Optimum Heat Treatment Conditions Research Articles

Transparent glass and glass‐ceramic in the binary system NaPO3‐Ta2O5

AbstractTransparent and homogeneous tantalum phosphate glasses were prepared in the binary system (100‐x)NaPO3‐xTa2O5 with x varying from 10 to 50 mol%. Thermal, structural, and optical properties, as well as crystallization mechanisms, were investigated by thermal analysis, X‐ray diffraction, Fourier‐transform infrared spectroscopy (FTIR) and Raman spectroscopies, optical absorption, transmission electron microscopy in terms of Ta2O5 content. FTIR and Raman results support the tantalum insertion in the phosphate chains with [TaO6] polyhedra cross‐linking the phosphate units. At higher Ta2O5 content, [TaO6] clusters are formed and connected to the phosphate network by P‐O‐Ta bonds. This structural evolution is in good agreement with the thermal features measured by differential scanning calorimetry (DSC) with a strong increase of the Tg temperatures up to 920°C, high thermal stability against crystallization for low Ta2O5 content and increasing of crystallization tendency for the most Ta‐concentrated samples. Besides, due to the progressive insertion of [TaO6] units, the precipitation of Na2Ta8O21 perovskite‐like phase was identified in the sample with 50 mol% of Ta2O5. The optimal heat treatment conditions were identified using DSC measurements and a transparent glass‐ceramic from 50NaPO3 to 50Ta2O5 composition was prepared. The obtaines glass‐ceramic has great potential for optical applications, such as host for rare‐earth ions, nonlinear optical materials, and ferroelectric domain.

Preparation and Characterization of Transparent Glass Ceramics Containing Na3Gd(PO4)2

Transparent glass ceramics with the mole percent composition of 21.3Na2CO3-2.2Gd2O3-38SiO2-36.5H3BO3-2.0P2O5 were prepared by melting crystallization method. The heat treatment system, crystal phase, micromorphology and transmittance of the samples were tested and characterized by differential scanning calorimetry analysis(DSC), X-ray diffraction (XRD), scanning electron microscopy(SEM) and UV-Vis-NIR, respectively. The optimum heat treatment condition is 730°C for 2h. The Na3Gd(PO4)2 crystal phase were precipitated homogeneously among the glass matrix. The results of FTIR spectra confirmed the presence of PO4 groups in the glass ceramics samples. The refractive index of glass ceramics and glass samples were measured. In the visible region, the transmittance of glass ceramics is up to 80%.

Evolution of dispersoids and their effects on elevated-temperature strength and creep resistance in Al-Si-Cu 319 cast alloys with Mn and Mo additions

The present work investigated the evolution of dispersoids during various heat treatments via Mn and Mo additions and studied their effects on the yield strength (YS) and creep resistance at elevated temperature in Al-Si-Cu 319 cast alloys. The results showed that the individual addition of Mn or Mo promoted the precipitation of α-dispersoids; however, the best effect was achieved by their combined addition. The optimum heat treatment condition was at 500 °C for 8 h; under this condition, the largest quantity of and the finest α-dispersoids were obtained, resulting in remarkable improvements in YS at both room and elevated temperatures. The creep resistance at 300 °C was enhanced owing to the additions of Mn and Mo. Compared with the properties of the base alloy, a 19% improvement in YS at 300 °C, doubling of threshold stress and a 50-fold reduction in the minimum creep rate on the creep property at 300 °C were achieved by the combined addition of Mn and Mo. The alloy with both Mn and Mo exhibited the lowest YS decline rate and no change in the minimum creep rate during prolonged thermal exposure at 300 °C for up to 1000 h, demonstrating the superior thermal stability achieved by the 319 alloys with the introduction of a sufficient number of dispersoids from Mn and Mo additions.

Selection of the optimal heat treatment conditions using advanced phase transformation models

The paper focuses on the problem of optimal cooling cycle selection for steel sheets after hot rolling in order to obtain a given phase composition using complex numerical model. The proposed model driven by diffusion of carbon with the moving boundary (Stefan problem) was designed and implemented on the basis of Level Set equations coupled with diffusion equation. Application of implicit method for interface evolution allows to overcome the limitations associated with the complicated representation of material microstructure, but also in a natural way reflects the impact of front curvature and influence of chemical forces on the velocity of the interface. The article discusses the details of the model as well as the applied optimization technique. Three test scenarios are analyzed and the results are discussed.

Investigations on the Tribological Properties of Heat-Treated Copper Composite Using Hybrid Quadratic–Radial Basis Function Model

This research investigates the effect of heat treatment on mechanical and tribological properties of Cu–11Ni–4Si—10 wt% B4C functionally gradient composite, which is fabricated by the centrifugal casting method. The cast specimens are solutionized at 700 °C for 90 min, followed by air quenching/water quenching. The specimens are artificially aged at different temperatures (500 °C, 550 °C, and 600 °C) and time (1 h, 2 h, and 3 h). The optimum heat treatment condition is established based on the microstructure, microhardness, and tensile strength. The specimens that are heat-treated at optimum condition are subjected to tribological tests by varying the load between 15.8 and 44.44 N and sliding velocity between 0.8 to 2.2 m/s for a sliding distance of 1000 m and 1500 m. The surface morphology and topography of the worn surface are analyzed using FESEM and AFM, respectively. The influence of load and sliding velocity on the wear rate of the specimens is explored using the mathematical models, which are developed using a hybrid polynomial–radial basis function. The results indicate that the load has a direct influence on the wear rate, while the wear rate follows crest parabolic pattern with an increase in the sliding velocity.

Determining the Optimum Conditions for Heat Treatment of Cold Rolling Mill Rolls by Studying Their Influence on the Microstructure and Properties of the Billet

Quality, reliability, and service durability of mill rolls are critical factors determining the quality of finished products and efficiency of rolling mills. The main problem that arises in the course of production of steel forged mill rolls is selection of reasonable conditions of heat treatment. As far as the size of the grain with an original structure and the pattern of distribution of separate structural components within the billet play a significant role in formation of final properties of the article, the objectives of this work are studying the heat treatment influence on the microstructure and hardness of steel mill rolls and development of reasonable process conditions on the basis of obtained data, in particular: determining the optimum conditions of primary heat treating the cold rolling mill rolls after their forging to reach the homogeneous structure and reduce the carbide grid score and carbide liquation; determining the optimum conditions of secondary thermal treatment of cold rolling mill rolls to provide the hardness within the range of about 300 HB, favorable structure for industrial frequency current hardening and reduction of carbide network score and carbide liquation; determining the hardening temperature, holding time and cooling rate to obtain the optimum structure and hardness within the range of 650-700 HB. Optimization of heat treatment conditions and analysis of steel microstructure have been performed with the application of cylindrical items (diameter 30 mm, height 20 mm) cut from the sample and template. Based on the study findings some microscopic images of steel microstructure after application of certain heat treatment conditions have been made and data on carbide network and current grain evaluation have been obtained

Optimization of Cryogenic Process for Enhancing the Wear Resistance of Novel HNMS Steel for Cryogenic Bearings of Launch Vehicle

Bearings are highly engineered components that have to tolerate vibratory stresses, bending moments, and high rotational speeds in cryogenic applications. AISI 440C is most widely used for antifriction bearings due to its good strength and high hardness but is prone to carbide banding and failure during service. High-nitrogen martensitic stainless steel (HNMS) was recently developed by partially substituting carbon with nitrogen. This article explores the possible improvement in wear properties by cryotreating HNMS steel. The hardening temperature was varied from 1050 to 1100 °C, cryosoaking period from 0 to 12 h at −196 °C, and tempering temperature from 100 to 300 °C for 1 h. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis revealed the presence of carbides and carbonitrides. The phase fraction and size of the precipitates was found to be influenced by the cryosoaking period. The carbide density variation with the cryosoaking period followed a sigmoidal curve. Eight hours of cryogenic treatment at −196 °C was observed to be the optimal cryosoaking period for HNMS steel. Maximum hardness (671 HV) and minimum wear rate (0.00714 mm3/m) and adhesive wear were observed for the optimum heat treatment condition. Compared to conventional hardening-tempering (HT) treatment, the optimized hardening-cryogenic-tempering (HCT) treatment cycle resulted in a 38% increase in hardness and a 31% decrease in the wear rate. The improved properties can be attributed to the presence of fine and uniform distribution of precipitates in the matrix and transformation of retained austenite to martensite.

Heat treatment effects on Inconel 625 components fabricated by wire + arc additive manufacturing (WAAM)—part 1: microstructural characterization

Wire + arc additive manufacturing (WAAM) is a versatile, low-cost, energy-efficient technology used in metal additive manufacturing. This WAAM process uses arc welding to melt a wire and form a three-dimensional (3D) object using a layer-by-layer stacking mechanism. In the present study, a Ni-based superalloy wire, i.e., Inconel 625, is melted and deposited additively through a cold metal transfer (CMT)-based WAAM process. The deposited specimens were heat-treated at 980 °C (the recommended temperature for stress-relief annealing) for 30, 60, and 120 min and then water quenched to investigate the effect of heat treatment on microstructure and phase transformation and to identify the optimum heat treatment condition. Microstructural results show that the heat treatment, in general, eliminates the brittle Laves phases regardless of the time without changing the grain morphology. However, an increment in the amount of the delta phase is observed with the longer heat treatment periods. Additionally, the size of MC (metal carbide) of Nb is also observed to increase with heat treatment time. This study provides an in-depth understanding of the correlation between heat treatment time and microstructure in additively manufactured Inconel 625, which can facilitate determining the optimum heat treatment condition in a later study.

Multilayer graphene nanobelts on SWCNT films for high current interconnect applications

In this work we propose multilayer graphene (MLG) nanobelts for high current interconnections with single wall carbon nanotubes (SWCNT) and compare these with metal contacts. MLG contacts were directly printed on the SWCNT, without any additional metal parts, demonstrating the possibility to use these materials as interconnections in microelectronics. Different work function metals Al, Ti and Pd were probed for the lowest contact resistance with the SWCNT. Ti contacts demonstrated the best results among the metals owing to its work function being closest to the SWCNT and therefore giving the lowest Schottky barrier. Even though Ti contacts show the lowest contact resistance, the current density for MLG contacts was higher, giving the best results for high current interconnection applications. Moreover, MLG contacts show a stable and repeatable resistance decrease under high current conditions. Heat treatment of the MLG and metal contacts was completed in vacuum, in order to further reduce the contact resistance and optimal heat treatment conditions were found at 600 °C.

Optimum circumstances for heat treatment mechanisms: soft magnetic properties and microstructural evaluation in nanocrystalline FeCuNbSiB alloys

In the present study the magnetic, magneto-optical, morphological and microstructural properties of the amorphous Fe83Cu1Nb3Si5B8 alloy were thoroughly investigated in accordance with various annealing circumstances. The kinetic nanocrystallization temperatures of certain ribbon were determined at the range of 500–515 °C. Furthermore, optimum heat treatment conditions were sought in the air atmosphere (AA), in vacuum (VA) and in vacuum with the presence of longitudinal magnetic field (LFA) at 70 A/m. This study aimed to put forward a quantitative explanation of the advantages of LFA in terms of several factors such as magnetic properties, microstructural evaluation and magneto-optical effects. The present nanocrystalline Fe83Cu1Nb3Si5B8 alloy has allowed the yielding of ultrafine grain structure correlated with the literature results. Accordingly, average grain size of 5.9 nm, saturation induction of 1.84 T and coercivity of 6.4 A·m−1 and saturation magnetostriction as low as 6 ppm were obtained as a result of LFA implementation. However, the sample subjected to VA under the same circumstances showed relatively lower magnetic and microstructural capability, with an average grain size of 9.8 nm, saturation induction of 1.73 T, coercivity of 14.7 A·m−1 and saturation magnetostriction of 14 ppm, in comparison with LFA. To ensure precise average grain size, both XRD data and TEM micrographs were separately considered. Even though saturation magnetostriction could not be completely eliminated, it was significantly minimized from 52 ppm to 35 ppm, 14 ppm and 6 ppm in the samples subjected to AA, VA and LFA, respectively.

Performance of TiO2 Fibers Prepared by Electrostatic Spinning As Lithium-Ion Battery Anode Material

This paper reports a one-dimensional (1D) TiO2 nanostructure with significantly enhanced conductivity. Anatase TiO2 with a 1D nanostructure was successfully prepared by the electrostatic spinning method, and the effect of calcination temperature on its electrochemical performance was studied. The samples prepared at different calcining temperatures (400, 450, and 480°C) were analyzed by physical and electrochemical methods to identify the optimal heat-treatment conditions. Temperature was found to be another important factor influencing the electrochemical performance of 1D materials besides their structure and morphology. The anatase TiO2 calcined at 450°C had a discharge capacity of 192.8 mA h g–1 at 0.2 C with over 96% capacity retention after 100 cycles. The improved lithium-ion intercalation properties of the rod-shaped TiO2 might be attributed to the relatively large specific surface area, short transport distance of the 1D structure, and freedom for the volume change accompanying lithium-ion intercalation.

Simple Detection of Hepatitis B Virus in Using Loop-Mediated Isothermal Amplification Method.

US Military and civilian personnel regularly deploy to regions that are endemic for the Hepatitis B virus (HBV), including the Western Pacific, Africa, Eastern Mediterranean, Southeast Asia, and Europe. When patients have life-threatening injuries that require any blood component that is not immediately available, they are typically transfused with locally collected fresh whole blood from a walking blood bank. Currently, there is no simple and easy method for sensitively screening fresh blood in deployed theaters of conflict. In order to fill the gap, we have developed a loop-mediated isothermal amplification (LAMP) assay to detect the presence of HBV in blood products. The primers were designed to target the gene of the pre-Surface/Surface antigen region of HBV. The amplification reaction mixture was incubated at 60°C for 60 min. The amplicon can be detected by a handheld fluorescence tube scanner or an immune-chromatography test strip. We were able to detect down to 10 copies of viral DNA by LAMP reaction for HBV DNA extracted from HBV-positive plasma. We also identified the optimal heat treatment condition (125°C for 10 min) for plasma specimens without requiring DNA extraction for the LAMP assay. The sensitivity of the assay was evaluated with polymerase chain reaction (PCR) confirmed HBV-positive samples. Using LAMP, we detected HBV in 107 out of 127 (84%) samples. This LAMP assay has the potential to be used in resource-limited settings to improve the safety of locally collected blood in endemic regions.

Optimization conditions for the electro-deposition of thin ZnTe film and effect of magnetic field

ZnTe is considered to be one of innovative semi-conducting materials because the theoretical energy band gap value is 2.26 eV suitable for solar cell or LED. And the further advantageous point is that the material of ZnTe is inexpensive and harmless. Among various synthesizing techniques, electro-deposition process has been investigated because the process is not expensive and suitable for mass production. In this study, optimum condition for producing the relatively thick film with strong magnetic field. The band gap value of thin ZnTe can be improved up to 2V in optimum conditions of electro-deposition and successive heat treatment. Furthermore, in order to achieve high performance of energy exchange, crystal orientation of ZnTe with cubic structure can be realized by electro-deposition of metal Te layer under strong magnetic field prior to ZnTe deposition.

Semi-solid state mixing of Mg-Zn-RE alloys—microstructure and mechanical properties

Mixing two kinds of alloys in semi-solid temperature range allows obtaining new one with superior properties. Critical challenges facing the process are determination of mutual interaction of slurries, selection of appropriate temperature process, and designing optimal heat treatment conditions. Two kinds of magnesium chips E21 and WE43B containing different compositions of rare earth elements and similar solidus-liquidus temperature ranges were mixed in equal weight/volume ratio using thixoforming technology. Granules were hot compressed at 400 °C/5 min/200 MPa and thixoformed at 625 °C, which corresponded to about 25% of the liquid phase. Structure of E21WE43B thixo-cast consisted of globular grains of average size 59 μm. They were surrounded by the eutectic mixture coming from both alloys. X-ray analysis confirmed the presence of magnesium solid solution as well as intermetallics Mg3Nd and Mg24Y5 phases located in interglobular areas. T6 heat treatment consisted of solutioning at 525 °C for 8 h and aging at 190 °C for 120 h leading to increase of hardness from 57 to 85 HV. High resolution transmission electron microscopy studies allowed identifying β’ planar precipitates, approximately 8 x 2 nm in size and coherent with matrix, homogeneously distributed in the α(Mg) in the T6 treated sample. They were responsible for strengthening of E21WE43B thixo-cast leading in consequence to yield strength 190 MPa at compression strength 475 MPa at plasticity 13.1%.

Enhanced compactness of oriented MFI zeolite films by heat treatment of seed layer

The achievement of compact and defect-free film structure is crucial for the application of b-oriented MFI zeolite film. In this work, a novel heat treatment technique was used to treat zeolite seeded substrates prior to secondary growth. The influence of the heat treatment parameters such as treat temperature and time on the final film morphology were systematically investigated. The relationship between film compactness and the parameters was established. Under the optimized treat temperature of 120 °C and treat time of 1 h, compact and uniform b-oriented MFI zeolite film was achieved. The applicability of the optimum heat treatment condition was validated by employing various film substrates.

Synthesis and ac electrical characterization of nickel oxide nanofibers

In this study, we present the synthesis of nickel oxide nanofibers through electrospinning technique at optimum processing and heat treatment conditions. The diameter and uniformity of electro-spun nickel oxide nanofibers were investigated as a function of PVP concentration. Uniform and homogeneous composite nanofibers were observed for PVP:Ni(CH3COO)2·H2O ratio of 1:1. X-ray diffraction and scanning electron microscopy of samples calcined at 600 °C revealed the formation of uniform but porous single phase nickel oxide nanofibers of an average diameter Electrical properties of nickel oxide nanofibers, obtained at optimum conditions, were studied using inter-digitated electrodes type device. Temperature-dependent impedance spectroscopy revealed different electro-active regions (grain and grain boundaries) and their activation energies were 0.24 and 0.36 eV, respectively. These results suggested less resistive grain than grain boundary in the employed temperature range, and hence, two different transport mechanisms.

Preparation and Characterization of Tb<sup>3+</sup>/Eu<sup>3+</sup> Co-Doped Na<sub>2</sub>O-Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Glass Ceramics

Tb3+/Eu3+co-doped sodium nepheline transparent glass ceramics with the weight percentage composition of 27Na2O-19Al2O3-23SiO2-13H3BO3-6TiO2-6ZrO2-3Tb4O7-3Eu2O3were prepared by melting crystallization method. The heat treatment system, crystal phase, micromorphology, transmittance and luminescent properties of the samples were tested and characterized by DSC, XRD, SEM, UV-Vis-NIR and fluorescence spectrometer, respectively. The results show that the optimum heat treatment condition of glass at 480°C nucleated 1h and 580°C grew 1h., the crystal phase was NaAlSiO4(35-0424), and the incorporation of rare earth ions did not affect the crystal phase. The transmittance of glass ceramics in the visible area can reach 78%. The effect of different Tb3+/Eu3+doping concentration on the luminescent properties of glass ceramic samples was discussed. It was found that there was a phenomenon of Tb3+to Eu3+energy transfer, and the luminescence effect was best when the percentage of mass of Tb3+/Eu3+was 1:1.

Fabrication and Magnetic Properties of Co₂MnAl Heusler Alloys by Mechanical Alloying.

We have applied mechanical alloying (MA) to produce nanocrystalline Co2MnAl Heusler alloys using a mixture of elemental Co50Mn25Al25 powders. An optimal milling and heat treatment conditions to obtain a Co2MnAl Heusler phase with fine microstructure were investigated by X-ray diffraction, differential scanning calorimeter and vibrating sample magnetometer measurements. α-(Co, Mn, Al) FCC phases coupled with amorphous phase are obtained after 3 hours of MA without any evidence for the formation of Co2MnAl alloys. On the other hand, a Co2MnAl Heusler alloys can be obtained by the heat treatment of all MA samples up to 650 °C. X-ray diffraction result shows that the average grain size of Co2MnAl Heusler alloys prepared by MA for 5 h and heat treatment is in the range of 95 nm. The saturation magnetization of MA powders decreases with MA time due to the magnetic dilution by alloying with nonmagnetic Mn and Al elements. The magnetic hardening due to the reduction of the grain size with ball milling is also observed. However, the saturation magnetization of MA powders after heat treatment increases with MA time and reaches to a maximum value of 105 emu/g after 5 h of MA. It can be also seen that the coercivity of 5 h MA sample annealed at 650 °C is fairly low value of 25 Oe.

Modelling of heat stability and heat‐induced aggregation of casein micelles in concentrated skim milk using a Weibullian model

Heat stability is known to be limited in concentrated skim milk leading to severe coagulation and sediment formation during storage. It has often been found to be in conflict with the extension of the shelf life by thermal treatment. A Weibullian model was used to describe the course of coagulation of casein micelles in concentrated skim milk of different total solids and at different heating temperatures. A maximum heating temperature–time–total solids relationship was calculated based on a certain maximum allowance of sediment formation. Optimal heat treatment conditions for concentrated skim milk of different total solids content could be defined.

Sorption properties of materials based on residual biomass

In this paper, we consider the possibility of using inexpensive and effective sorption materials based on plant raw materials, such as fruit rind, vegetable waste, fallen leaves, and the use of phytosorbents for the purification of sewage containing heavy metals and petroleum products. The use of vegetable waste for the manufacture of sorbents is a priority for solving environmental problems. It is suggested to use residual biomass as a sorption material, which is formed after extraction of lipids from C. sorokiniana microalgae and duckweed Lemna minor. To increase the sorption capacity, it was proposed to thermally modify the residual biomass. The optimum heat treatment conditions were 450 °C for 20 minutes with limited access to oxygen. The obtained biomass allows one to extract ions of heavy metals with efficiency of 91-93% for ions of lead, cadmium, zinc and copper. To increase the sorption capacity (A, mg/g) of the residual biomass, heat treated waste from the agro-industrial complex and chitosan were proposed as additives. The addition of chitosan makes it possible to obtain a sorption material in the form of granules, which is convenient to use. For the sorption materials obtained, microstructural studies were carried out, which allowed us to substantiate the sorption properties of the materials. The physical and mechanical properties of sorbents, such as abrasion, grindability, allow us to offer new materials for use on an industrial scale. In the article, a technological scheme for obtaining sorption materials from residual biomass is given.