Influences of Manufacturing-Related Microstructural Variations on Fatigue in Carbide-Rich Tool Steels

In cold-work applications, tool steels with high carbide contents are used as cutting and stamping tools. The tool service life is limited by wear resistance and fatigue strength. The relationship between manufacturing-related microstructural influences and fatigue strengths of tool steels has not yet been adequately investigated. To investigate these influences on high-cycle fatigue (HCF) strength (N_G = 10⁷), rotating bending tests are performed on AISI D2 and AISI M2/M3. Raw materials are produced by conventional ingot casting and subsequent hot working (HW) as well as in a powder metallurgy (PM) process with hot isostatic pressing (HIP) and forging. Herein, a statistically validated correlation of process-related defect size and the resulting fatigue strength is presented. Both PM steels show significantly higher HCF strength than the HW steels. Critical defects in PM appear to be exclusively small oxide inclusions. In contrast, fatigue cracks in HW are typically initiated by the fracture of large, blocky eutectic carbides. The main factor influencing HCF strength is defect size. Other critical features of the microstructure include matrix hardness, circularity, and defect type. Improvements in fatigue strength can be obtained by reducing the size of fracture mechanical defects, inclusions for PM, and eutectic carbides for HW microstructures.     

Locally Adapted Microstructures in an Additively Manufactured Titanium Aluminide Alloy Through Process Parameter Variation and Heat Treatment

Electron beam powder bed fusion (PBF-EB/M) has been attracting great research interest as a promising technology for additive manufacturing of titanium aluminide alloys. However, challenges often arise from the process-induced evaporation of aluminum, which is linked to the PBF-EB/M process parameters. This study applies different volumetric energy densities during PBF-EB/M processing to deliberately adjust the aluminum contents in additively manufactured Ti–43.5Al–4Nb–1Mo–0.1B (TNM-B1) samples. The specimens are subsequently subjected to hot isostatic pressing (HIP) and a two-step heat treatment. The influence of process parameter variation and heat treatments on microstructure and defect distribution are investigated using optical and scanning electron microscopy, as well as X-ray computed tomography (CT). Depending on the aluminum content, shifts in the phase transition temperatures can be identified via differential scanning calorimetry (DSC). It is confirmed that the microstructure after heat treatment is strongly linked to the PBF-EB/M parameters and the associated aluminum evaporation. The feasibility of producing locally adapted microstructures within one component through process parameter variation and subsequent heat treatment can be demonstrated. Thus, fully lamellar and nearly lamellar microstructures in two adjacent component areas can be adjusted, respectively.     

Enhancing Tungsten Oxide Gasochromism with Noble Metal Nanoparticles: The Importance of the Interface

Crystalline tungsten trioxide (WO₃) thin films covered by noble metal (gold and platinum) nanoparticles are synthesized via wet chemistry and used as optical sensors for gaseous hydrogen. Sensing performances are strongly influenced by the catalyst used, with platinum (Pt) resulting as best. Surprisingly, it is found that gold (Au) can provide remarkable sensing activity that tuned out to be strongly dependent on the nanoparticle size: devices sensitized with smaller nanoparticles display better H₂ sensing performance. Computational insight based on density functional theory calculations suggested that this can be related to processes occurring specifically at the Au nanoparticle-WO₃ interface (whose extent is in fact dependent on the nanoparticle size), where the hydrogen dissociative adsorption turns out to be possible. While both experiments and calculations single out Pt as better than Au for sensing, the present work reveals how an exquisitely nanoscopic effect can yield unexpected sensing performance for Au on WO₃, and how these performances can be tuned by controlling the nanoscale features of the system.     

Wear Behavior of Roller-Burnished High Interstitial Austenitic Stainless Steel Parts in Glass-Reinforced Plastic Melt

Herein this investigation, profiled high interstitial austenitic stainless steel parts are burnished on a profile-rolling machine, and afterward, the wear behavior is analyzed in a melt of glass-reinforced polypropylene. Wear and corrosion resistance are significant properties of steel parts in the plastics and food industries. The high work-hardening ability of high interstitial austenitic stainless steel enables burnishing parts with a significant local hardness to increase up to maximum values of ≈600 HV 1. Wear tests on a recently developed test stand reveal that the burnished austenitic stainless steel surface performs similarly to a nitrided surface of the standard nitriding steel 31CrMoV9 + QT with a hardness of ≈830 HV 0.5. Regarding the given advantage of corrosion resistance, it is concluded that roller burnishing supports the applicability of high interstitial austenitic stainless steel in plastics and food industries.     

Real and perceived feet orientation under fatiguing and non-fatiguing conditions in an immersive virtual reality environment

Virtual Reality - Lower limbs position sense is a complex yet poorly understood mechanism, influenced by many factors. Hence, we investigated the position sense of lower limbs through feet...     

Thermodynamic efficiency of membrane-assisted distillation processes

Membrane processes are considered as comparably mild separation processes offering the potential for significant energy savings compared with azeotropic distillation processes. Despite higher investment and material costs, they are of particular interest for improving the energy efficiency in the chemical industry. However, energy savings of more than 20%–30% are rarely reported and even a general superiority can be disputed. To further elucidate this controversial, the current study pursues a quantitative assessment of the thermodynamic efficiency of pervaporation and vapor permeation processes with stand-alone distillation and hybrid membrane-assisted distillation processes for the separation of azeotropic mixtures. The results confirm the case-dependent potential of distillation processes to outperform membrane-assisted separations in terms of energy efficiency, considering proper heat integration. Although energy efficiency is becoming significantly important, it should be considered in the context of economic performance to determine an optimal trade-off and to select the best process alternative during conceptual process design.     

Plasmonic Photoresistor Based on Interconnected Metal-Semiconductor Grating

Metal-semiconductor nanostructures in various configurations are extensively used in photodetection, photocatalysis, and photovoltaics. For photodetection purposes, the working principle is straightforward; on illumination, generated charge carriers in excess lead to a decrease in resistance. Notably, using an interconnected metal-semiconductor grating, it is observed and now reported an opposite response, an increase in the resistance. Such photoresistors are fabricated through wrinkle structuring and oblique angle material deposition methods. It is found that the controlled wrinkling leads to large-area 1D periodic structures with coexisting cracking perpendicular to the grating direction—such cracks are used as connections between the two-point contact measurement through the associated gold layer deposition. An enhanced current reduction is further observed on photoexcitation for an additional deposition of an amorphous titania layer. Subsequently, a discussion on the mechanisms and interaction between hot electron injection, charge carrier recombination, and thermalization is presented. Supported by numerical modeling, the angle-resolved plasmonic modes with the photoresistance can be correlated. The ease of layered deposition of the materials allows one to extend the studies on cavity-based structures with sandwiched titania layers as hotspots. This simple, scalable, and robust fabrication method thus promises an efficient routeway toward photosensor development in which plasmon-mediated hot electrons play a crucial role.