Nickel-based Inconel 718 is a very good candidate for selective laser melting (SLM). During the SLM process, Inconel 718 develops a complex and heterogeneous microstructure. A deep understanding of the microstructural features of the as-built SLM material is essential for the design of a proper post-process heat treatment. In this study, the microstructure of as-built SLM Inconel 718 was investigated at different length scales using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electron backscatter diffraction (EBSD) was also used to analyze the grain morphology and crystallographic texture. Grains elongated in the build direction and crossing several deposited layers were observed. The grains are not constrained by the laser tracks or by the melt pools, which indicates epitaxial growth controls the solidification. Each grain is composed of fine columnar dendrites that develop along one of their axes oriented in the direction of the local thermal gradient. Consequently, prominent crystallographic texture was observed and the dendrites tend to grow to the build direction or with occasional change of 90° at the edge of the melt pools. At the dendrite length scale, the microsegregation of the alloying elements, interdendritic precipitates, and dislocations was also detected.

Cold Spray (CS) is a deposition process, part of the thermal spray family. In this method, powder particles are accelerated at supersonic speed within a nozzle; impacts against a substrate material triggers a complex process, ultimately leading to consolidation and bonding. CS, in its modern form, has been around for approximately 30 years and has undergone through exciting and unprecedented developmental steps. In this article, we have summarized the key inventions and sub-inventions which pioneered the innovation aspect to the process that is known today, and the key breakthroughs related to the processing of materials CS is currently mastering. CS has not followed a liner path since its invention, but an evolution more similar to a hype cycle: high initial growth of expectations, followed by a decrease in interest and a renewed thrust pushed by a number of demonstrated industrial applications. The process interest is expected to continue (gently) to grow, alongside with further development of equipment and feedstock materials specific for CS processing. A number of current applications have been identified the areas that the process is likely to be the most disruptive in the medium-long term future have been laid down.

The microstructure and composition evolution of FeCoNiCrMn high entropy alloy during extreme deformation with a strain rate of 10⁸–10⁹ s⁻¹ induced by cold spray technology was investigated. In the region experiencing extremely large strain and high strain rate deformation, ultrafine nanograins with an average size of smaller than 100 nm were formed due to the occurrence of dynamic recrystallization. Additionally, the rapid redistribution of segregated Mn and Ni elements in extremely deformed FeCoNiCrMn was found for the first time. The reason for this phenomenon is the increased grain boundary area and dislocation density caused by extreme plastic deformation. GRAPHICAL ABSTRACT IMPACT STATEMENT The redistribution of Mn and Ni elements was found in extremely deformed FeCoNiCrMn. This finding enriches our knowledge on the microstructure evolution mechanism of high entropy alloys under extreme deformation.

Additive manufacturing techniques such as cold spray are translating from research laboratories into more mainstream high-end production systems. Similar to many additive processes, finishing still depends on removal processes. This research presents the results from investigations into aspects of the machinability of aluminum 6061 tubes manufactured with cold spray. Through the analysis of cutting forces and observations on chip formation and surface morphology, the effect of cutting speed, feed rate, and heat treatment was quantified, for both cold-sprayed and bulk aluminum 6061. High-speed video of chip formation shows changes in chip form for varying material and heat treatment, which is supported by the force data and quantitative imaging of the machined surface. The results shown in this paper demonstrate that parameters involved in cold spray directly impact on machinability and therefore have implications for machining parameters and strategy.

Copper particles embedded into polymer surfaces by cold spray (CS) have been confirmed as a method for antifouling (AF) protection. CS is a low-heat coating process which can be used or employed over large areas. The key parameters that indicate AF potency are particle penetration depth and copper surface coverage. Adaptation of this process towards industrial level requires the process inputs leading to the best outputs to be identified. In this paper, copper particles were deposited onto two polymers used in marine applications with CS, however, without the use of gas-heating hence deposition was free of any additional heat input. Analysis was carried out to determine which process conditions and material properties can lead to most effective AF coating results.