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.

https://www.mdpi.com/2076-3417/10/5/1563/pdf

Wire arc additive manufacturing of stainless steels: A review

Additive manufacturing is a process of transforming 3D CAD models into a finished part by adding layers of material. The technology is being used for more than three decades to make prototypes using polymer powders. Over the years, the technique has evolved, which currently allows the industries to manufacture functional parts out of different metals that have high complexity and limited lot size. Tungsten carbide (WC-Co) is a refractory metal with a very high melting point of around 2900 °C and is difficult to manufacture by conventional methods. Hence, tungsten carbide hardmetal parts are made by powder metallurgy technique, wherein tungsten carbide and binder metal powders (cobalt, nickel, iron or alloys of these metals) are pressed into the desired shape and sintered. However, due to the recent advancements, researchers have proven that complex tungsten carbide parts can be made by additive techniques. Hence, the article aims to summarize the three major techniques, Selective Laser Melting (SLM), Selective Laser Sintering (SLS), and Binder Jet 3D printing (BJ3DP) used in the manufacturing of tungsten carbide hardmetal parts. The process variables, metallurgical and mechanical characteristics, and challenges in manufacturing are presented which would serve as a knowledge pool for prospective researchers.

Additive Manufacturing of Tungsten Carbide Hardmetal Parts by Selective Laser Melting (SLM), Selective Laser Sintering (SLS) and Binder Jet 3D Printing (BJ3DP) Techniques

A study was carried out to investigate the influence of the initial powder features on the microstructure, the phase composition, and on the mechanical properties of WC-12%Co samples produced by binder jetting and densified by sintering in vacuum at 1400 °C and by sinter-HIPing. The initial powder consisted of a mixture of fine-grained and coarse-grained WC-based particles, and W2C-based ones. The density of the printed samples was 97.4% and 99.3% after sintering and sinter-HIPing, respectively. Layer-oriented porosity was observed only in sintered samples. The microstructure of the samples consisted of a mixture of fine and coarse WC grains, which can be the result of the coalescence of grains from anomalous coarse grains in the powder particles. Vickers hardness and transverse rupture strength of sinter-HIPed samples are 1205 HV and 2257 MPa, respectively, which is coherent with the microstructural analysis and close to coarse-grained commercial products.

Mechanical and microstructural characterization of WC-Co consolidated by binder jetting additive manufacturing

Controlling WC/Co two-phase microstructure of cemented carbides additive-manufactured by laser powder bed fusion: Effect of powder composition and post heat-treatment

An Al–Zn–Mg–Cu–Ta alloy was successfully fabricated by laser powder bed fusion (LPBF). The effect of the added Ta on the microstructures (cracks, grain sizes, and phase constitutions), mechanical properties (tensile strength and elongation), aging behavior, and corrosion resistances (full immersion and electrochemical corrosion performances) of the LPBF-fabricated Al–Zn–Mg–Cu alloy were investigated. The results exhibited that, Ta restrained hot tearing, refined microstructures, enhanced the tensile strength and ductility, accelerated the aging processing, and improved the corrosion resistance of the LPBF-fabricated Al–Zn–Mg–Cu alloy, significantly. The reason was that Ta not only reacted with Al to form in-situ Al 3 Ta to refine α(Al), but also dissolved in the second phases to inhibit their coarsening. 

Microstructure, mechanical properties, aging behavior, and corrosion resistance of a laser powder bed fusion fabricated Al–Zn–Mg–Cu–Ta alloy

WC-Co hardmetals are widely used in wear-resistant parts, cutting tools, molds, and mining parts, owing to the combination of high hardness and high toughness. WC-Co hardmetal parts are usually produced by casting and powder metallurgy, which cannot manufacture parts with complex geometries and often require post-processing such as machining. Additive manufacturing (AM) technologies are able to fabricate parts with high geometric complexity and reduce post-processing. Therefore, additive manufacturing of WC-Co hardmetals has been widely studied in recent years. In this article, the current status of additive manufacturing of WC-Co hardmetals is reviewed. The advantages and disadvantages of different AM processes used for producing WC-Co parts, including selective laser melting (SLM), selective electron beam melting (SEBM), binder jet additive manufacturing (BJAM), 3D gel-printing (3DGP), and fused filament fabrication (FFF) are discussed. The studies on microstructures, defects, and mechanical properties of WC-Co parts manufactured by different AM processes are reviewed. Finally, the remaining challenges in additive manufacturing of WC-Co hardmetals are pointed out and suggestions on future research are discussed.

/pdf/additive-manufacturing-of-wc-co-hardmetals-a-review-20z4ocs4xw.pdf

Yankun Yang

Papers

Additive manufacturing of WC-Co hardmetals: a review