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Grade 91 steel forms martensite during additive manufacturing and the extent of tempering of martensite significantly affects the mechanical properties of parts. Currently, there is a lack of quantitative understanding of the tempering kinetics for Grade 91 steel, and as a result, the effects of repeated thermal cycles on properties for different processing conditions cannot be determined. Here we evaluate the tempering kinetics by determining the constant terms in the Johnson Mehl Avrami kinetic equation from the tempering data available in the literature and the thermal cycles computed using a rigorously-tested heat and fluid flow model of multi-layer additive manufacturing. The raw tempering data are cleaned using a neural network to enhance accuracy. The lower layers experience repeating cycles of heating and cooling when the upper layers are added. As a result, the hardness is reduced owing to the tempering of martensite. In contrast, martensite formed in the upper layers is not tempered to the same extent and the hardness remains high. Therefore, the hardness of the part increases with the distance from the substrate. Variations in the heat input at different laser powers and scanning speeds significantly affect the extent of tempering. Since the method used here can provide a quantitative understanding of the tempering of martensite and the spatial variation of hardness, it can be used to tailor the microstructure and hardness of heat treatable printed metallic parts.

In situ and post-print defects, including excessive residual stresses and poor microstructural properties, are important concerns in the part design and setup stages of powder bed fusion (PBF) manufactured parts. Laser scan strategies are well known to be correlated with the development of these defects; however, due to the lack of complex scan strategy descriptors and the consequential imposition of simple scan strategies, these correlations are not well understood and are difficult to investigate. This work proposes a methodology for an intuitive quantitative descriptor of scan strategies that has the potential to provide quick prognoses to predict defects. To demonstrate this, a neural network is trained to accurately predict post-print residual stress distributions using the descriptor of a specified path. It is envisioned that this descriptor could allow for the circumvention of current costly prevention mechanisms and increase confidence and reliability in metal additive manufacturing technologies.

Today, chronic rhinosinusitis (CRS) is a symptomatic disease diagnosed by nasal endoscopy and eventually computed tomography scan, and is treated by pharmacotherapy or, when unsuccessful, by sinus surgery. With the advent of biologics, the diagnostic approach needs to be adjusted to appreciate CRS endotypes, introducing biomarkers, and the therapeutic options will be extended by the application of biologics. Specifically, type 2 immune reactions moved into the focus, similar to asthma, involving innate and adaptive immunity pathways to establish an often severe, persistent disease. The role for endotyping of CRS became evident for biologics, but also turned out to be meaningful for the decision on the selection of pharmacotherapy and the specific surgical approach to choose. Furthermore, considerations on the role of surgery and biologics needed to be elaborated to develop decision-making processes for patients with moderate-to-severe CRS with nasal polyps, with or without comorbid asthma, allowing us to adjust the treatment for patient groups based on endotyping (precision medicine). We here aim to guide the decisions in a rational way based on the current knowledge of the efficacy and complications or side effects of the recently enlarged therapeutic options. Personal experience has been added where knowledge was lacking in this fast moving field.

We present two prescriptions for broadband ($ {\sim} 77 - 252\;{\rm GHz} $∼77−252GHz), millimeter-wave antireflection coatings for cryogenic, sintered polycrystalline aluminum oxide optics: one for large-format (700 mm diameter) planar and plano–convex elements, the other for densely packed arrays of quasi-optical elements—in our case, 5 mm diameter half-spheres (called “lenslets”). The coatings comprise three layers of commercially available, polytetrafluoroethylene-based, dielectric sheet material. The lenslet coating is molded to fit the 150 mm diameter arrays directly, while the large-diameter lenses are coated using a tiled approach. We review the fabrication processes for both prescriptions, then discuss laboratory measurements of their transmittance and reflectance. In addition, we present the inferred refractive indices and loss tangents for the coating materials and the aluminum oxide substrate. We find that at 150 GHz and 300 K the large-format coating sample achieves $ (97 \pm 2)\% $(97±2)% transmittance, and the lenslet coating sample achieves $ (94 \pm 3)\% $(94±3)% transmittance.