Multi-material Samples Research Articles

Identification of ultrasound characteristics in viscoelastic architectured materials by angular measurements in double through-transmission

Recent advances in additive manufacturing of viscoelastic materials have paved the way towards the design of increasingly complex multi-material structures with heterogeneities from the micro- to the macroscale. However, the measurement of ultrasound characteristics in such viscoelastic structures is a challenging problem, due to the strong attenuation related to both the constituent materials and the architecture. We propose here a methodological framework to identify the phase velocity and attenuation in viscoelastic multi-material quasi-heterogeneous samples. The proposed approach relies on measurements achieved in double through-transmission at various incidence angles, referred as theta-scan. The forward modeling of the wave propagation in such media allows then to identify the ultrasound characteristics based on an inverse approach. Experiments were performed on multi-material samples made of a random pattern of inclusions of a soft elastomer inside a rigid glassy polymer. The effects of the volume fraction of the constituent materials on the ultrasound characteristics was evaluated. This methodology open the path towards ultrasonic measurements in highly attenuating architectures

Laser-based directed energy deposition of Monel K-500 and Stellite 6 multi-materials

ABSTRACT Laser-based directed energy deposition (L-DED) offers significant advantages for repairing metal structures, particularly in the marine and offshore industry where corrosion-resistant materials like Monel K-500 (a Ni-Cu alloy) lack strength and wear resistance. This study addresses this issue by producing Monel K-500 with high-strength Stellite 6 (a Co-Cr alloy). Two types of multi-material samples were created using L-DED: interlayered and mixed powder samples. The interlayered samples experienced cracking at the material interface, while the mixed powder samples were crack-free and exhibited improved mechanical properties, with yield strength increasing from 208.3 MPa to 490.2 MPa and ultimate tensile strength from 429.7 MPa to 887.0 MPa compared to single Monel K-500 samples. This research demonstrated the potential of in-situ alloying during the L-DED process to enhance alloy properties and highlighted the challenges of abrupt compositional changes leading to cracking, suggesting mitigation strategies for successful production.

Mechanical properties of steel–copper multi-material samples built by laser powder bed fusion using a graded energy input

Mechanical properties of steel–copper multi-material samples built by laser powder bed fusion using a graded energy input

Enabling Invar to Ti6Al4V transitions through copper in functionally graded laser powder bed fused components

This study examines the microstructural evolution, elemental distribution, phase composition, and hardness variations in multi-material samples fabricated using Laser Powder Bed Fusion (LPBF) with Invar and Ti6Al4V with compositional gradients mediated by copper. A range of compositional transitions from Invar to Ti6Al4V with different copper fractions are reported. Defects such as gas and keyhole pores were detected in well-deep keyhole mode areas, while lack of fusion defects were observed in samples with pure Cu interlayers due to poor wettability and processing parameter variations. Crack formation between interlayer gradient zones and Invar regions was linked to FeNi and CuNi intermetallic phases. Intermetallic compounds (e.g., FeNi, CuNi, TiFe, TiNi) significantly influenced the microstructure and mechanical performance. Vickers hardness testing shows varying hardness across different builds, with the highest hardness being observed in the gradient zone enabled by pure copper (approximately 620 HV). This study also underscores the need for tailored component design linking build processing parameters and compositional transitions in multi-material LPBF to achieve desired properties and component structural behaviour.

High-Precision Inkjet 3D Printing of Curved Multi-material Structures: Morphology Evolution and Optimization

Multi-material printing is a significant developmental trend in the field of rapid prototyping. However, research on the simulation and prediction of multi-material formation is still at the droplet level and unable to calculate the changes in multi-material interface morphologies caused by flow and solidification. Additionally, it is not possible to predict the overall morphologies of the multi-material interfaces in a sample. Therefore, this paper proposes a multi-material morphology evolution prediction model based on convolution gradient calculations. Using semi-empirical model of multi-material droplet sliding and spreading, overlapping flow, and the multi-material droplet film solidification model, precise predictions of deposition, flow, and solidification between multiple materials were achieved and extended to curved surface deposition. Based on the prediction results, we designed an iterative optimization method for the droplet distribution and droplet grayscale to realize high-precision jet deposition, solidification, and sintering integrated forming technology for multi-material samples. This method has an interface inclination prediction error of less than 0.8° and height error of less than 10 μm, with the interface inclination approaching 0° after iterative optimization. This method can be used for the high-precision printing of devices such as antennas and metamaterials. Based on microstrip antenna printing results, the center frequency was 14.9GHz, return loss at the center frequency was 34.22dB, and return loss was 10dB in the 13.6 to 15.4GHz band, providing a foundation for the conformal manufacturing of high-performance multi-material electronic devices.

Exploring single-shot propagation and speckle based phase recovery techniques for object thickness estimation by using a polychromatic X-ray laboratory source.

Propagation and speckle-based techniques allow reconstruction of the phase of an X-ray beam with a simple experimental setup. Furthermore, their implementation is feasible using low-coherence laboratory X-ray sources. We investigate different approaches to include X-ray polychromaticity for sample thickness recovery using such techniques. Single-shot Paganin (PT) and Arhatari (AT) propagation-based and speckle-based (ST) techniques are considered. The radiation beam polychromaticity is addressed using three different averaging approaches. The emission-detection process is considered for modulating the X-ray beam spectrum. Reconstructed thickness of three nylon-6 fibers with diameters in the millimeter-range, placed at various object-detector distances are analyzed. In addition, the thickness of an in-house made breast phantom is recovered by using multi-material Paganin's technique (MPT) and compared with micro-CT data. The best quantitative result is obtained for the PT and ST combined with sample thickness averaging (TA) approach that involves individual thickness recovery for each X-ray spectral component and the smallest considered object-detector distance. The error in the recovered fiber diameters for both techniques is , despite the higher noise level in ST images. All cases provide estimates of fiber diameter ratios with an error of 3% with respect to the nominal diameter ratios. The breast phantom thickness difference between MPT-TA and micro-CT is about 10%. We demonstrate the single-shot PT-TA and ST-TA techniques feasibility for thickness recovery of millimeter-sized samples using polychromatic microfocus X-ray sources. The application of MPT-TA for thicker and multi-material samples is promising.

Additive technology for forming multi-material samples of “stainless steel – high-entropy alloys” system

The Metal Paste Deposition (MPD) method offers several advantages in producing multi-materials compared to other additive technologies. While there have been studies conducted on multi-material production using this method, they are limited. Hence, a significant objective is to expand the research scope concerning multi-materials produced through the MPD method. This study aimed to examine samples of multi-material systems comprising 316L steel with CoCrFeMnNiW0.25 and 316L steel with CrMoNbWV obtained from metal paste. The investigation involved forming multi-material samples and analyzing the porosity, microstructure, phase composition, and hardness of the 316L steel metal paste after sintering. The findings lead to several conclusions: when forming multi-material samples of the 316L–CoCrFeMnNiW0.25 system, there is no necessity to create a transition zone using mixed 316L steel and CoCrFeMnNiW0.25 powders, as these alloys mix strongly within it. However, in the 316L–CrMoNbWV system, forming a transition zone of mixed powders is necessary to mitigate the effects of uneven shrinkage. Altering the sintering modes for multi-material samples of the 316L–CoCrFeMnNiW0.25 system is recommended; the temperature should be reduced by 30–45 °C compared to the sintering modes for 316L steel. After sintering the metal paste derived from 316L steel, the resulting sample exhibits large and small spherical pores. To minimize these defects, degassing can be employed. Additionally, reducing porosity can be achieved through hot isostatic pressing post-sintering. The microstructure following the sintering of the metal paste from 316L steel consists of coarse austenite grains with minimal ferrite accumulation at the grain interface.

Mechanical properties of the VZh159–CuCr1Zr alloy multi-material samples manufactured by selective laser melting

Selective laser melting (SLM) proves to be a suitable method for fabricating multi-material products, offering heightened performance. The objective of this study is to examine the mechanical properties of the VZh159–CuCr1Zr multi-material system produced through selective laser melting. We conducted tensile and compressive strength tests on these samples, followed by fractography, examination of polished sections, and a comparison of measured mechanical properties with existing data. Our findings are summarized as follows: the phase compositions in the regions of pure alloy denote solid solutions. X-ray diffraction (XRD) patterns of the interface zone reveal peaks corresponding to both alloys. The tensile strength of VZh159–CuCr1Zr multi-material samples, as measured in tensile tests, is σu = 430 ± 20 MPa, with a relative elongation of ε = 4.6 ± 0.3 %. Results from compressive strength tests show values of σu = 822 ± 23 MPa, and relative compression ε = 42.5 ± 1.5 %. Comparing these values with those of the pure CuCr1Zr alloy, the ultimate tensile strength is approximately 53 % higher (according to available data), while the conditional yield strength is about 80 % higher. Fractography of the VZh159–CuCr1Zr multi-material sample after tensile tests indicates that the interface zone exhibits both more ductile fracture features characteristic of the CuCr1Zr alloy (pits and a lack of a smooth surface) and less ductile features charac­teristic of the VZh159 alloy (microcracks). Examination of the polished section of a VZh159–CuCr1Zr multi-material sample after compressive strength tests reveals that the presence of a more ductile CuCr1Zr alloy in the interface zone contributes to arresting the crack, which propagates at a 45° angle to the direction of load application in the VZh159 alloy region.

Mechanical behavior of macroscopic interfaces for 3D printed multi-material samples made of dissimilar materials

Mechanical behavior of macroscopic interfaces for 3D printed multi-material samples made of dissimilar materials

Material extrusion of metals: Enabling multi-material alloys in additive manufacturing

This article discusses the use of Material Extrusion of Metals (MEX/M - defined in ISO/ASTM 52900) technology for producing multi-material components, which offers a cost-effective and efficient method without requiring major adaptations to existing equipment. The article presents the successful manufacture of 316L/17–4PH multi-alloy steel cubes for four different sintering temperatures using commercially available equipment and feedstock. The feasibility study of the multi-material samples was supported by analyzing the shrinkage, optical density, and microstructure as output parameters. Unlike other works, the multi-material produced parts showed regular shrinkage behaviour and no major deformation, indicating the possibility of creating functional parts without the need for post-processing. Interestingly, relevant findings were made on the different shrinkage values obtained for the constellations considered. Further in-depth investigation of each parameter involved in all the stages of the chain value (extrusion, debinding, and sintering) will be key to support the present results. Additional research into the mechanical and magnetic properties of the samples produced could lead this combination of materials to applications in various industries including automotive and aerospace.

Evaluation of 3D Printed Burr Hole Simulation Models Using 8 Different Materials

3D printing is increasingly used to fabricate three-dimensional neurosurgical simulation models, making training more accessible and economical. 3D printing includes various technologies with different capabilities for reproducing human anatomy. This study evaluated different materials across a broad range of 3D printing technologies to identify the combination that most precisely represents the parietal region of the skull for burr hole simulation. Eight different materials (polyethylene terephthalate glycol, Tough PLA, FibreTuff, White Resin, BoneSTN, SkullSTN, polymide [PA12], glass-filled polyamide [PA12-GF]) across 4 different 3D printing processes (fused filament fabrication, stereolithography, material jetting, selective laser sintering) were produced as skull samples that fit into a larger head model derived from computed tomography imaging. Five neurosurgeons conducted burr holes on each sample while blinded to the details of manufacturing method and cost. Qualities of mechanical drilling, visual appearance, skull exterior, and skull interior (i.e., diploë) and overall opinion were documented, and a final ranking activity was performed along with a semistructured interview. The study found that 3D printed polyethylene terephthalate glycol (using fused filament fabrication) and White Resin (using stereolithography) were the best models to replicate the skull, surpassing advanced multimaterial samples from a Stratasys J750 Digital Anatomy Printer. The interior (e.g., infill) and exterior structures strongly influenced the overall ranking of samples. All neurosurgeons agreed that practical simulation with 3D printed models can play a vital role in neurosurgical training. The study findings reveal that widely accessible desktop 3D printers and materials can play a valuable role in neurosurgical training.

Development and production of a CNC machined 420 stainless steel reinforced with Cu by hot pressing

Multi-material structures make it possible to obtain effective solutions to engineering problems by combining the benefits of different materials to meet the requirements of different working conditions. The aim of this multifunctional 420 stainless steel-copper structure is to create a hybrid solution in which copper acts as heat-transfer enhancer (through cooling channels) while maintaining the required mechanical properties of the steel matrix. This work focuses on a combined engineering process consisting of CNC machining through holes on a 420 stainless steel surface substrate and subsequent filling with copper by hot pressing. The influence of the copper filling on the physical, chemical, microstructural, mechanical, and thermal properties of this multi-material solution was analysed. The machined area (5% of the total surface area) consisted of nine holes with a diameter of approximately 1 mm. The multi-material samples showed high densification, homogeneous microstructures, and a well-defined and sharp interface between the two materials. The microhardness values measured for the 420 stainless steel and copper were 759 and 57 HV, respectively, and the thermal conductivity of the multi-material was ≅ 59% higher than the 420 stainless steel (39.74 and 16.40 W/m K, respectively).

Design and validation of a suction device to reduce cross-contamination in multi-material laser-based powder bed fusion

Powder suction modules for additive manufacturing systems in the field of multi-material laser powder bed fusion (PBF-LB/M) have a critical influence on the quality of the manufactured components. In particular, metal powder cross-contamination originating from insufficient removal of foreign particles during multi-material processing can lead to undesired changes in material properties. In this paper, a suction device was simulated, designed, and validated to reduce cross-contamination. Requirements and necessary characteristic values of the multi-material PBF-LB/M system, the powder suction module, and the materials used were determined. Furthermore, an iterative simulative method and procedure for the design of suction devices was applied. For this purpose, a flattened bell-shaped geometry with flow-optimized fins was presented. This design led to both a high flow velocity and a homogenous velocity distribution at the nozzle inlet for full-surface multi-material PBF-LB/M suction modules. The developed method was validated by applying it to the material combination of tool steel 1.2709 and copper alloy CW106C. The aim was to reduce the cross-contamination generated during the in-process on an SLM 280HL multi-material PBF-LB/M system. Multi-material samples were built using the original nozzle design as well as the newly developed improved powder suction module and investigated in terms of resulting cross-contamination using energy-dispersive X-ray spectroscopy. The improved suction module had a significantly higher flow velocity and a more homogenous velocity distribution at the nozzle inlet compared to the original suction module. Cross-contamination of the manufactured multi-material samples was reduced by up to 93 % due to the improved suction model.

Process optimization and study of the co-sintering behaviour of Cu-Ni multi-material 3D structures fabricated by spark plasma sintering (SPS)

The present work focuses on the possibility of manufacturing multi-material structures by spark plasma sintering (SPS), thereby broadening the field of application of this process by taking full advantage of the specific properties of individual materials. As a combination of dissimilar materials to be co-processed, CuCrZr and nickel are of particular scientific and technological interest. For the processing of complex 3D multi-material geometries made of highly dissimilar materials, the sintering behavior of each individual material should however be as identical as possible. Since both materials have different physical and mechanical properties, the sintering behavior of the two individual powder materials is first characterized at different uniaxial pressures, heating rates and holding times. A strategy to determine optimal sintering conditions for the processing of multi-material structures is then developed, based on representation of the densification data of each material in the form of master sintering curves (MSC) and surfaces (MSS). From the MSS, an optimal uniaxial pressure of 35 MPa was determined and the holding time to achieve dense multi-material structures at a temperature of 1223 K was estimated. Different configurations of CuCrZr-Ni multi-material samples were successfully sintered using these parameters and microscopic analyses showed that the relative density in these parts is >99.8, in both CuCrZr and Ni.

Finite-element-based resonant ultrasound spectroscopy for measurement of multi-material samples.

Understanding the elastic properties of materials is critical for their safe incorporation and predictable performance. Current methods of bulk elastic characterization often have notable limitations for in situ structural applications, with usage restricted to simple geometries and material distributions. To address these existing issues, this study sought to expand the capabilities of resonant ultrasound spectroscopy (RUS), an established nondestructive evaluation method, to include the characterization of isotropic multi-material samples. In this work, finite-element-based RUS analysis consisted of numerical simulations and experimental testing of composite samples comprised of material pairs with varying elasticity and density contrasts. Utilizing genetic algorithm inversion and mode matching, our results demonstrate that elastic properties of multi-material samples can be reliably identified within several percent of known or nominal values using a minimum number of identified resonance modes, given sample mass is held consistent. The accurate recovery of material properties for composite samples of varying material similarity and geometry expands the pool of viable samples for RUS and advances the method towards in situ inspection and evaluation.

Interface characteristics and mechanical behavior of additively manufactured multi-material of stainless steel and Inconel

Recently, direct energy deposition (DED) has been attracting considerable attention in metal additive manufacturing due to its capability of producing multi-materials and composition gradient materials with a high degree of geometrical design freedom and relatively high productivity compared to powder bed fusion processing. In this study, layered multi-materials of austenitic stainless steel (SS316L) and nickel-based superalloy (IN718) were fabricated using DED processing. The produced multi-materials showed a 500 μm thick composition gradient material zone (CGZ) at the interface between the SS316L/IN718 because of dilution. Further, in the CGZ, closer to the SS316L side, fine cracks containing the brittle Laves and NbC phases are detected. Despite the presence of cracks, the multi-material samples showed higher yield strength and ultimate tensile strength than those calculated by rule-of-mixtures. It is attributed to hetero-deformation-induced hardening by the evolution of geometrically necessary dislocations near the CGZ during tensile deformation.

Characterization of multi-material 316L-Hastelloy X fabricated via laser powder-bed fusion

The aim of this work is to provide firsthand knowledge of 316 L stainless steel (316 L) and Hastelloy X (HX) multi-material processing via laser powder bed fusion (PBF). Specifically, microstructure of the interface is studied using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Surface metrology is performed to characterize the resulting surface roughness at the interface followed by tensile and flexural testing of multi-material samples to characterize the mechanical properties of the interfaces. Results showed that use of proper process parameters for each individual material led to formation of a compositional gradient at the interface that stretched for 240 μm (10–12 layers) with no evidence of cracking or porosity. The interface exhibited higher surface roughness compared to 316 L or HX as measured by arithmetic mean height, Sa, and maximum valley depth, Sv, parameters. During tensile testing, samples failed in the 316 L region away from the interface, with comparable yield strength, ultimate strength, and ductility. Finally, it was concluded that the “naturally” formed interface created a compositional gradient which was defect free due to similar values of coefficient of thermal expansion, input energy density, and different Marangoni numbers of the materials.

Influence of bond interface over the lap-shear performance of 3D printed multi-material samples

Multi-material 3D printing offers new possibilities regarding product development, allowing design freedom and multiple materials choices in terms of colour and polymer type. Material extrusion technologies are among the most popular options for multi-material printing due to their low equipment cost and various thermoplastic materials. However, polymers’ compatibility and bond interface must be considered for multi-material components. Material Extrusion creates the parts layer by layer, and each layer is characterised by multiple lines of extruded thermoplastic at a defined width. Therefore, regardless of the 3D model’s surfaces, they are composed of numerous lines of material and voids. Depending on the 3D Printing process setup, the bonding mechanism between materials can be influenced due to the different characteristics of horizontal and vertical contact interfaces. For this reason, this paper aims to study the influence of process parameters over horizontal interface through lap-shear tests for multimaterials samples made of acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA), and polycarbonate (PC). The results show that bond interface strength can be improved by creating ways for the mechanical interlock of the materials.

Mechanical Behaviour of Macroscopic Interfaces for 3D Printed Multi-material Samples

The development of 3D Printing technologies introduced new possibilities regarding multi-material part production. Fused Filament Fabrication (FFF) is one of those technologies suitable for multi-material 3D printing. Usually, multi-material parts are manufactured from different blends of the same material, also known as multi-colour 3D printing, or from materials with good chemical compatibility. Conventionally, a simple face-to-face bond interface between parts’ bodies and a chemical bond between thermoplastics define the mechanical performance of multi-material components. In this regard, the paper aimed to investigate the strength of the contact interface of multi-material specimens using a geometrical approach. Therefore, multiple interlocking interfaces were investigated, such as omega shape, T-shape, dovetail, and others for samples made of low-compatibility thermoplastic materials, acrylic styrene-acrylonitrile (ASA), thermoplastic polyurethane (TPU). The results showed that macroscopic inter-locking interfaces are significantly increasing the mechanical properties.

Enhancing shape memory properties of multi-layered and multi-material polymer composites in 4D printing

The shape memory behavior of smart materials is widely used for stimulation or shape-shifting purposes. Shape memory polymers (SMPs) can shape and force recoveries accompanied by attractive attributes such as biocompatibility, biodegradability, and universality. In this paper, a thermoplastic elastomer (TPE) is used as a complementary material for 4D printed polylactic acid (PLA) structures to enhance their shape and force recovery properties and lower the stimulation temperature for more practical implementations. Two approaches are followed to provide SMP composites (SMPCs): multi-layered and multi-material lattices. In multi-layered lattices, specimens are comprised of separate layers and different ratios of SMP and TPE materials. For comparison, PLA-TPE filaments with the same ratios of multi-layered lattices are produced and used to fabricate multi-material lattices. Dynamic mechanical thermal analysis tests showed a reduction in the glass transition temperature of the manufactured PLA-TPE filament. X-ray diffraction test was conducted to prove that the crystallinity of the developed PLA-TPE material increases which explains the better shape memory effect in the multi-material specimens. Phase separation occurred in low ratios of TPE in PLA, discernible in field emission scanning electron microscope (FESEM) images, resultting in low quality in one of the developed PLA-TPE filaments. FESEM images also showed proper miscibility of TPE in PLA in higher ratios. Thermomechanical tests were done on printed specimens to examine and compare the shape and force recovery of the produced SMPCs. While the shape recovery of multi-material samples was not as good as multi-layered samples, both approaches have better shape recovery results than the PLA sample. Due to a lower glass transition temperature in multi-material lattices, their shape recovery process started at lower temperatures widening their potential practical applications. Force recovery of multi-material samples revealed a significant improvement which was due to more oriented crystalline polymer structures.