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Toxic metal reduction is at the forefront of many design considerations today; additive manufacturing has the ability to combine materials in ways other traditional processes cannot and has the potential to offer unique solutions to reduce hazardous materials needed in manufacturing. Tungsten carbide (WC) has been used as a substitute in wear applications where toxic processes are traditionally utilized, but it can be difficult to deposit high-quality, hard and durable coatings. Additionally, there is a need to apply WC coatings on surfaces not feasible with the current processes. Cold spray, a solid-state directed powder deposition process, is effective at depositing carbides, though powders must be thoughtfully designed to achieve desired mechanical properties. In this study, WC was investigated as a hard chrome alternative for wear applications. Various blend ratios and preparation methods were evaluated as feedstock powder and then sprayed. Feedstock characteristics were compared to cold spray performance. Cold spray consolidations were evaluated for coating porosity and hardness. It was found that when powder make-up and composition were optimized, a high-hardness and low-porosity material was made that will contribute to the reduction in dependency of Cr in wear-facing components.

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Additive manufacturing is a rapidly expanding field, encompassing many methods to manufacture parts and coatings with a wide variety of feedstock. Metal powders are one such feedstock, with a range of compositions and morphologies. Understanding subtle changes in the feedstock is critical to ensure successful consolidation and quality control of both the feedstock and manufactured part. Current standards lack the ability to finely distinguish almost acceptable powders from barely acceptable ones. Here, novel means of powder feedstock characterization for quality control are demonstrated for the solid-state AM process of cold spray, though similar methods may be extrapolated to other additive methods as well. These characterization methods aim to capture the physics of the process, which in cold spray consists of high strain rate deformation of solid-state feedstock. To capture this, in this effort powder compaction was evaluated via rapidly applied loads, flowability of otherwise non-flowable powders was evaluated with the addition of vibration, and powder electrical resistivity was evaluated through compaction between two electrodes. Several powders, including aluminum alloys, chromium, and cermet composites, were evaluated in this effort, with each case study demonstrating the need for non-traditional characterization metrics as a means of quality control and classification of these materials.

Machining and surface finishing is essential in the processing of many ceramics, however, it can be detrimental to subsequent performance as it introduces residual stresses and structural defects. Using micro-Raman spectroscopy the residual stress and crystallinity of hotpressed SiC tiles was examined after finishing with several different methods. 514 nm and 633 nm lasers in both conventional and confocal settings enabled stress as a function of depth to be assessed. Single crystal, electronics grade SiC was used for comparison. Compressive residual stresses were present at the surface and in the sub-surface region in all the samples, but the surface with lowest roughness and a mirror-like finish had the highest residual stress. Crystallinity in SiC is reduced by defects and stacking faults produced during machining and finishing. The finer surface finishes had higher residual stresses, but were actually found to have better crystallinity than the rough surfaces. The dependence of residual stress and crystallinity on surface roughness is attributed to a change in the mode of ceramic removal from energetic and brittle for rough finishes to ductile for the shallow cuts of smooth finishes. The dependence of stress and crystallinity on roughness means a balance must be struck between smoothness, crystallinity and stresses in choosing the best finish for a given application.