Microstructural features controlling very high cycle fatigue of nitrided maraging steel

Maraging steels belong to the group of ultra-high strength materials and are often used in critical aerospace, automotive and tooling components. By applying a surface treatment such as nitriding, the fatigue and wear resistance can be improved. The microstructural features that influence the (very) high cycle fatigue response of nitrided maraging steels are studied in this work. Although the used steel has practically no inclusions, it was found that small surface imperfections, introduced during processing, may form potential fatigue initiation points. The samples are nitrided during aging in order to form nitrided layers with various thicknesses, microstructures and hardness profiles without formation of a continuous (compound) iron nitride layer. Data from microhardness tests, scanning electron microscopy, electron backscatter diffraction, x-ray diffraction and transmission electron microscopy were used to characterize the microstructure of the layers. Bending fatigue tests were employed to evaluate the fatigue response of the steel. It was found that the best fatigue behavior is obtained in samples with a thin diffusion zone with a narrow constant hardness region. In this zone, coherent disc-shaped nitride precipitates are detected with TEM

Lanthanide-assisted deposition of strongly electro-optic PZT thin films on silicon: toward integrated active nanophotonic devices

The electro-optical properties of lead zirconate titanate (PZT) thin films depend strongly on the quality and crystallographic orientation of the thin films. We demonstrate a novel method to grow highly textured PZT thin films on silicon using the chemical solution deposition (CSD) process. We report the use of ultrathin (5–15 nm) lanthanide (La, Pr, Nd, Sm) based intermediate layers for obtaining preferentially (100) oriented PZT thin films. X-ray diffraction measurements indicate preferentially oriented intermediate Ln2O2CO3 layers providing an excellent lattice match with the PZT thin films grown on top. The XRD and scanning electron microscopy measurements reveal that the annealed layers are dense, uniform, crack-free and highly oriented (>99.8%) without apparent defects or secondary phases. The EDX and HRTEM characterization confirm that the template layers act as an efficient diffusion barrier and form a sharp interface between the substrate and the PZT. The electrical measurements indicate a dielectric constant of ∼650, low dielectric loss of ∼0.02, coercive field of 70 kV/cm, remnant polarization of 25 μC/cm2, and large breakdown electric field of 1000 kV/cm. Finally, the effective electro-optic coefficients of the films are estimated with a spectroscopic ellipsometer measurement, considering the electric field induced variations in the phase reflectance ratio. The electro-optic measurements reveal excellent linear effective pockels coefficients of 110 to 240 pm/V, which makes the CSD deposited PZT thin film an ideal candidate for Si-based active integrated nanophotonic devices

Magnetic properties of silicon steel after plastic deformation

The energy efficiency of electric machines can be improved by optimizing their manufacturing process. During the manufacturing of ferromagnetic cores, silicon steel sheets are cut and stacked. This process introduces large stresses near cutting edges. The steel near cutting edges is in a plastically deformed stress state without external mechanical load. The magnetic properties of the steel in this stress state are investigated using a custom magnetomechanical measurement setup, stress strain measurements, electrical resistance measurements, and transmission electron microscopic (TEM) measurements. Analysis of the core energy losses is done by means of the loss separation technique. The silicon steel used in this paper is non-grain oriented (NGO) steel grade M270-35A. Three differently cut sets of M270-35A are investigated, which differ in the direction they are cut with respect to the rolling direction. The effect of sample deformation was measured—both before and after mechanical load release—on the magnetization curve and total core energy losses. It is known that the magnetic properties dramatically degrade with increasing sample deformation under mechanical load. In this paper, it was found that when the mechanical load is released, the magnetic properties degrade even further. Loss separation analysis has shown that the hysteresis loss is the main contributor to the additional core losses due to sample deformation. Releasing the mechanical load increased the hysteresis loss up to 270% at 10.4% pre-release strain. At this level of strain, the relative magnetic permeability decreased up to 45% after mechanical load release. Manufacturing processes that introduce plastic deformation are detrimental to the local magnetic material properties

Ca:Mg:Zn:CO3 and Ca:Mg:CO3-tri- and bi-elemental carbonate microparticles for novel injectable self-gelling hydrogel-microparticle composites for tissue regeneration

Injectable composites for tissue regeneration can be developed by dispersion of inorganic microparticles and cells in a hydrogel phase. In this study, multifunctional carbonate microparticles containing different amounts of calcium, magnesium and zinc were mixed with solutions of gellan gum (GG), an anionic polysaccharide, to form injectable hydrogel-microparticle composites, containing Zn, Ca and Mg. Zn and Ca were incorporated into microparticle preparations to a greater extent than Mg. Microparticle groups were heterogeneous and contained microparticles of differing shape and elemental composition. Zn-rich microparticles were 'star shaped' and appeared to consist of small crystallites, while Zn-poor, Ca- and Mg-rich microparticles were irregular in shape and appeared to contain lager crystallites. Zn-free microparticle groups exhibited the best cytocompatibility and, unexpectedly, Zn-free composites showed the highest antibacterial activity towards methicilin-resistant Staphylococcus aureus. Composites containing Zn-free microparticles were cytocompatible and therefore appear most suitable for applications as an injectable biomaterial. This study proves the principle of creating bi- and tri-elemental microparticles to induce the gelation of GG to create injectable hydrogel-microparticle composites

CeO2-modified Fe2O3 for CO2 utilization via chemical looping

Both pure and mixed CeO2-Fe2O3 were prepared for CO2 reduction to CO by chemical looping. The crystallographic structure of the investigated materials was monitored in situ during H-2 reduction and CO2 oxidation. A solid solution of iron in ceria was identified. Up to 70 wt % CeO2, a distinct Fe2O3 hematite phase occurred next to the solid solution. At higher CeO2 content, no diffraction patterns corresponding to iron oxide phases were present, but upon H-2 temperature programmed reduction, a metal iron phase appeared. The Fe2O3 phase at lower CeO2 content, during H-2 temperature programmed reduction, completely reduced at 700 degrees C while the solid solution was only partially reduced. For all investigated samples, CO2 reoxidized iron in one-step to Fe3O4 from 500 degrees C during temperature programmed oxidation. Adding CeO2 to Fe2O3 was beneficial for the materials activity and stability. Isothermal redox cycles were performed without significant loss of CO2 conversion. The highest CO yield was obtained for 20 wt % CeO2-Fe2O3, but 50 and 70 wt % CeO2-Fe2O3 were the most stable combinations

Investigation of the effect of carbon on the reversible hydrogen trapping behavior in lab-cast martensitic Fe-C steels

The present study evaluates the active hydrogen trapping sites of three martensitic Fe-C alloys with a carbon content of 0.2 wt%, 0.4 wt% and 1.1 wt% by thermal desorption spectroscopy (TDS). The absence of additional alloying elements reduces the microstructural complexity and allows focussing on the carbon effects only. The TDS spectra are extrapolated towards cryogenic temperatures, enabling to deconvolute the desorption spectrum in Gaussian curves corresponding with H detrapping from lattice positions, dislocations, high angle grain boundaries and cementite. The activation energy for hydrogen desorption and the amount of H trapped at each site is further profoundly evaluated. It is found that the carbon content controls the amount of hydrogen trapped at dislocations and its activation energy for detrapping decreases with increasing carbon content. The trap density of the high angle grain boundaries is controlled only by the prior austenitic grain size and the corresponding activation energy for H desorption is independent of the carbon content. Hydrogen trapping at cementite was only detected in the samples with the highest carbon content (Fe-1.1C)