Precipitation behavior and martensite lath coarsening during tempering of T/P92 ferritic heat-resistant steel

Tempering is an important process for T/P92 ferritic heat-resistant steel from the viewpoint of microstructure control, as it facili- tates the formation of final tempered martensite under serving conditions. In this study, we have gained deeper insights on the mechanism underlying the microstructural evolution during tempering treatment, including the precipitation of carbides and the coarsening of martensite laths, as systematically analyzed by optical microscopy, transmission electron microscopy, and high-resolution transmission electron mi- croscopy. The chemical composition of the precipitates was analyzed using energy dispersive X-ray spectroscopy. Results indicate the for- mation of M3C （cementite） precipitates under normalized conditions. However, they tend to dissolve within a short time of tempering, owing to their low thermal stability. This phenomenon was substantiated by X-ray diffraction analysis. Besides, we could observe the precipitation of fine carbonitrides （MX） along the dislocations. The mechanism of carbon diffusion controlled growth of M23C6 can be expressed by the Zener＇s equation. The movement of Y-junctions was determined to be the fundamental mechanism underlying the martensite lath coarsening process. Vickers hardness was estimated to determine their mechanical properties. Based on the comprehensive analysis of both the micro- structural evolution and hardness variation, the process of tempering can be separated into three steps.

Hot deformation behaviors of a 9Cr oxide dispersion-strengthened steel and its microstructure characterization

The hot deformation behaviors of a 9 Cr oxide dispersion-strengthened(9 Cr-ODS) steel fabricated by mechanical alloying and hot isostatic pressing(HIP) were investigated. Hot compression deformation experiments were conducted on a Gleeble 3500 simulator in a temperature range of 950–1100°C and strain rate range of 0.001–1 s^(-1). The constitutive equation that can accurately describe the relationship between the rheological stress and the strain rate of the 9 Cr-ODS steel was established, and the deformation activation energy was calculated as 780.817 kJ/mol according to the data obtained. The processing maps of 9 Cr-ODS in the strain range of 0.1–0.6 were also developed. The results show that the region with high power dissipation efficiency corresponds to a completely recrystallized structure. The optimal processing conditions were determined as a temperature range of 1000–1050°C with strain rate between 0.003 and 0.01 s^(-1).

Effects of heat treatment on the microstructure and mechanical properties of Ni_(3)Al-based superalloys:A review

Ni_(3)Al-based alloys have drawn much attention as candidates for high-temperature structural materials due to their excellent comprehensive properties.The microstructure and corresponding mechanical properties of Ni_(3)Al-based alloys are known to be susceptible to heat treatment.Thus,a significant step is to employ various heat treatments to derive the desirable mechanical properties of the alloys.This paper briefly summarizes the recent advances in the microstructure evolution that occurs during the heat treatment of Ni_(3)Al-based alloys.Aside fromγ′phase andγphase,the precipitations ofβphase,α-Cr precipitates,and carbides are also found in Ni_(3)Al-based alloys with the addition of various alloying elements.The evolution in morphology,size,and volume fraction of various types of secondary phases during heat treatment are reviewed,involvingγ′phase,βphase,α-Cr precipitate,and carbides.The kinetics of the growth of precipitates are also analyzed.Furthermore,the influences of heat treatment on the mechanical properties of Ni_(3)Al-based alloys are discussed.

Evaluation on elevated-temperature stability of modified 718-type alloys with varied phase configurations

Inconel 718 is a Ni–Fe-based superalloy widely used in aerospace engines because of its excellent mechanical properties.However,the inferior stability of theγ″phase limits the application of Inconel 718,which coarsens rapidly at temperatures greater than 650°C.Further improving the temperature tolerance of Inconel 718 requires optimization of the phase configuration via modification of the alloy’s chemical composition.Given the aforementioned objective,this work was conducted to study the precipitation behavior and thermal stability of the strengthening phases with various structures in modified Inconel 718 alloys by tailoring the Al/Ti ratio.With increasing Al/Ti ratio,three particle configurations were formed:γ′/γ″composite,isolatedγ′,andγ′/γ″/γ′composite particles.The results of aging tests demonstrate that the isolatedγ′and theγ′/γ″/γ′composite structure exhibited better thermal stability at temperature as high as 800°C.The isolatedγ′exhibited a reduced coarsening rate compared with theγ′/γ″/γ′composite particles because the isolatedγ′phase was rich in Al,Ti,and Nb.However,theγ′/γ″composite particles coarsened and decomposed rapidly during aging at temperatures greater than 700°C because of the lower stability resulting from the larger number ofγ″particles.The obtained results provide necessary data for the compositional optimization of novel 718-type alloys.

Effect of heat treatment processing on microstructure and tensile properties of Ti-6Al-4V-10Nb alloy

Effects of heat treatment processing on the microstructure and mechanical properties of Ti-6Al-4V-10Nb alloy were investigated. The microstructures were investigated by SEM, TEM and XRD, and the mechanical properties were evaluated by tensile tests at room and elevated temperatures. The results indicate that the lath-like and globular primary α phase, secondary α phase and β phase are obtained after forging and heat treatment processing. The size of secondary α phase is much smaller than that of primary α phase. After heat treatment, the volume fraction of primary α phase is decreased, and that of secondary α phase is increased. With the increase of solution temperature, the volume fraction of primary α phase is gradually decreased, and that of secondary α phase is obviously increased. The yield strength and tensile strength of Ti-6Al-4V-10Nb alloy are significantly enhanced with the solution temperature increasing.

Coarsening behavior of MX carbonitrides in type 347H heat-resistant austenitic steel during thermal aging

In this work, the growth kinetics of MX （M - metal, X - C/N） nanoprecipitates in type 347H austenitic steel was systematically studied. To investigate the coarsening behavior and the growth mechanism of MX carbonitrides during long-term aging, experiments were performed at 700, 800, 850, and 900℃ for different periods （1, 24, 70, and 100 h）. The precipitation behavior of carbonitrides in specimens subjected to various aging conditions was explored using carbon replicas and transmission electron microscopy （TEM） observations. The corresponding sizes ofMX carbonitrides were measured. The results demonstrates that MX carbonitrides precipitate in type 347H austenitic steel as Nb（C,N）. The coarsening rate constant is time-independent; however, an increase in aging temperature results in an increase in coarsening rate of Nb（C,N）. The coarsening process was analyzed according to the calculated diffusion activation energy of Nb（C,N）. When the aging temperature was 800-900℃, the mean activation energy was 294 kJ·mol -1, and the coarsening behavior was controlled primarily by the diffusion of Nb atoms.

Effects of aluminum and titanium on the microstructure of ODS steels fabricated by hot pressing

Three oxide-dispersion-strengthened(ODS)steels with compositions of Fe-14Cr-2W-0.2V-0.07Ta-0.3Y_2O_3(wt%,so as the follows)(14Y),Fe-14Cr-2W-0.2V-0.07Ta-1Al-0.3Y_2O_3(14YAl),and Fe-14Cr-2W-0.2V-0.07Ta-0.3Ti-0.3 Y_2O_3(14YTi)were fabricated by hot pressing.Transmission electron microscopy(TEM)was used to characterize the microstructures and nanoparticles of these ODS steels.According to the TEM results,14Y,14YAl,and 14YTi ODS steels present similar bimodal structures containing both large and small grains.The addition of Al or Ti has no obvious effect on the microstructure of the steels.The spatial and size distribution of the nanoparticles was also analyzed.The results indicate that the average size of nanoparticles in the 14YTi ODS steel is smaller than that in the 14YAl ODS steel.Nanoparticles such as Y_2O_3,Y_3Al_5O_(12) and YAlO_3,and Y_2Ti_2O_7 were identified in the 14Y,14YAl,and 14YTiODS steels,respectively.

Morphology and quantitative analysis of O phase during heat treatment of hot-deformed Ti_2AlNb-based alloy

A 1040°C-hot-deformed Ti_2AlNb-based alloy solution-treated at 950°C and aged at different temperatures was quantitatively investigated. The microstructure, size of the phase, and microhardness of the deformed alloys were measured. The results indicated that the microstructure of the deformed Ti_2AlNb-based alloy specimens comprise coarse O lath, fine O lath, equiaxed O/α_2, and acicular O phase. More O phase was generated in the deformed alloy after heat treatment because the acicular O phase was more likely to nucleate and grow along the deformation-induced crystal defects such as dislocations and subgrain boundaries. After deformation and subsequent heat treatment, the acicular O phase of the resultant alloy became finer compared to that of the undeformed alloy, and the acicular O phase became coarser and longer with the elevated aging temperature, while the width of the O lath exhibited unobvious variations. The hot deformation facilitated the dissolution of the O lath but accelerated the precipitation of the acicular O phase. When the 950°C-solution-treated deformed Ti_2AlNb-based alloy was then aged at 750°C for different periods, the phase content was nearly invariable, O and B2 phases eventually reached equilibrium, and the microstructure became stable and homogeneous.

Effect of indium addition on the microstructural formation and soldered interfaces of Sn-2.5Bi-1Zn-0.3Ag lead-free solder

The microstructural formation and properties of Sn-2.5Bi-xln-lZn-0.3Ag （in wt%） alloys and the evolution of soldered interfaces on a Cu substrate were investigated. Apart from the relatively low melting point （about 195C）, which is close to that of conventional eutectic Sn-Pb solder, the investigated solder presents superior wettability, solderability, and ductility. The refined equiaxial grains enhance the me- chanical properties, and the embedded bulk intermetallic compounds （IMCs） （Cu6Sn5 and CusZns） and granular Bi particles improve the joint reliability. The addition of In reduces the solubility of Zn in the 13-Sn matrix and strongly influences the separation and growth behaviors of the IMCs. The soldered interface of Sn-2.5Bi-xln-lZn-0.3Ag/Cu consists of Cu-Zn and Cu-Sn IMC layers.

Editorial for special issue on advanced materials for energy storage and conversion

The ever-increasing environmental problems and energy challenges have called urgent demand for utilizing green,efficient,and sustainable energy,thus promoting the development of new technologies associated with energy storage and conversion systems.Amongst a wealth of energy storage devices,Li/Na/K/Zn/Mg ion batteries,metal-air batteries,and lithium-sulfur/all-solid-state batteries together with supercapacitors as advanced power sources have attracted considerable interest due to their conspicuous merits of high energy density,long cycle life,and good rate capability.

Effect of acicular ferrite on banded structures in low-carbon microalloyed steel

The effect of acicular ferrite （AF） on banded structures in low-carbon microalloyed steel with Mn segregation during both iso- thermal transformation and continuous cooling processes was studied by dilatometry and microscopic observation. With respect to the iso- thermal transformation process, the specimen isothermed at 550℃ consisted of AF in Mn-poor bands and martensite in Mn-rich bands, whereas the specimen isothermed at 450℃ exhibited two different morphologies of AF that appeared as bands. At a continuous cooling rate in the range of 4 to 50℃/s, a mixture of AF and martensite formed in both segregated bands, and the volume fraction of martensite in Mn-rich bands was always higher than that in Mn-poor bands. An increased cooling rate resulted in a decrease in the difference of martensite volume fraction between Mn-rich and Mn-poor bands and thereby leaded to less distinct microstrucmral banding. The results show that Mn segregation and cooling rate strongly affect the formation of AF-containing banded structures. The formation mechanism of microstructural banding was also discussed.

Effect of cold rolling and first precipitates on the coarsening behavior of γ″-phases in Inconel 718 alloy

The coarsening behaviors of γ″-phase particles in Inconel 718 alloy aged at 750, 800, and 850℃ were investigated by scanning electron microscopy（SEM）. Detailed observations and quantitative measurements were conducted to characterize the coarsening behavior of the γ″-phase under various aging conditions. The experimental results indicate that the existence of the δ-phase retards the formation and coarsening of the γ″-phase, without influencing its final particle size or amount. Moreover, when cold rolled with a reduction of 50%, the dimensions of the γ″ particles in Inconel 718 alloy decrease with increasing aging time. Furthermore, the coarsening behavior of the γ″-phase in the Inconel 718 alloy after a normal aging treatment（sample A） and that of the primary δ-phase（sample B） follow the Lifshitz–Slyozov–Wagner（LSW） diffusion-controlled growth theory; the thus-obtained activation energies for the γ″-phase are 292 k J·mol^-1 and 302 k J·mol^-1, respectively.

Effect of microstructure variation on the corrosion behavior of high-strength low-alloy steel in 3.5wt% NaCl solution

The effect of microstructure variation on the corrosion behavior of high-strength low-alloy（HSLA） steel was investigated. The protective property of the corrosion product layer was also explored. Experimental results reveal that the type of microstructure has significant effect on the corrosion resistance of HSLA steel. The measurement results of weight loss, potentiodynamic polarization curves, and electrochemical impedance spectroscopy indicate that the steel with acicular ferrite microstructure exhibits the lowest corrosion rate. Martensite exhibits a reduced corrosion resistance compared with polygonal ferrite. It is found that the surface of the acicular ferrite specimen uniformly covered by corrosion products is seemingly denser and more compact than those of the other two microstructures, and can provide some amount of protection to the steel; thus, the charge transfer resistance and modulus values of the acicular ferrite specimen are the largest. However, corrosion products on martensite and polygonal ferrite are generally loose, porous, and defective, and can provide minor protectiveness; thus, the charge transfer resistance values for polygonal ferrite and martensite are lower.

Structural refinement of 00Cr13Ni5Mo2 supermartensitic stainless steel during single-stage intercritical tempering

The 00Cr13Ni5Mo2 supermartensitic stainless steel was first tempered at 570-730°C for 2 h to observe the microstructure and hardness changes. The tempering temperature was set to 600, 650, and 700°C, which is below, equal to, and above the austenite transformation start temperature, respectively, for each holding period to investigate the effects of tempering time on the structure and properties of the steel. The microstructure of the specimens was examined by optical microscopy and transmission electronic microscopy, and the phase composition was detected by X-ray diffraction. As expected, lath refinement was observed in the steel tempered at 700°C, and the refinement degree significantly depended on the tempering time. Contrary to normal steel softening by tempering, the hardness performance of the steel was significantly enhanced primarily because of the refinement of martensite laths after single-stage intercritical tempering. It is believed that the reverse transformation of martensite（α′） to austenite（γ） is responsible for the refinement.

Evaluation of precipitation hardening in TiC-reinforced Ti_2AlNb-based alloys

Ti2AlNb-based alloys with 0.0 wt%, 0.6 wt%, and 2.0 wt% carbon nanotube（CNT） addition were fabricated from spherical Ti–22 Al–25 Nb powder by sintering in the B2 single-phase region. Phase identification and microstructural examination were performed to evaluate the effect of carbon addition on the hardness of the alloys. Carbon was either in a soluble state or in carbide form depending on its concentration. The acicular carbides formed around 1050℃ were identified as TiC and facilitated the transformation of α2 ＋ B2 → O. The TiC was located within the acicular O phase. The surrounding O phase was distributed in certain orientations with angles of 65° or 90° O phase particles. The obtained alloy was composed of acicular O, Widmanstatten B2 ＋O, and acicular TiC. As a result of the precipitation of carbides as well as the O phase, the hardness of the alloy with 2.0 wt% CNT addition increased to HV 429 ± 9.

Observation of the effect of angiojet to treat acute lower extremity arterial embolization

BACKGROUND Through significant advances in the treatment of peripheral arterial occlusive disease,acute ischemia of the lower extremity is still associated with significant morbidity,limb threat and mortality.The two main causes of acute ischemia in lower extremities are arterial embolism and atherosclerotic arteries.Timely recognition and treatment of acute limb ischemia in emergency situations is essential in order to minimize the duration of ischemia.AIM To investigate the application effect of angiojet thrombolysis in the treatment of acute lower extremity arterial embolization.METHODS Sixty-two patients with acute lower extremity arterial embolization admitted to our hospital from May 2018 to May 2020 were selected.Among them,the observation group(twenty-eight cases)had received angiojet thrombolysis,and the control group(thirty-four cases)had received femoral artery incision and thrombectomy.After thrombus clearance,significant residual stenosis of the lumen was combined with balloon dilation and/or stent implantation.When the thrombus removal was not satisfactory,catheter-directed thrombolysis was performed.The incidence of postoperative complications,recurrence rate and recovery of the two groups were compared.RESULTS There were no significant differences in postoperative recurrence(target vessel reconstruction rate),anklebrachial index and the incidence of postoperative complications between the two groups(P>0.05);there were statistically significant differences in postoperative pain score and postoperative rehabilitation between the two groups(P<0.05).CONCLUSION The application of angiojet in the treatment of acute lower limb artery thromboembolism disease is safe and effective,minimally invasive,quicker recovery after operation,less postoperative complications,which is more suitable for the treatment of femoral popliteal arterial thromboembolism lesions.If the thrombus removal is not satisfactory,the combination of coronary artery aspiration catheter and catheterized directed thrombolysis can be used.Balloon dilation and stent implantation can be considered for obvious lumen stenosis.

Intravascular fasciitis involving the external jugular vein and subclavian vein:A case report

BACKGROUND Intravascular fasciitis(IVF)is a rare nodular fasciitis that often involves the layers and lumens of blood vessels;therefore,it is easily misdiagnosed as a malignant tumor with invasion into blood vessels.CASE SUMMARY A 13-year-old boy was admitted due to a mass on the left side of his neck.Duplex ultrasonography revealed a circular solid hypoechoic mass in the external jugular vein,and magnetic resonance imaging revealed an enhanced longitudinal masslike lesion in the left supraclavicular fossa.Surgical treatment was arranged and completed,histopathological analysis showed a large amount of spindle cell proliferation,and immunohistochemistry showed that the spindle cells were positive for the expression of vimentin,caldesmon,and smooth muscle actin and negative for the expression of S-100 protein,desmin,CD34,and c-kit;Ki-67 staining revealed a low proliferative index(5%-10%),which confirmed the differentiation characteristics of myofibroblasts.Fluorescence in situ hybridization detected the rearrangement of USP6.IVF was subsequently diagnosed.CONCLUSION IVF is characterized by intraluminal,intramural and extramural involvement of small to large arteries or veins.Unless the doctor has a deep understanding of the disease or suspects that there is an initial indicator,IVF may be confused with other intravascular malignancies,leading to unnecessary radical surgery.Imaging examination combined with histopathological examination can improve the diagnostic accuracy of this disease.

Cardiac myxoma shedding leads to lower extremity arterial embolism:A case report

BACKGROUND Left cardiac myxoma(CM)is the most common benign tumor of primary cardiac tumors,but because of its special position caused by pathological physiology change,caused by the complications of the heavier,the surface is often accompanied by blood clots,once fall out,it causes peripheral vascular embolization,such as acute lower limb artery embo-lization,harmfulness is large,high morbidity,and easy to occur repeatedly.CASE SUMMARY A 67-year-old male patient suddenly appeared numbness and weakness of the left lower limb and could not walk without obvious incentive.The patient was finally diagnosed as left CM complicated with acute lower limb arterial embolism after completing cardiac ultrasound,computer tomography angiography,and histopathological analysis,such as hematoxylin-eosin stain staining,immunohistochemistry and special staining including alcian blue staining and periodic acid schiff staining.Arterial thrombosis was removed successfully by femoral artery thrombectomy,postoperative numbness and weakness of the patient’s left lower limb disappeared,skin temperature became warm,and dorsal foot artery pulsation was accessible.The patient was readmitted to the hospital 8 mo after discharge for left atrial mass resection,and was diagnosed as CM by postoperative histopathological examination.CONCLUSION Although CM is rare,it may be considered as the source of embolism in patients with acute limb ischemia.Repeated loss of thrombus on the tumor and its surface may lead to repeated embolism of peripheral vessels.Cardiac ultrasound is helpful for early diagnosis.Here,we use this case report to highlight left CM as an important cause of acute limb ischemia and to report our experience in the diagnosis and treatment of lower limb arterial embolism caused by CM detachment.

Vertically grown MoS_(2)nanosheets on graphene with defect-rich structure for efficient sodium storage

The synthesis of a perpendicular growth structure of MoS_(2)nanosheets on graphene for efficient sodium storage is challenging yet ideal due to the benefits of open ion diffusion channels and high electronic conductivity.In this study,we have successfully fabricated a novel structure of vertical MoS_(2)nanosheets on graphene,with ZnS nanoparticles serving as bonding points(MoS_(2)/ZnS/G),through a facile hydrothermal method.During the synthesis process,Zn^(2+)not only acts as a landing site for the vertical growth of MoS_(2)nanosheets but also triggers the formation of a defect-rich structure in the final samples.This unique architecture of MoS_(2)/ZnS/G effectively combines the advantages of a vertically aligned geometry and a defectrich structure for energy storage.The resulting structure displays shortened transport paths for electrons/ions,enhanced conductivity,improved structural integrity,and an increased number of active sites for promising electrochemical performance.As expected,when used as anode for sodium-ion batteries,the as-synthesize d MoS_(2)/ZnS/G exhibits excellent rate capability(high capacity of 298 mAh·g^(-1)at 5 A·g^(-1))and good cycling stability(a capacity decay of 0.056%per cycle after 500 cycles at 1 A·g^(-1)).According to the kinetic investigations,the electrochemical process of the MoS_(2)/ZnS/G sample is primarily governe d by a pseudocapacitive behavior,which enhances the charge/discharge kinetics and allows the MoS_(2)/ZnS/G structure to remain intact during cycling.

AtPUB19, a U-Box E3 Ubiquitin Ligase, Negatively Regulates Abscisic Acid and Drought Responses in Arabidopsis thaliana

Ubiquitination is an important protein post-translational modification, which is involved in various cellular processes in higher plants, and U-box E3 ligases play important roles in diverse functions in eukaryotes. Here, we describe the functions ofArabidopsis thaliana PUB19 （AtPUB19）, which we demonstrated in an in vitro assay to encode a U-box type E3 ubiquitin ligase. AtPUB19 was up-regulated by drought, salt, cold, and abscisic acid （ABA）. Down-regulation of AtPUB19 led to hypersensitivity to ABA, enhanced ABA-induced stomatal closing, and enhanced drought tolerance, while AtPUB19 overexpression resulted in the reverse phenotypes. Molecular analysis showed that the expression levels of a number of ABA and stress marker genes were altered in both AtPUB19 overexpressing and atpub19-1 mutant plants. In summary, our data show that AtPUB19 negatively regulates ABA and drought responses in A. thaliana.