Atieh Moridi

PURPOSE: Implantable metal plates and screws are essential tools for craniofacial reconstruction as they provide stable bony reduction to facilitate osteosynthesis. However, once bone healing has occurred, the hardware is a source of complications such as infection, bone loss (from stress shielding), palpability, or interference with bone growth in pediatric patients. Although resorbable materials like poly(L-lactide-co-glycolide) are clinically used, their limited strength compared to metallic implants restricts their utility. Thus, a degradable metal implant, which maintains structural integrity during bone healing and gradually reabsorbs afterwards could address these limitations. We previously demonstrated that combining iron (Fe), with its high strength and slow rate of degradation, with magnesium (Mg), with its lower strength but more rapid rate of degradation, via additive manufacturing (AM), achieves tunable degradation for metal implants. Here, we extend this work by evaluating the cytotoxicity of this Fe-Mg composite and their constituent metals under ISO 10993-5 standards to support their translational potential for craniofacial use. METHODS: The designed Fe-Mg composite was fabricated from a powder mixture containing approximately 20Vol% Mg using the Formalloy TM direct energy deposition printer. Small metal blocks (~10x20 mm 2 top surface area) were embedded in resin to control exposed surface for media extraction at a surface-area-to-volume ratio of 3 cm/mL in DMEM + 10% FBS at 37 C for 24 hours. Extracts (100 L/well) were applied to human foreskin fibroblasts (HFF-1), human fetal osteoblasts (hFOB), and murine fibroblasts (L929) seeded in 96-well plates (1500 cells/well). Cell viability was quantified by Calcein-AM/PI staining after 24 hours and compared to polyethylene (negative) and ethanol (positive) controls. Viability ≥70% was considered non-cytotoxic (according to ISO 10993-5 standard). RESULTS: Fe-Mg composite extracts demonstrated 75-80% cell viability across all three cell lines comparable to Fe extract-treated (73-77%) group and negative controls (84-92%), while Mg extracts significantly reduced viability (37-59%), likely due to Mg competition with Ca for membrane and matrix binding sites, and alkaline pH shift from rapid corrosion. A mild increase in turbidity and localized surface discoloration was observed in all three metal groups during the 24-hour extraction, suggesting early-stage corrosion and ion release of Fe and Mg. Despite these changes, cells remained viable after exposure to Fe-Mg and Fe extracts, confirming the absence of cytotoxicity in those groups. In vivo , both Fe-Mg and Fe plates showed progressive surface corrosion and mild capsule formation without evidence of systemic metal toxicity. Histology confirmed localized metal deposition with minimal inflammatory response, and serum metal levels remained within normal ranges. CONCLUSION: Additively manufactured Fe-Mg composite plates demonstrate favorable in vitro biocompatibility and in vivo degradation without systemic toxicity, make them promising candidates for bioresorbable craniofacial fixation. Ongoing optimization of Fe-Mg composite plates are being conducted to improve mechanical performance and absorption timeline to meet specific reconstructive demands.© 2026. Plastic Surgery Research Council | All rights reserved |*Source: https://ps-rc.org/meeting/Program/2026/54.cgi*

PURPOSE: Implantable metal plates and screws are essential tools for craniofacial reconstruction as they provide stable bony reduction to facilitate osteosynthesis. However, once bone healing has occurred, the hardware is a source of complications such as infection, bone loss (from stress shielding), palpability, or interference with bone growth in pediatric patients. Although resorbable materials like poly(L-lactide-co-glycolide) are clinically used, their limited strength compared to metallic implants restricts their utility. Thus, a degradable metal implant, which maintains structural integrity during bone healing and gradually reabsorbs afterwards could address these limitations. We previously demonstrated that combining iron (Fe), with its high strength and slow rate of degradation, with magnesium (Mg), with its lower strength but more rapid rate of degradation, via additive manufacturing (AM), achieves tunable degradation for metal implants. Here, we extend this work by evaluating the cytotoxicity of this Fe-Mg composite and their constituent metals under ISO 10993-5 standards to support their translational potential for craniofacial use. METHODS: The designed Fe-Mg composite was fabricated from a powder mixture containing approximately 20Vol% Mg using the Formalloy TM direct energy deposition printer. Small metal blocks (~10x20 mm 2 top surface area) were embedded in resin to control exposed surface for media extraction at a surface-area-to-volume ratio of 3 cm/mL in DMEM + 10% FBS at 37 C for 24 hours. Extracts (100 L/well) were applied to human foreskin fibroblasts (HFF-1), human fetal osteoblasts (hFOB), and murine fibroblasts (L929) seeded in 96-well plates (1500 cells/well). Cell viability was quantified by Calcein-AM/PI staining after 24 hours and compared to polyethylene (negative) and ethanol (positive) controls. Viability ≥70% was considered non-cytotoxic (according to ISO 10993-5 standard). RESULTS: Fe-Mg composite extracts demonstrated 75-80% cell viability across all three cell lines comparable to Fe extract-treated (73-77%) group and negative controls (84-92%), while Mg extracts significantly reduced viability (37-59%), likely due to Mg competition with Ca for membrane and matrix binding sites, and alkaline pH shift from rapid corrosion. A mild increase in turbidity and localized surface discoloration was observed in all three metal groups during the 24-hour extraction, suggesting early-stage corrosion and ion release of Fe and Mg. Despite these changes, cells remained viable after exposure to Fe-Mg and Fe extracts, confirming the absence of cytotoxicity in those groups. In vivo , both Fe-Mg and Fe plates showed progressive surface corrosion and mild capsule formation without evidence of systemic metal toxicity. Histology confirmed localized metal deposition with minimal inflammatory response, and serum metal levels remained within normal ranges. CONCLUSION: Additively manufactured Fe-Mg composite plates demonstrate favorable in vitro biocompatibility and in vivo degradation without systemic toxicity, make them promising candidates for bioresorbable craniofacial fixation. Ongoing optimization of Fe-Mg composite plates are being conducted to improve mechanical performance and absorption timeline to meet specific reconstructive demands.© 2026. Plastic Surgery Research Council | All rights reserved |*Source: https://ps-rc.org/meeting/Program/2026/54.cgi*

PURPOSE: Implantable metal plates and screws are essential tools for craniofacial reconstruction as they provide stable bony reduction to facilitate osteosynthesis. However, once bone healing has occurred, the hardware is a source of complications such as infection, bone loss (from stress shielding), palpability, or interference with bone growth in pediatric patients. Although resorbable materials like poly(L-lactide-co-glycolide) are clinically used, their limited strength compared to metallic implants restricts their utility. Thus, a degradable metal implant, which maintains structural integrity during bone healing and gradually reabsorbs afterwards could address these limitations. We previously demonstrated that combining iron (Fe), with its high strength and slow rate of degradation, with magnesium (Mg), with its lower strength but more rapid rate of degradation, via additive manufacturing (AM), achieves tunable degradation for metal implants. Here, we extend this work by evaluating the cytotoxicity of this Fe-Mg composite and their constituent metals under ISO 10993-5 standards to support their translational potential for craniofacial use. METHODS: The designed Fe-Mg composite was fabricated from a powder mixture containing approximately 20Vol% Mg using the Formalloy TM direct energy deposition printer. Small metal blocks (~10x20 mm 2 top surface area) were embedded in resin to control exposed surface for media extraction at a surface-area-to-volume ratio of 3 cm/mL in DMEM + 10% FBS at 37 C for 24 hours. Extracts (100 L/well) were applied to human foreskin fibroblasts (HFF-1), human fetal osteoblasts (hFOB), and murine fibroblasts (L929) seeded in 96-well plates (1500 cells/well). Cell viability was quantified by Calcein-AM/PI staining after 24 hours and compared to polyethylene (negative) and ethanol (positive) controls. Viability ≥70% was considered non-cytotoxic (according to ISO 10993-5 standard). RESULTS: Fe-Mg composite extracts demonstrated 75-80% cell viability across all three cell lines comparable to Fe extract-treated (73-77%) group and negative controls (84-92%), while Mg extracts significantly reduced viability (37-59%), likely due to Mg competition with Ca for membrane and matrix binding sites, and alkaline pH shift from rapid corrosion. A mild increase in turbidity and localized surface discoloration was observed in all three metal groups during the 24-hour extraction, suggesting early-stage corrosion and ion release of Fe and Mg. Despite these changes, cells remained viable after exposure to Fe-Mg and Fe extracts, confirming the absence of cytotoxicity in those groups. In vivo , both Fe-Mg and Fe plates showed progressive surface corrosion and mild capsule formation without evidence of systemic metal toxicity. Histology confirmed localized metal deposition with minimal inflammatory response, and serum metal levels remained within normal ranges. CONCLUSION: Additively manufactured Fe-Mg composite plates demonstrate favorable in vitro biocompatibility and in vivo degradation without systemic toxicity, make them promising candidates for bioresorbable craniofacial fixation. Ongoing optimization of Fe-Mg composite plates are being conducted to improve mechanical performance and absorption timeline to meet specific reconstructive demands.© 2026. Plastic Surgery Research Council | All rights reserved |*Source: https://ps-rc.org/meeting/Program/2026/54.cgi*

PURPOSE: Metallic plating systems composed of titanium and its alloys remain the standard treatment for craniofacial bony fixation but may require secondary removal due to infection, implant migration, or discomfort. Absorbable polymeric alternatives reduce those risks but lack sufficient strength for load-bearing applications. Thus, biodegradable metallic implants may eliminate complications and secondary procedures while maintaining the structural integrity. Our previous work demonstrated the fabrication of immiscible Fe-AZ31 composites via additive manufacturing with improved degradation kinetics over pure iron. This study aimed to evaluate the in vitro and in vivo biocompatibility of Fe-AZ31 composites for potential craniofacial fixation applications. METHODS: /mL surface-to-volume ratio in complete media at 37 °C and cell viability was measured by live/dead assay after 24 and 72 h exposure. For in vivo evaluation, Fe-AZ31, Fe, and titanium (Ti) plates were implanted subcutaneously in wild type mice for 6 weeks and 3 and 6 months. Implant degradation, histologic response, hematology, and serum biochemistry were assessed. RESULTS: Fe-AZ31 extracts demonstrated ≥70% cell viability across all cell types at both time points with normal cell morphology and adhesion, whereas AZ31 extracts caused marked cytotoxicity associated with pronounced alkalization (pH 10.53). In vivo, Fe-AZ31 implants exhibited gradual surface corrosion accompanied by mild, transient inflammation and minimal capsule formation over time. No systemic toxicity was observed. Hematology and serum biochemistry remained within the physiological limits. CONCLUSION: Additively manufactured Fe-AZ31 composites demonstrate acceptable cytobiocompatibility and favorable tissue responses, supporting their development as bioresorbable metallic fixation devices for craniofacial reconstruction.

Metallic plating systems composed of titanium and its alloys remain the standard treatment for craniofacial bony fixation but may require secondary removal due to infection, implant migration, or discomfort. Thus, biodegradable metallic implants may eliminate complications and secondary procedures while maintaining structural integrity. Our previous work demonstrated the fabrication of immiscible Fe-AZ31 composites via additive manufacturing with improved degradation kinetics over pure Iron. This study aimed to evaluate the in vitro and in vivo biocompatibility of Fe-AZ31 composites for potential craniofacial fixation applications. Pure iron (Fe), Mg alloy (AZ31) and Fe-AZ31 samples were fabricated for extract-based cytotoxicity testing using HFF-1 fibroblasts, L929 fibroblasts and hFOB osteoblasts. Metal extracts were prepared at a 3 cm^2/mL surface-to-volume ratio in complete media at 37C and cell viability was measured by live/dead assay after 24 and 72h exposure. For in vivo evaluation, Fe-AZ31, Fe, and Ti plates were implanted subcutaneously in wild type mice for 6 weeks, 3 and 6 months. Implant degradation, histologic response, hematology, and serum biochemistry were assessed. Fe-AZ31 extracts demonstrated >70% cell viability across all cell types at both timepoints with normal cell morphology and adhesion, whereas AZ31 extracts caused marked cytotoxicity associated with pronounced alkalization (pH 10). In vivo, Fe-AZ31 implants exhibited gradual surface corrosion accompanied by mild, transient inflammation and minimal capsule formation over time. No systemic toxicity was observed. Hematology and serum biochemistry remained within physiological limits. Additively manufactured Fe-AZ31 composites demonstrate acceptable biocompatibility and favorable tissue responses, supporting their development as resorbable metallic fixation devices for craniofacial reconstruction.

Metallic plating systems composed of titanium and its alloys remain the standard treatment for craniofacial bony fixation but may require secondary removal due to infection, implant migration, or discomfort. Thus, biodegradable metallic implants may eliminate complications and secondary procedures while maintaining structural integrity. Our previous work demonstrated the fabrication of immiscible Fe-AZ31 composites via additive manufacturing with improved degradation kinetics over pure Iron. This study aimed to evaluate the in vitro and in vivo biocompatibility of Fe-AZ31 composites for potential craniofacial fixation applications. Pure iron (Fe), Mg alloy (AZ31) and Fe-AZ31 samples were fabricated for extract-based cytotoxicity testing using HFF-1 fibroblasts, L929 fibroblasts and hFOB osteoblasts. Metal extracts were prepared at a 3 cm^2/mL surface-to-volume ratio in complete media at 37C and cell viability was measured by live/dead assay after 24 and 72h exposure. For in vivo evaluation, Fe-AZ31, Fe, and Ti plates were implanted subcutaneously in wild type mice for 6 weeks, 3 and 6 months. Implant degradation, histologic response, hematology, and serum biochemistry were assessed. Fe-AZ31 extracts demonstrated >70% cell viability across all cell types at both timepoints with normal cell morphology and adhesion, whereas AZ31 extracts caused marked cytotoxicity associated with pronounced alkalization (pH 10). In vivo, Fe-AZ31 implants exhibited gradual surface corrosion accompanied by mild, transient inflammation and minimal capsule formation over time. No systemic toxicity was observed. Hematology and serum biochemistry remained within physiological limits. Additively manufactured Fe-AZ31 composites demonstrate acceptable biocompatibility and favorable tissue responses, supporting their development as resorbable metallic fixation devices for craniofacial reconstruction.

Revision surgeries for implantable metal devices/plates are relatively common, often due to palpability/prominence, infection, or complications arising from stress shielding. The potential need for surgical removal of metal fixation plates could be obviated by using degradable metal implants that dissolve after the bone has healed. Iron is a promising candidate for a degradable metal, but its slow degradation rate limits its effectiveness. This study investigates the microstructural and degradation characteristics of a novel Fe‐AZ31 composite synthesized via directed energy deposition (DED). Immersion test on Fe‐AZ31 samples demonstrates improved degradation kinetics, with the composite degrading at ≈1.2 mm year −1 compared to ≈0.1 mm year −1 for pure iron. This enhanced degradation rate is attributed to various mechanisms, including Mg acting as sacrificial sites for corrosion, which leaves pits in iron, and Mg partially dissolving in Fe, potentially lowering its electrochemical potential. Furthermore, contributions from the additive manufacturing process like surface roughness and fine microstructure could also enhance degradation kinetics. Importantly, the composite exhibits a more controlled pH change with respect to AZ31 magnesium‐alloy, suggesting less release of hydroxyl ions, and consequently reduces hydrogen evolution. This work lays the foundation for further exploration of Fe‐AZ31 composite, opening up new possibilities for the development of advanced degradable implants.

PURPOSE: Implantable metal plates and screws are essential tools for craniofacial reconstruction as they provide stable bony reduction to facilitate osteosynthesis. However, once bone healing is complete, they become superfluous and can lead to complications such as infection, bone loss or uncomfortable palpability. In pediatric patients, metal implants may impede subsequent bone growth and may require removal. Although resorbable materials like poly(L-lactide-co-glycolide) are clinically used, their limited strength compared to metallic implants restricts their application. Thus, a degradable metal implant, which would be absorbed after bone healing is completed, presents an appealing solution. Combining Iron (Fe, slow degradation rate) and Magnesium (Mg, fast degradation rate), which both corrode under physiologic conditions, in a composite structure could be a viable path to achieve degradation tunability for metal implants. However, the major obstacle to the fabrication of Fe-Mg plates is the miscibility gap of these metals, where the melting point of Fe is above the boiling point of Mg, obviating traditional alloy manufacturing approaches. Therefore, in this study we utilize a novel additive manufacturing approach to create Fe-Mg composite implants as an initial step towards designing degradable craniofacial metal implants. METHODS: The designed Fe-Mg composite was fabricated from a powder mixture containing approximately 20vol% Mg using the Formalloy direct energy deposition printer. Small plates (10 x 2 x 0.6mm) with three holes (0.2mm diameter) were printed and tested in in vitro and in vivo experiments to evaluate degradation rate and surface corrosion. Fe-only plates manufactured similarly, and commercially available Titanium plates of comparable shape and weight were tested as controls. RESULTS:In vitro, plates were immersed in the Hank’s balanced salt solution at 37°C to recapitulate the physiological conditions for 24 weeks, demonstrating faster decomposition in Fe-Mg composite group compared to Fe-only group. After 6, 12 and 24 weeks of in vivo subcutaneous implantation, both Fe-Mg composite and Fe-only plates presented increased rust microparticle accumulation in the surrounding tissue capsule, especially the Fe-only group. In contrast, the Titanium plates remained inert and developed a thin capsule. Histologic study verified the iron deposition in the capsule in both Fe-Mg composite and Fe-only groups, with no evidence of off-target toxicity to liver, kidney, or other organs. Hematological and serum biochemical analysis, including Fe and Mg content, showed no differences between groups or time points. CT scans correlated the degradation rates between in vivo and in vitro, while scanning electron microscopy provided insights into surface corrosion and effects of the biological media on the metallic surfaces. CONCLUSION: The custom-designed Fe-Mg metallic composite plates demonstrated evidence of degradation without any local or systemic metal toxicity. By adjusting the volume fraction of Fe and Mg, as well as the geometry and porosity of the composition, the absorption rate of the biodegradable metallic implant can be tailored to meet specific clinical needs.

The melt flow in an Al-50vol% Sn immiscible alloy, produced by single-track laser melting of Al and Sn elemental powders, was studied in real time. High-speed synchrotron X-ray imaging was used to track the movements of Al and Sn liquids, and also to examine elemental distributions in the laser tracks, complimented by electron microscopy after solidification. Key aspects, including melt pool geometry, keyhole instability, and flow dynamics (flow pattern and velocity), were examined using digital image analysis. Relatively deeper melt pools formed at 400 W and 300 mm/s exhibited greater stability, with smooth surfaces, consistent outward flow, and minor vortices near the keyhole. In contrast, shallower pools produced at higher scanning speeds (>500 mm/s) demonstrated greater instability with increased surface waviness, and stronger velocity fluctuations, leading to numerous micro-vortices and increased Al-Sn heterogeneity. Velocity scale estimations, supported by experimental observations, examined the roles of vapour pressure, Marangoni effect, buoyancy, inertial, and surface tension forces in the flow. The results revealed that vapour pressure and mechanical waves dominated at high scanning speeds (shallow pools), while Marangoni forces were equally significant in deep pools at lower speeds (300 mm/s). Buoyancy was found to have minimal impact in both cases. Furthermore, the interaction between inertial and surface tension forces played a critical role in determining the degree of waviness of the pools’ surfaces. These findings offer valuable insights into melt pool dynamics during laser processing of immiscible alloys and other metallic systems using elemental powders, and provide guidance for developing high-fidelity computational fluid dynamics models. • Melt pool dynamics of immiscible Al-Sn was studied using synchrotron X-ray imaging. • By tracing Al and Sn, melt flow pattern and velocity were statistically examined. • Correlation between keyhole instability and melt flow was assessed. • Inertial and Marangoni forces were theoretically and experimentally examined.

Controlling microstructure in fusion-based metal additive manufacturing (AM) remains a significant challenge due to the many parameters that directly impact solidification condition. Multiprincipal element alloys (MPEAs), also known as high entropy alloys, offer a vast compositional space to design for microstructural engineering due to their chemical complexity and exceptional properties. Here, we use the FeMnCoCr system as a model platform for exploring alloy design in MPEAs for AM. By exploiting the decreasing stability of the face-centered cubic phase with increasing Mn content, we achieve notable grain refinement and breakdown of epitaxial columnar grain growth. We employ a multifaceted approach encompassing thermodynamic modeling, operando synchrotron X-ray diffraction, multiscale microstructural characterization, and mechanical testing to gain insight into the solidification physics and its ramifications on the resulting microstructure of FeMnCoCr MPEAs. This work aims toward tailoring desirable grain sizes and morphology through targeted manipulation of phase stability, thereby advancing microstructure control in AM applications.

Additive-manufactured TiAl 3 -reinforced aluminum matrix composite (AMC) materials were fabricated by forming TiAl 3 whiskers from an in-situ reaction in laser direct energy deposition (L-DED) between aluminum (Al) and titanium (Ti). The composite demonstrates enhancements in mechanical strength with tunability compared to the unreinforced material, while using feedstock mixtures of commercially available Al and Ti powder with standard size distributions. This enhancement in mechanical strength is attributed to load transfer from the strong TiAl 3 reinforcement and the Hall-Petch strengthening from the refined grain size of the Al matrix. Operando synchrotron analysis of the solidification sequence in laser powder bed fusion (L-PBF) of the Al-Ti material system, coupled with postmortem microstructural characterizations, reveals that the dispersed TiAl 3 whiskers refine Al grain size by promoting heterogeneous nucleation through in-situ inoculation. This study validates the methodology of forming reinforcement phases from in-situ reactions to enable the fabrication of enhanced, tunable AMC via L-DED or L-PBF.

Operando X-ray techniques have enabled real-time observation and analysis of metal additive manufacturing (AM) processes, providing invaluable insights into solidification mechanisms and melt pool behavior. In this perspective, we present the current state of the art in X-ray diffraction and imaging studies of laser-based metal AM processes, specifically Directed Energy Deposition and Powder Bed Fusion. We explore various data analyses that can be performed with time-resolved data, including phase identification, microstructural evolution, tracking melt pool behavior, and defect formation. Additionally, we highlight the limitations of existing operando studies and provide an outlook on overcoming these challenges. Additive manufacturing has emerged as a powerful approach for achieving properties that are not possible in conventionally processed alloys. This Perspective provides a state-of-art overview of the use of operando x-ray techniques for understanding solidification dynamics and melt pool behavior in additive processes.

<title>Abstract</title> Additive-manufactured TiAl₃-reinforced aluminum matrix composite (AMC) materials were fabricated by forming TiAl₃ whiskers from the in-situ reaction between aluminum (Al) and titanium (Ti). The composite demonstrates enhancement of mechanical strength with tunable ductility compared to unreinforced material while using a feedstock mixture of only commercially available Al and Ti powder of standard size distribution. The enhancement to mechanical strength is attributed to both load transfer from the strong TiAl₃ reinforcement and the Hall-Petch strengthening from the refined grain size of the Al matrix. Operando synchrotron analysis of the in-situ reactive printing (IRP) process, coupled with postmortem microstructural characterizations, reveals that the dispersed TiAl₃ whiskers refine Al grain size by promoting heterogeneous nucleation through in-situ inoculation. This study validates the capability of IRP to strengthen the integration of material and geometry design in additive manufacturing by enabling the fabrication of highly tunable AMC.

Controlling microstructure in fusion-based metal additive manufacturing (AM) remains a challenge due to numerous parameters directly impacting solidification conditions. Multiprincipal element alloys (MPEAs) offer a vast compositional design space for microstructural engineering due to their chemical complexity and exceptional properties. Here, we establish a novel alloy design paradigm in MPEAs for AM using the FeMnCoCr system. By exploiting the decreasing phase stability with increasing Mn content, we achieve notable grain refinement and breakdown of columnar grain growth. We combine thermodynamic modeling, operando synchrotron X-ray diffraction, multiscale microstructural characterization, and mechanical testing to gain insight into the solidification physics and its ramifications on the resulting microstructure. This work paves way for tailoring grain sizes through targeted manipulation of phase stability, thereby advancing microstructure control in AM.

Refractory metals and their carbides possess extraordinary properties when subjected to high temperatures and extreme environments. Consequently, they can act as key material systems for advancing many sectors, including space, energy and defence. However, it has been difficult to process these materials using the conventional routes of manufacturing. Additive manufacturing (AM) has shown a lot of potential to overcome the challenges and develop new material systems with tailored properties. This review provides a fundamental understanding of the challenges in the processing of refractory metals and their carbides, including microcracking, formation of brittle oxide phases and high ductile to brittle transition temperature (DBTT). We also highlight some of the novel approaches that have been taken to improve the processability of these challenging material systems using AM. These include in-situ reactive printing, ultrasonic vibration, laser beam shaping, multi-laser deposition and substrate pre-heating with a focus on microstructural changes to improve the properties of printed parts.

Acoustic Emission (AE) sensing is an in-situ real-time nondestructive monitoring method proposed for Additive Manufacturing (AM) to detect defects such as cracks. Previous AE research in AM mainly focused on developing algorithms to automatically detect the defects from AE signals without understanding the physical mechanisms or the signal characteristics that could be used as identifiers. We study AE signals during a laser spot welding on a powder bed to clearly distinguish between different physical mechanisms using their signal characteristics. We identified specific signals associated with 1) tensile cracks from cooling, 2) a powder effect on the substrate, and 3) sudden thermal expansion of the substrate. We used the spectral ratio between high frequency (70 – 150 kHz) and low frequency (10 – 40 kHz) spectral amplitudes in the frequency domain to classify and differentiate the source types. We found that porosity due to insufficient energy density did not produce detectable AE signals. Using a ball drop calibration technique, we used AE signals to estimate the absolute sizes of the tensile cracks. Crack sizes ranged from 40 μ m to 1 mm and were in general agreement with scanning electron microscope images of the fractures. We performed a line scanning test and successfully validated its potential for the application. Our findings provide a basic understanding of AE signal characteristics in AM, as well as the practical parameters used to separate the signal types.

Due to their remarkable mechanical and chemical properties, Ti–Al-based materials are attracting considerable interest in numerous fields of engineering, such as automotive, aerospace, and defense. With their low density, high strength, and resistance to corrosion and oxidation, these intermetallic alloys and metal-compound composites have found diverse applications. However, additive manufacturing and heat treatment of Ti–Al alloys frequently lead to brittleness and severe formation of defects. The present study delves into the interfacial dynamics of these Ti–Al systems, particularly focusing on the behavior of Ti and Al atoms in the presence of TiAl 3 grain boundaries under experimental heat treatment conditions. Using a combination of molecular dynamics and Markov state modeling, we scrutinize the kinetic processes involved in the formation of TiAl 3 . The molecular dynamics simulation indicates that at the early stage of heat treatment, the predominating process is the diffusion of Al atoms toward the Ti surface through the TiAl 3 grain boundaries. Markov state modeling identifies three distinct dynamic states of Al atoms within the Ti/Al mixture that forms during the process, each exhibiting a unique spatial distribution. Using transition time scales as a qualitative measure of the rapidness of the dynamics, it is observed that the Al dynamics is significantly less rapid near the Ti surface compared to the Al surface. Put together, the results offer a comprehensive understanding of the interfacial dynamics and reveal a three-stage diffusion mechanism. The process initiates with the premelting of Al, proceeds with the prevalent diffusion of Al atoms toward the Ti surface, and eventually ceases as the Ti concentration within the mixture progressively increases. The insights gained from this study could contribute significantly to the control and optimization of manufacturing processes for these high-performing Ti–Al-based materials.

Abstract Dynamic solidification behavior during metal additive manufacturing directly influences the as-built microstructure, defects, and mechanical properties of printed parts. How the formation of these features is driven by temperature variation (e.g., thermal gradient magnitude and solidification front velocity) has been studied extensively in metal additive manufacturing, with synchrotron x-ray imaging becoming a critical tool to monitor these processes. Here, we extend these efforts to monitoring full thermomechanical deformation during solidification through the use of operando x-ray diffraction during laser melting. With operando diffraction, we analyze thermomechanical deformation modes such as torsion, bending, fragmentation, assimilation, oscillation, and interdendritic growth. Understanding such phenomena can aid the optimization of printing strategies to obtain specific microstructural features, including localized misorientations, dislocation substructure, and grain boundary character. The interpretation of operando diffraction results is supported by post-mortem electron backscatter diffraction analyses.

Due to their remarkable mechanical and chemical properties, Ti-Al based materials are attracting considerable interest in numerous fields of engineering, such as automotive, aerospace, and defense. With their low density, high strength, and resistance to corrosion and oxidation, these intermetallic alloys and compound metal-metallic composites have found diverse applications. The present study delves into the interfacial dynamics of these Ti-Al systems, particularly focusing on the behavior of Ti and Al atoms in the presence of TiAl$_3$ grain boundaries under experimental heat treatment conditions. Using a combination of Molecular Dynamics and Markov State Model analyses, we scrutinize the kinetic processes involved in the formation of TiAl$_3$. The Molecular Dynamics simulation indicates that at the early stage of heat treatment, the predominating process is the diffusion of Al atoms towards the Ti surface through the TiAl$_3$ grain boundaries. The Markov State Modeling identifies three distinct dynamic states of Al atoms within the Ti/Al mixture that forms during the process, each exhibiting a unique spatial distribution. Using transition timescales as a qualitative measure of the rapidness of the dynamics, it is observed that the Al dynamics is significantly less rapid near the Ti surface compared to the Al surface. Put together, the results offer a comprehensive understanding of the interfacial dynamics and reveals a three-stage diffusion mechanism. The process initiates with the premelting of Al, proceeds with the prevalent diffusion of Al atoms towards the Ti surface, and eventually ceases as the Ti concentration within the mixture progressively increases. The insights gained from this study could contribute significantly to the control and optimization of manufacturing processes for these high-performing Ti-Al based materials.

Austenitic stainless steels 304 L (SS304) and 316 L (SS316) are additive manufactured under the same processing conditions to reveal two distinct microstructures. Particularly, the resulting grain morphology for SS304 is singular – there are subgrains dispersed across the sample; there is a wide range of grain size spanning nearly two orders of magnitude; and grain boundaries are convoluted, resembling a fractal object. The materials solidification pathway governed by chemical composition is responsible for the grain boundary fractality (ferrite-to-austenite solidification for SS304 and direct transformation to austenite for SS316). Operando X-ray diffraction studies at Cornell High Energy Synchrotron Source substantiate the solidification pathway of the materials. The findings from the study open up a new avenue for grain boundary engineering using additive manufacturing.