Effect Of Isothermal Treatment Research Articles

Effect of Isothermal Treatment on the Structure and Hardness of Pseudo-β Titanium Alloys

Effect of Isothermal Treatment on the Structure and Hardness of Pseudo-β Titanium Alloys

Effect of Isothermal Treatment on Mechanical and Tribological Properties of Alloy Zn – 40% Al – 2% Cu – 2% Si

Effect of Isothermal Treatment on Mechanical and Tribological Properties of Alloy Zn – 40% Al – 2% Cu – 2% Si

Effect of Isothermal Treatment on Microstructure and Performance of Micro/Nanostructure 2205 Duplex Stainless Steel Prepared by Aluminothermic Reaction

Using an appropriate heat treatment process to control the precipitation of the σ phase, while regulating the alloy structure and grain size, is one of the effective ways to obtain good comprehensive properties of duplex stainless steel (DSS). Herein, the feasibility and preparation parameters of micro/nanostructure 2205 DSS prepared by the aluminothermic reaction are explored. The microstructure and properties are further controlled by isothermal treatment at 1000 °C for a different time. The results show that the volume percentages of α and γ phases in the 1.0 h isothermal treated steel obtain a maximum value and a minimum value, corresponding to 60% and 36%, respectively. The evolution of microstructure with isothermal treatment also affects the content and morphology of the precipitated σ phase, which changes from continuous precipitation to granular precipitation at the α/γ phase boundaries, and its volume percentage obtains a minimum value when the isothermal treatment is performed for 1.0 h. With the increase of heat treatment time, the average grain size and volume fraction of nanocrystals increase gradually. Corresponding to the changes in microstructure and grain size, the maximum values of Vickers hardness and tensile properties of the alloy are obtained after 1.0 h isothermal treatment.

Effect of heat treatment on phenolic composition and radical scavenging activity of olive leaf extract at different pH conditions: a spectroscopic and kinetic study.

The present study focused on the effect of isothermal treatment (5-90 °C) and pH (2.0-6.0) of aqueous olive leaf phenolic extract solutions on the kinetics of degradation of single and total phenolic compounds and radical scavenging activity, with the objective of predicting and optimizing the thermal treatments in foods enriched with olive leaf extracts. The major compound, oleuropein, showed higher degradation at low pH2.0 and temperature-dependent reaction rates, which fitted well a first-order kinetic model, with an estimated activation energy of 98.03 ± 0.08 kJ mol-1 . Oleuropein hydrolysis resulted in a zero-order increase in hydroxytyrosol concentration at same pH (Ea = 71.59 ± 1.5kJ mol-1 ), whereas a 100-fold slower degradation rate was observed at higher pH. Verbascoside was only degraded at pH6.0, also following first-order kinetics. These changes in oleuropein and hydroxytyrosol concentrations led to significant changes in fluorescence maximum intensities centered around 315 and 360 nm and in the 425-500 nm spectral zone for samples at pH6.0, which could be associated with verbacoside degradation. Conversely, analysis of total phenolic content and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activity showed little changes, indicating a rather constant overall reducing capacity of the resulting pool of compounds after thermal treatments. The present study can contribute to the knowledge related to oleuropein and phenolic fraction degradation as a result of matrix (pH) and processing. The kinetic parameters obtained could be applied for predicting and optimizing the thermal treatments in foods and drinks enriched with olive leaf extracts. © 2022 Society of Chemical Industry.

Effect of isothermal treatment on the structural, microstructure, and physio-mechanical properties of Li2O-Al2O3-SiO2 glass–ceramic

Effect of isothermal treatment on the structural, microstructure, and physio-mechanical properties of Li2O-Al2O3-SiO2 glass–ceramic

Microstructure evolution and mechanical behavior of a lean duplex stainless steel aged at 475oC

In this research, the effects of isothermal treatments at 475 °C on the microstructure and mechanical properties of a UNS S32304 lean duplex stainless steel were investigated. Samples of the alloy under as received and aged conditions were analyzed by atomic force microscopy and magnetic force microscopy in order to evaluate the ability of these techniques to identify important aspects that characterize microstructural changes caused by aging. The mechanical behavior was evaluated by tensile tests, hardness tests, Charpy impact tests, crack extension resistance tests, force controlled axial fatigue tests and fatigue crack growth rate tests. The fracture surfaces of all tested specimens were analyzed by scanning electron microscopy. The results indicate that the α-phase spinodal decomposition occurred, with a tendency to saturation for a not too long aging time. The analysis by atomic/magnetic force microscopy allowed to identify characteristics regarding the preferential phase dissolution of the α phase that distinguish the alloy in the as received condition from the aged alloy. As a consequence of the formation of the α’ phase, the absorbed impact energy and the fracture toughness of the alloy decreased substantially. On the other hand, the tensile strength and the fatigue resistance increased significantly. • Possibility to effectively follow spinodal decomposition in a LDSS using the Scanning Probe Microscopy technique. • Short aging time after which the spinodal decomposition and the mechanical behavior of the steel tend to saturate. • Higher values for LDSS impact strength and fracture toughness compared to other duplex stainless steel grades. • An adequate heat treatment can provide interesting values of tensile, toughness and fatigue resistance for the LDSS.

Effect of Isothermal Treatment on Microstructure and Mechanical Properties of Cold-Deformed IF Steel

In this study, we investigated the recrystallisation kinetics of Ti-stabilised interstitial-free (IF) steel manufactured by the Mexican steel industry through the route of electric arc furnace with vacuum degassing, secondary refining, and subsequent continuous casting. The IF steel was hot-rolled at 950°C and then cold-rolled until deformation of 94% was attained, followed by recrystallisation at different times at a constant temperature of 780°C. In addition, the mechanical properties of the IF steel were assessed as a function of recrystallisation time. The results obtained from the mechanical property tests were presented in the form of plots of microhardness, yield strength, ultimate tensile stress, and deformation percent as functions of the recrystallised fraction with an indirect dependence on recrystallisation time. A graphical model of the recrystallisation behaviour showed the evolution of the microstructure, including phase transformations, hardness, and the mechanical properties determined from the tensile tests. In view of subsequent recovery and recrystallisation, stored energy analysis derived from the strain induced by deformation was presented. Furthermore, we determined the precipitates formed in the different processing stages of IF steel.

Isothermal Transformation of a Commercial Super-Bainitic Steel: Part I Microstructural Characterization and Hardness

The effects of isothermal treatment on the microstructure and hardness of commercial super-bainitic steel were investigated. A series of isothermal treatments were carried out at temperatures of 210-250 °C for different time periods. The results indicate that the bainitic reaction and hardness were very sensitive to the isothermal transformation temperature. The fine super-bainitic microstructure, containing the carbide-free bainitic ferrite lath and the carbon-enriched retained austenite film, can be produced by heating to 210 °C for 30 h, resulting in a hardness of 662 HV. By increasing the isothermal transformation temperature, the bainitic transformation kinetic is accelerated; however, this is at the expense of coarsening bainitic ferrite laths and decreasing the bainitic ferrite quantity. The relationship between hardness and microstructures obtained under different isothermal treatments, which is correlated with the carbon concentration, dislocation density, bainitic amount and super-bainite size, is discussed in detail.

Microstructure evolution and thixoforming behavior of 7075 aluminum alloy in the semi-solid state prepared by RAP method

The effects of isothermal treatments on the microstructural evolution and coarsening rate of semi-solid 7075 aluminum alloy produced via the recrystallization and partial remelting (RAP) process were investigated. Samples of 7075 aluminum alloy were subjected to cold extrusion, and semi-solid treatment was carried out for 5–30 min at temperatures ranging from 580 to 605°C. A backward-extrusion experiment was conducted to investigate liquid segregation during the thixoforming process. The results revealed that obvious grain coarsening and spheroidization occurred during prolonged isothermal treatments. In addition, higher soaking temperatures promoted the spheroidization and coarsening process because of the increased liquid fraction and the melting of second phases. Segregation of the liquid phase caused by the difference in fluidity between the liquid and the solid phases was observed in different regions of the thixoformed specimens.

Microstructural refinement of Ni-Cr-W superalloy by isothermal treatment near the liquidus

The solidification process of Ni-Cr-W superalloy was investigated by confocal scanning laser microscope (CSLM). The liquid fraction during solidification was obtained as a function of real time and temperature in reference with the in-situ observation. In this work, the effect of isothermal treatment near the liquidus on undercooling, grain initiation and the grain growth was studied, and an analytical model is developed to account for the effect of solute field on grain refinement. This study revealed that isothermal treatment near the liquidus restricted the growth of crystal and increased the number density of active particles for nucleation, giving rise to a finer grain size. The tensile results of Ni-Cr-W superalloy tested at different temperatures indicated fine grain microstructure can improve the mechanical properties at different temperatures.

Isothermal Crystallization of PC61BM in Thin Layers Far below the Glass Transition Temperature

An isothermal study was performed on 1.25 μm thin layers of PC61BM, a benchmark acceptor for organic photovoltaics. Using fast scanning chip calorimetry allowed for a scanning rate of 30 000 K·s–1, ensuring that all non-isothermal effects were avoided. The effect of isothermal treatments above and far below the glass transition was investigated. It was proven that PC61BM can crystallize below its glass transition, a behavior seen before for several organic glasses. Isothermal treatments as far as ca. 100 K below the glass transition lead to an initial enthalpic relaxation process around the glass transition, which over time gives rise to crystals melting around 300 °C. These observations show a remarkable similarity with the two-step nucleation mechanism documented in the literature. A standard crystallization process was observed for treatments above the glass transition. By combining chip calorimetry pretreatments with atomic force microscopy, different crystal morphologies were visualized for these two...

Effects of Isothermal Treatment on Amount of Retained Austenite in Cr Cast Irons

Effects of Isothermal Treatment on Amount of Retained Austenite in Cr Cast Irons

Effects of isothermal treatments on non-stoichiometrical preparation for the optimized perovskite structure of BiFeO3 bulk ceramics

Bismuth ferrite powders were synthesized by a simple solid state reaction method at the room temperature by non-stoichiometrical preparation. The fabricated BiFeO3 ceramics clearly exhibited phase transformations to BiFeO3 and secondly bismuth ferrites by an elevated temperature procedure and isothermal heat treatment. The isothermal heat treatments at 1123 K and 1148 K made rhombohedral BiFeO3 and ferroelectrics.

Nanomechanical behavior of yttria stabilized zirconia (YSZ) based thermal barrier coating

In the present study, the detailed evaluation of nanomechanical properties in terms of hardness and Young׳s modulus of duplex and compositionally graded YSZ based thermal barrier coating (TBC) have been evaluated by nanoindentation technique. Duplex and compositionally graded TBCs have been fabricated by thermal spray deposition technique. As TBCs are commonly applied for high temperature protection, effect of isothermal treatment in air (at 900°C and 1000°C) on nanomechanical properties has also been evaluated. Finally, the mechanical properties have been correlated with characteristics of the coating. The hardness and Young׳s modulus of the TBCs are found to increase with increased duration of thermal exposure. Modulus of resilience and resistance to plastic deformation of the duplex and compositionally graded TBC have also been evaluated at room temperature and with thermal exposure and discussed in detail.

The Effect of Isothermal Treatment on the Microstructure and Properties of High Performance Steels

The microstructure and properties of 600MPa grade steels produced by isothermal treatment has been studied. The influence of isothermal treatment temperature on the microstructure of steels has been investigated by the aid of Optical microscopy and TEM. The results show that after various isothermal treatments the microstructure of steels varies with the isothermal temperature. When the temperature is lower than 530°C the microstructure is mainly composed of granular bainite and lath bainite. Whereas when the temperature is higher than 580°C the polygonal ferrite and quasi polygonal ferrite appears and the microstructure consists of ferrite and fine lath bainite. Since the microstructures are complex and the yield ratio of steels under these conditions are all lower than 0.8. The strength of sample for 630°C isothermal treatment is the highest. The yield strength is over than 800MPa and the tensile strength is over than 1000MPa due to the fine precipitates containing copper. These copper containing precipitates formed during the isothermal transformation by the way of inter-phase precipitation.

Effect of Iso-Thermal Treatment on the Corrosion Behaviour of Low Carbon Steel (Nigerian C2R grade) in a Buffered Solution containing Chloride and Carbonate Ions

This work has investigated the corrosion behavior of low carbon steel subjected to four different modes of iso-thermal heat treatment and then immersed in a neutral buffer corrosive medium containing carbonate and chloride ions.The low carbon steel material was cut into twenty small pieces of length 18±2mm, put in groups of five and subjected to: Annealing, Hardening, Normalizing and tempering, each corresponding to an iso-thermal mode of treatment. The samples were ground and polished, and micrographs taken for each mode of treatment.The samples were then immersed into the corrosion medium; a neutral buffer and samples were withdrawn for measurement every 72 hours. The experiment lasted 360 hours (15 days). The weight loss due to corrosion of the samples, the corrosion rate of the samples and the pH variation of the samples were monitored against time of exposure. It was observed that samples which had undergone tempering mode of heat treatment turned out to be the ones with the best corrosion resistance.

Effect of Thermal Treatment on Nano-Crystallites and Phase Transformation of CaZrO<sub>3</sub>Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are multilayered coatings having the complex structure. In thermal spray coatings characteristic features of deposited molten particle and its microstructure is very important in defining coating properties. In this work stainless steel (AISI 316) was used as substrate material on which bond coat of Ni-20Cr and top coat of CaZrO3 were deposited by air plasma spraying method. Effect of isothermal treatment on the internal microstructure structure of lamella (splat) and phase changes in CaZrO3 coating was studied. The fractured surface of coatings was investigated to observe the splat morphology. It was observed that the nanocrystallites present within the splat grew with increase in temperature. Further, the monoclinic phase was formed as function of temperature and time.

Isothermal-Treatment-Induced Network Formation of Carbon Black in Isotactic Polypropylene/Carbon Black Composites

The effect of isothermal treatment on network formation of nanoscale dispersed carbon black (CB) particles in mild-compounded isotactic polypropylene (iPP)/CB composite is investigated. Network formation of CB took place in a quiescent melt without any flow and expansion since the isothermal treatment of the composite was carried out under high pressure conditions. TEM was used to inspect the network formation of the well-dispersed CB. Resistivity temperature and dynamic rheological behaviors of samples before and after isothermal treatment were examined to investigate the relationship between fillers’ network formation and electrical conductivity enhancement.

Effect of isothermal treatments on the magnetic behavior of nanocrystalline Cu–Ni–Fe alloy prepared by mechanical alloying

The present study concerns magnetic behavior of nanocrystalline Cu–Ni, Cu–Fe and Cu–Ni–Fe alloys prepared by mechanical alloying. It has been found that the magnetic properties e.g. H c, M r and M s of the nanocrystalline alloys were significantly influenced by the changes in microstructural constituents, grain size and evolution of phases. Microstructural changes in the alloys have been effected by carrying out isothermal treatments on the mechanically alloyed products in the temperature range of 450–650 °C. Phase evolution in the samples after the isothermal treatments were identified and characterized by X-ray diffraction (XRD) and differential scanning calorimetric (DSC) techniques and the results were correlated with the magnetic properties of the alloys.

Investigation of hydrogen induced cracking in 2205 duplex stainless steel in wet H 2S environments after isothermal treatment at 675, 750 and 900 °C

The effect of isothermal treatment (at 675, 750 and 900 °C) on HIC (hydrogen induced cracking) in sour environments containing hydrogen sulphide of a 2205 duplex stainless steel has been investigated. The performance and microstructure of failed material were characterized by optical microscopy, scanning electron microscopy and also X-ray diffraction. Two kinds of Cr-, Mo-enriched intermetallic phases, σ and χ, were found to precipitate preferentially at α/ γ interfaces and within α grains after different times of aging in the temperature range of 650–900 °C. After performing tests according to the NACE Standard TM 0284 (1987) the specimens were investigated by using quantitative metallography methods. The volume fraction of σ phase was changed with the time of aging and σ phase developed into coarse particles due to the high diffusibility of solute atoms at high temperatures. The variation of size and shape of σ phase particles was obtained by applying different heat treatment conditions to 2205 steel specimens. The results showed that 2205 duplex stainless steel containing nearly 12 vol.% of σ phase in dispersed conditions was resistant to step cracking in wet environments containing hydrogen sulphide. It was highly possible that a crack would propagate faster along the embrittled σ phase. However, very small cracks were found at austenite–ferrite boundaries where o phase particles were also present.