Experimental investigation on the geometric characteristics and mechanical properties of WAAM S308L stainless steel

Wire arc additive manufacturing (WAAM) has been considered as a promising technology for the production of large metallic structures with high deposition rates and low cost. Stainless steels are widely applied due to good mechanical properties and excellent corrosion resistance. This paper reviews the current status of stainless steel WAAM, covering the microstructure, mechanical properties, and defects related to different stainless steels and process parameters. Residual stress and distortion of the WAAM manufactured components are discussed. Specific WAAM techniques, material compositions, process parameters, shielding gas composition, post heat treatments, microstructure, and defects can significantly influence the mechanical properties of WAAM stainless steels. To achieve high quality WAAM stainless steel parts, there is still a strong need to further study the underlying physical metallurgy mechanisms of the WAAM process and post heat treatments to optimize the WAAM and heat treatment parameters and thus control the microstructure. WAAM samples often show considerable anisotropy both in microstructure and mechanical properties. The new in-situ rolling + WAAM process is very effective in reducing the anisotropy, which also can reduce the residual stress and distortion. For future industrial applications, fatigue properties, and corrosion behaviors of WAAMed stainless steels need to be deeply studied in the future. Additionally, further efforts should be made to improve the WAAM process to achieve faster deposition rates and better-quality control.

Correlation between arc mode, microstructure, and mechanical properties during wire arc additive manufacturing of 316L stainless steel

This study provides a comprehensive investigation into the microstructure, hardness, tensile strength, and bending fatigue behavior of a Wire Arc Additively Manufactured (WAAM) component composed of dissimilar materials—Carbon Steel (CS) and 316L stainless steel. Microscopic analysis reveals distinct microstructural characteristics, such as equiaxed ferrite grains in WAAM CS and a coarse columnar structure with delta-ferrite phases in WAAM 316L. A macroscopic phase map indicates a predominantly Body-Centered Cubic (BCC) structure near the interphase, suggesting element migration between CS and 316L due to high heat input. Higher magnification scans highlight martensitic structures on both sides of the interphase, with the CS side exhibiting larger grain sizes. Hardness assessment along the built direction shows a peak hardness of 407 HV near the interphase on the 316L side, contrasting with the CS side's average interphase hardness of 316 HV due to larger grain sizes. The yield strength of both WAAM CS and WAAM dissimilar material was consistently measured at 392 MPa. In comparison, WAAM 316L exhibited a slightly lower yield strength of 359 MPa. Notably, WAAM 316L demonstrated the highest tensile strength among the materials, reaching 656 MPa. Meanwhile, WAAM CS displayed a robust tensile strength of 503 MPa, and the WAAM dissimilar material exhibited a yield strength of 520 MPa. In terms of elongation, WAAM CS and WAAM 316L showcased values of 44.9% and 49.6%, respectively. On the other hand, WAAM dissimilar material exhibited a somewhat lower elongation of 20.4%, suggesting a different mechanical behavior in terms of ductility. Bending fatigue tests on WAAM 316L, WAAM CS, and the dissimilar material reveal a fatigue limit of approximately 225 MPa for WAAM 316L, 210 MPa for WAAM CS, and approximately 210 MPa for the dissimilar material. In the low-cycle and medium-cycle regimes, the dissimilar material exhibits slightly superior fatigue strength, potentially due to its marginally higher static strength. Notably, consistent fractures on the CS side during fatigue tests underscore a recurring behavior in the dissimilar material.

Wire + Arc Additive Manufacturing (WAAM) is a technology potentially offering reduction of material wastage, costs and shorter lead-times. It is being considered as a technology that could replace conventional manufacturing processes of Ti-6Al-4V, such as machining from wrought or forged materials. However, WAAM Ti-6Al-4V is characterized by coarse β-grains, which can extend through several deposited layers resulting in strong texture and anisotropy. As a solution, inter-pass cold rolling has been proven to promote grain refinement, texture modification and improvement of material strength by plastically deforming the material between each deposited layer. Nevertheless, with the increased interest in the WAAM technology, the complexity and size of the deposited parts has increased, and its application can be hindered by the low speed and complex/costly equipment required to perform rolling at this scale. Therefore, Machine Hammer Peening (MHP) has been studied as an alternative cold work process. MHP can be used robotically, offering greater flexibility and speed, and it can be applied easily to any large-scale geometry. Similarly to rolling, MHP is applied between each deposited layer with the new ECOROLL peening machine and, consequently, it is possible to eliminate texturing and reduce the β-grains size from centimeters long to approximately 1 to 2 mm. This effect is studied for thin and thick walls and no considerable change in grain size is observed, proving the applicability of MHP to large components. The yield strength and ultimate tensile strength increases to 907 MPa and 993 MPa, respectively, while still having excellent ductility. This grain refinement may also improve fatigue life and induce a decrease in crack propagation rate. In this study, it has been shown that MHP is a suitable process for WAAM Ti-6Al-4V applications, can be applied robotically and the grain refinement induced by very small plastic deformations can increase mechanical properties.

Mechanical testing and microstructural analysis of wire arc additively manufactured steels

Ti based alloys for aerospace and biomedical applications fabricated through wire + arc additive manufacturing (WAAM)

Additive manufacturing (AM) technologies have demonstrated a promising material efficiency potential in comparison to traditional material removal processes. A new directed energy deposition (DED) category AM process called wire arc additive manufacturing (WAAM) is evolving due to its benefits which include faster build rates, capacity to build large volumes, and inexpensive feedstock materials and machine tools compared to more technologically mature powder-based AM technologies. However, WAAM products present challenges like poor surface finish and lower dimensional accuracy compared to powder-based processes or machined parts, prevalence of thermal distortions, residual stresses, and defects like porosity, cracks, and humping, often requiring post-processing operations like finish machining and heat treatment. These post-processing operations add to the production cost and environmental footprint of WAAM-built parts. Therefore, considering the opportunities and challenges presented by WAAM, this paper analyses the environmental impact, production costs, and mechanical properties of WAAM parts and compares them with those achieved by laser powder bed fusion (LPBF) and traditional computer numerical control (CNC) milling. A high-strength low-alloy steel (ER70S) mechanical part with medium complexity was fabricated using WAAM. Based on the data collected during this experiment, environmental impact and cost models were built using life cycle assessment and life cycle costing methodologies. WAAM was observed to be the most environmentally friendly option due to its superior material efficacy than CNC milling and has a better energy efficiency than LPBF. Also, WAAM was the most cost-friendly option when adopted in batch production for batch sizes above 3. The environmental and cost potential of WAAM is amplified when used for manufacturing large products, resulting in significant material, emission, and cost savings. The fabricated WAAM part demonstrated good mechanical properties comparable to that of cast/forged material. The methodology and experimental data presented in this study can be used to calculate environmental impacts and costs for other products and can be helpful to manufacturers in selecting the most ecofriendly and cost-efficient manufacturing process.

Wire arc additive manufacturing (WAAM) has several industrial applications because of its advantages over other additive manufacturing methods. In this study, two stainless steel 347 walls, namely as-deposited (AD) wall, and inter-layer cold worked (CW) wall, were prepared using the WAAM method to investigate the isotropy of their mechanical properties and wear properties in vertical and horizontal directions. For the AD wall, the mean yield strength, ultimate strength, and elongation of horizontal samples were 410 MPa, 620 MPa, and 47%, respectively. In comparison, these values for the vertical (V) samples were 402 MPa, 590 MPa, and 49%, respectively. For the CW wall, the mean yield strength, ultimate strength, and elongation of horizontal samples were 815 MPa, 876 MPa, and 26%, respectively, while those of vertical samples were 722 MPa, 824 MPa, and 25%, respectively. The CW wall’s tensile test results indicated that inter-layer cold working intensified the anisotropy of tensile properties in both vertical and horizontal directions. Microstructural investigation revealed that inter-layer cold working and the heat resulted from subsequent layers deposition in the CW wall recrystallized the layers and reduced the grain size. Additionally, wear test results demonstrated that inter-layer cold working increased hardness and thus wear-resistance of the samples and reduced their friction. The results showed that the coefficient of friction (COF) and wear rates of the samples are not highly dependent on their direction.

Loss of elemental Mg during wire + arc additive manufacturing of Al-Mg alloy and its effect on mechanical properties

This paper reviews the potential of Wire Arc Additive Manufacturing (WAAM) for architecture. It uniquely addresses its feasibility by evaluating existing large-scale, real-world prototypes developed to date and compiling critical gaps identified in the literature. Although previous review papers concerning WAAM for architecture exist, they focus on the technical aspects of the technology, such as the mechanical properties, defects, and process parameters. No existing review analyzes which architectural applications are being implemented nor the scale and degree prototyping accomplished for each application. WAAM, a form of metal additive manufacturing using an electric arc to melt and deposit wire, offers unique advantages for the construction industry. It allows for high deposition rates, structural integrity, and cost-efficiency using steel. However, challenges such as producing large-scale components and limited design freedom and lower resolution compared to other additive manufacturing processes remain. This review first contextualizes WAAM within the broader landscape of additive manufacturing technologies for construction and examines its proposed architectural applications, such as steel connections, columns, trusses, and bridge elements. This study emphasizes the need for real-world experimentation through large-scale prototypes to assess the practicality and scalability of WAAM in architecture. The results of this study reveal that 36 architectural projects using WAAM exist in the literature, whose application range from structural (such as beams, columns, and nodes) to nonstructural components (such as facades and ornamental elements). Based on these, a classification for WAAM in architecture is proposed: (1) stand-alone WAAM structures, (2) printed connector pieces to join standard steel parts, and (3) reinforcement for conventional steel elements using WAAM. The size of typical functional prototypes to date averages 200 × 200 × 200 mm, with exceptional cases such as the diagrid column of 2000 mm height and the MX3D Bridge, which spans over 12 m. A detailed analysis of seven projects documents the scale and development of the prototypes, functional lab configuration, and process parameters. Through this review, the current technical feasibility of WAAM in architecture is established.

I-section steel columns strengthened by wire arc additive manufacturing - concept and experiments

Heat sources in wire arc additive manufacturing and their impact on macro-microstructural characteristics and mechanical properties – An overview

Wire arc additive manufacturing (WAAM) has recently gained considerable attention due to its capability to manufacture large-size metal with a length of one meter or above, with good microstructural and mechanical properties. However, the manufacture of critical components exposed to extreme environmental conditions, such as high stresses, remains the focus of most research studies. The applications of WAAM in high-tech industries, such as aerospace and marine modes, remain limited due to metallurgical challenges such as oxidation, porosity, cracking, and deformation, especially for high-strength aluminium alloys, including 6XXX and 7XXX series. The aforementioned metallurgical challenges in WAAM are minimized to some extent by another emerging technology, known as additive friction stir deposition (AFSD). AFSD is capable of manufacturing large-size and high strength (strength equal to or greater than that of the raw material) industrial components with fewer metallurgical defects and refined microstructures. However, this technology is in its developmental stage and possesses some challenges, such as oxidation, which is currently an emerging topic for researchers in metal additive manufacturing (AM). This paper reviews the potential of various additive manufacturing (AM) techniques for the manufacture of high-strength components, using either unweldable virgin or recycled high-strength aluminium alloys. The study also provides a comprehensive overview of the importance of recycling aluminium, as well as the challenges of utilizing aluminium (Al) alloys within metal AM. Considerations related to microstructure, the mechanical properties and metallurgical defects in both these technologies are extensively discussed and compared. The study concludes that both technologies are still being developed and experience various metallurgical issues, which need to be addressed to fully utilize WAAM and AFSD for critical applications. Further, the AFSD process is shown to be a better alternative to the WAAM process in the fabrication of Al components, where it possesses less metallurgical issues, higher strength and more refined microstructures. The literature suggests ultimate tensile stress (UTS) and average elongation percentage during AFSD in the range of 197.3 MPa–306 MPa and 8.6%–39% for Al alloys, respectively. However, slightly better UTS values in the range of 344 MPa–349 MPa and significant reduction in average elongation percentage to 5% is noted during WAAM process. Furthermore, AFSD exhibited significantly higher microhardness values (40.8 HV–151.4 HV) when compared to WAAM (73 HV–111 HV). Accordingly, the study notes that further numerical and experimental studies are needed to fully understand material flow in stirring zones during the AFSD process.

Evolution of microstructure and properties in 2219 aluminum alloy produced by wire arc additive manufacturing assisted by interlayer friction stir processing

Because of the flexible nature of 3D printing and additive manufacturing technology, manufacturing sector has been revolutionized. There is a possibility to manufacture different intricate geometrics that cannot be produced through conventional processes previously. The conventional design concepts such as design for manufacture (DFM) and design for assembly (DFA) have been modified and simplified. Wire arc additive manufacturing (WAAM) has emerged as one of the leading additive manufacturing (AM) processes due to its high deposition rate and economic feasibility. A lot of progress has been made to understand and improve this process and the mechanical properties associated with the fabricated parts. It is specifically cheaper to print large-scale metallic components using WAAM. This paper gives a thorough review of the work that has been done on WAAM by comparing different technological variants of WAAM, which include Metal Inert Gas (MIG), Tungsten Inert Gas (TIG) and Plasma Arc Welding (PAW). The study also discusses the mechanical properties of the fabricated components using different metals, the defects and challenges the process faces today and how they can be reduced. In the end the study also provides overview of WAAM applications in some of the industrial sectors such as construction, automotive, and structural etc.