Wire arc additive manufacturing (WAAM) is a significant area of interest within the field of additive manufacturing (AM). In the present research, WAAM technology was employed to deposit a Ni-based alloy on a ductile cast iron substrate to fabricate a bimetallic structure of Ni-45 %Fe alloy and ductile cast iron. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron back scattered diffraction (EBSD) and X-ray diffraction (XRD) were used to study phase transformations, microstructure and crystallographic texture development in interfacial regions as well as deposited material. The mechanical properties were also studied using micro-hardness and profilometry-based indentation plastometry (PIP) measurements. The results showed that a wide variety of phases are generated within the heat-affected zone (HAZ) and partially melted zone (PMZ). These phases form complex microstructures with single and double shell morphology. The deposited alloy has a face-centred cubic (FCC) structure, with some carbides and graphite that are formed during the solidification of the first deposited layer. The compositional changes were also observed across the interface. The texture of the deposited alloy showed around 30° deviation from 〈100〉 II building direction due to the shape and overlap of the melt pools. The present results provide a better understanding of interface development mechanisms during WAAM of bimetallic structures. The peak of the hardness across the interface was observed in PMZ because of the formation of a martensitic matrix. The PIP measurements showed that the σ_y and the UTS of deposited alloy are lower than the cast iron base metal.

Wire Arc Additive Manufacturing (WAAM) is a metal Additive Manufacturing (AM) technique that can produce fully dense metallic structures with virtually no porosity and at high productivity, compared to other currently available AM techniques such as Laser Powder Bed Fusion (L-PBF). As development of the technique is still ongoing, monitoring or post-fabrication inspection methods are under active investigation. In this work, we apply Resonant Ultrasound Spectroscopy (RUS) to samples fabricated from two different wires (construction steel and austenitic stainless steel) and quantitatively characterize isotropic and anisotropic elastic behaviour of the obtained dense parts. We find that an isotropic elastic model fits the construction steel samples well. For the 316 L polycrystal however, the isotropic elastic model is unsatisfactory, and an effective orthotropic elastic model is found to fit the resonance data. EBSD and XRD measurements are used to confirm and explain this difference in elastic behaviour between steel grades by the presence of a strong texture in the 316 L samples. Additionally, the texture data measured by EBSD are used to infer single crystal constants from the polycrystal resonance data using the Hill averaging scheme for one of the 316 L samples. We end by discussing the differences between the two elastic models used in the study (orthotropic and texture based) as well as the link between the measured resonances and microstructural descriptions of the samples.

This study explores the evolution of solidification microstructure of a laser powder bed fusion (L-PBF) martensitic stainless steel during solution annealing and aging. Quasi in-situ experiments using electron backscatter diffraction (EBSD) revealed that the finer, more equiaxed microstructure below the melt pool was susceptible to recrystallization and grain growth during solution annealing. The two distinct solidification microstructures below and inside the melt pool converged into a uniform grain morphology after solution annealing and aging processes. Graphical Abstract: (Figure presented.)

The microstructure development and texture evolution during friction stir welding of a dual-phase DP700 steel were investigated. Based on electron backscattered diffraction analysis, it was found that continuous dynamic recrystallization and discontinuous dynamic recrystallization are the operative recovery mechanisms for the ferrite phase in the stir zone. However, in addition to these mechanisms, geometrically dynamic recrystallization is also involved within the thermomechanically affected zone which is due to the lower strain rates in the thermomechanically affected zone. However, the continuous dynamic recrystallization was the predominant recovery mechanism for ferrite in both the stir zone and thermomechanically affected zone. Micro-texture examination showed that FSW develops typical shear texture components such as D₁, D₂ and F as well as the cube recrystallization texture for the ferrite phase within the stir zone. However, because of different thermomechanical conditions in various regions of the thermomechanically affected zone, additional shear texture components are developed, such as E, J and J¯ together with as D₁, D₂ and F, which were already observed in the stir zone. The absence of the cube recrystallization texture of ferrite in thermomechanically affected zone is attributed to insufficient recrystallization due to lowered strain and temperature in this zone. Study of the retained austenite constituent revealed that both shear textures, B and B¯ as well as recrystallization textures are developed in this phase within both the stir zone and thermomechanically affected zone.