Increasing Heat Treatment Time Research Articles

Effect of cooling rates and heat treatment time on Si phase of AlSi10Mg alloy manufactured by selective laser melting: Microstructure evolution and strengthening mechanism

As a processing technique to change the organization and properties of materials, heat treatment was widely used to strengthen metallic materials. This study examines the impact of varying cooling rates and heat treatment durations on the mechanical properties and microstructure of AlSi10Mg alloys produced through Selective laser melting (SLM). The heat treatment process was Solution Heat Treatment (SHT, 525oC), and the heat treatment time includes 1h, 2h, and 3h. Cooling methods consist of Refrigerant Cooling (RC), Water Cooling (WC), Air Cooling (AC), Oil Cooling (OC), and Furnace Cooling (FC). As the cooling rate decreases and the heat treatment time increases, the size of the formed Si phase particles varies from small to large, and the distribution deviates from inhomogeneous to homogeneous. In addition, the number of precipitated particles increases and then decreases. To investigate the impact of cooling rates and heat treatment time on the mechanical properties of AlSi10Mg alloys, quasi-static tensile and compression tests were performed. On the other hand, the tensile strength of the heat-treatment samples decreases while the ductility increases, and the Vickers hardness of the samples also decreases with decreasing cooling rate and increasing heat treatment time. The results of the study showed that the cooling rate and heat treatment time of the material had a greater effect on its tensile properties than on its compressive properties. The samples treated at 525oC - 2h - AC exhibited the highest tensile and compressive properties. Finally, the analysis of the strengthening mechanism of AlSi10Mg alloys through the presence of Si phase particles of varying sizes was conducted using transmission electron microscopy.

Broad emission in Bi-doped GeGaSe chalcogenide glass and glass-ceramic

Bi-doped Ge23.5Ga11.8Se64.7 glasses were prepared, and compositional dependence of broadband near-infrared photoluminescence at 1.26 μm was investigated. The maximum intensity of the emission appeared at 0.3 mol% Bi doped glasses. The glass was further annealed to create glass-ceramics, and their photoluminescence intensity was found to decrease as the heat treatment time increases. The broadband infrared photoluminescence of Bi ions in the glasses is mainly due to the low valence state of Bi, and broad emission from a half-width at full maximum up to 550 nm demonstrates potential applications of the glasses and glass-ceramics in new broadband fiber lasers and optical amplifiers.

Effect of heat treatment conditions on the phase transformation characteristics of nitinol

Nitinol is the most widely used shape memory alloy in medical applications. In this study, the effect of different heat treatment conditions on the phase transformation characteristics of medical-grade nitinol was investigated. Nickel-rich nitinol wires containing 50.6% nickel with a diameter of 120 μm were used in the experimental studies. The nitinol wires were heat treated for 10 minutes at heat treatment temperatures between 540 and 570 °C. Then, nitinol wires were heat treated at a heat treatment temperature of 550 °C between 8 and 14 minutes. The austenitic and martensitic transition temperatures of these samples were measured using differential scanning calorimetry (DSC). In the experiments with 10 minutes of heat treatment time, transition temperatures decreased, and hysteresis increased with the increase in heat treatment temperature. This is related to the amount of precipitates in the structure. In the experiments carried out at 550 °C, transition temperatures decreased, and hysteresis increased with increasing heat treatment time. Experimental studies showed that the austenite finish (Af) temperature of all nitinol wire samples was below 37 °C, and they will exhibit superelasticity in the human body.

The Influence of Heat Treatment on the Microstructure and Properties of a Cu-Bearing Ultra-Low Carbon Steel.

This study reveals the relationship between the Cu precipitates and mechanical properties of a Cu-baring ultra-low carbon steel after two-phase zone quenching and tempering at 923 K for 0.5-2.5 h. The tensile and microstructural properties were investigated as a function of heat treatment time. The contribution of the precipitation-strengthening mechanism to yield strength was calculated. The size, morphology, and distribution of the precipitated particles were observed using TEM. As the heat treatment time increased, the strength gradually decreased and then remained stable, and the elongation gradually increased and then remained stable. Additionally, the contributions of each strengthening mechanism to the yield strength under different heat treatments were 117, 107, 102, and 89 MPa, respectively. The size and quantity of the precipitates increased with the increase in heat treatment time. After tempering for more than 2 h, the precipitates continued to coarsen, but their quantity decreased. The precipitated Cu had a 3R structure with a length of approximately 17.1 nm and a width of approximately 9.7 nm, with no twinning inside. The stacking order was ABC/ABC. The stable Cu precipitation structure was FCC, maintaining a K-S orientation relationship 11¯1FCC Cu //(0 1 1) α, 1¯10FCC Cu//[11¯1] α.

Microstructure characterization and growth mechanism of ZrC whiskers prepared by precursor transformation method

ZrC whiskers were prepared on graphite through precursor transformation method. Effects of heat treatment temperature, catalyst concentration and heat treatment time on phase composition and microstructure of the ZrC whiskers were investigated. Growth mechanism of the ZrC whisker was analyzed. Results indicated that as heat treatment temperature increasing, catalyst activity increased and energy barrier for the carbothermal reduction reaction reduced, resulting in a gradual increase of both production and diameter of the ZrC whiskers. Catalyst could provide nucleation points for the ZrC whiskers, production and diameter of the ZrC whiskers firstly increased as the catalyst concentration increasing. While, when catalyst concentration was over high, length-diameter ratio of the ZrC whiskers decreased and some whiskers were agglomerated. Heat treatment time affected extent of the carbothermal reduction reaction. Production and length-diameter ratio of the ZrC whiskers increased firstly and then decreased with the increase of heat treatment time. When heat treatment temperature was 1600 °C, catalyst concentration was 0.4 mol/L, heat treatment time was 2 h, the ZrC whiskers with diameter of around 130 nm and length of tens of microns were synthesized. The whiskers were composed of a single-crystal ZrC core and an amorphous ZrO2 shell. Growth of the ZrC whiskers was controlled by solid-liquid-solid (S-L-S) mechanism and the Ostwald ripening mechanism.

Studying the Process of Phosphogypsum Recycling into a Calcium Sulphide-Based Luminophor.

Currently, one of the most important problems of environmental protection is the deep and complex processing of mineral raw materials. This problem is especially relevant when processing substandard ores and production waste, one of which is phosphogypsum. This study examines the process of CaSO4/CaS composite material formation during the reduction of phosphogypsum with citric acid. The composite structure formation mechanism is proposed. The resulting materials are characterized using various methods, including X-ray diffraction (XRD), transmission electron microscopy, the Scherrer method, thermogravimetric analysis (TGA), and FT-IR spectroscopy. The reduced sample emits orange radiation in the range of 500-750 nm with a quantum yield of 0.17. Experimental results showed that the sample decomposition process in the solid state consisted of two components with a predominant contribution from the long-lived component (~46 ns). The optimal conditions for producing luminescent materials by reducing phosphogypsum with citric acid were determined: a heat treatment temperature of 1073 K, a holding time of 60 min, and a reducing agent mole fraction of 37%. It was found that an increase in temperature with a simultaneous decrease in heat treatment time, as well as a decrease in temperature with a simultaneous increase in heat treatment time, led to a decrease in the luminescent properties of the synthesized material compared to optimal values. The results can be used to develop technology for recycling large-tonnage waste from the chemical industry into luminescent materials.

Influence of post-welding heat treatment on microstructure and peculiarity of 10Cr9Mo1VNb boiler steel welded by hot wire TIG

Hot wire tungsten noble gas (HW-TIG) soldering tests are conducted on 10Cr9Mo1VNb boiler steel with multi-layer and multi-pass, and the soldered joints are subjected to post-weld heat treatment (PWHT) at different temperatures and times from 740°C to 790°C and 1 hour to 4 hours. The influence of PWHT on the microstructure and peculiarity of the joints are analyzed by using hardness, metallography, room temperature tensile testing, Charpy impact testing, SEM, and other experimental methods. The results show that the PWHT can transform the martensite formed in the welding process into tempered martensite, which can significantly improve the uniformity of the microstructure and peculiarity of each area of the joint. When subjected to heat treatment at 740°C, both strength and ductility improve with the increase of heat treatment time, while the plasticity gets a slight decrease. However, when subjected to heat treatment at 790°C, strength, plasticity, and ductility decrease with the increase of time, mainly due to the carbide coarsening such as M23C6 in the joint.

Nanostructured Yb2SiO5/mullite-SiC/Si environmental barrier coating with long-term stability at 1250 °C

In this work, nanostructured Yb2SiO5/mullite-SiC/Si environmental barrier coatings (EBCs) were prepared to investigate the effect of heat treatment on the microstructure and phase transition of nanostructured Yb2SiO5/mullite-SiC/Si coatings. The Yb2SiO5 content and microstructure evolution in the coatings were thoroughly analyzed before and after heat treatment. The results demonstrate a slight decrease in the porosities of nanostructured Yb2SiO5 and mullite-SiC coatings, accompanied by a gradual growth in grain sizes with increasing heat treatment time, indicating the nanostructured EBCs show good resistance to sintering. Moreover, the thickness of thermal growth oxidation layer is only 200 nm at 1250 °C for 500 h of heat treatment. In particular, the presence of the Yb2O3 phase has been observed to exert a favorable influence on the thermal stability of nanostructured EBCs. This work provides an innovative strategy for designing advanced EBCs with excellent high-temperature thermal stability.

Nondestructive volumetric optical analysis of corroded copper oxidation using 1700nm swept-source optical coherence microscopy.

This study presents a novel nondestructive analysis method for precise characterization of corroded copper oxidation using optical coherence microscopy (OCM). By exploiting the partial light transmission through metallic oxide layers, we employed a specialized OCM system with a wavelength of 1700nm and enhanced the analysis accuracy compared to conventional optical coherence tomography (OCT). The developed OCM system featured a numerical aperture (NA) of 0.15, providing improved surface profiling and higher lateral resolution than OCT. we developed a peak-finding algorithm to accurately determine the thickness of the copper oxide layer from the acquired interference data with zero padding. Our method was validated by comparing the measured thickness profiles with those obtained from scanning electron microscope (SEM) images of corroded metals. The copper oxidation specimens were prepared after heat treatment for 1, 2, 4, and 8 h in an alumina tube furnace at a temperature of 900 °C to find the correlation between the OCM thickness measurement. Additionally, the acquired enface 3D images enabled the identification of local corrosion distribution within a 4 mm × 4 mm area. The en-face mapping images are utilized to analyze the uniformity of the metal oxidation process across the imaging area of the copper oxidation specimens. With an increase in heat treatment time, the median value of the thickness histogram for the copper oxide within the area consistently remained around 10 µm. However, the thickness variation ranged from -2 µm to 5 µm. This indicates that as the heat treatment time progresses, the thickness of the copper oxide becomes more non-uniform. Our technique holds great potential for nondestructive and noncontact detection of metal corrosion and assessment of corrosion rates in various industrial applications. Future research efforts could focus on expanding the application of OCM to different metals and exploring its commercialization prospects for practical implementation in diverse industries.

In-situ investigate on the microstructure evolution, deformation and fracture mechanism of Mg-Gd-Zn-Mn alloy with varies of LPSO volume fraction

The induction of long-period stacking ordered (LPSO) phase through heat treatment was an effective method to strengthen magnesium alloys. In this study, the volume fraction of lamellar LPSO in the Mg-4Gd-1Zn-0.5Mn alloy was controlled by optimizing the heat treatment process. The research findings showed that with increasing heat treatment time, the volume fraction of LPSO initially increased then decreased until disappearing. The alloy treated at 500 °C for 2 h exhibited the highest volume fraction of lamellar LPSO, increasing from 1.64% to 13.68%. Further in-situ tensile tests were conducted on two types of alloys contain higher LPSO fraction (HL) and lower LPSO fraction (LL) at ambient temperature. The increased critical shear stress (CRSS) and obstacle effects on dislocations caused by LPSO effectively enhanced the strength of the alloy. The dominant deformation mechanisms of both HL and LL alloys are basal slip and twinning during tensile deformation. However, the HL alloy activated more non-basal slip significantly, which was ascribed to the activation of non-basal slip by LPSO kinking during deformation. Additionally, the bending and kinking of LPSO effectively restricted crack initiation and propagation, thereby enhancing the plasticity. The HL alloy exhibited fewer twin boundaries after deformation, which was attributed to the hindrance of twinning extension by LPSO.

Investigation of the Effect of Heat Treatment Time in Case of Recrystallization of Al99.5

In this study the effect of heat treatment time was investigated in case of recrystallization of Al99.5 material samples. Two different type were manufactured based on the previously applied cold forming. 12% and 24% cold forming was applied to the samples before the heat treatment procedure, which was always at 570 °C and cooled in water. Six different heat treatment time were investigated, namely 5, 10, 30, 60, 120 and 240 minutes. After the recrystallization procedure the microstructure and the mechanical properties were determined. It was found that in the case of the 12% cold formed samples after 30-minute-long heat treatment there were still signs of the original microstructure, however it does not affect the mechanical properties. The yield strength and the ultimate tensile strength were independent of the heat treatment time; they were only dependent on the grain size which was expected. A strong dependency can be discovered between the elongation at break and the heat treatment time. A tangent hyperbolic function was fitted on the measured data, which showed that the asymptote was ~29% for both type of samples. This is a 25% increase compared to the 5-minute-long heat treatment time samples, and this value was reached after ~120 minutes. Another result was that the elongation at break dependency on the grain size is decreasing with increasing heat treatment time.

Development of an electric furnace for heat treatment of vermiculite with curved surfaces of firing modules

A new modification of electric modular firing furnaces for heat treatment of vermiculite with curved surfaces of firing modules is considered. The basic designs of such furnaces consist of three or two flat modules installed at an angle to each other for pouring material from one module to another and firing in a thermal field created by electric heaters. With the same length of the refractory base of curved modules, the heat treatment time increases by 23 %, and the exit velocity of the swelling vermiculite grains decreases to 0,6‒0,65 m/s, which is enough so that all particles, regardless of size, do not settle at the exit of the modules and do not form congestion. Increasing the duration of firing does not reduce the productivity of the furnace, but reduces the specific energy intensity of this process. The energy consumption and energy intensity of vermiculite firing have been reduced by 13 %, but the module design is not optimal. Optimization of the size and shape of modules to increase the energy efficiency of the furnace unit is the task of subsequent research.

Effect of high-temperature heat treatment on electrochemical corrosion behavior of laser cladding Fe-based alloy coating in H2SO4 solution

Double-layer Fe-based alloy coatings were fabricated on the surface of ductile cast iron using high-speed laser cladding. The electrochemical corrosion behavior of the coatings in 0.5 mol/L H2SO4 solution was analyzed after heat treatment (HT) at 950 ℃ for 1, 2, and 3 h. The results show that many fine and dispersed particles were precipitated in dendrites after 1 and 2 h HT. The precipitates in the dendrites of the 3 h heat-treated aggregated, nucleated, and grew up, forming the blocky. At the same time, the intergranular part of the long-chain structure began to dissolve and break. The corrosion rate decreased significantly with the increase in HT time. The specimen had the most-nobel self-corrosion potential (−0.15 V) and the best corrosion resistance after 3 h HT.

Coating of AISI 1018 steel with the pack-boriding method

In this study, AISI 1018 steel with low carbon content was coated with the pack-boriding method at 950 °C for 2h and 4h. A two-layer structure was observed in the 2h boronized material: the thin FeB phase and the more prominent Fe2B phase. In addition to this two-phase structure, undesirable phases (SiC and Fe3O4) were detected in the material boronized for 4h. It was observed that the wear resistance and hardness of the boronized materials increased greatly, which is explained by the hard FeB and Fe2B phases. In addition, as the heat treatment time increases, the thickness of the FeB phase increases while the thickness of the Fe2B phase decreases.

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.

Improvement of superelasticity conditions in Cu-based shape memory alloys for seismic control applications

Shape memory alloys (SMAs) are smart materials with self-centering characteristics that can be used to reduce the earthquake damage to structures. In this paper, the optimal thermal treatment to obtain the ideal mechanical properties of a CuAlBe SMA wires for seismic protection applications is discussed. For this purpose, the uniaxial cyclic and monotonic stress-strain response of a 1.4 mm-diameter wire subjected to heat treatments applied for different durations is evaluated. Wire specimens are tested in multiple environments at several strain amplitudes and loading protocols. The variation of mechanical properties over time is also addressed. Test results show that a minimum treatment time of 25 min at 750 °C (∼200 μm) is necessary for obtaining superelasticity at all ambient temperatures tested. Also, as the heat treatment time increases, the residual strain, functional fatigue, strength, energy dissipation and hysteresis degradation decrease, but the superelasticity limit and low cycle fatigue life are increased. However, a 35 min treatment (∼400 μm) causes the loops to become unstable at high temperatures and the training process is not efficient. The best conditions for seismic protection purposes are achieved with a 30 min treatment (∼300 μm), due to its maximum recoverable strain of 6.5 %, 3.6 % equivalent viscous damping, negligible residual strain and stable hysteresis under all temperatures evaluated and over time. A low-cycle fatigue model based on the Coffin - Manson relationship is also proposed.

Toward ultrahigh thermal conductivity graphene films

With increasing demands of high-performance and functionality, electronics devices generate a great amount of heat. Thus, efficient heat dissipation is crucially needed. Owing to its extremely good thermal conductivity, graphene is an interesting candidate for this purpose. In this paper, a two-step temperature-annealing process to fabricate ultrahigh thermal conductive graphene assembled films (GFs) is proposed. The thermal conductivity of the obtained GFs was as high as 3826 ± 47 W m−1 K−1. Extending the time of high-temperature annealing significantly improved the thermal performance of the GF. Structural analyses confirmed that the high thermal conductivity is caused by the large grain size, defect-free stacking, and high flatness, which are beneficial for phonon transmission in the carbon lattice. The turbostratic stacking degree decreased with increasing heat treatment time. However, the increase in the grain size after long heat treatment had a more pronounced effect on the phonon transfer of the GF than that of turbostratic stacking. The developed GFs show great potential for efficient thermal management in electronics devices.

Phase transformation behavior of Ti-1023 under static heat treatment and dynamic thermo-mechanical coupling

The phase transformation of a near-β titanium alloy is extremely sensitive to the processing technique, which significantly affects its mechanical characteristics. The spherical α phase increases the plasticity of a β titanium alloy, whereas its needle-like α phase prevents dislocations and increases the alloy strength. In this study, we investigate the microstructural evolution and orientation relationship of Ti-1023 alloy under static heat treatment and dynamic thermo-mechanical coupling at 750 °C. The results indicate that under the thermo-mechanical coupling conditions, the spherical α phase precipitates at grain boundaries and low-angle grain boundaries, and its volume fraction increases from 10.5% to 23.2% as the strain rate decreases. The Burgers orientation relationship (BOR) between the α/β phases is gradually disrupted as the strain rate increases. On heat treatment, the α phase at the grain boundaries becomes discontinuous in a strip-like shape, whereas that within the grain appears needle-like. The grain-boundary α phase becomes more continuous as the heat treatment duration is extended, and the α phase gradually broadens. Moreover, the precipitated α more tends to obey the BOR. These results could provide important reference for the regulation of the microstructure of a near-β titanium alloy and the optimization of the process parameters of its deformation heat treatment. • Phase transition behavior of Ti-1023 alloy under thermo-mechanical coupling and static heat treatment conditions was investigated. • The α phase is spherically precipitated under thermal coupling conditions, and the volume fraction reaches a maximum at a strain rate of 0.001 s −1 • Under static heat treatment conditions, α phase precipitates needle-like and gradually broadens with increasing heat treatment time. • Schematic of α phase precipitation under thermal-mechanical coupling and static heat treatment of the alloy.

Microstructure and mechanical properties of heat-treated Mg–6.2Li–3.5Al–3Y alloy

To further improve the mechanical properties of Mg–Li alloys, the microstructure evolution and mechanical properties of Mg–6.2Li–3.5Al–3Y alloy after different heat treatment processes (holding at 250 °C, 300 °C, 350 °C and 400 °C for 30 min, 60 min and 120 min, respectively) have been investigated in this study. It is found that the Mg2Y eutectic disappears after heat treatment, and the volume fraction of Al2Y precipitated phase decreases first and then increases with increasing heat treatment time. In addition, The tensile test results reveal that the tensile strength of the alloy increases first and then decreases with the increase of heat treatment time. The tensile strength and ductility of the alloy reach 182 MPa and 12.7%, respectively, after heat treatment at 400 °C for 30 min, which are 35.8% and 36.5% higher than those of as-cast alloy. The evolution of Mg2Y eutectic and Al2Y phase during heat treatment processes at different time and temperatures are analyzed in detail. It can be concluded that the tensile strength of the alloy is improved by the combined effects of precipitation hardening due to the formation of Al2Y phase, and the solid solution strengthening due to the decomposition of Mg2Y eutectic and Al2Y precipitated phase.

NdFeB esaslı kalıcı manyetik alaşımların manyetik özelliklerine uygulanan ısıl işlemdeki sürenin etkisi

In our current study, NdFeB-based permanent magnet ribbon alloys were produced by using melt spinning method, which is one of the rapid solidification methods and very common in the production of ribbon-shaped, amorphous and/or semi-crystalline alloys. During the production of each NdFeB alloy, 15 wt.% of waste magnet was included in the composition of the alloys. The produced permanent magnet alloys were heat treated for 5 and 10 minutes by using a heat treatment temperature of 710 °C and very high heating and cooling rates of 285 K/s. The effect of the heat treatment time applied at the same temperature on the magnetic properties of the strip alloys was investigated. While the increase in heat treatment time resulted in a remarkable change in magnetic coercivity and maximum energy product properties, there was not much change in the properties such as saturation magnetization and magnetic remenance. As clearly seen, increasing heat treatment time resulted in a continuous decrease in magnetic coercivity from 5030.5 Oe to 2279.4 Oe, maximum energy product first showed a dramatic increase from 62.02 kJ/m3 to 103.73 kJ/m3, and then a dramatic decrease to 38.63 kJ/m3, indicating a decrease in the permanent magnetism of the alloy.