This paper starts from the early developments and working principles of the additive manufacturing of polymers, continues with a glimpse on the extension to metals with identification and characterization of the two most widespread technologies, and ends with an overview of the recent developments in hybrid metal additive manufacturing. Earlier classifications of hybrid manufacturing with roots on the utilization of primarily processed raw materials in the form of ingots, sheets, rods, tubes, profiles, powders and pellets are revisited in the light of the emergence of a new type of hybridization resulting from the combination of additive manufacturing with traditional manufacturing processes. Special emphasis is given to the combination of additive manufacturing with forming processes with the two-fold objective of (i) increasing the applicability domain of metal additive manufacturing and overcoming its limitations related to low productivity, metallurgical defects, rough surface quality and lack of dimensional precision, and (ii) adding flexibility and fostering new applications of traditional forming processes.

Hybrid metal additive manufacturing: A state–of–the-art review

Micropore evolution in additively manufactured aluminum alloys under heat treatment and inter-layer rolling

Process response of Inconel 718 to wire + arc additive manufacturing with cold metal transfer

Wire arc additive manufacturing (WAAM) is a fusion manufacturing process in which the heat energy of an electric arc is employed for melting the electrodes and depositing material layers for wall formation or for simultaneously cladding two materials in order to form a composite structure. This directed energy deposition-arc (DED-arc) method is advantageous and efficient as it produces large parts with structural integrity due to the high deposition rates, reduced wastage of raw material, and low consumption of energy in comparison with the conventional joining processes and other additive manufacturing technologies. These features have resulted in a constant and continuous increase in interest in this modern manufacturing technique which demands further studies to promote new industrial applications. The high demand for WAAM in aerospace, automobile, nuclear, moulds, and dies industries demonstrates compatibility and reflects comprehensiveness. This paper presents a comprehensive review on the evolution, development, and state of the art of WAAM for non-ferrous materials. Key research observations and inferences from the literature reports regarding the WAAM applications, methods employed, process parameter control, optimization and process limitations, as well as mechanical and metallurgical behavior of materials have been analyzed and synthetically discussed in this paper. Information concerning constraints and enhancements of the wire arc additive manufacturing processes to be considered in terms of wider industrial applicability is also presented in the last part of this paper.

Wire Arc Additive Manufacturing: Review on Recent Findings and Challenges in Industrial Applications and Materials Characterization

Wire arc additive manufacturing of an aeronautic fitting with different metal alloys: From the design to the part

https://research-information.bris.ac.uk/files/213358067/1_s2.0_S0264127519305957_main.pdf

Wire + Arc Additively Manufactured Inconel 718: Effect of post-deposition heat treatments on microstructure and tensile properties

The aim of this work is to determine the impact of post-thermal treatments on the mechanical properties and microstructure of alloy 718 superalloy manufactured through modulated laser powder bed fusion. Three post-thermal treatments at 980 °C and 1200 °C with and without hot isostatic pressing are utilised, followed by standard ageing procedure. The tensile mechanical properties, microstructure, crystallography, morphology, fracture impact and hardness after each heat treatment are determined. It has been found that the heat treatment procedure at 980 °C significantly affects the tensile properties while leading to no change in grain size or orientation, and formation of twined grains. A temperature of 1200 °C with and without pressure causes considerable grain growth in comparison with the as-built and 980 conditions and significant formation of twinned grains. Hot isostatic pressing was found to produce the tensile mechanical properties close to those of wrought alloy 718. 

Investigation of novel post-thermal treatments of alloy 718 fabricated by modulated laser powder bed fusion

In this study, the effect of crack orientation on the fracture behaviour of two compact tension C(T) specimens extracted from a Wire + Arc Additively Manufactured (WAAM) wall made from Inconel (IN) 625 nickel-base superalloy was investigated. Both specimens had different levels of ductile tearing but their load vs. crack mouth opening displacement (CMOD) behaviour was relatively similar. The total-and-elastic strain distribution around a crack tip was measured in both specimens using Digital Image Correlation (DIC) and neutron diffraction respectively. The results show that the strain distribution and deformation around the crack tip are different in the two directions. In the specimen with crack orientation parallel to the build direction, banding was observed in both the total strain maps and the deformation pattern. Neutron diffraction measurements on this specimen also showed non-monotonic elastic strain evolution, suggesting the occurrence of intergranular load shedding mechanisms. These were not observed in the specimen with crack orientation perpendicular to the build direction. Electron Backscatter Diffraction (EBSD) maps show that the WAAM IN625 material is strongly textured with coarse columnar grains elongated in the build direction. The effect of microstructure has been correlated with the differences in strain distribution in the two specimens.

Effect of Crack Orientation on Fracture Behaviour of Wire + Arc Additively Manufactured (WAAM) Nickel-Base Superalloy

Making laser powder bed fusion (L-PBF) additive manufacturing process sustainable requires effective powder recycling. Recycling of Ti6Al4V powder in L-PBF can lead to powder oxidation, however, such impact on laser-matter interactions, process, and defect dynamics during L-PBF are not well understood. This study reveals and quantifies the effects of processing Ti6Al4V powders with low (0.12 wt%) and high (0.40 wt%) oxygen content during multilayer thin-wall L-PBF using in situ high speed synchrotron X-ray imaging. Our results reveal that high oxygen content Ti6Al4V powder can reduce melt ejections, surface roughness, and defect population in the built parts. With increasing oxygen content in the part, there is an increase in microhardness due to solid solution strengthening and no significant change in the microstructure is evident. 

Raja Khan

Papers

Wire + Arc Additively Manufactured Inconel 718: Effect of post-deposition heat treatments on microstructure and tensile properties

Investigation of novel post-thermal treatments of alloy 718 fabricated by modulated laser powder bed fusion

Effect of Crack Orientation on Fracture Behaviour of Wire + Arc Additively Manufactured (WAAM) Nickel-Base Superalloy

In situ monitoring the effects of Ti6Al4V powder oxidation during laser powder bed fusion additive manufacturing