Nanocomposite‐Beschichtungen auf CBN‐Werkzeugen

Nanocomposite coatings on CBN‐tools CBN (cubic boron nitride) cutting materials are often used to improve the properties of cutting tools. This allows new applications and processes, which are not possible with common cutting materials (e.g. hard metals). Today CBN cutting materials are mostly coated to estimate the wear by an optical evaluation. Coatings on CBN cutting materials for enhancement of the tribological properties are normally not used. For improvement of the properties of used CBN tools during the cutting process a coating technology was developed. This technology combines the advantages of CBN cutting materials with the excellent properties (e.g. hardness, temperature stability) of nanostructured materials. Investigations with different coating systems and pre‐treatment processes were done to test the CBN cutting tools. These investigations have been shown, that nanocomposite coatings can be used to enhance the tool life of CBN cutting tools. Important for an increase in the tool life is a very good coating adhesion, which can be reached by special adhesion layers and an optimized coating structure.     

Large‐Scale Synthesis of Freestanding Layer‐Structured PbI2 and MAPbI3 Nanosheets for High‐Performance Photodetection

Recently, due to the possibility of thinning down to the atomic thickness to achieve exotic properties, layered materials have attracted extensive research attention. In particular, PbI₂, a kind of layered material, and its perovskite derivatives, CH₃NH₃PbI₃ (i.e., MAPbI₃), have demonstrated impressive photoresponsivities for efficient photodetection. Herein, the synthesis of large‐scale, high‐density, and freestanding PbI₂ nanosheets is demonstrated by manipulating the microenvironment during physical vapor deposition. In contrast to conventional two‐dimensional (2D) growth along the substrate surface, the essence here is the effective nucleation of microplanes with different angles relative to the in‐plane direction of underlying rough‐surfaced substrates. When configured into photodetectors, the fabricated device exhibits a photoresponsivity of 410 mA W^?1, a detectivity of 3.1 × 10¹¹ Jones, and a fast response with the rise and decay time constants of 86 and 150 ms, respectively, under a wavelength of 405 nm. These PbI₂ nanosheets can also be completely converted into MAPbI₃ materials via chemical vapor deposition with an improved photoresponsivity up to 40 A W^?1. All these performance parameters are comparable to those of state‐of‐the‐art layered‐material‐based photodetectors, revealing the technological potency of these freestanding nanosheets for next‐generation high‐performance optoelectronics.     

Werkzeugbeschichtungen für die Trockenbearbeitung

Tool coatings for dry machining During dry machining a strain collective consisting of mechanical, thermal, and chemical loads is imposed upon the cutting edge. Compared to conventional machining using cooling lubrication fluids, the loads are increased in dry cutting. A feasible solution to protect the cutting edge from thermal wear, abrasion, and tribo‐oxidation is the application of hard coatings. Newly developed Cr_xAl_yY_zN, Cr_xAl_yB_zN and Cr_xAl_ySi_zN PVD coatings were both evaluated in tribological model tests and machining tests concerning their suitability for dry cutting applications. Herein, the used coating technology and the coating properties are described in detail. The measured tool wear and the process forces give further hints for the optimization of the coating system.     

Schneiden und Schweißen mit dem CO2-Laser

Cutting and Welding Using a CO₂-Laser. Among the various types of lasers the CO₂ laser is particulary suitable for materials working. It has a very high efficienty (15–20 %) and a high output power (up to several kW). When the laser light is focused by means of a lens or a mirror, a power density of more than 10⁹ W/cm² is attained in continuous operation. The laser need not be applied in vacuum. The CO₂ laser is a suitable cutting tool for numerous materials, e. g. for metals such as titanium or steel, for combustible materials such as paper, textiles, wood, and plastics, and also for hard and brittle materials such as aluminium oxide and silicon carbide. If the metals are cut in an oxidizing atmosphere, the cutting speed may be increased. The cutting width however is determined by the size of the laser spot. In addition, experiments are reported in which the CO₂ laser was used for welding steel, titanium, plastics, quartz, and glass. The advantages of the laser for this application are discussed. Another important field of application is the growth of single crystals. In several fields the laser is in competition with the electron gun. Therefore, the laser technique is compared with the electron beam technique.     

Spanende Bearbeitung von Bauteilen aus Al‐Matrix‐Verbundwerkstoffen

Machining of Components of Al Matrix Composites The microstructure of metal matrix composites consists of hard reinforcements which are embedded in a metal matrix. The high hardness of the reinforcements leads to a difficult processing of these materials. The present paper demonstrates the machining of components of Al matrix composites for the automotive and the aircraft industry. The components are SiC particle reinforced brake drums, cylinder blocks with local Si particle and Al₂O₃ short fiber reinforced cylinder liners and TiB₂ particle reinforced extrusion molding profiles. The investigations illustrate that good results can be achieved when machining these components by turning, boring, drilling and milling with polycrystalline diamond (PCD) or CVD diamond thick‐film cutting tool materials.     

The effect of polysiloxane on the properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-NbC composite material produced by pyrolysis process

Recently, studies have been developed in order to obtain Al₂O₃-NbC composite materials. The reinforced materials have shown good potential to be used as cutting tool materials at high-speed cutting and high temperature as a substitute to WC-Co material. The main disadvantage to produce these alumina-reinforced materials is the necessity to use pressure assisted sintering or high sintering temperatures to produce dense bodies. Manufacturing of composite ceramic materials derived from polymer reactive filler has been intensively investigated. Polymer pyrolysis is a relatively new and very promising method for obtaining ceramic material in complex shapes and lower sintering temperatures. This work investigated a ceramic composite matrix based in SiC_xO_y and Al₂O₃ and reinforced with NbC obtained by means of the active fillers pyrolysis process. The results obtained in this work demonstrate that using a mixture of polysiloxanes produces a composite material with better properties when compared to others polymer materials.     

Synthesis, characterization and photoluminescence studies of ZnOrod@SnO2 nanocomposites

The synthesis of II-VI semiconductor (ZnO_rod@SnO₂) nanocomposite materials with core-shell morphology has been reported. ZnO nanorods were grown by hydrothermal technique using zinc acetate as the reactant. SnO₂ was coated on the nanorods by a simple technique of colloid chemistry. The formation of tin dioxide shell on the ZnO nanorods was confirmed by the TEM images of the resultant materials. The formation of the nanocomposite was also supported by XRD pattern. The effect of tin dioxide shell on the optical properties of ZnO was investigated by photoluminescence spectroscopy and Raman spectroscopy.     

Recent Advances in New Hard High‐Pressure Nitrides

Since the discovery of spinel nitrides in 1999, there has been a lot of effort in basic science to further develop advanced nitrides and electronic nitrides. The aim and scope of the research in this field is to synthesize novel nitrides for structural and functional applications. Silicon‐based spinel nitrides combine ultrahigh hardness with high thermal stability against decomposition in different environments, suggesting potential applications as cutting tools. These materials are also expected to show interesting optoelectronic properties, which may lead to applications in light‐emitting diodes. The synthesis of spinel silicon and germanium nitrides at ultrahigh pressures and temperatures, as well as the successful synthesis of tin nitride at ambient pressure, has created an enormous impact on both the basic science and technological development of advanced nitrides. Moreover, the discovery of novel phases of transition metal nitrides, such as Zr₃N₄ and Hf₃N₄ with a Th₃P₄ structure, as well as the recently reported nitrides of Pt and Mo, demonstrates the scientific potential of high‐pressure synthesis techniques in the field of materials science. Here, the state of the art in the field of novel hard materials based on nitrides synthesized reproducibly under high pressure is reviewed.     

Mechanical and optical characteristics of superhard nanocomposite TiN/a-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and TiCN/a-SiCN coatings produced by PECVD

There is a continuous need for new hard and superhard (H > 40 GPa) materials for applications ranging from protective coatings for cutting tools and aerospace to automobile industries, MEMS and others. In this work nanocomposite hard coatings fabricated by plasma-enhanced chemical vapor deposition from TiCl₄/SiH₄/CH₄/N₂/H₂/Ar gas mixtures were found to possess unique properties such as superhardness, high toughness, and interesting optical properties and colors. The mechanical characteristics such as hardness and Young’s modulus were determined by depth-sensitive indentation. Film microstructure was studied by XRD, SEM, TEM, ERD-TOF, XPS, and AFM. Optical properties like color, refractive index and extinction coefficient were evaluated using combined spectrophotometry and spectroscopic ellipsometry. This multitechnique approach allowed us to determine the structure-property relationships. We have shown that nc-TiN/a-Si₃N₄ exhibits a hardness of 45 GPa, while the novel nc-TiCN/a-SiCN provides a hardness of 57 GPa in addition to a very high resistance to plastic deformation (1.8 GPa).     

A Crosslinked Polytetrahydrofuran‐Borate‐Based Polymer Electrolyte Enabling Wide‐Working‐Temperature‐Range Rechargeable Magnesium Batteries

A polymer‐based magnesium (Mg) electrolyte is vital for boosting the development of high‐safety and flexible Mg batteries by virtue of its enormous advantages, such as significantly improved safety, potentially high energy density, ease of fabrication, and structural flexibility. Herein, a novel polytetrahydrofuran‐borate‐based gel polymer electrolyte coupling with glass fiber is synthesized via an in situ crosslinking reaction of magnesium borohydride [Mg(BH₄)₂] and hydroxyl‐terminated polytetrahydrofuran. This gel polymer electrolyte exhibits reversible Mg plating/stripping performance, high Mg‐ion conductivity, and remarkable Mg‐ion transfer number. The Mo₆S₈/Mg batteries assembled with this gel polymer electrolyte not only work well at wide temperature range (?20 to 60 °C) but also display unprecedented improvements in safety issues without suffering from internal short‐circuit failure even after a cutting test. This in situ crosslinking approach toward exploiting the Mg‐polymer electrolyte provides a promising strategy for achieving large‐scale application of Mg‐metal batteries.     

Room‐Temperature Mechanical Properties of V20Nb20Mo20Ta20W20 High‐Entropy Alloy

Refractory high‐entropy alloys (HEAs) have shown promising high temperature strengths, while their mechanical behaviors at room temperature are rarely reported. In this work, the room‐temperature mechanical properties of V₂₀Nb₂₀Mo₂₀Ta₂₀W₂₀ refractory HEA under various different loading modes including tension, compression, bending, shear loading, and microhardness are investigated. The results show that this alloy exhibits very high compressive strength but quite low strengths under tension, bending, and shear loading, similar to the conventional brittle materials. However, pronounced plasticity and slip bands are observed in compression samples, and no indentation cracking is observed in low‐load microhardness tests, which indicate the potential ability of plastic deformation in this refractory HEA. The present work suggests that the microstructure or composition of this HEA should be carefully tailored before its practical usage to suppress its large tendency for cracking and eventually improve its ductility and strength under tension.

     

Macro‐ and Nanomechanical Properties and Strain Rate Sensitivity of Accumulative Roll Bonded and Equal Channel Angular Pressed Ultrafine‐Grained Materials

Several processes of severe plastic deformation are suitable for the production of materials with ultrafine‐grained microstructures which are known to exhibit high strength and often good ductility as well as strain rate sensitive behavior. The most promising ones are equal channel angular pressing (ECAP) for bulk material and accumulative roll bonding (ARB) for the production of sheet material. In order to evaluate the influence of the process on these mechanical properties and the strain rate sensitivity, tensile tests, and nanoindentation tests were performed on material produced up to similar effective plastic strains of ε_ARB = 6.4 and ε_ECAP = 6.3. It could be shown that the macroscopic strength is slightly higher for ARB than for ECAP material and vice versa in nanoindentation. Independent of the testing method, the strain rate sensitivities and activation volumes are similar for both materials. Thus, both processes performed up to similar effective plastic strains lead to comparable improvements in the mechanical properties. Additionally it could be shown, that this comparison allows the identification of the dominant deformation mechanism which is responsible for the observed strain rate sensitivity.     

Conjuncted Pyro‐Piezoelectric Effect for Self‐Powered Simultaneous Temperature and Pressure Sensing

Ferroelectric materials use both the pyroelectric effect and piezoelectric effect for energy conversion. A ferroelectric BaTiO₃‐based pyro‐piezoelectric sensor system is demonstrated to detect temperature and pressure simultaneously. The voltage signal of the device is found to enhance with increasing temperature difference with a sensitivity of about 0.048 V °C^?1 and with applied pressure with a sensitivity of about 0.044 V kPa^?1. Moreover, no interference appears in the output voltage signals when piezoelectricity and pyroelectricity are conjuncted in the device. A novel 4 × 4 array sensor system is developed to sense real‐time temperature and pressure variations induced by a finger. This system has potential applications in machine intelligence and man–machine interaction.     

Interfacial Engineering Coupled Valence Tuning of MoO3 Cathode for High‐Capacity and High‐Rate Fiber‐Shaped Zinc‐Ion Batteries

Aqueous Zn‐ion batteries (ZIBs) have garnered the researchers' spotlight owing to its high safety, cost effectiveness, and high theoretical capacity of Zn anode. However, the availability of cathode materials for Zn ions storage is limited. With unique layered structure along the [010] direction, α‐MoO₃ holds great promise as a cathode material for ZIBs, but its intrinsically poor conductivity severely restricts the capacity and rate capability. To circumvent this issue, an efficient surface engineering strategy is proposed to significantly improve the electric conductivity, Zn ion diffusion rate, and cycling stability of the MoO₃ cathode for ZIBs, thus drastically promoting its electrochemical properties. With the synergetic effect of Al₂O₃ coating and phosphating process, the constructed Zn//P‐MoO_3?x@Al₂O₃ battery delivers impressive capacity of 257.7 mAh g^?1 at 1 A g^?1 and superior rate capability (57% capacity retention at 20 A g^?1), dramatically surpassing the pristine Zn//MoO₃ battery (115.8 mAh g^?1; 19.7%). More importantly, capitalized on polyvinyl alcohol gel electrolyte, an admirable capacity (19.2 mAh cm^?3) as well as favorable energy density (14.4 mWh cm^?3; 240 Wh kg^?1) are both achieved by the fiber‐shaped quasi‐solid‐state ZIB. This work may be a great motivation for further research on molybdenum or other layered structure materials for high‐performance ZIBs.     

Introduction of Planar High Pressure Torsion (P‐HPT) for Fabrication of Nanostructured Sheets

A new severe plastic deformation process based on conventional high pressure torsion is introduced. The process, called planar high pressure torsion (P‐HPT), is capable of inducing large shear strains into materials with planar geometries, such as sheets or strips and can basically be implemented on every standard HPT machine. The principles of this technique will be presented and accompanied by a case‐study, where P‐HPT will be applied on a sheet of pure copper with dimensions of 220 × 110 mm² and a thickness of 0.75 mm. For comparison, the material is deformed by conventional high pressure torsion using standard specimens with a diameter of 8 mm as well. It will be shown that the mechanical properties and microstructure obtained by P‐HPT correspond well to conventional high pressure torsion results.

     

Effect of electrolytic hydrogenation on the process of cutting of carbon steels

We study the effects of preliminary electrolytic hydrogenation of 20 and U8 carbon steels and a cutting tool on some parameters of the process of orthogonal cutting. The power consumption observed in the process of cutting of 20 and U8 steels (the forceP _z ) decreases in the presence of hydrogen. This effect is maximum if we hydrogenate the blanks. Hydrogen also decreases the bulk characteristics of the process of deformation of steel (surface roughnessR _a and chip shrinkagek) and localizes the cutting zone. Its influence on the strain hardening of materials in the cutting zone is ambiguous. Thus, for 20 steel, cold-hardening is intensified but, for U8 steel, becomes weaker. We analyze the regularities of the behavior of these parameters from the viewpoint of the influence of hydrogen on the deformation and fracture processes in steels. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 4, pp. 139–144, July–August, 1997.     

Hybrid PbS Quantum‐Dot‐in‐Perovskite for High‐Efficiency Perovskite Solar Cell

In this study, a facile and effective approach to synthesize high‐quality perovskite‐quantum dots (QDs) hybrid film is demonstrated, which dramatically improves the photovoltaic performance of a perovskite solar cell (PSC). Adding PbS QDs into CH₃NH₃PbI₃ (MAPbI₃) precursor to form a QD‐in‐perovskite structure is found to be beneficial for the crystallization of perovskite, revealed by enlarged grain size, reduced fragmentized grains, enhanced characteristic peak intensity, and large percentage of (220) plane in X‐ray diffraction patterns. The hybrid film also shows higher carrier mobility, as evidenced by Hall Effect measurement. By taking all these advantages, the PSC based on MAPbI₃‐PbS hybrid film leads to an improvement in power conversion efficiency by 14% compared to that based on pure perovskite, primarily ascribed to higher current density and fill factor (FF). Ultimately, an efficiency reaching up to 18.6% and a FF of over ≈0.77 are achieved based on the PSC with hybrid film. Such a simple hybridizing technique opens up a promising method to improve the performance of PSCs, and has strong potential to be applied to prepare other hybrid composite materials.     

Reverse Saturable Absorption Induced by Phonon‐Assisted Anti‐Stokes Processes

In materials showing reverse saturable absorption (RSA), optical transmittance decreases at intense laser irradiation. One approach to application of these materials is to protect the sensors or human eyes from laser damage. To date, research has mainly concentrated on thin films and suspensions of graphite and its nanostructure (including nanotubes, graphene, and graphene oxides), which are mainly used as an optical limiter for nanosecond laser pulses. Moreover, thin individual pieces of semiconductor usually exhibit increased transmittance due to saturable absorption when the laser energy (E_laser) is higher than the band gap (E_B). Here, it is shown that indirect gap semiconductor WSe₂ exhibits high RSA on exposure to a femtosecond laser under E_laser > E_B near band gap excitation, which is attributed to the longitudinal optical phonon‐assisted anti‐Stokes transition by the annihilation of phonons and the absorption of photons. An optical limiting threshold (≈21.6 mJ cm^?2) lower than those reported for other optical‐limiting materials currently for femtosecond laser at 800 nm is observed.     

Space‐Confined Growth of Individual Wide Bandgap Single Crystal CsPbCl3 Microplatelet for Near‐Ultraviolet Photodetection

Perovskite photodetectors (PDs) with tunable detection wavelength have attracted extensive attention due to the potential application in the field of imaging, machine vision, and artificial intelligence. Most of the perovskite PDs focus on I‐ or Br‐based materials due to their easy preparation techniques. However, their main photodetection capacity is situated in the visible region because of their narrower bandgap. Cl‐based wide bandgap perovskites, such as CsPbCl₃, are scarcely reported because of the bad film quality of the spin‐coated Cl‐based perovskite, due to the poor solubility of the precursor. Therefore, ultraviolet detection using high‐quality full inorganic perovskite films, especially with high thermal stability of materials and devices, is still a big challenge. In this work, high‐quality single crystal CsPbCl₃ microplatelets (MPs) synthesized by a simple space‐confined growth method at low temperature for near‐ultraviolet (NUV) PDs are reported. The single CsPbCl₃ MP PDs demonstrate a decent response to NUV light with a high on/off ratio of 5.6 × 10³ and a responsivity of 0.45 A W^?1 at 5 V. In addition, the dark current is as low as pA level, leading to detectivity up to 10¹¹ Jones. Moreover, PDs possess good stability and repeatability.     

Impact of Al and Cr alloying in TiN-based PVD coatings on cutting performance during machining of hard to cut materials

The microstructure and electronic structure of nanodispersed (Al₆₇Ti₃₃N) and (Ti₁₀Al₇₀Cr₂₀N) PVD coatings were investigated by high-resolution transmission electron microscopy (HRTEM) and electron spectroscopy techniques: X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS). The grain size measured by HRTEM was 5-20 nm for Al₆₇Ti₃₃N and TiAlCrN type coatings, correspondingly. The spinodal decomposition of Al supersaturated nitrides under its deposition was found. Chromium increases the metastable solubility of h-AlN in c-Ti_1 − xAl_xN. The lifetime of the cutting tools with Al-rich coatings has been evaluated under ball nose end milling of hardened tool steel H13 (HRC 50-52) and aerospace materials. TiAlCrN coatings are preferable for steel machining, and AlTiN coatings are better for aerospace material processing. It was found that AlTiN coating has lower hardness but higher plasticity and improved impact fatigue fracture resistance. The TiAlCrN coating has much better hot hardness and oxidation stability at high temperatures, but it is stiffer than AlTiN.