The Effect of Scan Length on the Structure and Mechanical Properties of Electron Beam-Melted Ti-6Al-4V

Electron beam melting (EBM) is a powder bed fusion-based additive manufacturing process in which selective areas of a layer of powder are melted with an electron beam and a part is built layer by layer. EBM scanning strategies within the Arcam AB^® A2X EBM system rely upon governing relationships between the scan length of the beam path, the beam current, and speed. As a result, a large parameter process window exists for Ti-6Al-4V. Many studies have reviewed various properties of EBM materials without accounting for this effect. The work performed in this study demonstrates the relationship between scan length and the resulting density, microstructure, and mechanical properties of EBM-produced Ti-6Al-4V using the scanning strategies set by the EBM control software. This emphasizes the criticality of process knowledge and careful experimental design, and provides an alternate explanation for reported orientation-influenced strength differences.     

Potenzial von freien Flankenmodifikationen für Beveloidverzahnungen

In recent years the beveloid gear, also known as conical involute gear, is shifting more and more into the spotlight. The beveloid gear has been an important part of marine transmissions for years and is nowadays used to transmit the torque of the output shaft of the gearbox onto the front axle in a four wheel drive vehicle. The small need of design space and the reduced amount of design parts necessary in comparison to conventional transfer gearboxes, distinguish the beveloid gear. The conjugate flank of beveloid gears promises the best operational behavior. However because of its geometry the conjugate flank cannot be manufactured with standard manufacturing processes. Standard modification such as crowning offer a possibility to enhance the operational behavior of involute beveloid gears but cannot reach the whole potential given by conjugated beveloid gears. Therefore, the objective of the following report is to investigate the potential of free flank modifications of beveloid gears regarding the operational behavior. After a brief overview on existing geometry optimization methods for beveloid gears, the method for free flank modifications by means of a weighted objective function is defined and applied to an example gear. The results of the investigation show that free flank modifications offer a high level of improvement of the operational behavior. The comparison with a non-modified gear, a gear with standard modifications and a gear with free flank modifications for three different load steps proves that free flank modifications offer a higher durability and lower noise excitation.     

轻油部分循环对丙丁烷收率的影响及其应用

油田轻烃回收装置随着原料气气质、气量的变化,丙丁烷的收率普遍偏低。提高丙丁烷的收率成了许多浅冷装置急待解决的问题。轻油部分循环法是方法之一,该方法从脱丁烷塔塔底引一股稳定轻油循环至蒸发器前的管线中,从而对汽液平衡施加影响。本文考虑温度、压力和组成对烃类混合物相平衡的影响,选用ＳＲＫ真实气体状态方程研究轻油循环掺合比与丙丁烷收率的关系。经计算表明,在温度、压力一定时,只要有轻油循环,丙丁烷的收率就要提高,且随着掺合比的增加而增加,但增幅不尽相同。适宜的掺合比应根据经济分析的结果来确定。在油田气轻烃回收浅冷分离工艺的技术改造中运用轻油部分循环法可有效地提高丙丁烷的收率。     

Ferroelectric order in individual nanometre-scale crystals

Ferroelectricity in finite-dimensional systems continues to arouse interest, motivated by predictions of vortex polarization states and the utility of ferroelectric nanomaterials in memory devices, actuators and other applications. Critical to these areas of research are the nanoscale polarization structure and scaling limit of ferroelectric order, which are determined here in individual nanocrystals comprising a single ferroelectric domain. Maps of ferroelectric structural distortions obtained from aberration-corrected transmission electron microscopy, combined with holographic polarization imaging, indicate the persistence of a linearly ordered and monodomain polarization state at nanometre dimensions. Room-temperature polarization switching is demonstrated down to ~5?nm dimensions. Ferroelectric coherence is facilitated in part by control of particle morphology, which along with electrostatic boundary conditions is found to determine the spatial extent of cooperative ferroelectric distortions. This work points the way to multi-Tbit/in(2) memories and provides a glimpse of the structural and electrical manifestations of ferroelectricity down to its ultimate limits.     

From Single Molecules to Thin Film Electronics,Nanofibers, e‐Textiles and Power Cables: Bridging Length Scales with Organic Semiconductors

Organic semiconductors are the centerpiece of several vibrant research fields from single‐molecule to organic electronics, and they are finding increasing use in bioelectronics and even classical polymer technology. The versatile chemistry and broad range of electronic functionalities of conjugated materials enable the bridging of length scales 15 orders of magnitude apart, ranging from a single nanometer (10^?9 m) to the size of continents (10⁶ m). This work provides a taste of the diverse applications that can be realized with organic semiconductors. The reader will embark on a journey from single molecular junctions to thin film organic electronics, supramolecular assemblies, biomaterials such as amyloid fibrils and nanofibrillated cellulose, conducting fibers and yarns for e‐textiles, and finally to power cables that shuffle power across thousands of kilometers.     

The role of microcrystalline structure on optical scattering characteristics of semi-crystalline thermoplastics and the accuracy of numerical input for IR-heating modeling

Infrared (IR) heating is widely used for thermoforming of thermoplastic polymers. The key benefit of radiation heating is that a significant amount of the radiative energy penetrates into the polymers thanks to their semi-transparency. For the case of heating unfilled semi-crystalline polymers, the relation between their microcrystalline structure and optical properties is the key to develop a predictive IR-heating model as microcrystalline structure introduces an optically heterogeneous medium. In this study, a relation between the microcrystalline structure of a polyethylene (PE) and its effect on the thermo-optical properties was experimentally analyzed considering a two-step analysis. At very first step, the relation was analyzed considering samples with identical thicknesses and different morphologies, characterized here in terms of degree of crystallinity (X_c (%)). Using Fourier Transform Infrared (FT-IR) spectroscopy and integrating sphere, optical characteristics of the PE samples were analyzed in near-infrared (NIR) and middle-infrared (MIR) spectral ranges. The analyses showed that a slight variation in X_c (%) has a great effect on the optical characteristics of PE, particularly the transmission characteristics in NIR range. The wavelength-dependent effect of X_c (%) on the transmission behaviors opened a discussion about the fact that the microcrystalline structures -in particular spherulites or their substructures such as lamellae- are responsible for optical scattering. Using the optical properties obtained from the two-step experimental analyses, two different thermo-optical properties were calculated, namely extinction and absorption coefficients, and used as a numerical input for the parametric numerical studies. The numerical studies were performed using an in-house developed radiation heat transfer algorithm -RAYHEAT-. Both the experimental and numerical analyses demonstrated the importance of the optical scattering regarding the identification of thermo-optical properties, used as a numerical input for radiation heat transfer models.     

Space neutron spectrometer design with SSPM-based instrumentation

The compact, robust nature of the CMOS solid-state photomultiplier (SSPM) allows the creation of small, low-power scintillation-based radiation measurement devices. Monitoring space radiation including solar protons and secondary neutrons generated from high-energy protons impinging on spacecraft is required to determine the dose to astronauts. Small size and highly integrated design are desired to minimize consumption of payload resources.RMD is developing prototype radiation measurement and personal dosimeter devices using emerging scintillation materials coupled to CMOS SSPM’s for multiple applications. Spectroscopic measurements of high-energy protons and gamma-rays using tissue-equivalent, inorganic scintillators coupled to SSPM devices demonstrate the ability of an SSPM device to monitor the dose from proton and heavy ion particles, providing real time feedback to astronauts. Measurement of the dose from secondary neutrons introduces additional challenges due to the need to discriminate neutrons from other particle types and to accurately determine their energy deposition. We present strategies for measuring neutron signatures and assessing neutron dose including simulations of relevant environments and detector materials.     

Optimization of parameters of the linear TOF-SIMS spectrometer by DOE method

Time of flight SIMS spectrometers are widely used in many industrial and scientific applications. Mass spectra of secondary ions ejected from a bombarded surface supply valuable data on its composition and give insights into physical and chemical processes at the surface. The data quality depends on several parameters, which control the spectrometer functioning. This contribution presents our work on an application of a so-called Design of Experiments (DOE) procedure to optimize working parameters of a home-assembled linear TOF-SIMS spectrometer. The efficiency of optimization procedures was tested for mass spectra of positive ions sputtered from Al surface under keV Ar ion bombardment. In particular, we show that use of the method leads to a large increase both of the mass resolution and of the signal/noise ratio (S/N), i.e. improves two quantities, which play a crucial role in mass spectrometry measurements. In addition, it is shown that DOE' method allows to reduce significantly the number of test measurements, and therefore to shorten the adjusting procedure to a minimum.     

Crystallization and microstructural evolution of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–La<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-ceramics

Crystallization and microstructure of glasses with the molar compositions 1MgO·1.2Al₂O₃·2.8SiO₂·1.2TiO₂·xLa₂O₃ (x = 0.1 and 0.4) were thermally treated at different temperatures in the range from 950 to 1250 °C and then analyzed by X-ray diffraction and scanning electron microscopy, in combination with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was found that the microstructure is first homogeneous with the precipitation of randomly distributed crystals and then indialite domains with embedded perrierite and rutile crystals are formed. For higher temperatures or prolonged times, more domains appear and expand into the bulk of the sample. Finally, the entire sample consists of the indialite domains and the boundaries that are enriched in rutile, perrierite, and magnesium aluminotitanate. Nevertheless, very distinct differences are observed between the samples with different La₂O₃ concentrations. For the sample with x = 0.4, the domains were detected at lower temperatures, while the quantity and size of the domains increase faster due to the promoted precipitation of indialite. For the sample with x = 0.1, in addition to the domain boundaries, secondary boundaries between the “regions” (assemblages of the domains) are observed in a larger length scale. The average size of the crystalline phases found between the “regions” is larger than that typically observed at the domain boundaries. The sizes of the crystals at the boundaries decrease with higher concentrations of La₂O₃, and the crystals (especially perrierite) within the domains become larger, resulting in a more homogeneous microstructure. This results in better dielectric properties, i.e., much higher quality factor for the sample with x = 0.4 in comparison to that with x = 0.1 after heat-treatment at 1150 or 1250 °C.