Increasing Solution Temperature Research Articles

Evaluation of H2O2, H2, and bubble temperature in the sonolysis of water and aqueous t-butanol solution under Ar: Effects of solution temperatures and inorganic additives of NaCl and KI

The yields of H2O2 and H2 formed in the sonolysis of aqueous solution under noble gas are representative indexes for understanding the chemical effects of ultrasonic cavitation bubbles. In this study, the yields of H2O2 and H2 formed under Ar were evaluated as a function of the concentration of NaCl or KI. When these yields were analyzed by using a normalization technique, it was confirmed that the yields of H2 were more clearly related to Ar solubility than those of H2O2, suggesting that H2 is a more real probe to understand the chemical effects of cavitation bubbles in water. The effects of NaCl on sonochemical formation of oxidants were also compared with those of KI. When aqueous t-butanol solution was sonicated, the yields of H2 and the maximum temperature attained in a collapsing bubble (bubble temperature) decreased with increasing solution temperature and salt concentration, suggesting that these parameters affected the quantity related to the number (and/or size) of active bubbles as well as the quality related to the bubble temperatures.

Effects of solution treatment on microstructure and properties of Ti-5.7Al-3.9Sn-0.91Mo-3.4Zr-0.40Si-0.38Nb-0.95Ta titanium alloy

This study investigated the effects of solution treatments under various conditions on the matrix and silicides microstructure and their impact on the mechanical properties of high-temperature Ti60 (Ti-5.7Al-3.9Sn-0.91Mo-3.4Zr-0.40Si-0.38Nb-0.95Ta) titanium alloy. The microstructure evolution during solution treatments was characterized, and the tensile properties at 600 °C and room temperature (RT) were investigated. The results show that the fraction and grain size of martensite and silicides can be tailored through solution treatments. With increasing solution temperature, the fraction of primary α (αp) phase and silicides decreases, while that of the transformed β (βt) microstructure increases. After solution treatment at 1025 °C, the yield strength (YS) and ultimate tensile strength (UTS) reach 685.0 MPa and 900.8 MPa, respectively, at 600 °C, increasing by 18.0% and 27.0%, respectively, compared to the initial state. The elongation (EL) remains at 16.2%. The strengthening mechanisms of Ti60 alloy include grain boundary strengthening of the αp phase and martensite formed during rapid cooling, as well as precipitation strengthening of the silicides. With increasing solution temperature from 950 °C to 1025 °C, the fraction of martensite strengthening increases from 38.4% to 89.3%, while the fraction of precipitation strengthening of silicides decreases from 3.63% to 1.17%.

The effect of post heat treatment on microstructural evolution and mechanical properties of Ti2AlNb intermetallic alloy prepared by point-forging and laser-deposition

Ti2AlNb-based intermetallic alloy is considered to be the latest class of light-weight structural material severing in the range of 600∼750 °C. Hybrid interlayer point-forging with laser-deposition (PF-LD) provides a new idea to produce near-net-shape Ti2AlNb part with promising mechanical performance. The present work mainly investigated the effect of post heat-treatment on microstructural evolution and tensile mechanical properties of PF-LDed Ti2AlNb alloy. The experimental results demonstrated that solution-treated at 940 °C–1020 °C followed by aging at 840 °C was effective to regulate phase morphology and tensile mechanical properties. With the consecutive increase of solution temperature, more fine-lamellar O-phase was reprecipitated within parent B2/β matrix during secondary aging treatment. The ultimate tensile strength was enhanced significantly from 1055.5 MPa to 1148.1 MPa with the help of precipitation hardening effect. In the meantime, stronger stress accumulation introduced by fine-lamella also exerted a detrimental impact on tensile strain capability, and the elongation after failure decreased from 10.9 % to 7.4 % with increasing solution temperature. Considering above results, this study provides a basic research for exploring the heat treatment of PF-LDed Ti2AlNb-alloy, and it is feasible to obtain high-strength and high-ductility properties by tailoring phase morphology.

Corrosion behaviour of superaustenitic stainless steel N08029 in harsh acidizing environment

It is vital to examine the resistance to corrosion of corrosion resistant alloys (CRAs) in severe oilfield corrosive environments such as acidizing to validate their performance. Super austenitic stainless steel (SASS) UNS N08029 was recently developed to offer competitive and improved corrosion resistance in extreme and aggressive environments. However, no systematic studies have evaluated the N08029 performance in acidizing conditions. In this study, N08029 was investigated in harsh acidizing conditions of different HCl concentrations (up to 25 % HCl), long immersion duration (up to 48 h), and at elevated temperatures (up to 80 °C) using both weight loss and electrochemical measurement techniques. Interestingly, all the test methods show that the corrosion resistance of the SASS increases with increasing the concentration of HCl acid. This may be due to the formation of ferric chloride protective layer on the steel surface after the dissolution of the formed chromium oxide layer by the increasing acid concentration. The decrease in the corrosion rate observed at higher HCl concentrations is because the higher concentration of HCl causes the more ferric chloride layer to form on the metal's surface. This layer protects the metal from further acid attack. Also, after 24 h immersion duration, a decrease in corrosion rate with further increase immersion duration was observed which may is also due to the formation of more ferric chloride protective layer. However, the corrosion resistant of the SASS was observed to decrease with increase in temperature of the test solution. The decreased resistance of the SASS to corrosion with increase in temperature is associated with the instability or damage of the passive/protective film on the surface of the SASS at elevated temperatures.

Determination of Critical Micelle Concentration (CMC) of Sodium Stearate Solution in Distilled Water

Surfactant is an organic compound having polar and nonpolar parts. The specific conductivity of sodium stearate surfactant in double distilled water has been studied by conductometric method at three temperatures (298.15, 308.15, and 318.15) K. conductivity of the surfactant increases with increase in temperature and concentration of solution. Critical Micelle Concentration (CMC) of sodium stearate was determined attemperature 298.15 K is 0.00095Mol/lit using the easy plot software. FESEM image shows themorphological structure of the sodium stearate surfactant.

Effects of solution aging treatments on microstructure features, tensile properties and low-cycle fatigue behavior of Ti-6.2Al-4.26Mo-1.33Mn alloy

High-performance titanium alloy fasteners play an important role in the aerospace industry as important general basic parts. This work developed a high-elastic-modulus Ti-6.2Al-4.26Mo-1.33Mn alloy with good balance of strength and plasticity through regulating its primary equiaxed α (αp) phase with solution aging treatment. The influence of αp on the tensile properties and low-cycle fatigue (LCF) behavior of the alloy was investigated systematically, and the crack propagation mechanism of fatigue fracture of titanium alloy was revealed. The results show that with increasing solution temperature, the content of αp phase decreases from 43.6 % to 15.1 % in the range of 825 °C–925 °C, and the LCF life is increased by almost 2 times. However, the size of αp phase is almost unchanged with a diameter of about 2.3 μm. With the increase in solution temperature, the tensile strength of the alloy is improved, while the plasticity decreases gradually. At the solution temperature of 875 °C, the ultimate tensile strength (UTS) of the alloy is 1350 MPa, which is 18.6 % higher than the as-forged alloy, with an elongation (El) of >7 %. Moreover, the fatigue performance is also significantly improved, which is associated with the reduced αp phase that was characterized to act as crack initiations and crack propagation path.

Investigation on work hardening rate of Al-Zn-Mg-Cu alloy under solid solution process and thermomechanical coupled multi-step fast aging process

In this paper, the work hardening rate of Al-Zn-Mg-Cu alloy in the conditions of solid solution and thermo-mechanical coupled fast aging were investigated separately, and the main research content and results are as follows. Under the solid solution processes at different temperatures, the uniaxial tensile test curves of work hardening rate are relatively dispersed at a lower strain rate, and the work hardening rate increases with the increase of solution temperature. Then, as the strain rate increasing, the work hardening rate curves at each solution temperature gradually converge, until all curves intersect at a common intersection point. The above mechanism is attributed to the comprehensive effect of precipitates, solid solutions, and dynamic strain aging in the matrix. For the thermo-mechanical coupled aging, the work hardening rate has a great different with that of solid solution process. Consequently, the influence of pre-deformation on the work hardening rate were investigated, which concludes the curve shape type and the softening coefficient. The introduction of dislocation have some significant influences on the work hardening rate. Firstly, it makes the shape of work hardening rate curves change from shape 1 to shape 2. On the other hand, as the pre-deformation increasing, the variation law of softening coefficient shows an abnormal trend that is different from the ordinary law, which is due to the coordinated effect between dislocation density and dislocation induced precipitation. Furthermore, in order to reveal the internal mechanism in depth, the microstructure are observed by TEM (Transmission electron microscope). Finally, a targeted set of analytical models for work hardening rate were established, especially the mathematical explanation of the multicollinearity phenomenon of work hardening rate curves in the solid solution condition.

Effect of Temperature and NaClO on the Corrosion Behavior of Copper in Synthetic Tap Water

The corrosion behavior of copper was investigated in synthetic tap water with and without sodium hypochlorite (NaClO) at different temperatures during immersion for 70 d by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical measurement techniques. The weight loss corrosion rate and pit depth of copper first increase and then decrease with the change in solution temperature from 25 to 80 °C. This is mainly related to the corrosion products formed on the copper surface. The main corrosion products change from Cu2O and Cu2(OH)2CO3 to CuO with the increase in solution temperature. The presence of 3 ppm NaClO slightly increases the weight loss corrosion rate and pit depth of copper under all temperatures except for 50 °C and reduces the temperature of the maximum corrosion rate from 50 to 40 °C. Free chlorine reduction accelerates the cathodic reaction of the corrosion process.

Corrosion properties and mechanism of Ti43Zr27Mo5Cu10Be15 amorphous composites in various conditions

The in situ Ti43Zr27Mo5Cu10Be15 amorphous composites were investigated for their corrosion properties in solutions of NaCl, HCl, H2SO4 and NaOH. Electrochemical testing, SEM, EDS and XPS analyses revealed that pitting in NaCl and HCl solutions caused local surfaces damage. Amorphous matrix corrodes slightly in H2SO4 solution. Uniform corrosion occurred in NaOH solution without passive film formed, leading to the worst corrosion resistance. The optimal corrosion performances for NaCl and HCl solution are achieved at 0.5 mol l−1 and 0.75 mol l−1 separately which is related to the shortage of oxygen content in the solutions. While, the best corrosion performances for H2SO4 and NaOH solution are at 0.25 mol l−1. Moreover, the research on the effect of temperature was conducted in 3.5 wt% NaCl solution, it was found that Ti43Zr27Mo5Cu10Be15 amorphous composites exhibited good corrosion resistance at 298 K, while the E corr declined with increasing solution temperature.

Effect of Two-Step Solution Treatments on the Microstructure and Mechanical Properties of B357 Aluminum Alloy

AbstractThis study investigates the effect of two-step solution treatments and aging times on the microstructure and mechanical properties of B357 Al–Si alloy, part of the most widely used cast aluminum alloy. Three sets of artificial aging heat treatments were conducted on the tensile samples prepared from B357 alloy produced by low-pressure die casting. Firstly, the conventional artificial aging heat treatment (T6) was carried out by solutionizing the tensile samples at 543 °C for 8.5 h, water quenching at 60 °C, and then artificially aging for 8.5 h at 160 °C. In the two-step solution treatment, the samples were solutionized at 400, 440, 480, and 520 °C for 4 h and then solutionized at 543 °C for 8.5 h and water quenched to 60 °C and then artificially aged for 8.5 h at 160 °C. Thirdly, the samples were solutionized at 480 °C for 4 h, solutionized at 543 °C for 8.5 h, water quenched to 60 °C, and artificially aged for 3–192 h. Despite different solutioning and aging processes, no significant differences were observed in the microstructures of the samples. Si particle coarsening was observed with increasing solution temperature (400–520 °C) and aging times (3–192 h). Si-containing dispersoids and dispersoid-free zones (DFZ) were observed in the primary-α matrix. While DFZ width increased with temperature and aging, dispersoid zones in primary-α dendrites significantly decreased. Differential Scanning Calorimetry (DSC) analysis shows that two-step solution treatment in B357 alloy increases β′ precipitates for Mg2Si precipitation strengthening. The two-step solutionized and aged sample showed the best combination of strength and ductility among all aged samples. B357 alloy exhibited the highest yield and tensile strength (309.7, 366.1 MPa) with 6% elongation for two-step solutionizing and 48 h aging. All aged B357 alloys showed ductile fracture as the primary fracture mode. However, brittle fractured Si particles were observed on the fracture surfaces.

Influences of solution temperature on microstructures and performance of electron beam welded joints of laser powder bed fusion TC11 thin-walled samples

The effects of subtransus treatment (750 °C, 800 °C, 850 °C, 900 °C, and 950 °C) as well as supertransus treatment (1100 °C) on the microstructures and mechanical performance of electron beam welded (EBW) joints of laser powder bed fusion (LPBF) TC11 alloy were investigated. At a solution temperature of 950 °C, globular α phases and transformed β phases were observed in the joint. When the solution temperature exceeded the β transus temperature (Tβ), α colonies and massive α phases emerged in the joints, resulting in Widmanstatten structures. The base metal (BM) exhibited the highest microhardness, followed by the heat affected zone (HAZ), whereas the fusion zone (FZ) demonstrated the lowest microhardness. As the solution temperature increases, the microhardness of joints decreases at first and then increases. Notably, the joint subjected to a solution temperature of 850 °C exhibited the lowest microhardness. When the solution temperature was ≥900 °C, transformed β phases emerged within the joints, resulting in an elevation of microhardness. Below Tβ, the elongation of welded joints gradually augmented while the tensile strength reduced at first and then increased with the rising solution temperature. Microstructures in joint with solution temperature of 950 °C consisted of lamellar α phases, globular α phases, and transformed β phases. As a result, the joint exhibited an optimal balance between strength (1103.1 ± 34.9 MPa) and plasticity (9.37 ± 0.20%). Ductile fracture characteristics with dimples on the fracture surface were observed in the tensile samples. Therefore, it can be concluded that a solid solution temperature of 950 °C is optimal for LPBF TC11 alloy.

Adaptation of a heat-treatment condition to a precipitation-hardened nickel-based superalloy produced by laser powder bed fusion

This study evaluated the microstructural evolution and mechanical properties of a novel printable nickel-based superalloy subjected to a solution aging treatment. The microstructures of the alloys in as-fabricated and solution-treated states were characterized using a combination of electron backscatter diffraction analysis and scanning electron microscopy. The findings indicate that the cellular crystals gradually transitioned into equiaxed grains with increasing solution temperature. The grain orientation shifts from the <001> orientation perpendicular to the building direction to a random orientation. The average grain size increased, the proportion of low-angle grain boundaries (LAGBs) decreased, and the percentage of annealing twin boundaries (TBs) increased from 0.18% in the as-fabricated state to 65.68% at 1230 °C solution treatment (ST). After lower-temperature ST, a large amount of primary γ′ and η phases precipitated in the as-fabricated alloy, with spherical and needle-like shapes, respectively. As the solution temperature increased, the quantity of the primary γ′ phase gradually decreased, and the η phase became relatively more elongated. At 1130 °C ST, both phases dissolved; following aging treatment, γ′ phase precipitated fully. High strength (1493 MPa) was achieved after direct aging treatment, attributed to the combination of cellular structures and numerous LAGBs produced during deposition with the complete precipitation of γ′ phase during aging. This study demonstrated that laser powder bed fusion alloys can achieve excellent mechanical performance through direct aging without needing ST.

Influence of quenching plus aging on microstructures and mechanical properties evolutions for Ti-Al-Sn-Zr-Mo-Si-Nb-Ta-Er-C near-α high temperature titanium alloys

The microstructures and mechanical properties of β-forged and as-heat treated high temperature titanium alloys were carefully investigated. Heat treatments with solution processes varying from 940℃～1010℃ and aging at 650℃ after water quenching were adopted. After forging, prior β grains were squashed and elongated. The content of the primary α phase decreased with increasing solution temperatures, while the content of the transformed β structures increased. After water quenching plus aging processes, super-fine secondary α lamellas with widths of 80～400 nm precipitated in transformed β structure. Secondary nano-scale silicides with a size of ～82 nm re-precipitated. More α2 phase particles with a mean size of 8.00 nm were dispersively and uniformly precipitated. After heat treatment at 1000℃, the room temperature ultimate strength and yielding strength were enhanced by 241 MPa and 228 MPa, reaching 1256 MPa and 1151 MPa, respectively. The high temperature ultimate strength and yielding strength were enhanced by 119 MPa and 128 MPa, reaching 756 MPa and 669 MPa, respectively. The high temperature elongation increased to 13.6%. The excellent mechanical properties compared to the previously studied were ascribed to the precipitation of super-fine secondary α lamellas in βt, dispersed nano-scale silicides and α2 particles, and the superior mixing proportion of Pα and βt acquired after optimization of heat treatments.

Synergistically achieving high strength and impact toughness in Ti–6Al–4V-0.5Mo-0.5Zr alloy pipe with bimodal microstructure

To achieve high strength and high impact toughness, three kinds of bimodal microstructure of Ti–6Al–4V-0.5Mo-0.5Zr alloy pipe were tailored through solution treatment at the α+β phase region (860 °C, 890 °C, and 920 °C) and followed by aging at 500 °C. The bimodal microstructure consists of the primary α (αp) and β-transformed domain (βt), in which the secondary α phase (αs) precipitated in the β matrix, with different volume fraction. With the increase in solution temperature, the grain size of αp remained unchanged while the volume fraction decreased. At the same time, the volume fraction of βt and the width of αs phase increased. Furthermore, the content of low-angle grain boundaries inside the αp phase decreased. Subsequent aging resulted in finer precipitation of αs within the βt domain. Solution treatment at 890 °C and ageing at 500 °C (denoted as the STA890 sample) achieved an excellent combination of yield strength 903 MPa, tensile strength 1023 MPa, elongation 12.9%, and impact energy 31 J. With the increase of αs width, the strength of the alloy decreased, and the ductility increased slightly. Higher impact energy originated from {10 1‾ 2} tension twins activated in the STA890 sample during the impact loading process, αp and βt underwent severe bending and plastic deformation. The present study provides a feasible industrial heat treatment strategy for improving impact energy with high strength of the α+β titanium alloy pipe used for oil drilling.

Chemotherapeutics-Loaded Poly(Dopamine) Core-Shell Nanoparticles for Breast Cancer Treatment.

Chemophotothermal therapy is an emerging treatment of metastatic and drug-resistant cancer anomalies. Among various photothermal agents tested, poly(dopamine) provides an excellent biocompatible alternative that can be used to develop novel drug delivery carriers for cancer treatment. This study explores the synthesis of starch-encapsulated, poly(dopamine)-coated core-shell nanoparticles in a one-pot synthesis approach and by surfactant-free approach. The nanoparticles produced are embellished with polymeric stealth coatings and are tested for their physiologic stability, photothermal properties, and drug delivery in metastatic triple-negative breast cancer cell (TNBC) lines. Our results indicate that stealth polymer-coated nanoparticles exhibit superior colloidal stability under physiologic conditions, and are excellent photothermal agents, as determined by the increase in temperature of solution in the presence of nanoparticles, upon laser irradiation. The chemotherapeutic drug-loaded nanoparticles also showed concentration-dependent toxicities in TNBC and in a brain metastatic cell line. SIGNIFICANCE STATEMENT: This study develops, for the first time, biocompatible core-shell nanoparticles in a template-free approach that can serve as a drug delivery carrier and as photothermal agents for cancer treatment.

Improving the comprehensive mechanical property of the AlSi10Mg alloy via parameter adaptation of selective laser melting and heat treatment

In this work, the AlSi10Mg alloys with distinct molten pool structures, namely fish-scale and lamellar, were fabricated by using selective laser melting (SLM) technology. The effects of solid solution temperature on the microstructural evolution and mechanical properties of the two types of alloys were systematically investigated. The relationship among initial structure, heat treatment and mechanical properties was revealed. The experimental results showed that for the alloy with fish-scale structure, Si diffused more easily after solid solution treatment due to the finer eutectic network, resulting in a larger Si particle size. At 510 °C, the nano Si particles in the fish-scale sample basically disappeared, but a small amount of nano Si particles still existed in the lamellar sample, leading to a bimodal distribution in the Si particle size. Different sizes and distributions of Si particles present different strengthening mechanisms and affect the nucleation and growth of recrystallized grains in the α-Al matrix, leading to significant differences in mechanical properties. The strength of the lamellar sample decreased with increasing the temperature, and the abnormally growth of grains could be found after being treated at 510 °C, resulting in a poor mechanical property. The strength of fish-scale sample first decreased and then increased with the increase of solid solution temperature. When the alloy with fish-scale structure was solid solution treated at 510 °C, Si particles could promote the nucleation of recrystallized grains but hinder their growth, and the ultimate tensile strength decreased from 478.8 MPa of SLMed state to 393.4 MPa, a reduction of 17.8%, while the elongation increased from 7% to 21%, an increase of 300%, showing an excellent overall mechanical property. Therefore, the present study demonstrates that adjusting the SLMed molten pool structure and heat treatment parameters is necessary to obtain a good combination of microstructure and mechanical property.

The beneficial effect of yttrium microalloying in the solid solution treatment of AISI 321 stainless steel：Grain refinement and inclusions modification

Solid solution treatment is an important means of regulating the microstructure and mechanical properties of austenitic stainless steel, and a suitable solid solution process window is critical for austenitic stainless-steel service. In this paper, the effect of (RE) yttrium and solid solution temperatures on the microstructure and mechanical properties of austenitic stainless steel was investigated by adding trace amounts of RE yttrium to AISI 321 stainless steel with different solid solution temperature treatments. The results show that the austenite grains gradually coarsen with the increase of solid solution temperature, and the addition of RE yttrium effectively inhibits the coarsening of grains and keeps an excellent the comprehensive mechanical properties of AISI 321 stainless steel at 1150 °C for 30 min, this indicates that the addition of RE yttrium broad solid solution process window for AISI 321 stainless steel. In addition, the RE yttrium microalloying has a positive modification effect on the carbonitrides with refinement and spherization, which has a good contribution to the strength and plasticity retention of the material. This research is expected to provide more options for the heat treatment of austenitic stainless steels.

Effect of Fly Ash on the Mass Transfer Performance of CO2 Removal Using MEA and DEA Solutions in a Packed Tower

The accumulation of uncollected fly ash from flue gas in post-combustion CO2 capture processes is a significant concern in current coal-fired power plants due to its potential impact on the performance of CO2 absorbent and absorption towers. In order to determine the effect of fly ash on the mass transfer performance of CO2 absorption into monoethanolamine (MEA) and diethanolamine (DEA) aqueous solutions, experimental studies were carried out using a small-sized packed tower equipped with θ-ring random packing. These studies were conducted under various operating parameters, including solution temperature, liquid/gas ratio (L/G), packing height, and fly ash concentration. The results show that the effect of fly ash on the outlet CO2 concentration was primarily observed during the initial stages of the experimental process. Moreover, the presence of fly ash leads to a reduction in the volumetric overall mass transfer coefficient (KGav) when using MEA and DEA solution, and increasing the fly ash concentration further exacerbates this negative impact. However, the effect of fly ash on the reduction in KGav is not significantly related to its chemical composition but rather depends on the operational parameters. With increasing solution temperature, liquid/gas ratio (L/G), and packing height, the KGav values for different solutions exhibit an upward trend. The negative effect of fly ash on KGav remains relatively stable for MEA as solution temperature and packing height increase. Compared to MEA, fly ash has a greater negative effect on DEA solution under the same experimental conditions. The analysis reveals that the detrimental effect of fly ash on KGav primarily stems from its ability to alter the distribution state of the absorption liquid within the packed tower.

Hydrogen bonding regulation on phase change in stimuli responsive copolymer aqueous solution

Hydrogen bonding (HB) is vital for the phase transition and physical properties of stimuli responsive copolymers. However, the governing mechanism remains unclear. Herein, we investigated the HB dynamics in a representative thermo-responsive copolymer (PNIPAM-AM) aqueous solution. Three types of HB were identified: polymer-polymer chain (CO:H–N), polymer chain-water molecule (CO:H–O) and water-water molecules (H–O:H–O) by vibrational spectroscopy. Increasing polymer concentration, the H–O:H–O softened and CO:H–O stiffened, leading to the destruction of HB network in water-water clusters. Upon increasing solution temperature, CO:H–O softened while CO:H–N stiffened, resolving the dehydration and cross-linking of polymer chains. Confinement of water molecules in the “cages” (∼ tens to hundreds of micrometers) after sol-gel phase transition was visualized, disclosing the mechanism of water holding capacity of PNIPAM-AM. The correlation of molecule vibration and copolymer microscopic structure was established, contributing to the fundamental understanding of phase behavior and physical properties regulations in stimuli responsive copolymer aqueous solution.

Microstructure evolution and coarsening behavior of precipitated O phase in Ti–22Al–24Nb-0.5Mo (at. %) alloy during the heat treatment

Microstructure evolution and coarsening behavior of precipitated O phase were systematically investigated in this study, and the corresponding microstructures were characterized by scanning electron microscopy and transmission electron microscopy. The results showed that the original microstructure was composed of lath O phase, α2 phase and B2 matrix. The precipitated O phase presented different morphologies and sizes during heat treatment. With the increase of solution temperature and holding time, the O phase occurred coarsening, with a thickness ranging from 0.73 increased to 2.64 μm. But the volume fraction decreased from 57.65 to 18.40 %. During aging treatment, large amounts of fine secondary acicular O phase have precipitated from the matrix. As the aging temperature increases, the O phase underwent coarsening and the thickness increases from 0.70 to 1.40 μm. However, the aging temperature has little effect on the precipitation of acicular O phase, and the volume fraction decreases from 37.66 to 33.32 %. Research found that the small-sized O phase gradually dissolved in the matrix, while the large-sized O phase grew. This phenomenon can be explained by Ostwald ripening mechanism. The TEM analysis revealed that the O phase occurred separation, mainly due to the diffusion of solute atoms and the embedding of B2 matrix. Meanwhile, the O phase had been completed and segmented. The coarsening mechanism of the O phase was also explained by the boundary splitting mechanism and terminal migration mechanism.