures, it was observed that the grain recrystallization lead to a reduction in mechanical strength without a significant improvement in ductility, therefore making a low temperature heat-treatment that retains the AM microstructure an interesting alternative to strengthen CP-Ti.

Parameter and Deposition Strategy Analysis for WAAM Processing of AISI 410 Stainless Steel

Wire + Arc Additive Manufacturing (WAAM®) is an additive manufacturing (AM) process capable of producing near net shape parts while reducing costs and thus gathering increased attention from researchers and manufacturers. Although a significant amount of work has already been published relating to the WAAM processing of stainless steels, it was mainly focused on austenitic stainless steels, with martensitic grades still lacking investigation. AISI 410 is a martensitic stainless steel that, due to its high hardness, demonstrates high wear resistance, being used in parts requiring high resistance to abrasion. Processing this material by WAAM allows for the creation of near net shape parts, leading to a reduction in machining, while at the same time allowing the creation of complex geometries which would be difficult, or outright impossible to obtain otherwise. In this work the effects of different processing parameters on WAAM processed AISI 410 steel, using Cold Metal Transfer (CMT) welding equipment, were investigated, as well as different deposition strategies for the fabrication of a test artifact using an AM software. It was demonstrated that it is possible to process AISI 410 steel by WAAM using an AM software to define deposition strategies and parameters based on the part design and previous experimental trials. The goal to deposit a complex part with high hardness and tensile strength, especially attractive properties to parts requiring high resistance to wear was achieved.

Abnormal annealing-induced strengthening in Ni39.3Al15.7Fe45 eutectic medium entropy alloy

Cold-working combined with annealing is frequently used to enhance strength of traditional alloy materials. However, this thermal-mechanical processing is not adapted to the preparation for some near net shape parts. In this paper, a dual-phase Ni39.3Al15.7Fe45 eutectic medium entropy alloy (EMEA) was prepared by vacuum arc melting and abnormal annealing-induced strengthening is demonstrated and analyzed via XRD, SEM, EDS, TEM and room temperature tensile testing. It is found that the Ni39.3Al15.7Fe45 EMEA is composed of FCC solid solution phase and BCC phase. After annealing, ordered L12 phase precipitated from FCC solid solution, which induces a significant increment of tensile strength and a weak decrease of tensile plasticity. The tensile strength and elongation are 991 MPa and 24.1 % at as-cast state, the tensile strength and elongation are 1279 MPa and 22.4 % after annealing at 700 °C for 1 h.

Optimization of process parameters effects on mechanical properties of selective laser melted iron samples

AbstractSelective laser melting is an additive manufacturing technology whereby parts are built through selective melt of a powder bed by a laser beam. This technology is used to produce net shape parts in 3D printers. In this study, the effect of selective laser melting parameters on the mechanical properties (ultimate tensile strength and hardness) of iron has been experimentally extracted, and the optimum levels of the parameters have been determined for optimum mechanical properties using signal‐to‐noise analysis. The selected parameters include the laser power, the laser scanning speed, and the laser hatch distance, and the design of experiments was done by the Taguchi method. The main effects of factors and interactions were considered in this paper. The results show that the optimum parameter levels for the ultimate tensile strength include the laser power of 200 W, the laser scanning speed of 600 mm/s, and the hatch distance of 70 μm. The optimal parameters for hardness are similar to the maximum tensile strength, except that the optimum hatch distance is 60 μm.

The effect of microstructure on the tensile and impact behaviour of short-glass fibre-reinforced polyamide 6.6 as assessed by micro-computed tomography

Injection moulding of short-fibre-reinforced thermoplastics opens a new dimension in the field of mass production of complicated net-shaped parts with accurate dimensions and the new challenge is to produce parts with tailored properties. However, the layered structure frequently observed in these composites strongly affects their mechanical behaviour and constitutes the main difficulty in transferring the results of tests performed on standard specimens to actual components and parts. In addition, to use injection-moulded composite materials safely, their mechanical behaviour under different loading conditions must be well understood. In the present work, the effect of microstructure, in terms of fibre length and orientation, on the tensile and impact behaviour of injection-moulded short-glass fibre-reinforced polyamide 6.6 was investigated. Digital reconstruction of the three-dimensional structure of samples, differently oriented with respect to the melt flow path, was obtained by the high-spatial-resolution non-destructive technique of synchrotron radiation micro-computed tomography (micro-CT). Automatic evaluation of the fibre length distribution was developed by a global method based on the mean fibre length distribution, computed from the star length distribution (SLD). The results of uniaxial tensile tests and Izod impact experiments were successfully correlated with morphological analysis of fractured surfaces and the results of SLD. These studies revealed important changes in fibre orientation distribution when the sample orientation is changed with respect to melt flow direction, which also strongly influenced the composite mechanical response.

Microstructure and mechanical properties of additively manufactured AlSi10Mg lattice structures from single contour exposure

Metal-based additive manufacturing techniques offer the ability to produce complex, near net shape parts that would be impossible or prohibitively expensive to manufacture via traditional casting and machining methods. Low density lattice structures for lightweight construction are one such example. However, there currently are no well-developed guidelines for designing and reliably manufacturing these structures. Literature on the topic is fragmented and usually only covers a limited aspect of the complex relations between process parameters, microstructure, lattice geometry and mechanical properties. This work covers the edge case of small diameter struts manufactured from AlSi10Mg via Laser Powder Bed Fusion (L-PBF) using the single contour exposure strategy, which is necessary to ensure sufficient geometric accuracy. Various cubic strut-based lattice geometries are manufactured using four laser parameter combinations corresponding to different area energy densities and beam offsets. The influence of process parameters and heat treatment on the microstructure and mechanical properties is investigated. Results show that the microstructure of filigree lattice struts can be tailored by the selection of process parameters, resulting in either uniform or core–shell structures depending on the laser power, while the macroscopic mechanical properties are mainly determined by the lattice geometry and relative density.

Laser-powder bed fusion process optimisation of AlSi10Mg using extra trees regression

Aluminium alloys have a wide range of applications, especially in the fields of aviation and aerospace. Near net-shape parts with a great structural complexity can be produced using additive manufacturing techniques. However, understanding the Laser-Powder Bed Fusion (L-PBF) process itself and the correlations between different process parameters and the mechanical properties is often very challenging. In order to achieve insights into the whole printing process, statistical tools such as Designs Of Experiment (DoE) are usually applied. In this study, we examined the additive manufacturing of AlSi10Mg, a well-studied aluminium alloy used for L-PBF, and the modelling of its printing process by applying machine learning. The influences of different printing parameters (i.e. laser power, laser spot size, hatching distance, layer height and scanning speed) on the mechanical properties (i.e. density, tensile strength and hardness) were examined by generating different machine learning models based on data obtained with DoE and additional experiments. The best performing models were evaluated regarding the printing process and the respective testing procedures used to measure the mechanical properties. Mean coefficients of determination ranging from 56.44 % to 98.54 % were achieved. Finally, a processing window for producing dense samples with high tensile strengths and high hardness values was found.

The Influence of Surface Irregularities on the Mechanical Properties of Thin-Walled Wire and Arc Additively Manufactured Parts

Wire and Arc Additive Manufacturing (WAAM) is a metal additive manufacturing process commonly used to deposition medium to large, near net-shaped parts. It can efficiently use materials and deposit objects with fewer assembly parts. The main disadvantage of WAAM is the surface quality. This work investigates the geometry shift defect that could be formed due to the wear of the welding contact tip. As a result of the wear, the filler wire deviates from the nominal position, and errors occur in the positioning of individual layers of printed parts. The main objective of this work is to investigate the influence of surface irregularities on the mechanical properties of as-deposited thin-walled WAAM parts. Finite element modeling of static and cyclic tensile and compressive tests showed that the surface waviness formed during layer-by-layer deposition increases the stress level under static loading applied transversely to the deposited layers. Surface waviness also significantly reduces the life of parts under cyclic loading. Replacement of a worn contact tip causes the layers to shift, and the resulting load eccentricity increases the stress level. Uneven stress distribution throughout the cross section means reduced material usage efficiency. During compressive loading, the load eccentricity destabilizes, causing the specimen to deform after exceeding the yield strength in stress concentration zones. The relationship between unmachined and machined walls with equivalent stresses was obtained, allowing the influence of surface waviness on the strength and durability of structures to be considered at the design stage.

Passive intensity modulation of a pattern for fabricating near-net shaped features in microscale metal additive manufacturing

A large variation in part size across the projection area of the microscale selective laser sintering process is caused by non-uniform intensity projected onto the substrate by the digital micromirror device (DMD). A corrective gray scale mask with varying intensities was mapped according to a sintered array of parts. The variance in part size across the area was reduced by as much as 45% by using this technique. This approach can be extended to in real-time process control to create a more uniform distribution of heat and in turn better near net shape parts across the projection area.

Towards electroforming of copper net-shape parts on fused deposition modeling (FDM) printed mandrels

Towards electroforming of copper net-shape parts on fused deposition modeling (FDM) printed mandrels

Characterization of micro-sandwich structures via direct ink writing epoxy based cores

Sandwich structured (SS) composites demonstrate considerable flexural stiffness and high strength-to-weight ratios and can be tailored as functional materials. Historically they have been constrained to specific material types and geometry due to limitations in manufacturing methods. However, employing additive manufacturing (AM), specifically direct ink writing (DIW), can provide an alternative method for making SS composites with complex and controllable micro and mesostructures with multifunctionality targeted at desired mechanical, thermal, and electrical properties. DIW, an extrusion-based AM technique, uses a viscous and thixotropic ink with desired components that, once printed, is cured to obtain the final complex net shape parts. In this paper, a novel hybrid AM technique is employed to manufacture SS composite materials containing bisphenol A-based epoxy core and carbon fiber reinforced polymer (CFRP) face sheets that are fabricated via DIW and vacuum infusion process (VIP), respectfully. We demonstrate that the fabrication of these SS composites can be tailored from a thermosetting material, from which additives and/or various lattice structures can be manufactured to achieve enhanced and desirable mechanical integrity with functional properties. Surface topology and mechanical testing techniques are used to characterize the fabricated hybrid SS composites to study and assess mechanical stability. A rheo-kinetic cure model was developed for the core material to allow for additive manufacturing process requirements while ensuring complete cross-linking for the thermoset-based core material. Because of the ability to obtain relatively small core-thickness and controlled architecture, this method now allows for fabricating layered micro-sandwich structures for realizing further light-weighting in relevant applications.

A novel approach on production of carbon steels using graphene via powder metallurgy

ABSTRACT Powder metallurgy (P/M) allows producing net or near net-shaped ferrous parts at lower temperatures compared to conventional casting. Carbon steels have a wide range of applications due to their comparatively low cost. So far, iron powders have been compacted and sintered with graphite to produce carbon steels via P/M. However, many studies have been published on the usage of graphene nanoplatelets (GNPs) in metal matrix composites, in recent years. To the best of our knowledge, there is no study on the investigation of the effect of GNPs on microstructural, mechanical, and tribological properties of ferrous materials. For this purpose, carbon steels containing different amounts of GNPs (0.25, 0.50, 0.75 wt.%) were fabricated via P/M. To better understand its effect, graphite was also used at the same contents. Results show that graphene reinforced samples had nearly 11%, 25%, 10% higher tensile strength, hardness, and wear resistance, respectively than graphite-reinforced samples at 0.25 wt.% reinforcement ratio. However, the graphene with a reinforcement ratio of more than 0.5 wt.% showed lower tensile properties nearly 15% compared to graphite-reinforced steels due to its agglomeration.

Determining rational process parameters for selective laser melting of powder titanium alloy VT6

The current pace of development seen by the aerospace industry requires manufacturing techniques that would enable to make parts in the shortest possible timeframe and at minimum cost. Additive manufacturing technology, which is applied in blanking operations, should be described as an innovative area that ensures reduced labour intensity and manufacturing costs. Additive manufacturing technology allows to obtain blanks that are close to the geometry of the final part, i.e. near net shape parts. Additive technology makes it possible to produce unique hollow parts with sophisticated cooling channels of any shape, as well as mesh filter elements with the cell size determined by the size of the powder granules. Thus, printing of parts using metal powders would be of special interest for the aerospace industry. Selective laser melting (SLM) as one of the additive manufacturing areas is of relevance for the aerospace industry as it enables to obtain parts with a more sophisticated geometry in comparison with conventional technology. One of the key stages in the SLM process design that defines the mechanical properties of the synthesized material includes identifying rational parameters of scanning. This paper describes the results of a study that attempted to determine rational scanning parameters for powder titanium alloy VT6. Rational parameters of scanning were established through statistical processing of experimental data. Thus, they include the laser power of 275 W, the scanning pitch of 0.12 mm, the scanning speed of 805 mm/sec, with the layer thickness of 50 μm. The paper describes the results of a uniaxial tensile test carried out with cylindrical specimens produced at 0o, 45o and 90o to the dosing unit and at 0o, 45o, 60o, 90o to the base platform.The research work described in this paper was carried out by the staff of the Shared Knowledge Centre on its equipment using CAM technology; Agreement No. RFMEFI59314X0003.

Additive manufacturing of carbon fiber reinforced ceramic matrix composites based on fused filament fabrication

For the first time, carbon fiber reinforced ceramic matrix composites (CMC) were successfully fabricated by additive manufacturing (AM) using the fused filament fabrication (FFF) technology, filaments (“CF-PEEK”) with thermoplastic polyetheretherketone (PEEK) as the matrix and C-precursor, and carbon short-fibers (< 250 μm) as reinforcements. In order to prevent a re-melting of the as-printed CFRPs (C-fiber reinforced plastics) during pyrolysis at 1000 °C in N2ensuring the freedom of design and complex parts, a prior crosslinking step at 325 °C with a dwell time of 48 h in air was introduced to stabilize and crosslink the CFRP. Due to the stabilization and the printing of degassing channels for the pyrolysis, near net shape and complex CMC parts with different C-fiber orientations (0°; ±45°; 90°) were obtained by the liquid siliconization infiltration process (LSI). The manufactured C/C-SiC parts were characterized regarding their microstructure and mechanical properties. The reinforcing C-fibers were successfully protected during the LSI-process and flexural strengths of almost 60 MPa were obtained.

On the relationship between cutting forces and anisotropy features in the milling of LPBF Inconel 718 for near net shape parts

The versatility and potential applications of additive manufacturing have accelerated the development of additive/subtractive hybrid manufacturing methods. LPBF processes are exceptionally efficient at producing complex-shaped, thin-walled, hollow, or slender parts; however, finishing machining operations are necessary to ensure part assembly and surface quality. Rapid solidification during LPBF processes generates columnar grain structures in alloys. This is associated with crystalline textures and anisotropy, and therefore, mechanical properties are highly dependent on space directions, thus affecting cutting force and its variability.In this study, theoretical and experimental analyses examined the effects of LPBF parameters on cutting forces and the anisotropy of alloys. Therefore, an oblique cutting Taylor based model was proposed to quantify the crystallographic effects on the shear strength. For this, the tool geometry, tool position, and laser scanning strategy were considered along with the microstructures, crystallographic textures and grain morphologies of two samples with different layer thicknesses (low-volumetric energy density (VED) and high-VED) using scanning electron microscopy and electron backscatter diffraction. Peripheral milling operations had been performed under 54 experimental conditions to evaluate the interactions between the machining parameters along with the layer thickness and the microstructural characteristics of printed alloys. The analysis revealed a significant interaction between the direction of the plane of the shear band and the grain orientation along the main axis. Three milling configurations were evaluated. The effects of the layer thickness on the evolution of the cutting force were elucidated. Additionally, the low-VED sample exhibited higher anisotropy in the cutting force compared to the high-VED one. The anisotropy in the latter corresponds to a high, dense <001> ring-like texture; however, the crystallographic effect is lower in the low-VED sample. A good correlation between the cutting force fluctuation and the predicted Taylor factor was obtained. Lastly, the grain boundary density was acceptably correlated with the level of cutting force for both the printed cases.

RETRACTED: Development of Bulk Metallic Glasses and their Composites by Additive Manufacturing - Evolution, Challenges and a Proposed Novel Solution

RETRACTED ARTICLE: Bulk metallic glasses (BMGs) and their composites (BMGMCs) have emerged as competitive materials for structural engineering applications exhibiting superior tensile strength, hardness along with very large elastic strain limit. However, they suffer from lack of ductility and subsequent low toughness due to the inherent brittleness of the glassy structure which makes them amenable to failure without appreciable yielding. Various mechanisms and methods have been proposed to counter this effect out of which, recently Additive Manufacturing has gained widespread attention. It is proposed that additive manufacturing can overcome these difficulties in single step due to inherent existence of very high cooling rate in the process which is essential for glass formation. This, when coupled with careful selection of alloy chemistry is proposed to be the best solution to fabricate near net shape parts in a single step with excellent properties. In this report, an effort has been made to describe one possible route to achieve this. Solidification processing employing carefully selected inoculants based on edge to edge matching technique along with the carefuly controlled inoculation procedure is proposed to reflect upon enhanced mechanical properties. It is hypothesized that number density, size and distribution of ductile crystalline phase would best be able to improve microstructure and hence properties. This is meant to be controlled by manipulating type, size and the amount of inoculants. The proposed methodology is claimed to bear maximum potential.

Modelling and simulation of the freeze casting process with the phase-field method

The freeze casting process is a novel manufacturing method for both near net-shape parts as well as directed porous structures as employed by filters and implants. Depending on the choice of liquid and processing conditions a very wide range of pore shapes and sizes can be achieved. In order to predict the resulting microstructure, a phase-field model is developed on the basis of the grand potential formalism. The model and its parametrization approximate the freeze-casting process of water by linking its thermodynamics with established theory. Directional solidification simulations with varying suspension concentrations, velocities and temperature gradients are carried out. From these, microstructural lengths are determined and linked with the processing parameters, so as to derive linkages between the microstructure and the processing conditions.