Effect of process parameters on surface texture generated by laser polishing of additively manufactured Ti-6Al-4V

Although there have been numerous attempts to define how different laser polishing parameters affect the generated surface roughness, there has been no detailed investigation of how their effects can be combined to optimize the process. This paper applies statistical analysis to model and predict the resulting surface roughness for laser post-processing of components made of Ti-6Al-4V and produced by laser powder bed fusion. This model is based on analysis of a wide ranging experimental programme investigating how the interaction of the governing parameters, i.e., laser power, number of repetitions, axial feed rate, scanning speed, and focal position, affected surface roughness. The experimental programme was the result of a robust Design of Experiments analysis and experimental analysis using ANOVA. It is expected that the outcomes will contribute towards the understanding of how the governing parameters influence the laser polishing process and final surface roughness, and would be a tool for optimizing their selection. The results of the ANOVA (analysis of variance) revealed that the most significant parameters are scanning speed followed by laser power and then axial feed rate. In addition, a clear tendency for the estimated Ra to decrease with the increase in laser power at lower values of axial feed rate and of scanning speed, and a focal position in the region of 2 mm. It is noted that the process parameters were varied over wide ranges, including extreme values, which made it difficult to accurately model the dependent variable over the full range of experimental trials

Magnetic domains and magnetic stability of cohenite from the Morasko iron meteorite

International audienceMagnetic properties, texture and microstructure of cohenite grains from Morasko iron meteorite have been investigated using electron backscattered diffraction, Bitter pattern technique, magneto-optical imaging method and magnetic force microscopy. Cohenite shows much stronger magnetic contrast compared to kamacite because it is magnetically harder than the Fe-Ni alloy, and thus causes higher stray fields. A surprising result is the high stability and reversibility of the global stripe-like magnetic domain structure in cohenite when applying high magnetic fields up to 1.5 T, and exposing it to high temperatures above the Curie temperature of about 220 °C. Heating up to 700 °C under atmosphere conditions has shown that cohenite remains stable and that the global magnetic domain structures mainly recover to its preheating state. This observation suggests that magnetic domains are strongly controlled by the crystal anisotropy of cohenite. Branching magnetic domain structures at the grain boundary to kamacite can be annealed, which indicates that they are very sensitive to record deformation. EBSD observations clearly demonstrate that increasing deviation from the easy [010] crystallographic axis and stress localization are the main factors controlling the distortion of Bitter patterns, and suggest a high sensitivity of the cohenite magnetic domain structure to local microstructural heterogeneities. The results of this study substantiate the theory that cohenite can be a good recorder of magnetic fields in planetary core material

Structural Analysis of Aliphatic versus Aromatic Substrate Specificity in a Copper Amine Oxidase from <i>Hansenula polymorpha</i>

Copper amine oxidases (CAOs) are responsible for the oxidative deamination of primary amines to their corresponding aldehydes. The CAO catalytic mechanism can be divided into two half-reactions: a reductive half-reaction in which a primary amine substrate is oxidized to its corresponding aldehyde with the concomitant reduction of the organic cofactor 2,4,5-trihydroxyphenylalanine quinone (TPQ) and an oxidative half-reaction in which reduced TPQ is reoxidized with the reduction of molecular oxygen to hydrogen peroxide. The reductive half-reaction proceeds via Schiff base chemistry, in which the primary amine substrate first attacks the C5 carbonyl of TPQ, forming a series of covalent Schiff base intermediates. The X-ray crystal structures of copper amine oxidase-1 from the yeast <i>Hansenula polymorpha</i> (HPAO-1) in complex with ethylamine and benzylamine have been determined to resolutions of 2.18 and 2.25 Å, respectively. These structures reveal the two amine substrates bound at the back of the active site coincident with TPQ in its two-electron-reduced aminoquinol form. Rearrangements of particular amino acid side chains within the substrate channel and specific protein–substrate interactions provide insight into the substrate specificity of HPAO-1. These changes begin to account for this CAO’s kinetic preference for small, aliphatic amines over the aromatic amines or whole peptides preferred by some of its homologues

Preliminary Characterization of Submarine Basalt Magnetic Mineralogy Using Amplitude‐Dependence of Magnetic Susceptibility

Abstract The past ∼200 million years of Earth's geomagnetic field behavior have been recorded within oceanic basalts, many of which are only accessible via scientific ocean drilling. Obtaining the best possible paleomagnetic measurements from such valuable samples requires an a priori understanding of their magnetic mineralogies when choosing the most appropriate protocol for stepwise demagnetization experiments (either alternating field or thermal). Here, we present a quick, and non‐destructive method that utilizes the amplitude‐dependence of magnetic susceptibility to screen submarine basalts prior to choosing a demagnetization protocol, whenever conducting a pilot study or other detailed rock‐magnetic characterization is not possible. We demonstrate this method using samples acquired during International Ocean Discovery Program Expedition 391. Our approach is rooted in the observation that amplitude‐dependent magnetic susceptibility is observed in basalt samples whose dominant magnetic carrier is multidomain titanomagnetite (∼TM60–65, (Ti0.60–0.65Fe0.35–0.40)Fe2O4). Samples with low Ti contents within titanomagnetite or samples that have experienced a high degree of oxidative weathering do not display appreciable amplitude dependence. Due to their low Curie temperatures, basalts that possess amplitude‐dependence should ideally be demagnetized either using alternating fields or via finely‐spaced thermal demagnetization heating steps below 300°C. Our screening method can enhance the success rate of paleomagnetic studies of oceanic basalt samples