Different Stages Of Heat Treatment Research Articles

Структура сплавов для постоянных магнитов типа (Sm,Zr)(Co,Cu,Fe)z и механизм формирования высококоэрцитивного состояния

Owing to the high temperature stability of hysteretic characteristics and corrosion resistance under external actions, (Sm,Zr)(Co,Cu,Fe)z-based magnets are widely used in devices operating at high temperatures, most critical constructions of aerospace engineering and defense technology, and in traction electric motors for transport engineering. A number of modern research methods are used to study in detail the structure and phase composition of the (Sm,Zr)(Co,Cu,Fe)z alloys with z = 5.5 – 7.0 in as-cast state and after heat treatment, which includes the solid solution treatment at 1150 – 1180 °С for 5 h, subsequent water quenching, isothermal aging at 800 °С for 20 h, and cooling (stepped aging) from 800 to 400 °С at an average cooling rate of 100 °С/h. The results obtained allowed us to suggest the schematic diagram of grain-boundary constituent transformation at different stages of heat treatment of (Sm,Zr)(Co,Cu,Fe)z permanent magnets prepared by powder metallurgy. The formation mechanism of high-coercivity state of (Sm,Zr)(Co,Cu,Fe)z permanent magnets in the course of complete heat treatment cycle is given as the sequence of phase transformations accompanied by redistribution of a number of alloy components.

Nanostructural dimension and oxygen vacancy synergistically induced photoactivity across high surface area monodispersed AuNPs/ZnO nanorods heterojunction

Inhibiting the electron-hole recombination by adequate surface modification is a significant challenge for developing highly efficient photoanodes. This report envisions a structural synergism between a surface oxygen vacancy and metal/semiconductor contact area to significantly boost up the charge separation and injection efficiency of ZnO nanorods (NRs) in photoelectrochemical (PEC) performance. A three-dimensional photoanode is designed by vertically aligning the ZnO NRs and tuned their dimension by varying the annealing temperature and time followed by their decoration with AuNPs. Different stages of heat treatment created high oxygen vacancy, which is a key factor in tailoring the PEC activity. The ZnO NRs-A offered 75.5% average contact area for hosting the 16 nm diameter AuNPs, whereas, the ZnO NRs-B delivered 47.8%. The ZnO NRs-B with high oxygen defects exhibits a similar photoactivity shown by large dimensional ZnO NRs-A. After decorating with AuNPs, the AuNPs/ZnO NRs-A delivered ~3-fold increases in photocurrent than AuNPs/ZnO NRs-B, suggesting the photoactivity enhancement is mainly contributed from the effective charge transfer across the heterojunction between the electron mediating AuNPs and ZnO NRs, which reduces the electron-hole pair recombination. Besides, having higher oxygen vacancies, the AuNPs/ZnO NRs-B exhibited substantial photoactivity similar with AuNPs/ZnO NRs-A. The comparison of the incident photon-to-current and the applied bias photon-to-current efficiencies of the AuNPs/ZnO NRs with the reported photoanodes further authenticated the enhanced PEC performance of AuNPs/ZnO NRs. This work opens up a potential approach to metal-semiconductor heterojunction design by reduction of electron-hole recombination in PEC water splitting and solar energy conversion applications. A three-dimensional (3-D) photoanode was designed based on vertically aligned ZnO nanorods followed by their homogeneous decoration with AuNPs and their defects versus metal/semiconductor heterojunction induced photoelectrochemical behavior was investigated. • The PEC performance of ZnO nanorods was improved by the decoration of AuNPs nanocomposite on SrTiO 3 substrate. • Different approaches were employed for tuning the dimension of ZnO NRs by varying the annealing temperature and time. • Decoration of AuNPs enhances the oxygen vacancy of ZnO NRs and hence the electron-hole pair recombination was evaded . • The ZnO NRs-B exhibited oxygen defects induced PEC performance than ZnO NRs-A in visible light region. • The AuNPs/ZnO NRs-A delivered plasmonic and metal/semiconductor contact area induced PEC performance .

Analysis of heat treatment parameters on the properties of selected tool steels M390 and M398 produced with powder metallurgy

This paper deals with the comparison of two tool steels M390 and M398 produced by powder metallurgy of the MICROCLEAN type. The primary use of steel is in the plastics industry to produce screws for injection moulding machines. The main purpose of the paper is to analyze the hardness after different stages of heat treatment. The first part of the article evaluates the hardness of steels after hardening, which was performed using a hardening dilatometer DIL805A. A total of 8 different controlled cooling measurements were performed, for both types of powdered tool steels, from a maximum rate of 100 °C/s to a minimum of 0.01 ° C/s. Based on the results of the first set of samples from the hardening dilatometer, the optimal cooling time is evaluated to achieve the highest hardness of both materials. This rate was used to heat treat a second set of samples that had undergone a quenching process from which a selected group was quenched to -78 °C. Freezing was performed to reduce the amount of residual austenite. Before measuring the hardness, the samples were tempered at temperatures of 200, 400, 600 °C for 2x2h. The measured hardness values were then compared with data from the manufacturer BÖHLER.

Magnetic Properties and Domain Structure of Alloy Sm(Co, Fe, Cu, Zr)7.5 in Different Stages of Heat Treatment

Magnetic Properties and Domain Structure of Alloy Sm(Co, Fe, Cu, Zr)7.5 in Different Stages of Heat Treatment

Comparative analysis of long noncoding RNAs in angiosperms and characterization of long noncoding RNAs in response to heat stress in Chinese cabbage

Long noncoding RNAs (lncRNAs) are widely present in different species and play critical roles in response to abiotic stresses. However, the functions of lncRNAs in Chinese cabbage under heat stress remain unknown. Here, we first conducted a global comparative analysis of 247,242 lncRNAs among 37 species. The results indicated that lncRNAs were poorly conserved among different species, and only 960 lncRNAs were homologous to 524 miRNA precursors. We then carried out lncRNA sequencing for a genome-wide analysis of lncRNAs and their target genes in Chinese cabbage at different stages of heat treatment. In total, 18,253 lncRNAs were identified, of which 1229 differentially expressed (DE) lncRNAs were characterized as being heat-responsive. The ceRNA network revealed that 38 lncRNAs, 16 miRNAs, and 167 mRNAs were involved in the heat response in Chinese cabbage. Combined analysis of the cis- and trans-regulated genes indicated that the targets of DE lncRNAs were significantly enriched in the “protein processing in endoplasmic reticulum” and “plant hormone signal transduction” pathways. Furthermore, the majority of HSP and PYL genes involved in these two pathways exhibited similar expression patterns and responded to heat stress rapidly. Based on the networks of DE lncRNA-mRNAs, 29 and 22 lncRNAs were found to interact with HSP and PYL genes, respectively. Finally, the expression of several critical lncRNAs and their targets was verified by qRT-PCR. Overall, we conducted a comparative analysis of lncRNAs among 37 species and performed a comprehensive analysis of lncRNAs in Chinese cabbage. Our findings expand the knowledge of lncRNAs involved in the heat stress response in Chinese cabbage, and the identified lncRNAs provide an abundance of resources for future comparative and functional studies.

Phase transformations of the nanostructured iron-platinum system upon heating

Joint reduction with hydrazine from aqueous solutions of precursors produced nanostructured powders of the Fe – Pt system in three characteristic phase regions. The samples were subjected to heat treatment in the range up to 800 ° C and characterized at all stages by X-ray diffraction and high-resolution electron microscopy; the elemental composition of the samples was refined by the method of optical emission spectroscopy with inductively coupled plasma. In the initially obtained samples, only a part of the substance is detected by diffraction-the largest, platinum-rich crystals with dimensions of about 10 nm (established from TEM images and broadening of diffraction lines). The fcc-type cubic lattice parameters and the composition of the observed crystals were estimated from the distances between the regular bands in TEM images, identified with atomic rows, based on the composition dependence of the bulk characteristics of mixed iron-platinum phases (according to ICDD databases). In the course of heating, the processes of phase transformation are traced in detail, the parameters of the resulting crystal structures of intermetallic compounds are fixed, and the mechanisms of these transformations are discussed. Based on the measured lattice parameters, the thermal expansion coefficients of some mixed phases are calculated and the phase compositions are estimated at different stages of heat treatment.

Structure of Alloys for (Sm,Zr)(Co,Cu,Fe)z Permanent Magnets: II. Composition, Magnetization Reversal, and Magnetic Hardening of Main Structural Components.

Experimental series of alloys for (Sm,Zr)(Co,Cu,Fe)Z permanent magnets are presented in the concentration ranges that provide wide variations of (4f)/(4d)/(3d) ratios of comprising elements. Optical metallographic analysis, observation of the surface domain structure upon magnetization reversal (Kerr effect), electron microprobe analysis, and measuring the major hysteresis loops of samples at different stages of heat treatment are used to study processes related to the development of the highly coercive state of these samples. It was found that the volume fractions of two main structural components A and B, which comprise 90% of the total sample volume, rigorously control the coercivity at all stages of thermal aging. At the same time, structural components A and B themselves in samples being in the high-coercivity state differ qualitatively and quantitatively in the chemical composition, domain structure and its development in external magnetic fields and, therefore, are characterized by different morphologies of the phases comprising the structural components. Two stages of phase transformations in the sample structure are observed. During isothermal annealing, the cellular structure develops within the B component, whereas, during stepwise (slow) cooling or quenching from the isothermal aging temperature to 400 °C, a phase structure evolves within both the cell boundaries in B and the structural component A. The degree of completion of the phase transformations within micro- and nano-volumes of the components determines the ultimate hysteretic characteristics of the material.

Microstructure, magnetic and mechanical properties of Fe–28Cr–15Co–1Si cast magnets containing Mo and Ti additives

In this study, the development of Fe–28Cr–15Co–1Si–xM, M = Ti and Mo, x = 1, 2, 3 (wt.%) cast permanent magnets by a thermomagnetic treatment was investigated. The alloys were melted in a vacuum induction furnace (VIM) using pure raw materials and then cast in alumina tubes. Structural, mechanical, and magnetic properties of the alloys were evaluated at different stages of heat treatment. Specimens in the solution annealed condition, showed a coarse grain with a body-centered cubic (BCC) structure (α phase), which decomposes into two α1 and α2 phases by a spinodal transformation during the thermomagnetic treatment. By addition of Mo to Fe–28Cr–15Co–1Si alloy, the strain energy of decomposition increases by concentrating in the α2 phase. This results in a difference in the lattice parameter between α1 and α2 phases and an improvement in the magnetic properties of the alloy. The presence of Ti in the alloys raised the amount of α1 phase, which eventuates in the suppression of the unwanted σ or γ phases in the annealed state. Ti and Mo additions also affect the development of shape anisotropy in the ferromagnetic α1 particles, which in turn improves the magnetic properties of the alloys. The best magnetic properties turn out to be in Fe–28Cr–15Co–1Si–3Mo, and Fe–28Cr–15Co–1Si–2 Ti alloys: Br = 0.98 T (9.8 kg), Hc = 67.66 kA/m (0.85 kOe) and (BH)max = 41.27 kJ/m3 (5.2 MGOe), and Br = 0.93 T (9.3 kg), Hc = 65.27 kA/m (0.82 kOe) and (BH)max = 38.09 kJ/m3 (4.8 MGOe), respectively. The hardness test results verified that in the Fe–Cr–Co-based alloys with spinodally decomposed structure, the internal stresses are more effectual than composition gradients on the alloy’s strength.

Influence of Heat Treatment Parameters on the Corrosion Resistance of Additively Manufactured Ti–6Al–4V Alloy

The corrosion resistance of a heat-treated Ti–6Al–4 V alloy fabricated using the additive manufacturing (AM) method was investigated through a series of electrochemical techniques, including potentiodynamic polarization, electrochemical impedance spectroscopy, and critical pitting temperature measurements, in an effort to improve the corrosion resistance of AM Ti–6Al–4 V subject to different stages of heat treatment. During this process, we reported that the corrosion resistance of the AM Ti–6Al–4 V alloy significantly reduced, which we attributed to both preexisting α′ phases and newly emerging precipitates. After heat treatment at 650 °C and 750 °C, the corrosion resistance of AM Ti–6Al–4 V worsened further after cooling compared to the original as-received sample because of the existence of the α′ phase (without decomposition) and precipitates. However, at 850 °C and 1000 °C, the heat-treated samples demonstrated much better corrosion resistance compared to the as-received sample, possibly because of the complete transformation of the α′ phase into the α phase and the evolution of a β phase. Based on these experimental results, we believe that adequate heat treatments such as rapid cooling illustrate added advantages for the enhanced corrosion resistance of AM Ti–6Al–4 V alloys.

Model of Fractal Particles of Hydrated Zirconium Dioxide, Based on Small-Angle Neutron Scattering Data

The parameters of the mesostructure of amorphous zirconium dioxide and their evolution at different stages of heat treatment are determined by small-angle neutron scattering. Particles of amorphous zirconium dioxide, which form mass fractals with the dimension Dv = 2.21, are rearranged into surface fractals with a surface dimension of Ds = 2.52 upon annealing at a temperature of 400°C or higher. In the resulting system, a shell with a fractal structure is formed over a dense core (a cluster of nanoparticles of zirconium dioxide with a constant density). Transformation of the fractal system from a mass fractal into a surface one is characterized by the appearance of a core, and its growth is due to the crystallization of hydrated zirconia particles at high temperatures. A model for the formation of a fractal particle, implying the existence of a core–shell surface fractal system, is proposed. The characteristic radius of ZrO2 nanoparticles increases from 14 to 200 A with an increase in the annealing temperature from 400 to 600°C.

STUDY OF THE MICROSTRUCTURE OF MARTENSITE-BAINITE STEELS AND NICKEL ALLOYS WHEN MODELING HEAT TREATMENT MODES USING A DILATOMETRIC METHOD

We present the results obtained using the equipment available at the Center for collective use “Composition, structure, properties of structural and functional alloys” NRC “Kurchatov Institute” — CRISM “Prometey”: DIL 805A/D (TA Instruments) and DIL 402C (Netzsch) dilatometers. Dilatometric analysis which provides determination of the temperature coefficient of linear expansion and the temperature of phase transitions, as well as evaluation of the transformation kinetics, can also allow simulation of heat treatment modes to identify the size of the former austenitic grain using vacuum etching and conduct the research aimed at improving the technology of thermal and thermomechanical processing (TMO) of steels and alloys. The experiments were carried out both in vacuum and in dynamic helium atmosphere. The main methodological difficulties that we have faced with are described. For steels of martensite and martensite-bainite class (38KhMA, 38KhN3MFA, 20Kh3NMFA) conditions of vacuum etching in the chamber of the dilatometer are specified. The efficiency of the method for martensite-bainite steels in determination of the grain size compared to traditional methods of etching is deminstrated. The effect of thermodeformation parameters on the size of austenitic grain is estimated. When modeling the heat treatment modes by the dilatometric method, the microstructure of KhN55MVTs nickel alloy was also analyzed. Changes in the size and morphology of the grain structure at different stages of heat treatment are revealed. The obtained results were used to adjust the current modes of heat treatment and obtain a uniform fine-grained structure. The combined application of dilatometric and metallographic analyzes after vacuum etching of the material decreases the production costs attributed to obtaining the desired microstructure upon thermal and thermomechanical processing of the products and blanks.

The microstructure of Nb3Sn superconductors differing in the number of copper inserts at various stages of heat treatment

Superconducting materials with a high critical current density in magnetic fields up to 16 T at a temperature of 4.2 K are required to create magnetic systems of high-energy physics devices. We have studied the change of the microstructure of model samples of various designs with an internal tin source, differing in the number of copper separators (three, six and without them) at different stages of heat treatment. The formation of the following intermediate phases was studied: Cu3Sn, Cu6Sn5 and triple Cu-Sn-Nb phase after annealing at 370°C/100 h, by the use of scanning and transmission electron microscopy. The formation of the Nb6Sn5 phase on Nb filaments located close to the tin source and copper separators was studied after heat treatment at a temperature of 665°C from 10 minutes to 25 hours. The results of the analysis led us to understand the kinetics of the Nb3Sn and Nb6Sn5 formation in internal tin superconductors with an increased current-carrying capacity and a low level of hysteresis losses.

Electrolytic cell-free 57Co deposition for emission Mössbauer spectroscopy

We have developed a simple, inexpensive and efficient method for an electrochemical preparation of samples for emission Mössbauer spectroscopy (EMS) and Mössbauer sources. The proposed electrolytic deposition procedure does not require any special setup, not even an electrolytic cell. It utilizes solely an electrode with a droplet of electrolyte on its surface and the second electrode sunk into the droplet. Its performance is demonstrated using two examples, a metallic glass and a Cu stripe. We present a detailed description of the deposition procedure and resulting emission Mössbauer spectra for both samples. In the case of a Cu stripe, we have performed EMS measurements at different stages of heat-treatment, which are required for the production of Mössbauer sources with the copper matrix.

Precipitation behavior of strip cast Al–Mg–0.4Sc–0.15Zr alloy under single and multiple-stage aging processes

In this study the precipitation behavior of an Al–Mg–0.4Sc–0.15Zr alloy produced by strip casting (FLEXCAST) technology at Novelis is investigated. As-cast, as well as different cold rolled specimens, were heat treated in a single-stage aging process, and a double-stage aging process was examined. Conventional mechanical properties and microstructural measurements were performed on both the as-cast and processed materials. In addition, TEM studies were performed at different stages of heat treatment. The mechanical properties results show that peak aging at 300°C is dependent on the prior amount of cold rolling, hence the dominant effect is recovery especially at the short period of aging. The results also indicate that even at the relatively long time of aging, i.e. 200h, the structure is not dominated by the formation of precipitates. Observations indicate that only at a relatively high aging temperature, i.e. 450°C, substantial amounts of non-coherent precipitates are present in the microstructure.

Effect of Heat Treatment on Microstructure and Mechanical Properties of 2.25Cr–1Mo Steel

AbstractThe effect of heat treatment on microstructure and mechanical properties of a ferritic heat‐resistant steel, 2.25Cr–1Mo, was investigated. The characteristics of carbides, i.e., size, morphology, distribution, and composition, in different stages of heat treatment were examined by using transmission electron microscopy (TEM) and energy dispersive X‐ray (EDX). As the heat treatment proceeded from normalizing and tempering (NT, the delivery state), simulated post‐welding heat treatment (PWHT), to step cooling (SC), the carbides evolved from M3C, Mo2C to M7C3, M23C6. The uniformly dispersed carbides, e.g., Mo2C, M7C3, and M23C6, are responsible for the excellent mechanical properties and creep resistance of the steel. The result demonstrates that the coarsening of carbides deteriorates impact toughness and the morphology, crystal structure, and chemical composition of carbides are also important influencing factors.

Characterization of phase transformation behaviour and microstructural development of electroless Ni–B coating

Phase transformation behaviour of amorphous electroless Ni-B coating with a targeted composition of Ni-6wt% B is characterized in conjunction with microstructural development and hardness. Microscopic observations of the as-deposited coating display a novel microstructure which is already phase separated at multiple length scales. Spherical colonies of similar to 5 mu m consist of 2-3 mu m nodular regions which are surrounded by similar to 2-3 mu m region that contains fine bands ranging from 10 to 70 nm in width. The appearance of three crystalline phases in this binary system at different stages of heat treatment and the concomitant variation in hardness are shown to arise from nanoscale fluctuations in the as-deposited boron content from 4 to 8 wt%. High temperature annealing reveals continuous crystallization up to 430 degrees C, overlapping with the domain of B loss due to diffusion into the substrate. The implications of such a microstructure for optimal heat treatment procedures are discussed. (C) 2011 Elsevier B.V. All rights reserved.

General characteristics of chemical and structural transformations of polyvinyl alcohol fibre in conditions of high-temperature treatment

The role of phosphorus-nitrogen-containing pyrolytic additives in formation of polyunsaturated threedimensional structures in polyvinyl alcohol which stimulate coking in different stages of heat treatment is established. The possibility of obtaining unactivated carbon-fibre materials with high sorption activity from PVA fibre was demonstrated.

Comparison of the formation kinetics of silver nanoparticles of photo-thermo-refractive glass after ultraviolet and electron irradiation

We present experimental results on the formation of silver nanocrystals in photo-thermo-refractive glasses during heat treatment after ultraviolet and fast-electron irradiation. We compare the optical density spectrum of samples at different stages of heat treatment. We show that the difference in the formation kinetics of silver nanoparticles is determined by the spatial redistribution of silver ions during electron irradiation and the change in the chemical composition of near-surface layers of glass.

Thermal conductivity of carbon nanofiber mats

The anisotropic thermal conductivity of novel vapor grown carbon nanofiber (VGCNF) based paper-like mats was measured for increasing volume fraction and at different stages of heat-treatment. These nanofiber mats were prepared to exhibit high in-plane and low through-plane thermal conductivities with the goal of assessing their potential as 2-D heat spreaders. The in-plane thermal conductivity of the mats varied from 12 W/m-K to 157 W/m-K for volume fractions of 0.067 and 0.462, respectively, while the corresponding through-plane thermal conductivities were measured to be 0.428 W/m-K and 0.711 W/m-K. Heat treatment to temperatures above 3000 °C increased the through-plane thermal conductivity of the mats by an order of magnitude. However, the in-plane thermal conductivity, at best, was only seen to double. A model is proposed to describe the arrangement of nanofibers in the mats, and analytical expressions were used to estimate the thermal conductivity of an individual nanofiber using experimental results. Thermal conductivities of approximately 1400 W/m-K and 1600 W/m-K were calculated for individual VGCNFs heat treated to temperatures of around 1100 °C and above 3000 °C, respectively.

EXAFS and EPR studies of inclusion compounds of the trans-[Cu(en)2(H2O)2]2+ in cucurbit[8]uril

This work describes EXAFS and EPR studies of inclusion compounds of the trans-[Cu(en)2(H2O)2]2+ complex in the macrocyclic cavitand CB[8] at different stages of heat treatment in the hydrogen atmosphere in a temperature range of 200–330°C. The structure and composition of the nearest environment of copper atoms are characterized, and the interatomic distances and coordination numbers are determined. It is shown that the structure of the copper complex inside the cavitand CB[8] remains unchanged at the first stage of complex preparation and upon heating up to 280°C in hydrogen atmosphere. The copper environment corresponds to four nitrogen atoms and two oxygen atoms. Further temperature treatment at 330°C causes decomposition of the complex inside the cavitand without the formation of copper clusters.