Effect of laser quenching and subsequent heat treatment on the structure and wear resistance of a cemented steel 20KhN3A

The martensite-austenite structures that are formed under the action of continuous laser irradiation in the 20KhN3A steel subjected to various regimes of cementation have been studied by metallography, electron microscopy, and X-ray diffraction. It has been established that a decrease in the amount of retained austenite in the laser-quenched structures from 40–90 to 5–35 vol % resulted from cold treatment at ?196°C exerts only a small (within 10%) effect on the abrasive wear resistance of the cemented steel; the effect is negative upon microcutting and positive upon microscratching. An increase in the carbon concentration from 0.8 to 1.2 wt % in the martensite-austenite structures that are formed in the cemented steel under the action of laser irradiation and upon cold treatment leads to changes in the abrasive wear resistance by no more than 10–13%. The presence of 20–40 vol % metastable retained austenite retards the decrease in the abrasive wear resistance of the quenched steel upon subsequent low-temperature tempering. It has been shown that the laser quenching and additional cold treatment positively affect the resistance of rolling bearing units of drill bits to contact-fatigue fracture.     

Role of the strengthening phases in abrasive wear resistance of laser-clad NiCrBSi coatings

The influence of the strengthening phases on the tribological characteristics (wear intensity, specific work of wear, coefficient of friction) and the wear mechanisms in two-body abrasion tests with abrasives of different hardnesses (corundum Al₂O₃, ~2000 HV and silicon carbide SiC, ~3000 HV) has been investigated for PG-SR2 (Cr₂₃C₆, 1000–1150 HV), PG-10N-01 (Cr₇C₃, 1650–1800 HV; CrB, 1950–2400 HV), and 75% PG-SR2 + 25% TiC (TiC, 2500–2900 HV; (Cr,Ni)₂₃(C,B)₆ and (Ti,Cr)(C,B), ~2000 HV) coatings. The dominant role of the strengthening phases (compared with the role of the metal matrix) in the abrasive wear resistance of laser-clad NiCrBSi coatings has been estimated. Different wear mechanisms have been identified and, accordingly, different levels of coatings wear resistance have been achieved depending on the ratio between the hardness of the strengthening phases (carbides, borides, carboborides) and abrasive particles.     

Features of electromagnetic methods for testing the wear resistance of medium-carbon structural steel subjected to laser or bulk hardening and tempering

Features of applying attachable eddy-current transducers of two types (with a flat end surface and a protruding ferrite rod core with localities 5–6 and 3–4 mm in diameter, respectively) for testing the structural state, hardness, and abrasive wear resistance of structural steel 45X (0.45 mass % C and 0.85% Cr), which was hardened under the action of continuous laser radiation, have been studied. The feasibilities of the eddy-current and coercimetric techniques for evaluating the wear resistance of a medium-carbon steel subjected to laser or bulk hardening and tempering in the temperature range 75–600°C have been studied.     

Combination of thresholding and fitting methods for measuring nanoparticle sizes and size distributions in (S)TEM

The practical need for a simple and reliable tool for routine size analysis of nanoparticles with diameters down to a few nm embedded in a polymer matrix motivated the development of a new approach. The idea underlying the method proposed in this work is to combine intensity thresholding and contrast fitting procedures in the same software for particle recognition and measurements of sizes and size distributions of nanoparticles in transmission and scanning transmission electron microscopy images. Particle recognition in images is performed in an interactive process of manual setting the numerical threshold level after image preprocessing. We show that fitting the calculated gray level distribution to the real images is able to provide a maximum accuracy in measurements of the particle diameters in contrast to thresholding approaches. The fitting procedure is applied in the vicinity of nanoparticle images with the mass‐thickness, diffraction, and chemical contrast. The grayscale function associated to the nanoparticle thickness is described using polynomial with degree ? 2 and undetermined coefficients. The program for particle detection and size measurement— An alyzer of Na noparticles ( AnNa )—has been written and is described here. It was successfully tested on systems containing Ag nanoparticles grown and stabilized in aqueous solutions of different polymers for biomedical use and is available from the authors.     

Possibilities of Nondestructive Testing of Physico-Mechanical Characteristics of Hypereutectoid Carbon Steels with the Structures of Isothermal Austenite Decomposition

The possibilities of estimating the hardness, the wear resistance under abrasive action and sliding friction, the impact strength, and the internal stresses of the U9 steel (with 0.94% of carbon) with the initial fine-lamellar pearlite structure annealed at 650°C during 2–600 min on the basis of magnetic and electrical characteristics, readings of an eddy-current instrument, and parameters of electromagnetic-acoustic conversion are studied. A comparative analysis of the magnetic, electromagnetic, strength, and tribological characteristics of the U10 and U15 hypereutectoid steels (with 1% and 1.53% of carbon, respectively) subjected both to isothermal treatment at 330–650°C (with formation of pearlite and bainite structures) and to additional short-time annealing at 650°C is carried out.     

Ferroelectricity in Polar Polymer‐Based FETs: A Hysteresis Analysis

There is an increasing number of reports on polar polymer‐based ferroelectric field effect transistors (FeFETs), where the hysteresis of the drain current–gate voltage (I_d–V_g) curve is investigated as the result of the ferroelectric polarization effect. However, separating ferroelectric effect from many of the factors (such as charge injection/trapping and the presence of mobile ions in the polymer) that confound interpretation is still confusing and controversial. This work presents a methodology to reliably identify the confounding factors which obscure the polarization effect in FeFETs. Careful observation of the I_d–V_g curves, as well as monitoring the I_d–V_g hysteresis and flat band voltage shift as a function of temperature and sweep frequency, identifies the dominant mechanism. This methodology is demonstrated by using 15 nm thick high glass transition temperature polar polymer‐based FeFETs. In these devices, room temperature hysteresis is largely a consequence of charge trapping and mobile ions, while ferroelectric polarization is observed at elevated temperatures. This methodology can be used to unambiguously prove the effect of ferroelectric polarization in FeFETs.     

Strong Photoacoustic Signal Enhancement by Coating Gold Nanoparticles with Melanin for Biomedical Imaging

Photoacoustics is a powerful biomedical imaging and detection technique, because it is a noninvasive, nonionizing, and low‐cost method facilitating deep tissue penetration. However, suitable contrast agents need to be developed to increase the contrast for in vivo imaging. Gold nanoparticles are often discussed as potential sonophores due to their large absorption cross‐section and their tunable plasmon resonance. However, disadvantages such as toxicity and low photoacoustic efficiency in the tissue transparency window prevail, preventing their clinical application. As a result, there remains a strong need to develop colloidal photoacoustic contrast agents which absorb in the tissue transparency window, exhibit high photoacoustic signal, and are biocompatible. Here, a facile synthetic approach is presented to produce melanin shells around various gold nanoparticle geometries, from spheres to stars and rods. These hybrid particles show excellent dispersability, better biocompatibility, and augmented photoacoustic responses over the pure melanin or pristine gold particles, with a rod‐shape geometry leading to the highest performance. These experimental results are corroborated using numerical calculations and explain the improved photoacoustic performance with a thermal confinement effect. The applicability of melanin coated gold nanorods as gastrointestinal imaging probes in mouse intestine is showcased.     

Propagation of Magnetostatic Surface Waves in a Dissipative Ferrite Plate

In the geometry of a plane-parallel in-plane magnetized ferrite plate with dissipation, the dispersion of forward and backward magnetostatic surface waves propagating in an arbitrary direction relative to the field has been investigated. Dispersion curves as functions of the imaginary and real parts of the complex wave number has been constructed. The group velocity of both wave propagation and increase of wave attenuation have been considered. The frequency range of the experimentally observable waves has been estimated at a specified level of sensitivity of the measuring instruments.     

Estimation and optimization of maximum deviations in dynamical control system under complexly shaped disturbances

The game problem of designing dynamical systems that are optimal with respect to extreme deviations subject to external actions is solved. The maximum (over time) of the absolute value of the function characterizing the quality of motion is used as the measure of deviation. A method for describing the set of possible external actions as a set of outputs of an additional dynamic block??a reference input generator (RIG) is proposed. The chief application domain of the results is the design of servomechanisms with the minimal extreme tracking error deviation. An example of designing a hydraulic servo drive is discussed.