Cold Metal Research Articles

Investigating the Tribological Performance and Wear Mechanisms of Stainless Steel 316L in Cold Metal Transfer-Based Wire Arc Additive Manufacturing Under Varied Loads and Thermal Inputs

Abstract In recent years, cold metal transfer (CMT)-based wire arc additive manufacturing (WAAM) has gained significant attention in the manufacturing sector, particularly for its ability to produce components with low thermal input and high deposition rates. This study investigated the tribological behaviour of SS316L walls fabricated using CMT-based WAAM, employing a ball-on-plate linear reciprocating test with tungsten carbide (WC) counter body under varying thermal inputs and applied loads (15 N, 20 N, and 25 N). The tests were conducted for 10 minutes at a frequency of 15 Hz and a stroke length of 2 mm. Results indicate that the coefficient of friction (COF) increased slightly with applied loads, yielding an average COF of 0.22 across all loads. Wear rate analysis revealed that both increased applied load and heat input led to a higher wear rate, with the maximum wear rate (3.39 × 10−3 mm3/m) occurring at high heat input and 25 N, while the minimum wear rate (1.2 × 10−3 mm3/m) was observed at low heat input and 15 N. Vickers microhardness results demonstrated an inverse relationship between hardness and heat input, with hardness increasing by 11% as heat input decreased from high to low. FESEM analysis of wear tracks showed significant craters, abrasive grooves, delamination, surface cracks, and particle adhesion, identifying an abrasive-dominant wear mechanism with surface fatigue, partial adhesion, and oxidative wear. Wear debris analysis showed sharper angular particles and larger irregularly shaped flakes. X-ray diffraction (XRD) spectra confirmed δ-ferrite and γ-austenite phases pre- and post-wear, with post-wear analysis showing an α′-martensite peak, indicating phase transformation during wear.

Characterization and Expression Analysis of the bHLH Gene Family During Developmental Stages and Under Various Abiotic Stresses in Sanghuangporus baumii

Background: Basic helix–loop–helix (bHLH) transcription factors (TFs) widely exist in eukaryotic organisms and play a key role in plant growth and development in response to environmental stresses. Sanghuangporus baumii, an important medicinal mushroom known for its anticancer properties, has limited research on the bHLH gene family. Methods: This research utilized the genomic data from S. baumii to identify bHLH family members, and their gene structure, conserved motifs, and phylogenetic relationship were characterized. Additionally, we conducted an analysis of promoter cis-elements and predicted protein interaction networks. We also examined the expression profiles of bHLH genes during different developmental stages and in response to four abiotic stresses: heat, cold, oxidative stress, and heavy metal exposure. Finally, we overexpressed the candidate gene SbbHLH3 in yeast to assess its tolerance to these different stress conditions. Results: A total of 12 SbbHLH genes were identified in S. baumii, and the members of the bHLH gene family displayed a variety of physicochemical characteristics, reflecting their diverse array of functions. Based on homology, the SbbHLH proteins are more closely related to those found in Lentinula edodes and Pleurotus ostreatus. The analysis of promoter cis-elements showed that SbbHLHs contain several elements associated with abiotic stress response, and a network prediction identified 28 bHLH-interacting proteins. Expression pattern analysis revealed that most SbbHLH genes exhibited a positive response to different developmental stages and abiotic stresses. Notably, the overexpression of SbbHLH3 significantly enhanced stress tolerance in yeast. Conclusions: This study provides a comprehensive assessment of the bHLH family in S. baumii, delivering new genetic resources for breeding resistant varieties.

Effect of cyclic heat treatment on microstructure and mechanical properties of ultra-high strength steel fabricated by wire + arc additive manufacturing with cold metal transfer

Effect of cyclic heat treatment on microstructure and mechanical properties of ultra-high strength steel fabricated by wire + arc additive manufacturing with cold metal transfer

Advanced visual sensing and control in CMT-based WAAM processes

Wire Arc Additive Manufacturing (WAAM) can flexibly produce high-performance parts that meet the requirements of deep-sea environments, but it has problems with insufficient molding accuracy and surface smoothness, which require improved precision and quality. To address these challenges, this paper establishes a WAAM experimental system based on Cold Metal Transfer (CMT) technology. First, the influence of process parameters on multi-layer single-channel forming was studied. Second, a structured light visual sensing system based on a high-speed camera was developed. Finally, a method for controlling the camera’s triggering mode at low voltage was designed, effectively eliminating arc interference. The experiment extracted and preprocessed the laser stripe ROI (Region of Interest), extracted geometric size information of the weld seam, and then performed median filtering to extract the centerline and feature points. By constructing a CMT-based WAAM monitoring system, high reliability and quality control of the manufacturing process and weld formation have been achieved.

Microstructure, Wear and Corrosion Performance of Cold Metal Transfer Additive Manufactured (Ni, Ti)-Modified Nickel Aluminum Bronze Alloy

Microstructure, Wear and Corrosion Performance of Cold Metal Transfer Additive Manufactured (Ni, Ti)-Modified Nickel Aluminum Bronze Alloy

Stress corrosion behavior and microstructure analysis of Al-Zn-Mg-Cu alloys fabricated by CMT wire arc additive manufacturing with different post-treatments

In this study, Al-Zn-Mg-Cu alloys components were fabricated by cold metal transfer (CMT) wire arc additive manufacturing (WAAM), and the stress corrosion cracking (SCC) behavior of the alloys with different post-treatments was studied by combining in-situ electrochemical impedance spectroscopy (EIS) with slow strain rate tensile. The hot-rolling process was employed to close the internal pores of the WAAM products, following by single-stage aging (T6) to further improve the mechanical properties of the products. The elongation loss and SCC susceptibility index of T6 sample are 38.0% and 43.0%, respectively, which exceed those of the hot-rolled sample at 35.5% and 37.0%. Furthermore, the corrosion fracture of the T6 sample exhibits intensive secondary cracks, indicating an increased SCC susceptibility. The stress corrosion process is classified into four stages based on the trend of the EIS: (Ⅰ) Initial stage of corrosion; (Ⅱ) Corrosion products accumulation stage; (Ⅲ) Corrosion products coverage stage; (Ⅳ) Approaching fracture stage. The hot-rolled samples have reduced SCC susceptibility due to the presence of coarse grain boundary precipitates (GBPs) which can act as the irreversible traps to capture hydrogen. The ultimate tensile strength and elongation of T6 sample reached 568.3 ± 11.5MPa and 9.1 ± 0.7%, respectively. However, the small-sized GBPs and wider precipitates-free zone reduced its SCC resistance. This study found that the hot-rolling process can fully exploit the mechanical property potential of Al-Zn-Mg-Cu alloys and improve their SCC resistance, which is an important guiding significance for the practical application of WAAM technology in Al-Zn-Mg-Cu alloys.

Effect of boundary conditions on residual stress in cold metal transfer-based wire arc additively manufactured steel components

Effect of boundary conditions on residual stress in cold metal transfer-based wire arc additively manufactured steel components

Effect of Al–Mg Filler Wires on Weldability of Cold Metal Transfer Welded AlSi10Mg Alloys Fabricated Using Laser Powder Bed Fusion

Effect of Al–Mg Filler Wires on Weldability of Cold Metal Transfer Welded AlSi10Mg Alloys Fabricated Using Laser Powder Bed Fusion

Hot compression behavior and 3D processing maps of Mg-Gd-Y-Zn alloy formed by cold metal transfer wire arc additive manufacturing

Based on hot compression experiments, the hot deformation behavior and workability of the Mg-Gd-Y-Zn alloy fabricated by cold metal transfer wire arc additive manufacturing (WAAM-CMT) were studied. The compression experiments were performed at temperatures ranging from 350 to 500 °C, with strain rates between 0.001 and 1 s−1. The results indicate that the peak stress of the alloy decreases significantly with lower strain rates and higher deformation temperatures. Combined with the analysis of the Arrhenius type equation (Eq.), the average value of the recrystallization activation energy (Q) was 308.4 kJ/mol. Utilizing the Zener-Hollomon parameter, we derived the constitutive Eq. for the deposited Mg-Gd-Y-Zn alloy during hot deformation: [Formula: see text]. Using the dynamic material model, we established a three-dimensional (3D) processing maps for the deposited Mg-Gd-Y-Zn alloy. The main instability domain were temperatures from 350 to 385 °C with strain rates of 0.1 to 1.0 s−1, and temperatures from 435 to 500 °C with strain rates of 0.4 to 1.0 s−1. Considering the power dissipation map, the stable and power-efficient forming domains is in the temperature range from 435 to 500 °C and strain rate range from 0.001 to 0.04 s−1. Due to dynamic recrystallisation (DRX), the grain of the deposited Mg-Gd-Y-Zn alloy is significantly refined after hot deformation. These findings provide valuable guidance for selecting integrated process equipment and optimizing deformation parameters for additive and on-line micro-forged magnesium rare earth alloys.

Metal Transfer Behavior and Molten Pool Dynamics in Cold Metal Transfer Pulse Advanced Additive Manufacturing of 7075 Aluminum Alloy.

Wire arc additive manufacturing (WAAM) with a special arc mode of cold metal transfer pulse advanced (CMT-PADV) is an ideal additive manufacturing process for fabricating aerospace components, primarily high-strength aluminum alloys, offering advantages such as high deposition rates and low cost. However, the numerical simulation of the CMT-PADV WAAM process has not been researched until now. In this study, we first developed a three-dimensional fluid dynamics model for the CMT-PADV WAAM of 7075 aluminum alloy, aiming at analyzing the droplet transition and molten pool flow. The results indicate that, under the CMT-PADV mode, droplet transition follows a mixed transition mode, combining short-circuiting and spray transition. The Direct Current Electrode Positive period of the arc accelerates droplet spray transition, significantly increasing molten pool flow. In contrast, the Direct Current Electrode Negative period of the arc predominantly features droplet short-circuiting transition with low heat input and a weak impact on the molten pool. The periodic switching of the current polarity of CMT-PADV mode results in periodic variations in molten pool size and volume, reducing heat input while maintaining high deposition quality. The revelation of this mechanism provides process-based guidance for low-defect, high-performance manufacturing of critical components.

Quantification of Rapid Cooling of Glycerol/Water Solutions Based on Photoluminescence from Thioflavin T.

Rapid cooling to a solid state allows intermediates in chemical and biomolecular processes that occur in solution near room temperature to be trapped for subsequent measurements by magnetic resonance spectroscopies, electron microscopy, or other techniques. In time-resolved solid state nuclear magnetic resonance and rapid freeze-quench electron paramagnetic resonance studies, solutions are typically frozen by spraying into a cold bath or onto a cold metal surface. Although simulations suggest freezing on millisecond or submillisecond time scales, direct experimental measurements of cooling rates have been elusive. Here, we describe a method for quantification of rapid cooling rates based on measurements of temperature-dependent photoluminescence from thioflavin T (ThT). In our experiments, a jet of ThT solution in glycerol/water, with 10.8 m/s jet velocity and 30 μm diameter, freezes on a cold, rotating copper surface. Images of ThT photoluminescence on the copper surface indicate that the cooling rate of the solution increases linearly with the surface velocity over the 0.45-6.2 m/s range. At surface velocities greater than 3.8 m/s, the time to cool from 300 to 260 K or from 300 to 230 K is less than 100 μs or less than 700 μs. The experimental results do not agree quantitatively with calculations in which a layer of glycerol/water cools by thermal conduction when suddenly brought in contact with a cold copper surface. Discrepancies between experimental results and simplistic calculations illustrate the importance of direct measurements of cooling rates.

Ultra-light Mg-Li alloy with high modulus prepared by cold metal transfer-based directed energy deposition

Ultra-light Mg-Li alloy with high modulus prepared by cold metal transfer-based directed energy deposition

Polyurethanes as Biomaterials in Medicine: Advanced Applications, Infection Challenges, and Innovative Surface Modification Methods

Abstract Polyurethanes (PUs) are exceptionally versatile polymers widely utilized in medicine due to their outstanding mechanical properties, biocompatibility, and adaptability to various applications. This article explores advanced applications of polyurethane biomaterials in medicine, the challenges posed by infections associated with their use, and innovative surface modification techniques to improve their functionality. PUs are employed in a diverse array of medical devices, including non-implantable applications such as wound dressings, catheters, and infusion sets; short-term implants like bone stabilizers and tracheostomy tubes; and long-term implants such as tissue regeneration scaffolds, artificial blood vessels, and heart valves. Despite their many advantages, their use carries a significant risk of infections, including ventilator-associated pneumonia, infective endocarditis, and urinary tract infections. An important challenge lies in bacterial biofilms, which complicate treatment and enhance bacterial resistance to antibiotics. To address these issues, innovative PU surface modification methods are being developed, including laser texturing, nanoparticle deposition with antibacterial properties, ion implantation, cold metal spraying, the integration of biodegradable and biocompatible components, and plasma modifications. These advanced techniques aim to enhance polyurethane biomaterials’ antibacterial properties and biocompatibility, thereby reducing infection risks and improving clinical outcomes. This article underscores the importance of ongoing research to effectively combat biomaterial-associated infections and broaden the medical applications of polyurethanes. The development of advanced surface modification methods holds great promise for improving patient quality of life and the efficacy of medical treatments.

Effect of burnishing strategies on surface integrity, microstructure and corrosion performance of wire arc additively manufactured AZ31 Mg alloy

AZ31 Mg alloy is an emerging material that has received considerable attention in aerospace, automotive, and temporary biodegradable implant applications owing to its attractive properties, such as low density, high specific strength, and biodegradability. Nevertheless, some shortcomings in Mg alloys are their low ductility, which is associated with challenging its manufacturing, and poor corrosion resistance associated with unreliable components. Therefore, a cold metal transfer wire arc additive manufacturing (CMT-WAAM) process is used to manufacture AZ31 Mg alloy and achieved 29.4 % ductility by controlling the gas porosity, keyhole porosity, and internal cracks. Further, severe plastic deformation is induced on the surface of deposited parts by low plasticity burnishing (LPB) with parallel and cross-pattern burnishing to modulate their surface to slow down the kinetics of the corrosion damage. The average surface roughness (Sa) of the cross-burnishing pattern is 0.235 μm, which is 123.6 % lower than the parallel burnished and 261.7 % lower than the milled specimens. The residual stress (RS) of WAAM is 40 MPa with a tensile nature; however, it is drastically reduced and develops compressive RS of 45 MPa under a parallel burnishing pattern and 62 MPa under a cross-burnishing pattern. Moreover, LPB with cross pattern deformed ∼395 μm depth of WAAMed AZ31 workpiece, which is ∼ 45 % higher than deformed depth (∼272 μm) by parallel pattern burnishing. The electrochemical corrosion rate of the WAAM specimen is 9.71 mm/year, and it is reduced to 1.82 mm/year under LPB caused by compressive residual stress and grain refinement.

Machine learning-based prediction of CoCrFeNiMo0.2 high-entropy alloy weld bead dimensions in wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is a promising method to fabricate large-sized components. By adjusting WAAM process parameters, dimensions of WAAM-produced weld beads can be optimized. To this end, the current study adopted the cold metal transition (CMT) process to produce different-sized beads of CoCrFeNiMo0.2 high-entropy alloy (HEA), varying WAAM parameters and linking them with the formed bead dimensions and bead-substrate contact angles. Three machine learning algorithms, namely back propagation neural network (BPNN), support vector regression (SVR), and random forest regression (RFR), were used to predict bead dimensions and contact angles under various WAAM parameters. The BPNN model has great prediction performance in the height of beads. The SVR model has the highest accuracy in predicting the width and cross-sectional area of beads. The RFR outperforms the other two models in contact angles prediction. This work not only provides a reference for the WAAM of high-entropy alloys, but also provides new ideas for predicting bead size in WAAM.

Study on the Microstructure and Properties of Al Alloy/Steel CMT Welding–Brazing Joints Under Different Pulse Magnetic Field Intensities

Butt welding experiments on 6061 Al alloy and Q235B steel of 2 mm thickness were conducted using an ER4047F flux-cored wire as the filler metal, after adding a pulsed magnetic field into the process of cold metal transfer (CMT) welding. The effect of the pulsed magnetic field intensity on the macro morphology, microstructure, tensile strength and corrosion resistance of the welding–brazing joint was analyzed. The results showed that when the pulsed magnetic field intensity increased from 0 to 60 mT, the wettability and spreadability of the liquid metal were improved. As a result, the appearance of the Al alloy/steel joint was nice. However, when the pulsed magnetic field intensity was 80 mT, the stability of the arc and the forming quality of the joint decreased, which resulted in a deterioration in the appearance of the joint. A pulsed magnetic field with different intensities did not alter the microstructure of the joint. All of the joint was composed of θ-Fe2(Al,Si)5 and τ5-Al7.2Fe1.8Si at the interface and Al-Si eutectic phase and α-Al solid solution at the weld seam zone. Actually, with the pulsed magnetic field intensity increasing from 0 mT to 60 mT, the IMC thickness in the interfacial layer gradually reduced under the action of electromagnetic stirring. Also, the grain in the weld seam was refined, and elements were distributed uniformly. But when the pulsed magnetic field intensity was 80 mT, the grain in the weld seam began to coarsen, and the intermetallic compound (IMC) thickness was too small, which was unfavorable for the metallurgical bonding of Al alloy and steel. Therefore, with the increase in pulsed magnetic field intensity, the tensile strength of the joints first increased and then decreased, and it reached its maximum of 187.7 MPa with a pulsed magnetic field intensity of 60 mT. Similarly, the corrosion resistance of the joint first increased and then decreased, and it was best when the pulse magnetic field intensity was 60 mT. The Nyquist plot and Bode plot confirmed this result. The addition of a pulsed magnetic field caused less fluctuation in the anode current density, resulting in less localized corrosion of the joint using the scanning vibrating electrode technique (SVET). The XPS analysis showed the Al-Fe-Si compounds replacing the Fe-Al compounds in the joint was the main reason for improving its corrosion resistance under the action of a pulsed magnetic field.

Metallic 2D and 3D re-entrant honeycomb auxetics produced by WAAM

This study addresses the main challenges in manufacturing large-scale metallic auxetic structures, characterised by a negative Poisson’s ratio, focusing on achieving suitable geometry control, surface finish, and structural integrity using Wire Arc Additive Manufacturing (WAAM). Specifically, the research employs the Cold Metal Transfer (CMT) process to fabricate 2D and 3D carbon steel auxetic cells. The primary objective is to address the challenges associated with the production of these structures. A comprehensive experimental and numerical analysis was conducted to investigate the influence of various factors, such as internal defects or geometric irregularities, such as pores and surface waviness, on the mechanical behaviour of the 2D and 3D auxetic cells under tensile and compressive loads, respectively. The compression tests revealed that despite minor defects and geometric imperfections, the manufactured cells consistently exhibit a negative Poisson’s ratio. This suggests that the WAAM-produced auxetic structures are viable and capable of maintaining their unique mechanical properties. Furthermore, the study emphasises the significance of parameters such as orientation and the number of auxetic cells in governing the overall auxetic behaviour of the components.

Experimental studies on dilution, microstructural, mechanical and wear characteristics of Inconel 718 deposited over stainless steel 304 employing cold metal transfer process

In this research, the sinewave weaving technique is used by the Cold Metal Transfer process for hard-facing the Inconel 718 over the Stainless Steel 304. A microstructural study exhibited columnar grains that were transformed into equiaxed grains. Scanning Electron Microscopy (SEM) – Energy Dispersive X-ray analysis (EDX) results confirm the element’s segregation and secondary phase’s formation. Outcomes of hardness, tensile, impact measurements, and wear analysis show that a hard-faced layer offers better hardness and wear resistance.

Effect of Welding Torch Mode on Heat Input, Microstructure, and Mechanical Performance of Inconel 625 via Wire‐Arc‐Directed Energy Deposition

Cold metal transfer‐based wire‐arc directed energy deposition offers high molding efficiency and the capability to produce large, complex structural components. However, the grain structure and mechanical performance of the deposited parts are significantly influenced by the thermal history during deposition. This study prepared Inconel 625 samples using two different torch modes (vertical and tilt). The effects of two torch modes and build heights on the molten pool temperature are investigated, and the solidification structure and mechanical performance of the parts at various locations are analyzed. Results show that the deposited samples primarily consisted of columnar dendrites growing epitaxially along the deposition direction, with Laves phase particles distributed in blocks and chains among the dendrites. Tilting the torch contributed to grain refinement and reduced Laves phase precipitates, resulting in samples with high strength. Additionally, the tensile performance of the deposited samples exhibits anisotropy.

Wear performance enhancement of interface layer in CMT-WAAM fabricated ER4043/ER5356 Bimetallic wall through Friction Stir Surface Treatment

Abstract The cold metal transfer (CMT) based wire arc additive manufacturing (WAAM) technique has limited wear applications compared to other manufacturing methods due to its lower wear resistance. However, integrating friction stir processing (FSP) with WAAM can enhance mechanical or wear performance, making it a promising and reliable manufacturing process for aerospace, automotive, and marine applications. In this work, CMT-WAAM technique has been used to fabricate a bimetallic wall of aluminium alloys (ER4043/ER5356), employing a bidirectional depositional strategy. The impact of FSP on the interface layer of the WAAM wall, serving as a post-processing treatment on the wall's surface, is studied in terms of microstructure and microhardness. Additionally, a pin-on-disk wear test is performed on the interface layer of both WAAM and FSP-treated WAAM walls under loads of 20N, 30N, and 40N. Results from optical and Field emission scanning electron microscopy (FESEM) microstructures revealed the grain refinement in the stirred zone, with a higher wt. % of Mg through Energy Dispersive Spectrometer (EDS) analysis. X-ray diffraction (XRD) identifies various intermetallic compounds, including Al12Mg17, Al3.21Si0.47, and Mg2Si, with higher peak intensities in the FSP-treated wall. Electron Backscatter Diffraction (EBSD) analysis indicates a decrease in the average grain size of stirred area, which is ~72.40 µm in unstirred area and ~5.57 µm in stirred area due to the local strain concentration effect during FSP. Grain refinement during FSP leads to an increase in average hardness by 35.9%. The wear rate and coefficient of friction (COF) get reduced, credited to high-temperature dynamic recrystallization and continuous grain recovery in FSP. Scanning electron microscope (SEM) analysis of worn surfaces highlights abrasion, delamination, and adhesion as significant wear mechanisms.