Material Extrusion 3D Printing Research Articles

Continuous Carbon Fiber Reinforced SiC Ceramic Matrix Composites by Vertical Fiber Laying Combined with Material Extrusion 3D Printing

3D printing is reported in the fabrication of continuous carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC CMCs), however, there are layer defects in the 3D printed materials, manifested as weak mechanical properties between layers. Therefore, it is essential and urgent to study how to improve the mechanical properties of 3D printed Cf/SiC CMCs at the layers. In this article, a novel processing technique which combined vertical fiber laying method with material extrusion (ME) 3D printing is proposed to manufacture Cf/SiC CMCs. A self‐developed 3D printing fixed‐axis rotating lifting synchronizer is adopted. The vertical fiber laying of continuous carbon fibers (Cf) in Z‐direction is introduced into the X−Y printing plane. Five cycles of precursor infiltration and pyrolysis (PIP) are performed to achieve the densification of Cf/SiC CMCs. The effects of Cf bundle numbers on the flexural strength and fracture work of Cf/SiC CMCs are studied. The best performing composite is Cf/SiC CMC with six bundles, and the maximum flexural strength and fracture work is 63.84 ± 6.62 MPa and 1291.99 ± 161.39 J m−3, respectively. Compared with pure SiC, the fracture work of Cf/SiC CMC with 6 bundles Cf is increased by 2.54 times.

Dimensional accuracy of acrylonitrile butadiene styrene and polylactic acid samples printed in vacuum-assisted material extrusion system

This paper discusses the impact of integrating a vacuum system into a material extrusion 3D printing process for acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) materials. The study aimed to investigate the effect of a vacuum system on the dimensional accuracy of the printed samples. Upon completion of the printing process, the samples’ dimensions were carefully assessed using a Coordinate Measuring Machine (CMM). The geometrical dimensions measured are the diameter, corner radius, fillet, thickness, width, length and angle. Based on the result obtained, the material has yet to reach 100% of the desired geometry, which was identified due to the shrinkage of the material after the printing process. The results show that the vacuum system improved material flow and reduced dimensional deviations by reducing air molecules and minimizing convection. The results indicated a significant enhancement in dimensional accuracy for both ABS and PLA samples when using the vacuum system. ABS samples showed a 4% increase in accuracy, while PLA samples exhibited a 2% improvement compared to samples printed without vacuum assistance. These improvements were achieved by optimizing process parameters such as layer height (0.15 mm), infill percentage (10%), printing speed (45 mm s−1), and bed temperature (60 °C). These parameters were selected to ensure finer details, improved precision, structural support, stability, better adhesion, and reduced warping.

Mechanical and Electrical Properties of Polyethylene Terephthalate Glycol/Antimony Tin Oxide Nanocomposites in Material Extrusion 3D Printing.

In this study, poly (ethylene terephthalate) (PETG) was combined with Antimony-doped Tin Oxide (ATO) to create five different composites (2.0-10.0 wt.% ATO). The PETG/ATO filaments were extruded and supplied to a material extrusion (MEX) 3D printer to fabricate the specimens following international standards. Various tests were conducted on thermal, rheological, mechanical, and morphological properties. The mechanical performance of the prepared nanocomposites was evaluated using flexural, tensile, microhardness, and Charpy impact tests. The dielectric and electrical properties of the prepared composites were evaluated over a broad frequency range. The dimensional accuracy and porosity of the 3D printed structure were assessed using micro-computed tomography. Other investigations include scanning electron microscopy and energy-dispersive X-ray spectroscopy, which were performed to investigate the structures and morphologies of the samples. The PETG/6.0 wt.% ATO composite presented the highest mechanical performance (21% increase over the pure polymer in tensile strength). The results show the potential of such nanocomposites when enhanced mechanical performance is required in MEX 3D printing applications, in which PETG is the most commonly used polymer.

A Review on Process Parameter Optimization in Material Extrusion Additive Manufacturing using Thermoplastic

Material extrusion is one of the most commonly used additive manufacturing techniques which utilizes thermoplastics as the building material. The quality and performance of parts produced via material extrusion depends highly on the process parameters selected. This paper reviews the work done by various researchers on optimizing key process parameters like extrusion temperature, layer thickness, infill percentage, infill pattern etc. in material extrusion 3D printing using thermoplastics like PLA, ABS and nylon. The effects of these parameters on properties like surface roughness, dimensional accuracy, mechanical strength are discussed. Statistical tools like Taguchi method and response surface methodology that have been applied for parameter optimization are also reviewed. The review highlights the need for further process optimization studies considering part design, build orientation and post processing to unleash the full potential of material extrusion 3D printing..

Investigation of the Effectiveness of Silicon Nitride as a Reinforcement Agent for Polyethylene Terephthalate Glycol in Material Extrusion 3D Printing.

Polyethylene terephthalate glycol (PETG) and silicon nitride (Si3N4) were combined to create five composite materials with Si3N4 loadings ranging from 2.0 wt.% to 10.0 wt.%. The goal was to improve the mechanical properties of PETG in material extrusion (MEX) additive manufacturing (AM) and assess the effectiveness of Si3N4 as a reinforcing agent for this particular polymer. The process began with the production of filaments, which were subsequently fed into a 3D printer to create various specimens. The specimens were manufactured according to international standards to ensure their suitability for various tests. The thermal, rheological, mechanical, electrical, and morphological properties of the prepared samples were evaluated. The mechanical performance investigations performed included tensile, flexural, Charpy impact, and microhardness tests. Scanning electron microscopy and energy-dispersive X-ray spectroscopy mapping were performed to investigate the structures and morphologies of the samples, respectively. Among all the composites tested, the PETG/6.0 wt.% Si3N4 showed the greatest improvement in mechanical properties (with a 24.5% increase in tensile strength compared to unfilled PETG polymer), indicating its potential for use in MEX 3D printing when enhanced mechanical performance is required from the PETG polymer.

Mapping 3D printed part density and filament flow characteristics in the material extrusion (MEX) process for filled and unfilled polymers

ABSTRACT Material extrusion (MEX) 3D printing offers a promising avenue for fabricating metal and ceramic components, where highly loaded polymer filaments are 3D-printed and sintered. Achieving nearly 100% 3D-printed part density is critical in this process, as porosity during printing compromises part properties after sintering. However, challenges arise due to the unfavourable mechanical and rheological properties of MEX metal filaments, leading to slow print-speeds, filament breakage, and inconsistent extrusion. This work explores these process-property correlations by developing process maps for bound metal filaments and unfilled polymer systems. This study throws light on the significance of back-flow and back-pressure in calculating the pressure drop across the nozzle, especially in a diverse set of material systems represented by hard and stiff PLA, soft and flexible TPU, and brittle and fragile bronze filaments. Additionally, ANOVA identified the effect of print conditions on measured variables, while regression models helped predict the behaviour of a given material under different process conditions. Therefore, this study enables material design and discovery for bound-metal filaments while addressing critical knowledge gaps, thereby paving the way for high-density 3D-printed components.

Material extrusion 3D printing of ceramic structures with overhangs: rheological aspect and introduction of powder-on-demand supporter

Additive manufacturing (AM), represented as a manufacturing process, which is easily applicable to intricate designs, is widely considered in a variety of industries as a simple and cost-effective solution that complements or replaces traditional manufacturing processes. However, due to the demanding properties of ink materials employing ceramic materials, more stringent considerations are required in selecting an appropriate printing technique and implementing the rheological properties of the ceramic ink suitable for the selected printing technique. Here, material extrusion (ME) was selected as a 3D technique applicable to ceramic materials, and the rheological requirements of ceramic pastes that maximize their printability in ME were scrutinized in detail. It was found that the viscoelastic properties of the ceramic pastes played an important role in determining the flowability, cumulative height, and overhang angles that can be allowed in ME. A new supporter system for overhangs, powder-on-demand supporter (PODS), was introduced to ME and demonstrated to understand if PODS can further extend the limits in cumulative height and overhang angles allowed in ME.

Functionalization of Cyclic Olefin Copolymer for Enhanced Electrical Conductivity in Material Extrusion 3D-Printing: Potential Applications in Laboratory Environments and Small-Scale Experiments

Functionalization of Cyclic Olefin Copolymer for Enhanced Electrical Conductivity in Material Extrusion 3D-Printing: Potential Applications in Laboratory Environments and Small-Scale Experiments

Effect of powder characteristics on the microstructure and performance of CuSn10 parts by material extrusion 3D printing

Two water-atomised, one gas-atomised and treated CuSn10 powders were employed as initial materials to prepare bronze products by material extrusion (MEX) printing technology. The results highlight a significant impact of powder morphology and particle size on both the microstructure and mechanical performance of CuSn10 products. Among the single-size powders, the 3D printed parts, utilising −1000 mesh gas-atomised CuSn10 powders as raw materials, achieved a remarkable hardness of 76.5 HB. For dual-granularity CuSn10 powders, the printed parts from 80%/400500 mesh and 20%/−1000 mesh powders have the optimal performance, reaching a relative density of 98.88% and tensile strength of 355.46 MPa. Successful printing and sintering of various gear parts underscore MEX printing as a viable method for producing high-performance bronze components.

Material extrusion 3D printing of large-scale SiC honeycomb metastructure for ultra-broadband and high temperature electromagnetic wave absorption

Electromagnetic (EM) wave absorbing materials have been widely used in various equipment to reduce the interference caused by EM waves. However, current EM wave absorbing materials are limited by narrow absorption bandwidth under high temperatures due to a lack of structural design. Herein, SiC ceramic and large-scale SiC honeycomb metastructure were monolithically fabricated by material extrusion 3D printing. The real permittivity and imaginary permittivity of as-obtained SiC ceramic approached 10 and 2.3 within the frequency of 2–18 GHz. After optimized structure design, the as-obtained SiC honeycomb metastructure exhibited broadband EM performance of −10 dB effective bandwidth from 4.85 to 39.49 GHz (34.64 GHz) when the incident angle was 60° at room temperature. Moreover, the as-obtained SiC honeycomb structure had a stable broadband −10 dB effective bandwidth of above 35 GHz when the incident angle is 60° even after in-situ 1000 °C and ex-situ 1600 °C erosion in the air atmosphere. Broadband EM wave absorption under oblique incident wave was also achieved from 30° to 60° both in transverse electric (TE) polarization and transverse magnetic (TM) polarization. This novel strategy unravels the potential of additive manufacturing of high-performance EM wave absorbers for high temperature environment applications.

Mechanical analysis and biodegradation of oxides-based magneto-responsive shape memory polymers for material extrusion 3D printing of biomedical scaffolds

The development of advanced smart polymers, characterized by superior strength, exceptional quality, biodegradability, and lightweight structures, stands as a paramount concern in the context of biomedical implant materials. Aiming at the requirements of a tracheal scaffold, this research focuses on developing magnetic shape memory polymers using solvent evaporation method and characterizing their morphology, viscoelastic, thermodynamic, mechanical and shape memory properties. Furthermore, an assessment of degradation is conducted, along with an evaluation of tensile strength both pre- and post-degradation. The findings reveal that the dispersion of Fe3O4 nanoparticles exhibits homogeneity at a 15 wt% concentration but tends to aggregate at high proportions. The glass transition temperature increases with the addition of Fe3O4, while less than 10% ratio of the Fe3O4 cannot activate the magnetic actuation. Notably, the tensile and elastic modulus for the 15 wt% Fe3O4 composition measure at 59.70 MPa and 24.68 MPa, respectively, and exhibit a diminishing trend with higher nanofiller content. Subsequently, it demonstrates favorable thermal and magnetic shape memory behavior, yielding reasonable shape recovery ratios. Over a degradation period of 120 days, a reduction in average weight loss was observed for 15 wt% concentration, while higher for higher concentrations due to their non-uniform dispersion. Post-degradation, the tensile strength experiences a decline with proportional reduction of 41.15%, 37.61%, 47.13%, 42.46%, and 54.77%, respectively. Based on the finite element analysis, the multi-objective optimization of the structural parameters of the tracheal stent was carried out, and manufactured by material extrusion 3D printing. Finally, the stability, flexibility and compression properties of the scaffold were tested by relevant experimental tests, which ensured the suitability (foldability) of scaffolds. In conclusion, the developed magnetic shape memory polymers showed promising potential for biomedical scaffolds preparation.

Bicomponent melt-spinning of filaments for material extrusion 3D printing

In material extrusion (MEX) 3D printing, the layer-by-layer structure often presents challenges such as poor adhesion, void formation and rough surfaces, which can compromise the mechanical properties of printed parts and limit their applications. This study investigates whether 3D printing from bicomponent core-sheath filaments instead of printing from conventional monofilaments provides a potential solution to some of the described issues. Based on different material selections, various bicomponent filaments, comprising a rigid core and a soft sheath, were produced through co-extrusion and overcoating extrusion techniques. Tensile properties of 3D-printed specimens with different raster angles (0° vs 45°) from bicomponent filaments are compared to the properties of reference specimens printed from conventional monofilaments. While similar mechanical properties were observed for some 3D-printed specimens from bicomponent filaments (e.g., polylactic acid (PLA)-based), as compared to reference specimens, some core-sheath combinations of polyamide (PA) demonstrated a noticeable improvement of the mechanical properties of 3D-printed specimens, particularly for 45° raster angles. In particular, bicomponent filaments comprising a carbon fiber reinforced PA (PACF) core and a pure PA sheath exhibited improved processability and enhanced structural strength. Moreover, two overcoated filaments consisting of polyethylene terephthalate (PET) and polyphenylene sulfide (PPS) monofilament cores with a copolyester (CoPES) sheath were prepared for 3D printing. 3D-printed parts made from PET/CoPES overcoated filaments exhibited good compatibility and satisfactory results when printed at temperatures above the melting point of PET. These findings demonstrate the potential of bicomponent filaments to enhance both printability and mechanical performance of 3D-printed parts, offering new avenues for material selection and design optimization in various 3D printing applications.

Numerical study on effect of process parameters on material extrusion 3D printing (ME3DP) for porous bone tissue engineering scaffolds

Bone tissue engineering (BTE) holds promise for treating bone defects, and 3D-printed porous scaffolds are pivotal for tissue regeneration. This study explores the impact of material extrusion 3D printing (ME3DP) process parameters (i.e., layer height and extrusion temperature) on 3D-printed porous scaffolds made of polyetherimide (PEI) material for BTE. The intricate relationships shaping scaffold dimensional accuracy, residual stresses, and warpage tendencies were unveiled using comprehensive numerical simulations. Our findings reveal that higher layer heights enhance dimensional stability, especially at lower printing temperatures, reducing maximum displacements. Consequently, lower layer heights lead to higher warpage critical values. This insight is instrumental in optimizing the material extrusion 3D printing (ME3DP) process, vital for precise net shape in BTE applications. Furthermore, residual stresses also revealed a correlation between higher printing temperatures and increased residual stresses. These findings emphasize the necessity of balancing material flow, printing temperature, and layer height for scaffold quality. Therefore, the right balance between precision and mechanical stability is critical for producing high-quality scaffolds that meet BTE requirements.

Optimization of critical process control parameters in MEX additive manufacturing of high-performance polyethylenimine: energy expenditure, mechanical expectations, and productivity aspects

The demand for 3D-printed high-performance polymers (HPPs) is on the rise across sectors such as the defense, aerospace, and automotive industries. Polyethyleneimine (PEI) exhibits exceptional mechanical performance, thermal stability, and wear resistance. Herein, six generic and device-independent control parameters, that is, the infill percentage, deposition angle, layer height, travel speed, nozzle temperature, and bed temperature, were quantitatively evaluated for their impact on multiple response metrics related to energy consumption and mechanical strength. The balance between energy consumption and mechanical strength was investigated for the first time, contributing to the sustainability of the PEI material in 3D printing. This is critical considering that HPPs require high temperatures to be built using the 3D printing method. PEI filaments were fabricated and utilized in material extrusion 3D printing of 125 specimens for 25 different experimental runs (five replicates per run). The divergent impacts of the control parameters on the response metrics throughout the experimental course have been reported. The real weight of the samples varies from 1.06 to 1.82 g (71%), the real printing time from 214 to 2841 s (~ 1300%), the ultimate tensile strength from 15.17 up to 80.73 MPa (530%), and the consumed energy from 0.094 to 1.44 MJ (1500%). The regression and reduced quadratic equations were validated through confirmation runs (10 additional specimens). These outcomes have excessive engineering and industrial merit in determining the optimum control parameters, ensuring the sustainability of the process, and the desired functionality of the products.Graphical

Characterization of Radiation Shielding Capabilities of High Concentration PLA-W Composite for 3D Printing of Radiation Therapy Collimators.

This work evaluates the radiation shielding capabilities of the PLA-W composite for MV energy photons emitted by a linear accelerator and the feasibility of manufacturing a clinically-used collimator grid in spatially fractionated radiotherapy (SFRT) using the material extrusion (MEX) 3D printing technique. The PLA-W filament used has a W concentration of 93% w/w and a green density of 7.51 g/cm3, characteristics that make it suitable for this purpose. Relevant parameters such as the density and homogeneity distribution of W in the manufactured samples determine the mass attenuation coefficient, directly affecting the radiation shielding capacities, so different printing parameters were evaluated, such as layer height, deposition speed, nozzle temperature, and infill, to improve the protection performance of the samples. Additionally, physical and mechanical tests were conducted to ensure structural stability and spatial variability over time, which are critical to ensure precise spatial modulation of radiation. Finally, a complete collimator grid measuring 9.3 × 9.3 × 7.1 cm3 (consisting of 39 conical collimators with a diameter of 0.92 cm and center-to-center spacing of 1.42 cm) was manufactured and experimentally evaluated on a clinical linear accelerator to measure the radiation shielding and dosimetric parameters such as mass attenuation coefficient, half-value layer (HVL), dosimetric collimator field size, and inter-collimator transmission using radiochromic films and 2D diode array detectors, obtaining values of 0.04692 cm2/g, 2.138 cm, 1.40 cm, and 15.6%, respectively, for the parameters in the study. This shows the viability of constructing a clinically-used collimator grid through 3D printing.

Characterization of the Dimensional Precision, Physical Bonding, and Tensile Performance of 3D-Printed PLA Parts with Different Printing Temperature

In this study, tensile test specimens were fabricated using a material extrusion 3D-printer at various printing temperatures to evaluate the development of physical bonds within the same layer as well as in between previous layers. The tensile test specimens were fabricated using PLA material, with printing temperatures ranging from 180 °C to 260 °C. Experimental investigations were conducted to investigate the dimensional accuracy and physical appearance of the parts across printing temperatures. Uniaxial tensile tests were conducted at a strain rate of 1 mm/min and repeated five times for each variable in accordance with the ASTM D638-14 standard. Results showed that increasing the printing temperatures yielded parts with better tensile properties. An approximate difference of 40% in tensile strength was observed between specimens fabricated under the two most extreme conditions (180 °C and 260 °C). The changes in tensile properties were attributed to bonding mechanisms related to interlayer bonding strength and a reduction in voids within the internal geometry. Analysis of the fracture surface using scanning electron microscopy (SEM) revealed fewer and smaller voids within the internal geometry for parts printed at higher temperature. The percentage area of voids reduced significantly when the printing temperature was increased from 180 °C to 220 °C. The tensile properties continuously improved with the printing temperature, with parts printed at 220 °C exhibiting the highest dimensional accuracy. The findings offer insight into the impact of the printing temperature on both the external physical bonds between printed roads, affecting the physical appearance and dimensional accuracy, and the internal bonds, affecting the tensile properties of the fabricated parts.

Multifunctional HDPE/Cu biocidal nanocomposites for MEX additive manufactured parts: Perspectives for the defense industry

In this study, we investigated the performance improvement caused by the addition of copper (Cu) nanoparticles to high-density polyethylene (HDPE) matrix material. Composite materials, with filler percentages of 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 wt% were synthesized through the material extrusion (MEX) 3D printing technique. The synthesized nanocomposite filaments were utilized for the manufacturing of specimens suitable for the experimental procedure that followed. Hence, we were able to systematically investigate their tensile, flexural, impact, and microhardness properties through various mechanical tests that were conducted according to the corresponding standards. Broadband Dielectric Spectroscopy was used to investigate the electrical/dielectric properties of the composites. Moreover, by employing means of Raman spectroscopy and thermogravimetric analysis (TGA) we were also able to further investigate their vibrational, structural, and thermal properties. Concomitantly, means of scanning electron microscopy (SEM), as well as atomic force microscopy (AFM), were used for the examination of the morphological and structural characteristics of the synthesized specimens, while energy-dispersive X-ray spectroscopy (EDS) was also performed in order to receive a more detailed picture on the structural characteristics of the various synthesized composites. The corresponding nanomaterials were also assessed for their antibacterial properties regarding Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) with the assistance of a method named screening agar well diffusion. The results showed that the mechanical properties of HDPE benefited from the utilization of Cu as a filler, as they showed a notable improvement. The specimen of HDPE/Cu 4.0 wt% was the one that presented the highest levels of reinforcement in four out of the seven tested mechanical properties (for example, it exhibited a 36.7% improvement in the flexural strength, compared to the pure matrix). At the same time, the nanocomposites were efficient against the S. aureus bacterium and less efficient against the E. coli bacterium. The use of such multi-functional, robust nanocomposites in MEX 3D printing is positively impacting applications in various fields, most notably in the defense and security sectors. The latter becomes increasingly important if one takes into account that most firearms encompass various polymeric parts that require robustness and improved mechanical properties, while at the same time keeping the risk of spreading various infectious microorganisms at a bare minimum.

Automated non-destructive 3D printing filament material properties monitoring based on electric permittivity, longitudinal encoding and diameter multi-axes real-time measurements

Rapid prototyping is an essential part of today’s research and development process. The ability to produce objects quickly, cost-effectively and on-site is critical to meeting this fundamental requirement. One of the factors that leads to inconsistencies and defects in the produced parts is the uncompensated change in material properties used in the material extrusion 3D printing manufacturing process. This creates the need for a real-time, low-cost filament quality monitor that can characterize the material properties of the filament along its length. This can be achieved by tracking the variation in measured capacitive tube capacitance and diameter of different sensor types over multiple selected axes and encoding the results to a specific fragment of filament used in material extrusion 3D printing. With such collected data it is possible to monitor factors such as material moisture, roundness, internal and external defects, component proportions, relative electrical permeability, Poisson’s ratio and material type. This work presents the first proof of concept of such a device and describes its operating principle in detail. As examples of applications, filament material type recognition is presented based on the characteristics of several types of filaments from different manufacturers, the process of moisture absorption over time for selected filaments is described, and the detection of defects of varying degrees is shown.

Increasing the isotropy of 3D printed poly(ether ether ketone) using a combination of bimodal polymer blends and post-process thermal annealing

Tough, semi-crystalline polymers such as poly(ether ether ketone) (PEEK) have recently gained popularity as Material Extrusion (ME) 3D printing feedstocks, but exhibit significant anisotropy when printed using fused filament fabrication (FFF). In this study, we seek to improve interlayer adhesion in PEEK FFF samples by combining the use of bimodal molecular weight polymer blends and post-process thermal annealing. Optimization of the loading of a secondary low molecular weight additive (LMWA) in the blend and identifying effective annealing temperatures leads to increases in the transverse tensile strength of PEEK prints by 250%. We interpret this strength improvement to be a product of tailoring the distribution of polymer crystallinity to induce trans-layer crystallization, which is facilitated by the addition of the LMWA. Thermal and optical analyses of annealed blend samples indicate that crystal structures are homogenously distributed within and between printed layers. The spatial distribution of crystals, and the resulting mechanical properties of the printed samples, are enhanced with incorporation of the LMWA and prescribed post-deposition annealing. The formulation and annealing protocols described herein represent a rational method to control the crystallization in FFF printed samples from crystalline polymers to maximize layer adhesion and improve print isotropy.

Polypropylene for material extrusion: Evidence that flow-enhanced crystallization restricts welding

We present a comprehensive investigation into the effect that both the crystallization kinetics and the molecular weight of polypropylene feedstock have on the welding properties in material extrusion 3D-printing (MatEx). As sufficient welding at the interfaces between printed layers may be restricted by the onset of crystallization, there is a delicate balance between polymer interdiffusion and the development of spherulites within the weld region. We monitor these processes during a cooling cycle using a well-established theoretical model that requires full characterisation of the rheology and crystallization. The model shows that the largest effect of increasing molecular weight is a reduction in interdiffusion; this mechanism leads to a reduction in the weld strength as demonstrated by mechanical testing. For the highest molecular weight feedstock, we find that the fracture pattern changes from plastic deformation to brittle mode. Furthermore, we observe that the spherulites within the weld are about an order of magnitude smaller than in other samples. These observations cannot be described by the quiescent crystallization kinetics alone. Our findings suggest that it is a flow-enhanced crystallization mechanism that accelerates nucleation leading to smaller spherulites developing in the weld earlier in the cooling process. This significantly restricts interdiffusion at the welds.