Solution Heat Research Articles

Effect of heat treatment on the microstructure and recrystallization of an SLM nickel-based superalloy

Heat treatment is essential for selective laser melting (SLM) of nickel-based superalloys. However, the conventional solution heat treatment method of cast superalloys usually leads to serious recrystallization in the samples. The recrystallized grain boundaries under high-temperature conditions reduce the strength of the alloy, which hinders their widespread applications in aerospace. In this work, a nickel-based superalloy with high γ′ content fabricated by SLM was heat-treated at different solution temperatures. The microstructure of the alloy in different heat-treated states was also characterised. A sub-solvus heat treatment was proposed, which can effectively reduce residual stress and inhibit recrystallization. The microstructure showed that the dislocation density was significantly reduced and recrystallized after the solution heat treatment at 1285 ℃/2 h+1290 ℃/2 h+1295 ℃/4 h and 1250 ℃/0.5 h, and the proportion of recrystallization were 60.0 % and 42.9 %, respectively. However, after sub-solvus heat treatment at 1240 °C/0.5 h, the sample dislocation density decreased and the volume fraction of recrystallization (3.2 %) was slightly higher than that of the as-SLM sample (2.5 %). The sample maintained a strong cubic texture in the build direction. After sub-solvus + aging heat treatment, the microstructure maintained a columnar grain structure. The γ/γ′ interfacial dislocation networks and dislocations pile-up were the main dislocation configurations.

Tensile and High Cycle Fatigue Performance at Room and Elevated Temperatures of Laser Powder Bed Fusion Manufactured Hastelloy X.

The application potential of additive manufacturing nickel-based superalloys in aeroengines and gas turbines is extensive, and evaluating their mechanical properties is crucial for promoting the engineering application in load-bearing components. In this study, Hastelloy X alloy was prepared using the laser powder bed fusion process combined with solution heat treatment. The tensile and high cycle fatigue properties were experimentally investigated at room temperature as well as two typical elevated temperatures, 650 °C and 815 °C. It was found that, during elevated-temperature tensile deformation, the alloy exhibits significant serrated flow behavior, primarily observed during the initial stage of plastic deformation at 650 °C but occurring throughout the entire plastic deformation process at 815 °C. Notably, when deformation is small, sawtooth fluctuations are significantly higher at 815 °C compared to 650 °C. Irregular subsurface lack of fusion defects serve as primary sources for fatigue crack initiation in this alloy including both single-source and multi-source initiation mechanisms; moreover, oxidation on fracture surfaces is more prone to occur at elevated temperatures, particularly at 815 °C.

Forecasting vaping health risks through neural network model prediction of flavour pyrolysis reactions

Vaping involves the heating of chemical solutions (e-liquids) to high temperatures prior to lung inhalation. A risk exists that these chemicals undergo thermal decomposition to new chemical entities, the composition and health implications of which are largely unknown. To address this concern, a graph-convolutional neural network (NN) model was used to predict pyrolysis reactivity of 180 e-liquid chemical flavours. The output of this supervised machine learning approach was a dataset of probability ranked pyrolysis transformations and their associated 7307 products. To refine this dataset, the molecular weight of each NN predicted product was automatically correlated with experimental mass spectrometry (MS) fragmentation data for each flavour chemical. This blending of deep learning methods with experimental MS data identified 1169 molecular weight matches that prioritized these compounds for further analysis. The average number of discrete matches per flavour between NN predictions and MS fragmentation was 6.4 with 92.8% of flavours having at least one match. Globally harmonized system classifications for NN/MS matches were extracted from PubChem, revealing that 127 acute toxic, 153 health hazard and 225 irritant classifications were predicted. This approach may reveal the longer-term health risks of vaping in advance of clinical diseases emerging in the general population.

Influence of cooling rate during the heat treatment process on the precipitates and ductility behavior of inconel 718 superalloy fabricated by selective laser melting

IN718 superalloy by elective laser melting (SLM) has shown great application prospects in the aerospace engine key parts. Different phases are precipitated during the SLM forming process. Although the Laves phase could be dissolved in dendrites by heat treatment, the specific evolution of the second phase particles is still unclear. In this work, the influences of solution and aging heat treatment, as well as cooling rate on the precipitates and ductility behavior of IN718 superalloy fabricated by SLM were systematically investigated. The medium temperature (980 °C) solution treatment regimes included three different colling rates and the control group only underwent aging treatment were studied. The results indicated that high temperature solid solution treatment effectively improved compositional segregation and significantly enhanced homogeneity of microstructure. The reduce of cooling rate at 980 °C was beneficial to the extension time and increased the number of δ phase precipitation. An appropriate number of δ phase improves the notch sensitivity and nails grain boundaries. In addition, the complex dislocations and second phase particles retards the migration of slip dislocations during ductility deformation process, which enhances the strength of SLM-ed IN718. The yield strength of specimens increases from 680 MPa to 1205 MPa. The microhardness is greatly improved as compared with as-deposited IN718, and the highest microhardness reaches 485 HV. The results provide a technical support and reference for formulating the heat treatment schedule of IN718 prepared by SLM.

Phase-field approach assisted solution heat treatment efficient design for novel multicomponent Co-based superalloys

Fast homogenization without incipient melting is the key to designing solution heat treatment (SHT) process for single crystal superalloys. In this paper, a multicomponent phase-field model coupled with solidus temperature is developed for dynamically tracking incipient melting temperature, TIM, of alloy during SHT. The simulation process runs completely automatically only by inputting the composition information of as-cast specimen. Based on the obtained TIM-time profile, the holding temperature and the time of SHT are determined. Applying this approach to Co–30Ni–11Al–4W–1Ta–4Ti–5Cr single crystal specimen, a gradual increased TIM from 1247 °C to 1293 °C within 72,000 s is obtained, and thus a stepwise SHT process with a short time of less than 20 h is designed. The experimental verification shows that after SHT, the segregation coefficient of the slowest diffusing element W decreased from more than 2 to 1.065, the content of harmful secondary phase has decreased to below 0.1%, and no incipient melting occurs.

Investigation on effect of high-efficiency solid solution and hot stamping process on microstructure evolution and mechanical properties of high-strength aluminum alloy

Aluminum alloy has become an important lightweight material in the automotive industry due to its excellent performance. The development of hot stamping technology has effectively promoted the application of high-strength aluminum alloys in auto parts. However, aluminum alloy hot stamping requires a long time for solid solution and aging heat treatment, which hinders its mass production application in the existing mature hot stamping production line. Therefore, this paper studies the effect of a high-efficiency solid solution and hot stamping process on the microstructure and mechanical property strengthening mechanism of high-strength aluminum alloy. The contact heating and hot stamping experiment device was designed. It was found that the temperature rise rate of the sheet during the contact heating process could reach 44.51 °C/s. The experiment results show that contact heating treatment with a solution temperature of 480 °C and a solution time of 20s can achieve the high-efficient solution treatment of the sheet metal. The high-temperature deformation behavior of 7075-T6 at different temperatures (300-450 °C) and different strain rates (0.01∼1/s) under the condition of high-efficiency solid solution rapid heating was studied.

Differential scanning calorimetry of age-hardenable aluminium alloys: effects of sample preparation, experimental conditions, and baseline correction

Precipitation processes in age hardenable aluminium alloys are often investigated by differential scanning calorimetry (DSC). The endothermic and exothermic peaks of the DSC signal correspond to the dissolution and formation of phases, respectively. However, parasitic effects can lead to an unintended curvature of the DSC signal. Although a baseline correction can be used, some imperfections typically remain. Additionally, sample preparation and experimental conditions can influence the precipitation sequence itself and, therefore, the DSC curve. In this study, we investigate the influence of sample preparation by milling and punching on DSC curves for three different aluminium alloys: EN AW-2024, EN AW-6082, and EN AW-7075. Additionally, the influence of quenching and natural ageing was investigated for EN AW-6082. We found that deformation introduced by punching the DSC samples with a piercing die after heat treatment leads to a change in the precipitation kinetics in 2xxx, 6xxx, and 7xxx series alloys. The influence was strongest for punching the samples after solution heat treatment and less significant for punching after artificial ageing. The influence of sample preparation can be avoided by punching the samples before solution heat treatment. If this is not practicable, milling of the samples is a good alternative. The choice of quenching medium and short storage at room temperature before measurement (5 min) had only small effects on the DSC curves. Moreover, the start temperature of the measurement was found to be crucial. For observing phases forming below 100 °C and for low-bias baseline correction, the measurement should start at low-temperatures (i.e. ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document} − 50 °C).

Microstructure and fracture toughness of 850°C quenched and aged Zr-2.5Nb alloy

The Zr-2.5Nb alloy pressure tubes manufactured by Water Quenched and Aged (WQA) fabrication route has reportedly exhibited superior resistance against in-reactor dimensional changes. WQA route comprises three consecutive thermo-mechanical treatments viz., solution heat treatment (SHT), cold working and vacuum aging, which govern the final microstructure and therefore fracture toughness of the pressure tube material. This work describes the influence of SHT soaking duration, degree of cold working and aging temperature on the microstructure and fracture toughness of WQA Zr-2.5Nb alloy. WQA pressure tubes are expected to have better resistance to in-reactor dimensional changes. However, if proper care of hydrogen absorption during thermo-mechanical processing is not taken, though resistance to creep will improve expectedly but fracture toughness at ambient temperature will deteriorate.

Study on the heat and mass transfer characteristics of wet air and solution on the surface of corrugated packings at lower ambient pressure

Study on the heat and mass transfer characteristics of wet air and solution on the surface of corrugated packings at lower ambient pressure

Tailoring the microstructure and deformation mechanisms of an additively manufactured nickel-based superalloy by post-aging heat treatment

Laser powder bed fusion (LPBF) is a new method for preparing the nickel-based superalloy hot-end components. This study systematically investigated the microstructural characteristics and mechanical performance of a γ′-strengthened Haynes 230 alloy after solution heat treatment (SHT) and aging heat treatment (AHT). The results indicate that γ′ phases continue to grow as the AHT temperature increases. The volume fraction of γ′ phases increases first and then decreases. The maximum γ′ phase fraction can be achieved at 750 °C. The yield strength (YS) of the AHT samples at 25 °C and 800 °C increases first and then decreases, which is mainly caused by γ′ phase fraction evolution. The SHT+750 sample presents an excellent integration of tensile performance at 25 °C and 800 °C. The primary deformation mode at 25 °C is stacking fault (SF) shearing. The δ precipitation and high-density Lomer-Cottrell (L-C) locks are the primary reasons for the higher work hardening rate of the SHT+850 sample. The transition of the dominant deformation mechanism from SF shearing at 25 °C to Orowan bypassing at 800 °C leads to a dramatic reduction in the YS of the SHT+850 sample.

Programming and validation of a novel green procedure for the production of essential oil from Lavandula angustifolia

Lavandula angustifolia (lavender) essential oil (LEO) is extremely popular and beneficial. In the present study, LEO was extracted with green ultrasound-assisted supercritical CO2 (UscCO2) and other classical methodologies. The highest yield of LEO (5.32 % (w/w)) was achieved with the UscCO2 process, followed by hexane extraction (4.32%), scCO2 extraction (3.94 %) and hydrodistillation (HD; 3.69 %). The contents of two dominant aromatic ingredients, linalool (29.93 %) and linalyl acetate (35.08 %), obtained by the UscCO2 procedure were also the highest. Remarkably, the linalyl acetate content in UscCO2-derived LEO was nearly triple that in LEO extracted via HD (12.33 %). The novel UscCO2 technique not only provided the highest LEO quality but also revealed the highest extraction efficiency under mild extraction parameters. The dynamic solubility of LEO in the UscCO2 and scCO2 procedures was further determined to confirm the kinetic efficacy. The dynamic solubility was simulated with three density-based models, which provided excellent agreement with the experimental results. The approximate heat of vaporization, total heat of solution and heat of solvation obtained from UscCO2 dynamic extraction of LEO were significantly lower than those obtained from the scCO2 procedure. The kinetic and thermal effects of ultrasonic energy substantially contributed to the excellent performance of UscCO2.

Optimizing Tensile Properties and Hardness of Inconel 718 by Cold Rolling

The as-received commercial Inconel 718 material was solid solution heat treated (ST), cold-rolled (CR), and precipitation-hardened (PH) to investigate the effects of deformation on the tensile properties, hardness, and texture. Three sets of specimens (0%, 20%, and 50% CR) were ST at 1100 °C/1 h, CR, and aged (720 °C/8 h + 650 °C/8 h) for the analysis. The ultimate tensile strength (UTS), 0.2% yield strength (YS), and elongation of 50% deformed condition were 1645 MPa, 1512 MPa, and 3.8%, respectively. The 20% deformation resulted in a balanced UTS (1348 MPa), YS (1202 MPa), and elongation (11%). The contribution of precipitation hardening to the strength decreased, while the contribution of CR increased with an increasing percentage of deformation. As the level of deformation increased, the size and quantity of γ″ decreased proportionally. The CR specimens produced a high density of nano/micro twins with twin planes oriented perpendicular to the RD-ND surface. The gradient of crystal orientation and internal features of large austenitic grains were generated by their preferred rotation. The cross-slip of screw dislocations induced a complete β-fiber consisting of {110}<112>, {112}<111>, and {123}<634>, with doubled intensity at the higher deformation. Additionally, the specimens were highly susceptible to the twinning-induced orientation emerged by a predominant <110>//ND. In the as-deformed condition, an incomplete but intense α-fiber, clustered between {110}<001> and {110}<112>, was characterized. Apart from achieving the highest strength, the current work demonstrates the effects of CR on the material strength without the complex influences of δ precipitates.

Effect of interrupted cooling on microstructural evolution and microhardness of FGH97 nickel-based PM superalloy

Interrupted cooling experiments of FGH97 nickel-based powder metallurgy (PM) superalloy with different cooling rates were carried out using a DIL805A quenching dilatometer. The microstructural evolution of the γ′ precipitates during cooling after solution heat-treatment was investigated by means of field emission scanning electron microscopy (FE-SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Vickers microhardness tests were performed on the samples that were interrupted at different temperatures to establish a relationship between microstructure and mechanical properties. The results revealed that the secondary γ′ precipitates preferentially nucleated at a higher temperature, and gradually grew during the cooling stage. Meanwhile, the morphology of the secondary γ′ precipitates transitioned from spherical to cubic, to rounded cuboidal, to a butterfly-like shape, and ultimately splitting into octo-cubes, whose driving force was attributed to the mutual competition between surface energy and elastic strain energy. During the initial stages of the cooling process, the microhardness decreased due to the growth and coarsening of the secondary γ′ precipitates. As the temperature decreased, the supersaturation within the matrix became sufficient to overcome the energy barrier for a second burst of nucleation, the tertiary γ′ phases precipitated, resulting in an increase in microhardness.

The effect of Hafnium on the microstructure and tensile property in a Ni-based superalloy

The effects of Hafnium on the microstructure and tensile property of a Ni-based superalloy after solution heat treatment and long-term thermal exposure were investigated with field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD). The results revealed reveal that Hf intensified intensifies the element segregation and promoted promotes the precipitation of MC carbide and honeycomb-like Ni5Hf phase in the as-cast alloy. The solid solution strengthening and second phase (MC) strengthening effects are both enhanced in the alloy doping 0.5 wt% Hf after solution heat treatment. Therefore, the tensile yield strength at 700 °C of the alloy with 0.5 wt% Hf is higher than that in the Hf-free alloy. Otherwise, a large amount of the low melting point Ni5Hf phases appear in the alloy with 0.8 wt% Hf. Ni5Hf phase is prone to become the crack initiation, which decreases diminishes the yield strength in the alloy with 0.8 wt% Hf. The addition of 0.5 wt% Hf can inhibit the formation of needle-like δ phase at grain boundary due to the decrease of grain boundary energy and diffusion rate at grain boundary. Therefore, the 700 °C tensile strength and ductility increase simultaneously in the alloy with 0.5 wt% Hf after thermal exposure at 700 °C.

Effect of ultrasonic shot peening on microstructure and mechanical properties of GH3230 superalloy during selective laser melt solution heat treatment

Additive manufacturing (AM) is widely used because of its well-known advantages, but there are some disadvantages including microstructure inconsistencies and harmful residual stresses, which can lead to premature part failure. In this study, the microstructure, and mechanical properties of GH3230 alloy processed by AM are changed by a new post-treatment method, which combines thermal solution treatment (ST) and ultrasonic shot peening (USP). The microstructure evolution of GH3230 after ST and USP after ST is investigated experimentally. The experimental results show that equiaxed crystals and M23C6 carbides appear after solution treatment. After ST, USP is performed, and the gradient microstructure is formed perpendicular to the shot peening surface. Dislocation entanglement and grain refinement occur in the plastically deformed layer. In addition, the carbide interacts with the dislocation. After ST, USP can produce a high level of residual compressive stress in the plastic deformation layer. This combination of ST and USP helps to improve the mechanical properties of additive manufactured parts by changing their microstructure and residual stress distribution.

Effect of heat treatment on the microstructure and mechanical properties of biocompatible Ti–Ta–Nb–Zr alloys prepared by selective laser melting

Abstract In this paper, a low elastic modulus, non-cytotoxic Ti-10Ta-2Nb-2Zr titanium alloy was prepared by selective laser melting additive manufacturing. The effect of annealing and solution heat treatment on the structure, mechanical properties, and tribological behavior were investigated. The results show that the microstructure was composed of the main α′ phase and a small amount of β phase. Heat treatment improved strength and elongation. The ultimate tensile strength (UTS) and elongation of the deposited specimen were 807 ± 8.74 MPa and 6.6 ± 0.75 %, respectively. After annealing, the UTS was nearly the same, but the elongation increased to 15.3 ± 0.95 %. After solution and aging, the UTS and elongation increased to 873 ∼ 813 MPa and 9.25–11.9 %, respectively. The elastic modulus of the deposited specimen was 120 ± 6.81 GPa. The elastic moduli of heat treated specimens ranged from 74 ± 4.04 to 96 ± 5.13 GPa. The elastic moduli of heat treated specimens were close to that of β-type titanium alloys. The wear mechanism was mainly abrasive wear and oxidative wear. Compared with the deposited and annealed specimens, the solution and age treated specimens had low friction coefficients and much better wear resistance. In terms of properties and cost, the designed alloy has great potential in the medical implant field.

Bonding Strength of 12Cr-0.4C/Low Carbon Steel (LCS) Weld Joint After Solid Solution Heat Treatment

Bonding Strength of 12Cr-0.4C/Low Carbon Steel (LCS) Weld Joint After Solid Solution Heat Treatment

Effect of Heat Treatments on Microstructure and Mechanical Properties of Fe-Mn-Ni-Al-Gd Shape Memory Alloy

There are significant scientific and industrial efforts to develop and optimize Iron-based shape memory alloys (SMA) such as FeMnNiAl for cost-sensitive applications. This alloy system shows shape memory and superelastic properties across a large temperature range. However, many studies have pointed out the need for rather complex thermo-mechanical treatments for the optimization of the SMA properties. In addition, works considering the effects of alloying on the development of microstructures that are more conducive to pseudo-elasticity in this system remain limited. Hence, systematic studies aiming at the investigation of the microstructural evolution of the FeMnNiAl(Gd) system are of great interest. In this study, solution heat treatment is done to tune the microstructure for optimum mechanical properties. The effect of phase distribution on mechanical properties is investigated at different heat treatments. Whereas cyclic heat treatment induced abnormal grain growth (AGG) in all samples, so large grains were obtained. The phase variation and elemental composition are analyzed by X-ray diffraction and Energy Dispersive Spectroscopy, respectively. The microstructure and phase distribution are observed using Scanning Electron Microscope and then related to the microhardness results. The microstructure has a good correlation with mechanical properties where the fine distribution of phases results in a higher hardness number.

Anomalous electromagnetic wave absorption of MAX phase ceramic powder achieved through high entropy solid solution and melt pool heat transfer preparation method

Anomalous electromagnetic wave absorption of MAX phase ceramic powder achieved through high entropy solid solution and melt pool heat transfer preparation method

Practical synthesis of (S)‐pyroglutamic acid

AbstractA simple and rapid synthesis of (S)‐pyroglutamic acid was developed by the thermal cyclodehydration of (S)‐glutamic acid under solvent‐free conditions, with continuous swirling during heating (220°C) to ensure homogeneity of the melt. The reaction proceeds until the bubbles disappear, not exceeding 5 min. The heating immediately ceases, then cooling the reaction vessel to prevent degradation and racemization. (S)‐pyroglutamic acid is obtained in 70% yield, and the enantiomeric ratio is 97:3. The same reaction under microwave heating in an aqueous solution afforded a low yield of racemic product.