Single Stage Heat Treatment Research Articles

A Novel Two-Stage Heat Treatment with Medium-Temperature Aging Influence on Microstructure, Al3(Sc, Zr) Nanoprecipitation, and Application Properties, Enhancing Selective Laser Melting of Al-Mg-Sc-Zr Alloy.

Al–Mg–Sc–Zr alloy fabricated through selective laser melting (SLM) is an additive manufacturing alloy with promising industrial potential. In this study, as-printed specimens were subjected to either single-stage or two-stage heat treatment processes to investigate the effect of temperature from room temperature to high temperature on the specimens’ tensile and fatigue properties to establish a reliable reference for aerospace applications. The tensile test results indicated that the heat treatment contributed to determine the properties of the nanoprecipitate Al3(Sc, Zr) with a strengthening phase, improving tensile strength. Moreover, the dynamics strain aging (DSA) effect vanished as temperature increased. It is noteworthy that the nanoprecipitation was distributed at the boundary of the melting pool after single-stage heat treatment with the highest tensile properties in all tests. In addition, the microstructure observed after the two-stage heat treatment indicated a melting pool interface decomposition, and the nanoprecipitation was homogeneously scattered over the Al matrix, increasing strength and further delaying fatigue crack transmission. Those features build a high-fatigue-resistance foundation. TEM analysis also confirmed the promotion of Sc thermal diffusion and an Al3(Sc, Zr) precipitation transformation mechanism under two-stage heat treatment, corresponding to aforementioned inferences. The SLM Al–Mg–Sc–Zr alloy with two-stage heat treatment brings about balance between tensile properties and fatigue resistance, providing new insight into additive manufacturing with Al alloys.

Physico-chemical properties and structural transformations in the synthesis of boroalumosilicate glass-crystal materials

The aim of this work is to study the areas of glass formation and metastable liquation of the pseudo-ternary system (MgO·Al2O3)-B2O3-SiO2, and study of the crystallization process of glasses of cordierite composition. The crystallization process of glasses of cordierite composition containing B2O3 by a single-stage heat treatment at 1000 oC and 1200 oC, the nature of crystallization, the thermal properties of glasses and glass crystalline materials of the system (MgO·Al2O3)-B2O3-SiO2 were studied. It revealed that during the isolation of a boron-containing solid solution, the residual glassy phase enriched with oxides of MgO and Al2O3, which lead to an increase in the thermal expansion coefficient of the glass phase. The research results provide possibility to synthesize glass-ceramics with certain thermophysical parameters by stopping further glass crystallization at the stage of formation of a certain amount and ratio of the required crystalline and glassy phases.

Characterization of Waste-Integrated Multi-hybrid Structure for Enhancing Corrosion Resistance of High-Carbon Steel

Due to their exceptional properties, low-cost high-carbon steels have long been extensively utilized in many industrial applications. However, their corrosion resistance is poor for many applications and requires further enhancement. Various methods have been developed to achieve this, but they suffer from some limitations. In the work presented herein, a single-stage heat treatment process was applied at low temperature and utilizing waste materials for comparison as new resources, being shown to be a cost-effective approach. In the framework of this study, a multi-hybrid coating structure was developed on the surface of high-carbon steel by applying a single-step heat treatment process and utilizing various waste materials, namely metallurgical slag, glass, and automotive shredder residue (ASR). The results reveal that not only was the process completed in a short time but significant enhancements in the corrosion resistance and hardness performance were achieved. Analyses were performed by high-resolution laser scanning confocal microscopy, electron probe microanalysis (EPMA), focused ion beam-scanning electron microscopy (FIB-SEM), and atomic force microscopy (AFM) in peak force quantitative nanomechanical (PF-QNM) mode. The electrochemical corrosion performance was tested using Tafel method. Both the Young’s modulus and corrosion resistance of the steels treated using the waste materials were improved compared with the base material. This approach opens a new perspective for utilizing waste materials to obtain environmentally sustainable products in a cost-effective fashion, thereby reducing reliance on new resources as well as disposal of waste materials in landfill.

BaBi2Ta2O9 based glass-ceramics: Influence of ZrO2 on crystallization kinetics, microstructure and dielectric properties

BaBi2Ta2O9 (BBT) based ferroelectric glass-ceramics (GCs) with different zirconium oxide (ZrO2) content used as nucleating agent are synthesized via glass melt-quenching technique followed by temperature controlled crystallization. The effect of ZrO2 as a nucleating agent on the crystallization mechanism, microstructure and dielectric properties of BBT based GCs has been studied for the first time. Crystallization kinetics studies facilitated successful controlled crystallization of ZrO2 doped BBT based GCs around the exothermic peak temperature using double stage and single-stage heat-treatments, which was otherwise difficult in the undoped glass. The dielectric constant increased while the loss and dissipation factors decreased with increase in zirconia content in the GCs. The dielectric properties obtained from single-stage and double-stage heat-treated GCs have been compared and correlated to the corresponding microstructures of the GCs. With 5 mol % ZrO2, dielectric constant of 181 with loss of 0.04 has been obtained for the sample fabricated by single-stage ceramization around the 2nd crystallization peak temperature.

Manipulation of slag separation properties from pig iron nuggets with flux additions to dried greenball mixture

ABSTRACTPig iron nugget process is one of the direct smelting processes developed as an alternative to the traditional blast furnace process. Throughout the process, slag-free pig iron nuggets, which have similar properties to the blast furnace pig iron and white cast iron, are produced by single-stage heat treatment of dried greenballs. During the process, slag separation from the metallized areas can be enhanced by adjustment of the slag’s chemical and physical properties. The objective of this research was to investigate the effects of flux addition rates (basic to acid ratio) to the dried greenball mixture on pig iron nugget production and slag separation. Thus, this study involved the heat treatment of six different greenball mixtures, which contained various amounts of limestone addition (basic to acid ratios, 0, 0.63, 1.02, 1.42, 1.85, and 2.29) utilizing a laboratory-scale resistance box furnace or simultaneous differential scanning calorimetry and thermalgravimetric analyzer. The samples produced by heating in the box furnace were analyzed for their morphological and chemical properties utilizing optical microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), macroscopic observations, iron titrations, and atomic absorption spectroscopy. It was determined that the highest percentage of iron yield in the nugget for the process and the highest distribution of iron in magnetic slag were obtained when utilizing the greenball mixture, which contained 7.5 wt% limestone as flux (basic to acid ratio of 1.42).

Study of electrical conductivity of Li2O-B2O3-SiO2-Li2SO4 glasses and glass-ceramics

Glasses and glass-ceramics have been synthesized in Li2O-B2O3-SiO2-Li2SO4 system using melt-quenching and single stage heat treatment. The electrical conductivity of both glass and glass-ceramic samples has been measured. The conductivity increases with Li2SO4 addition. The maximum ionic conductivity of 4.08×10−4S/cm at 523K has been found for the glass composition 40Li2O:30B2O3:15SiO2:15Li2SO4 and it has been found that conductivity of glass-ceramics is less compared to corresponding glass. The ionic nature of conductivity has been confirmed using transport number measurement. With Li2SO4 addition glass transition temperature and density decreases indicating weakening of the glass structure and expansion of the network, leading to increase in conductivity. The phase identification in glass-ceramics has been done using XRD technique. Composition analysis has been done using SEM/EDS.

Influence of electron-hole recombination on optical properties of boro-silicate glasses containing CdS quantum dots

Semiconductor (CdS) quantum dots were grown in a glass matrix (SiO2-B2O3-ZnO-Na2O-K2O) by controlled heat treatment. Growth of CdS quantum dots were confirmed by optical absorption (UV–vis), photoluminescence (PL), micro-Raman spectroscopy, X-ray diffraction (XRD) and High resolution transmission electron microscopy (HRTEM). The structural modification occur in glass matrix were studied with Fourier transform infrared spectroscopy (FTIR). Clusters formation due to heat treatment was studied by field emission gun scanning electron microscopy (FEG-SEM). The observed experimental data shows that the CdS QDs size is very well controlled by single stage heat treatment. Size dependent blue shift in optical energy band gap and blue energy shift in PL intensity was observed with annealing time. The overall study of these glasses suggests these glasses are useful as an optical filters.

Effect of Single and Duplex Stage Heat Treatment on the Microstructure and Mechanical Properties of Cast Ti–6Al–4V Alloy

The effect of single and duplex stage heat treatment on the microstructure and mechanical properties of cast Ti–6Al–4V alloy was studied. The single stage heat treatment (SSHT) involved solution annealing at 935 °C for 10 min followed by water quenching, while the duplex stage heat treatment (DSHT) involved solution annealing at 935 °C for 10 min, furnace cooling to 600 and 700 °C, followed by isothermal holding for 30 min and subsequent water quenching. The properties characterization was conducted using microstructure investigation along with tensile, hardness, and Charpy impact tests. The impact fracture surfaces were observed using Scanning Electron Microscope. After SSHT, an increase in the tensile strength and hardness at the expense of the tensile elongation and impact toughness was recorded as compared with the as-cast alloy. This is attributed to the formation of a brittle α′ martensite phase in the microstructure after quenching from 935 °C. On the other hand, DSHT enhances the percent elongation and impact toughness over the as-cast alloy and SSHT. The formation of α′ martensite-free microstructure as well as controlling the composition of the different microstructural constituents during DSHT optimizes the mechanical properties.

The Mechanical Properties of AA2024 as Function of the Interrupted Ageing Conditions

A comprehensive and systematic study using hardness, tensile test and Kahn tear test was undertaken to follow property development during the recently promoted interrupted ageing treatment. In contrast to the reported claims hardness remains lower than that of single stage heat treatment. Toughness does not improve substantially and deteriorates further as re-ageing time is prolonged. For most cases, the effect of interrupted ageing could not produce a simultaneous improvement in mechanical properties. TEM observations indicate the size and distribution co-existing S” and S phases upon re-ageing depend on interrupted condition.

On the development of two characteristically different crystal morphology in SiO2–MgO–Al2O3–K2O–B2O3–F glass-ceramic system

The present work demonstrates how crystals with two different characteristic morphologies can be formed in SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass-ceramic system by adopting two sets of heat treatment experiments. In our study, single stage heat treatment experiments were performed at 1,000 degrees C for varying holding time of 8-24 h with 4 h time interval and as a function of temperature in the range of 1,000-1,120 degrees C with 40 degrees C temperature interval. The constant heating rate of 10 degrees C/min was employed for both sets of experiments. The microstructural changes were investigated using Fourier transformed infrared spectroscopy (FT-IR), SEM-EDS and XRD. For temperature variation batches, the microstructure is characterized by interlocked, randomly oriented mica plates ('house-of-cards' morphology). An important and new observation of complex crystal morphology is made in the samples heat treated at 1,000 degrees C for varying holding times. Such morphology appears to be the results of composite spherulitic-dendritic like growth of mica rods radiating from a central nucleus. The possible mechanism for such characteristic crystal growth morphology is discussed with reference to a nucleation-growth kinetics based model. The activation energy for crystal nucleation and Avrami index are computed to be 388 kJ/mol and 1.3 respectively, assuming Johnson-Mehl-Avrami model of crystallization. Another important result is that a maximum of around 70% of spherulitic-dendritic like crystal morphology can be obtained after heat treatment at 1,000 degrees C for 24 h, while a lower amount (approximately 58%) of interlocked plate like mica crystals is formed after heat treatment at 1,040 degrees C for 4 h.

Processing and properties of a glass-ceramic from coal fly ash from a thermal power plant through an economic process

Coal fly ash from a thermal power plant with the addition of selected oxides was used for the preparation of a glass-ceramic with high mechanical properties through an economic process. The starting materials were fly ash, shell (ark shell) as a source of CaO and TiO 2 as a nucleating agent to reduce the melting temperature and to promote internal crystallization. A nuclei formed with Fe and Ti ions from the ash components and added materials, respectively, which had a synergetic effect to induce nuclei in the glass for devitrification. Under a single stage heat treatment, a new crystalline phase formed in the microstructure of glass-ceramics having a crystal size of 2.09×0.36×0.096 μm 3 with a high aspect ratio, 12. The resulting mechanical properties (hardness, strength, fracture toughness, elastic constant and wear rate) of the glass-ceramic indicated good possibilities for use in structural materials.

Production and Properties of Glass-Ceramic from Incinerator Fly Ash

To recycle waste materials, the work is concerned with development of a glass-ceramic from a Korean incinerator fly ash with a high content of Cl. As a pre-treatment of ash, water washing the fly ash was used to remove the high Cl content before melting the ash. The process induced internal crystallization of fly ash after melting under a single stage heat treatment without adding nucleating agents into the ash. As a result, fracture stress of 220MPa and fracture toughness of 1.7 MPam 1/2 were found in the glass-ceramic, which were high values compared to others reported. Thus, the present process suggests that a good glass-ceramic produced from an incinerator ash could be applicable for structural materials in terms of economical and environmental points.

Glass-ceramic produced from a municipal waste incinerator fly ash with high Cl content

This study is concerned with recycling waste materials, focusing on the development of a glass-ceramic from Korean incinerator fly ash with a high Cl content, and the evaluation of its physical properties. In the process, water washing as a pre-treatment before melting the fly ash was used to remove the large amount of Cl in the ash, and to reduce the melting temperature of the fly ash. As a result, glass was obtained at 100 degrees lower than the non-water-washed fly ash. Also, internal crystallization occurred under a single stage heat treatment (at 850–950 °C for 20–240 min) without adding other materials to the ash. It was found that the glass-ceramic was composed of three crystals, gehlenite, augite, and calcium aluminium oxide. Hardness of 8.3 GPa, fracture toughness of 1.7 MPam1/2, elastic constant of 145 GPa, and thermal expansion coefficient of 10.5–11.5×10−6/K were found in the glass-ceramic, which were high values compared with others reported. Thus, the present process suggests that such glass-ceramic produced from an incinerator ash could be applicable for structural materials in terms of economic and environmental points.

Microstructure and properties of CaO–ZrO2–SiO2 glass–ceramics prepared by sintering

For the development of a new wear resistant and chemically stable glass-ceramic glaze, the CaO–ZrO 2 –SiO 2 system was studied. Compositions consisting of CaO, ZrO 2 , and SiO 2 were used for frit, which formed a glass-ceramic under a single stage heat treatment in electric furnace. In the sintered glass-ceramic, wollastonite (CaSiO 3 ) and calcium zirconium silicate (Ca 2 ZrSi 4 O 12 ) were crystalline phases composed of surface and internal crystals in the microstructure. The internal crystal formed with nuclei having a composition of Ca 1.2 Si 4.3 Zr 0.2 O 8 . The CaO–ZrO 2 –SiO 2 system showed good properties in wear and chemical resistance because the Ca 2 ZrSi 4 O 12 crystals positively affected physical and mechanical properties.

Crystallization Phenomina and Vetrification From a Fly Ash With Large Content of Cl

To recycle waste materials, this work was focused on development of glass-ceramic from incinerator fly ash with a large content of Cl and its physical property was evaluated. In the process, water washing as a pre-treatment before melting the fly ash was used to remove large amount of Cl component in the ash and to reduce melting temperature. As a result, glass was obtained at below <TEX>$100^{\circ}C$</TEX> compared to the melting temperature before washing the ash. Also, internal crystallization occurred under single stage heat treatment (at <TEX>$850-950^{\circ}C$</TEX> for 20-340min) without adding other materials into the ash. It was shown that the glass-ceramic was composed of four crystals, diopside, anorthite, akermanite, and unknown phase. Hardness of 8.3GPa was found in the glass-ceramic, which is a high value compared to reported others. Thus, the present process suggests that a good glass-ceramic produced from an incinerator ash could be applicable for structural materials in terms of economic and environmental points.

Magnetic Properties of .ALPHA.-Fe-Nd2Fe14B Exchange Spring Magnets Synthesized by Mechanical Alloying.

The possibility of producing isotropic permanent magnets with enhanced energy product has drawn lot of attention recently. The synthesis of two phase (hard and soft) nanocrystalline exchange coupled magnets by many research groups using different techniques and the various combination of two phases is an indication to the level of research interest in this area. The nitrogenated or carburized rare earth compounds with 2:17 or 1:12 structure as the hard phase was the focal point of many groups. However, the choice of Nd2Fe14B as the hard phase with the attractive advantages of single stage heat treatment, no drawbacks of incomplete nitrogenation or carburization and the possibility of higher sintering temperature has tilted the scale in its favor. The present article reports on the results of the synthesis of exchange spring magnets of Nd2Fe14B and α-Fe and their magnetic properties by mechanically alloying the powder mixture of Nd2Fe14B and iron. The magnets exhibit a spring back greater than 80% and a maximum energy product of 45 kJ/m3. The observed large spring back is an indication of the good coupling between the hard and the soft phases. The low energy product is attributed to the low coercivity of the starting Nd2Fe14B powder and requires further improvement.

Magnetic Properties of .ALPHA.-Fe-Nd(Fe,TM)12Nx Exchange Spring Magnets Synthesized by Mechanical Alloying.

The possibility of producing isotropic permanent magnets with enhanced energy product has drawn lot of attention recently. The synthesis of two phase (hard and soft) nanocrystalline exchange coupled magnets by many research groups using different techniques and the various combination of two phases is an indication to the level of research interest in this area. The nitrogenated or carburized rare earth compounds with 2:17 or 1:12 structure as the hard phase was the focal point of many groups. However, the choice of Nd2Fe14B as the hard phase with the attractive advantages of single stage heat treatment, no drawbacks of incomplete nitrogenation or carburization and the possibility of higher sintering temperature has tilted the scale in its favor. The present article reports on the results of the synthesis of exchange spring magnets of Nd2Fe14B and α-Fe and their magnetic properties by mechanically alloying the powder mixture of Nd2Fe14B and iron. The magnets exhibit a spring back greater than 80% and a maximum energy product of 45 kJ/m3. The observed large spring back is an indication of the good coupling between the hard and the soft phases. The low energy product is attributed to the low coercivity of the starting Nd2Fe14B powder and requires further improvement.

A theoretical and experimental assessment of systematic errors in nucleation experiments

Equations are derived for the fractional underestimate in the number of particles per unit volume, N v , and in nucleation rates, I 0, as obtained by stereological techniques from reflected light microscopy or SEM for typical cases of crystal nucleation in glasses. Three cases are considered: (i) instantaneous heterogeneous nucleation (mondispersed systems of particles); (ii) simultaneous homogeneous nucleation and growth in a single-stage heat treatment (uniform distribution of particles from the critical size to D M, where D M is the largest diameter); (iii) case (ii) with a double heat treatment (uniform size distribution from D M, the smallest diameter, to D M). Comparison with experimental nucleation data for BaO SiO 2 and Na 2O CaO SiO 2 glasses demonstrates that the equations derived predict well the observed underestimations Typical experiments with optical microscopy lead to underestimates from 3% to 14% for case (iii) and up to 50% for case (ii). To minimize these errors one should use a high magnification objective lens with reflection or transmitted light microscopy, or electron microscopy.

Sintering and crystallization phenomena in Silceram glass

An investigation has been carried out on the feasibility of employing a CaO-MgO-Al2O3-SiO2 glass-ceramic (known as Silceram) as a matrix for a fibre composite produced by a powder route. Some important properties of the parent glass, e.g. surface energy, viscosity, have been measured as well as the kinetics and structural aspects of the sintering and crystallization processes. It was found that the crystallization of the main phase, diopside, occurred from the surface of individual particles and internally with activation energies of 392 to 452 kJ mol−1 and 258 to 323 kJ mol−1 respectively. However, the surface crystallization was only dominant when the glass powder was fine (<38μm). The work has demonstrated that this glass-ceramic shows promise as the matrix component of a composite because (i) both sintering and crystallization may be achieved by a single stage heat treatment at relatively low temperatures of 900° C to 1000° C, because the glass powder can be compressed and sintered by viscous flow before crystallization commences, and (ii) the resulting microstructure is fine, and in the case of the hot-pressed material there is negligible porosity.