Aging Treatment Research Articles

Preparation of an environmentally friendly water-soluble sizing agent and its application in CF/PPESK composites

In this study, a series of high temperature resistant water-soluble thermoplastic sizing agents were designed and synthesized to improve the interfacial bonding of CF/PPESK composites. The effects of the ratio of water-soluble functional monomer (PPL) and high temperature resistant monomer (DHPZ) on the performance of the pastes were investigated. The results showed that the sizing agent with PPL: DHPZ = 6: 4 had the best performance, and its thermal decomposition temperature was up to 348 °C, which met the requirements of the composite molding process. The ILSS and flexural strength reached the peaks of 67.2 MPa and 1526.5 MPa. The retention rates were 89.7 % and 81.8 %, respectively, after hydrothermal aging treatment, compared with 77.7 % and 79.2 % for the epoxy sizing agent. The bottleneck of traditional epoxy sizing agent and CF/PPESK composites molding process mismatch has been broken.

Nanocrystallization and precipitation behavior evolution of AZ80 magnesium alloy during multi-directional compression

In response to the growing demand for high-performance magnesium alloys in the aerospace and transportation industries, researchers conducted a study on the AZ80 magnesium alloy. The primary objective was to achieve a nanocrystalline structure in the alloy through severe plastic deformation using low-strain multi-directional compression at room temperature. Subsequently, an aging treatment was performed to induce the transformation of the structure into a stable state. The study aimed to investigate the morphology and mode of the second phase precipitation in the magnesium alloy after undergoing severe plastic deformation. The research findings revealed that the application of multi-directional and multi-pass compression during room temperature deformation of the magnesium alloy effectively prevented instability and fracture. Moreover, this process facilitated the accumulation of larger true strain. As the number of compression passes increased, deformation twins became increasingly denser, particularly in the intersecting areas. Consequently, ultrafine high-angle grain structures were preferentially formed in these regions. Furthermore, the number of fine-grained areas gradually increased with each deformation pass. After ΣΔε 5.12, the grain size was refined to a range of 100–200 nm. Additionally, the aging treatment following severe plastic deformation brought about a significant change in the traditional lamellar precipitation mode of the second phase Mg17Al12 in the magnesium alloy. Instead, spherical precipitation occurred.

Mechanical Properties and Microstructure of Laser Powder Bed Fusion‐Processed 18Ni300 Maraging Steel According to Direct Aging Treatment Conditions

The nonequilibrium microstructures produced by laser‐based additive manufacturing can enhance the mechanical properties of metallic alloys. However, the optimal post‐treatment conditions will change according to the initial microstructure induced by the manufacturing process employed. Therefore, this study investigates the optimal direct aging conditions for the post‐treatment of laser powder bed fusion‐processed 18Ni300 maraging steel by changing the aging temperature and time. The aging time required to achieve maximum tensile strength decreased as the aging temperature increased, and an increase in the aging temperature accelerated the evolution of nanoscale precipitates. The results indicate that the optimal direct aging conditions of 520 °C for 2 h achieved the largest tensile strength (≈2100 MPa) and precipitate area fraction. Notably, the reduced aging time at this temperature compared with that under conventional aging conditions (8 h at 460 °C or 490 °C) minimizes the thickening of the (Mo,Ti)‐rich segregation, which otherwise contributes to austenite reversion and strength reduction owing to overaging. Thus, the optimal direct aging conditions for additively manufactured maraging steel components are different from those for conventionally produced maraging steel components. This understanding of the microstructural changes induced by direct aging according to the initial non‐equilibrium state provides vital information for enhancing the performance of additively manufactured metallic alloys.

A novel high-Mn duplex twinning-induced plasticity lightweight steel with high yield strength and large ductility

In this study, we report a novel high-Mn Fe–21Mn–6Al–4Si–1C (wt.%) duplex lightweight steel with concurrent chemical ordering and twinning-induced plasticity effects. This steel is capable of achieving an exceptional combination of strength and ductility following either cold-rolling and annealing at 1000 °C or subsequent short-term aging at 550 °C. In its as-annealed state, this steel primarily consists of γ-austenite and α-ferrite, with α-ferrite appearing as dispersed particles within fully recrystallized γ grains. Furthermore, L′12- and D03-type ordered nanodomains exist within these two phases, respectively. The aging treatment negligibly affects the size and volume fraction of both the γ-austenite and α-ferrite, yet it enhances the degree of ordering as well as the size and volume fraction of their ordered nanodomains, leading to a rise in yield strength from ∼800 to ∼1062 MPa and a decline in total elongation from ∼60.4% to ∼44.4%. The high yield strength of this steel originates from multiple strengthening mechanisms involving dislocation interactions with solute atoms, ordered nanodomains, γ grain boundaries and γ/α phase boundaries. This steel plastically deforms via planar slip during the initial stages. The rather small γ grain size, coupled with the presence of hard α-ferrite particles, fosters the dynamic slip band refinement (DSBR) effect, thereby enhancing the flow stress sufficiently to trigger deformation twinning in the steel during the later stages. The DSBR effect, combined with the progressive formation of deformation twins, stacking faults and Lomer-Cottrell locks, imparts pronounced strain hardenability to this steel, leading to its outstanding ductility.

The Role of Chorionicity in Placenta-Related Disorders

Introduction: Twin pregnancy is associated with higher rates of maternal morbidities including gestational diabetes and hypertension. Dichorionic twins are believed to have greater placental mass. Our objective was to study the incidence of two placenta-related disorders: gestational diabetes and hypertension, in dichorionic versus monochorionic twin pregnancies. Methods: Patients’ data of all consecutive twin pregnancies over a period of 12 years were collected from medical records. Data on chorionicity were retrieved from 1st trimester ultrasound reports. Maternal complications including gestational hypertension and diabetes were collected, and incidence was compared between dichorionic and monochorionic twin pregnancies. Records lacking chorionicity data and cases with pregestational diabetes were excluded. Results: A total of 960 twin pregnancies, 121 monochorionic and 839 dichorionic, were included. Average maternal age did not differ significantly between the groups. The median gestational age at delivery was 36.0 weeks in monochorionic and 36.7 in dichorionic twins. Primiparity (40.4% vs. 23.1%, p < 0.001) and the rate of infertility treatments (51.5% vs. 7.4%, p < 0.001) were both more common in the dichorionic group. The incidence of gestational hypertension disorders was 14% in monochorionic versus 11% in dichorionic twins (p = 0.36). Gestational diabetes was more common in dichorionic compared to monochorionic twins (9.4% and 2.5%, respectively); however, logistic multivariate analysis showed that gestational diabetes was highly correlated with maternal age (p < 0.001) and infertility treatments (p < 0.001) but not with chorionicity (p = 0.136). Conclusion: Our results may imply that greater placental mass does not increase the risk for gestational hypertension and diabetes. This might support the role of additional multiple maternal factors associated with these complications.

Evaluation of Seed Quality of Grain Corn Varieties through Accelerated Ageing

In an accelerated ageing test carried out to evaluate seed quality two hybrid grain corn varieties, 4546 and 888, were subjected to ageing conditions to assess their tolerance. The objective was to identify any differences between the varieties in their ability to maintain seed quality under accelerated ageing conditions. These tests simulate and hasten the natural ageing process of seeds, providing insight into their performance during storage over time and under adverse conditions. Following the ageing process, factors such as germination rate, vigour, and overall seed quality were assessed. The seeds of hybrid grain corn varieties 4546 and 888 were exposed to accelerated ageing by maintaining them at 40°C and 100% relative humidity in a growth chamber. Evaluations were conducted at intervals of 0, 48, 96, and 144 hours. The overall results indicated that seed quality in grain corn deteriorates following accelerated ageing treatment. Variety 4546 showed a rapid decrease in germination, germination rate, and seedling vigour throughout the testing period. Both varieties experienced an increase in moisture content from 11% to 20% during the ageing process. Additionally, the electrical conductivity of seed leachate increased for both varieties as the testing progressed. The experiment concluded that the 888 grain corn variety outperformed 4546 in all evaluated parameters. The 4546 variety was found to be highly sensitive to accelerated ageing.

Enhancement of the compressive performances of additive manufactured Corrax maraging stainless steel lattice by heat treatment

The objective of this study was to investigate the influences of integrated solution and aging treatment (SAT) on the compressive properties of laser powder bed fusion (LPBF) Corrax maraging stainless steel lattices. Cubic and face-centered cubic with Z-axis strut (FCCZ) lattices were produced and used to formulate two types of functionally-graded material (FGM) lattices. The lattices with FGM directions parallel and vertical to the stress were designated as FGM-P and FGM-V lattices, respectively. The compressive performances and fracture mechanisms were identified experimentally by digital image correction and theoretically by finite element analysis.The results show that SAT can significantly increase the specific strengths of these lattices by 34–42 %. The compressive performances and fracture mode of the FGM-V sample principally corresponded to the rule of mixture. However, the FGM-P sample did not follow the rule of mixture because its deformation concentrated only in the cubic-dominated regions. Moreover, the SEAs of the cubic and FGM-P samples were respectively improved by 30 % and 19 % by SAT, given their higher compressive strength and stable stress–strain curve. SAT can be applied to further extend the future application of these materials as cost-effective, high-performance lightweight structural materials.

Effect of Annealing Temperature on the Strength and Toughness of Ti‐55531 Titanium Alloy After Multiple Heat Treatment

Herein, it is aimed to reveal the effect of annealing temperature on α microstructure parameters and mechanical properties of Ti‐55531 alloy under the multiple heat‐treatment process of “solution (855 °C) + annealing (700, 730, 760 °C) + aging (600 °C).” The microstructure is characterized by using optical microscopy, scanning electron microscopy, and transmission electron microscope. In the results, it is indicated that the annealing temperature does not change the volume fraction of the αs phase of Ti‐55531 alloy. The as‐annealed precipitation‐free zone αs phase renucleates after aging treatment, resulting in a bimodal distribution of αs phase in the matrix. The higher the annealing temperature, the larger the average size of αs phase and the greater the heterogeneity in the alloy. Additionally, the heterogeneity of αs phase affects further the plasticity and the crack propagation path of the alloy. With the increase of annealing temperature, the strength of Ti‐55531 alloy decreases slowly, but the elongation and the impact toughness of the alloy increases rapidly resulting from the heterogeneity of αs phase under multiple heat‐treatment conditions.

Scalable intracellular delivery via microfluidic vortex shedding enhances the function of chimeric antigen receptor T-cells.

Adoptive chimeric antigen receptor T-cell (CAR-T) therapy is transformative and approved for hematologic malignancies. It is also being developed for the treatment of solid tumors, autoimmune disorders, heart disease, and aging. Despite unprecedented clinical outcomes, CAR-T and other engineered cell therapies face a variety of manufacturing and safety challenges. Traditional methods, such as lentivirus transduction and electroporation, result in random integration or cause significant cellular damage, which can limit the safety and efficacy of engineered cell therapies. We present hydroporation as a gentle and effective alternative for intracellular delivery. Hydroporation resulted in 1.7- to 2-fold higher CAR-T yields compared to electroporation with superior cell viability and recovery. Hydroporated cells exhibited rapid proliferation, robust target cell lysis, and increased pro-inflammatory and regulatory cytokine secretion in addition to improved CAR-T yield by day 5 post-transfection. We demonstrate that scaled-up hydroporation can process 5 × 108 cells in less than 10 s, showcasing the platform as a viable solution for high-yield CAR-T manufacturing with the potential for improved therapeutic outcomes.

Role of intermediate phases on microstructures, wear and corrosion resistance in new-developed (α + β) titanium alloy

A new (α + β) Ti alloy has been designed and prepared in this work, and the results show that three intermediate phases will be transformed including α′′ martensite, O′ and ω. Upon continuous heating, the α′′ martensite decomposes gradually and disappears before α precipitation. The ω and O′ domains are generated continuously upon aging, and such two intermediate phases co-exist when α phase nucleation occurs. It has been proved that the ω and O′ domains play a direct role in promoting α phase formation. Through the ω and O′ domains assisting α nucleation mechanism, a uniform distribution of fine α precipitates can be obtained after aging. Under the treatment of pre-aging at 300 °C plus aging at 600 °C, the α phase having smallest size and largest number density is obtained, resulting in highest wear resistance and corrosion resistance. For this sample, its average friction coefficient and wear ratio are 0.174 and 3.75×10−4 mm3/(N·m), respectively. During friction tests, the mixture of abrasive wear, adhesive wear and oxidation wear should be activated. Due to the formation of passivation films on the alloy surface, this alloy has exhibited better anti-corrosion properties than Ti-6Al-4 V alloy, and its corrosion current density in 3.5 wt% NaCl solution can be reduced to 1.79×10−8 A·cm−2. Compared with the samples under duplex aging treatments, the direct aged sample also presents outstanding anti-corrosion properties.

Assessing Knowledge of Vietnamese Nurses about Prevention and Treatment of Anaphylaxis: A Cross-Sectional Study

Background: Anaphylaxis greatly affects the psychology of patients as well as medical staff. Therefore, knowing about the way of prevention and treatment of anaphylaxis by nurses plays a key role in improving patient's caring services. Objectives: This study was conducted to describe the current state of nurse’s knowledge about the prevention and treatment of anaphylaxis and collect some relative factors. Methods: An analytical cross-sectional study was conducted with 82 nurses from March to May 2022. The questionnaire included 31 items to assess nurses' knowledge about anaphylactic state, anaphylaxis prevention, and treatment. The Chi-square test was used to compare categorical variables. Results: Most nurses had correct knowledge about anaphylactic symptoms, and common causes, with 82.9% and 81.7%. The percentage of nurses with good knowledge about anaphylaxis prevention and treatment recorded a moderate level (76.8%). Only 27.2% of nurses did not know about the type of new drug used for anaphylaxis treatment, while 28.2% recognized adrenalin dosage being used for adults. There were significant differences in knowledge about anaphylaxis prevention and treatment of nurses and ages, years of work, and number of times being trained on anaphylaxis (p&lt;0.05). Conclusion: Nursing knowledge about anaphylaxis prevention and treatment was a moderate level, in particular, knowledge about drugs for emergency treatment of anaphylaxis was limited. Therefore, training sessions need to focus on helping nurses for better understanding of the medicines and the way of using them to be proactive in emergency reactions.

Pterostilbene, a Dimethyl Derivative of Resveratrol, Exerts Cytotoxic Effects on Melanin-Producing Cells through Metabolic Activation by Tyrosinase.

Pterostilbene (PTS), which is abundant in blueberries, is a dimethyl derivative of the natural polyphenol resveratrol (RES). Several plant species, including peanuts and grapes, also produce PTS. Although RES has a wide range of health benefits, including anti-cancer properties, PTS has a robust pharmacological profile that includes a better intestinal absorption and an increased hepatic stability compared to RES. Indeed, PTS has a higher bioavailability and a lower toxicity compared to other stilbenes, making it an attractive drug candidate for the treatment of various diseases, including diabetes, cancer, cardiovascular disease, neurodegenerative disorders, and aging. We previously reported that RES serves as a substrate for tyrosinase, producing an o-quinone metabolite that is highly cytotoxic to melanocytes. The present study investigated whether PTS may also be metabolized by tyrosinase, similarly to RES. PTS was oxidized as a substrate by tyrosinase to form an o-quinone, which reacted with thiols, such as N-acetyl-L-cysteine, to form di- and tri-adducts. We also confirmed that PTS was taken up and metabolized by human tyrosinase-expressing 293T cells in amounts several times greater than RES. In addition, PTS showed a tyrosinase-dependent cytotoxicity against B16BL6 melanoma cells that was stronger than RES and also inhibited the formation of melanin in B16BL6 melanoma cells and in the culture medium. These results suggest that the two methyl groups of PTS, which are lipophilic, increase its membrane permeability, making it easier to bind to intracellular proteins, and may therefore be more cytotoxic to melanin-producing cells.

Real-life effects of pharmacological osteoporosis treatments on bone mineral density by quantitative computed tomography.

Monitoring of bone mineral density (BMD) is used to assess pharmacological osteoporosis therapy. This study examined the real-life effects of antiresorptive and osteoanabolic treatments on volumetric BMD (vBMD) of the spine by quantitative computed tomography (QCT). Patients aged ≥ 50years with a vBMD < 120mg/ml had ≥ 2 QCT. For analysis of therapy effects, the pharmacological treatment and the duration of each therapy were considered. Identical vertebrae were evaluated in all vBMD measurements for each patient. A linear mixed model with random intercepts was used to estimate the effects of pharmacological treatments on vBMD. A total of 1145 vBMD measurements from 402 patients were analyzed. Considering potential confounders such as sex, age, and prior treatment, a reduction in trabecular vBMD was estimated for oral bisphosphonates (-1.01mg/ml per year; p < 0.001), intravenous bisphosphonates (-0.93mg/ml per year; p = 0.015) and drug holiday (-1.58mg/ml per year; p < 0.001). Teriparatide was estimated to increase trabecular vBMD by 4.27mg/ml per year (p = 0.018). Patients receiving denosumab showed a statistically non-significant decrease in trabecular vBMD (-0.44mg/ml per year; p = 0.099). Compared to non-treated patients, pharmacological therapy had positive effects on trabecular vBMD (1.35mg/ml; p = 0.001, 1.43mg/ml; p = 0.004, 1.91mg/ml; p < 0.001, and 6.63mg/ml; p < 0.001 per year for oral bisphosphonates, intravenous bisphosphonates, denosumab, and teriparatide, respectively). An increase in trabecular vBMD by QCT was not detected with antiresorptive agents. Patients treated with teriparatide showed increasing trabecular vBMD. Non-treatment led to a larger decrease in trabecular vBMD than pharmacological therapy.

Microstructural Evolution and Mechanical Properties of Nb‐Containing Medium‐Mn Low‐Density Steels

Microalloying of Nb has been commonly utilized to enhance the structure and mechanical properties of advanced high‐strength steel (AHSS), but its application in medium‐Mn low‐density steel has been relatively understudied. This study aims to investigate the evolution of nano‐scale precipitates and mechanical properties of Fe‐12Mn‐9Al‐3Cr‐1.4C‐0.02/0.04Nb low‐density steels. The findings reveal that the austenite grain size of 0.04Nb steels is approximately half that of 0.02Nb steels due to the precipitation of NbC particles. Moreover, the addition of Nb is found to elevate the formation energy of κ‐carbide, thereby impeding its growth and coarsening. Consequently, the intragranular κ‐carbides in 0.04Nb steels are consistently smaller than those in 0.02Nb steels, with no coarsened intergranular κ‐carbides detected in either steel variant after aging treatment at 723–823 K. Despite a slight reduction on precipitation strengthening of κ‐carbides with higher Nb content, the yield strength of 0.04Nb steels exceeds that of 0.02Nb steels by ≈71 MPa, mainly due to additional fine grain strengthening and dislocation strengthening. The strengthening mechanisms in the Nb‐containing low‐density steels are analyzed quantitatively. The role of Nb in regulating the microstructure and mechanical properties of medium‐Mn low‐density steels is comprehensively discussed, offering valuable insights for the alloy design of low‐density steel.

Microstructure and Shape Memory Properties of Gas Tungsten Arc Welded Fe-17Mn-5Si-10Cr-4Ni-(V, C) Shape Memory Alloy.

In this study, microstructure, mechanical, and shape memory properties of the welded Fe-based shape memory alloy (Fe-SMA) plates with a nominal composition of Fe-17Mn-5Si-10Cr-4Ni-(V, C) (wt.%) by gas tungsten arc welding were investigated. The optimal heat input to ensure full penetration of the Fe-SMA plate with a thickness of 2 mm was found to be 0.12 kJ. The solidified grain morphology adjacent to the partially melted zone was columnar, whereas the equiaxed morphology emerged as solidification proceeded. The ultimate tensile decreased after welding owing to the much larger grain size of the fusion zone (FZ) and heat-affected zone (HAZ) than that of the base material (BM). Weldment showed lower pseudoelastic (PE) recovery strain and higher shape memory effect (SME) than those of the plate, which could be ascribed to the large grain size of the FZ and HAZ. Recovery stress (RS) slightly decreased after welding owing to lower mechanical properties of weldment. On the other hand, aging treatment significantly improved all PE recovery, SME, and RS via carbide precipitation. Digital image correlation analysis revealed that HAZ showed the lowest SME after heating and cooling, implying that the improved SME of FZ compensated for the low SME of the HAZ.

Enhancing strength-ductility synergy in metastable β-Ti alloys through β-subgrains-mediated hierarchical α-precipitation

Titanium alloys can achieve ultrahigh strength through precipitation hardening of secondary α-phase (αs) from β-matrix but often compromise ductility due to the conventional strength-ductility trade-off. In this study, a new strategy based on β-subgrains-mediated hierarchical α-precipitation is devised to balance the conflict in Ti-6Al-2Mo-4Cr-2Fe (wt.%) alloy through a unique combination of hot rolling, short-term solid solution, and aging treatment, i.e., RSST+A. Tensile testing reveals that the RSST+A samples exhibit ultrahigh strength of ∼1581 MPa and decent ductility of ∼8.4 %, surpassing ∼1060 MPa and ∼2.7 % of the corresponding RSST counterparts without final aging treatment. This remarkable strengthening and counterintuitive ductilizing is attributed to the architecting of β-subgrains-mediated hierarchical α-precipitates as a result of our specific processing approach. The designed short-term solution introduces abundant β subgrains that are transformed from the retained intensive dislocations during hot rolling. The β subgrain boundaries subsequently promote a dramatic precipitation of α allotriomorphs (αGB) and Widmanstätten side-plates (αWGB), which effectively subdivides β grains into numerous tiny independent deformation units. Consequently, plastic strain is uniformly partitioned into a large number of small aged β subgrains during tension, which strongly impedes strain localization that would typically occur across multiple β subgrains in the fashion of long straight slip bands in the case of the RSST samples. Furthermore, the hierarchical α structure also postpones uncontrollable cracking even when structural damage occurs at the last stage of straining. These findings demonstrate that appropriately manipulating microstructure through elaborately designing processing routes enables unexpectedly ductilizing high-strength titanium alloys in the precipitation-hardening state.

The effect of direct aging treatment on microstructure and mechanical properties of the GH4099 superalloys produced by selective laser melting

The effect of direct aging (DA) treatment on microstructure and mechanical properties of the GH4099 superalloys produced by selective laser melting (SLM) was investigated by the microhardness tests, room- (RT) and high-temperature (HT) tensile tests, field emission scanning electron microscopy (FE-SEM), and electron backscattered diffraction (EBSD) in this study. Both microhardness and RT tensile results show that DA treatment improves mechanical properties more than solution-aging (SA) treatment. By analyzing the effect of the microstructural features on the yield strength, we found that the dominant strengthening mechanisms responsible for higher yield strength of the DA specimens are the grain size hardening of fine γ matrix, high-density dislocation strengthening, Orowan dislocation bypass strengthening of smaller but dense M23C6-type carbides, and chemical strengthening of smaller but dense γ΄ nanoprecipitates. Furthermore, a transgranular fracture is a dominant fracture type for RT tensile specimens produced by DA treatment. Conversely, the failure type of SA tensile specimens is a typical intergranular fracture mechanism. The underlying mechanism for the above phenomenon is attributed to the effects of transgranular and intergranular M23C6-type carbides.

Effect of aging treatment on the microstructure, cracking type and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam

This study aimed to provide a comprehensive understanding of how aging treatments (namely, HT1 and HT2) affect the microstructure, cracking behavior, and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam (PBF-LB) method. Although both aged samples demonstrated similar grain structure and recrystallization behavior according to the electron backscatter diffraction (EBSD) analysis, as well as the precipitation of bimodal γ′ phase and MC- and M23C6-type carbides, notable differences were observed in the size and morphology, particularly the γ′ phase. The HT1 sample displayed coarsened primary γ′ phase, with sizes reaching up to 2 μm and exhibiting varied morphologies, including irregular and cuboidal shapes. Additionally, this treatment led to the formation of some γ′-γ eutectic regions and plate-like η phase, along with the decomposition of MC-type carbides into M23C6-type carbides. In contrast, the HT2 sample displayed uniformly distributed spherical primary γ′ phase with sizes ranging from 70 to 120 nm, accompanied by very fine secondary γ′ phase. Furthermore, it was found that changes in both aged sample microstructures could result in the formation of strain-age cracks due to the γ′ phase formation and liquation cracks due to the partial remelting of lower melting point phases. The findings also revealed that with the application of aging treatments, the hardness of the as-fabricated sample (339.8 ± 3.4 HV) increased to 440.2 ± 5.6 HV and 508.1 ± 4.8 HV for the heat treatment of HT1 and HT2, respectively.

Dynamic plastic deformation at liquid nitrogen temperature and aging effects on microstructure and properties of Cu-0.3Zr-0.15Cr alloys

The 9R phase is rarely formed in copper alloys because of its high stacking fault energy. In this study, we generated a large amount of 9R phase in Cu-0.3Zr-0.15Cr alloys by dynamic plastic deformation (DPD) at liquid nitrogen temperature for the first time, and revealed the transformation mechanism of 9R to nanotwins. The process of DPD + aging treatment enables the alloy to obtain excellent comprehensive properties (strength of 657 MPa, electrical conductivity of 75.2 % IACS, and elongation of 14.6 %), which are derived from the heterogeneous microstructure composed of ultrafine structures, coarse grains, and nano precipitated phases. In addition, we have evaluated the phase transformation kinetics after DPD at liquid nitrogen temperature. This work provides a new way to better understanding the microstructure transition and precipitation kinetics under dynamic plastic deformation with aging treatment at liquid nitrogen temperature.

Synergy of γ′ phase, MC carbide and grain boundary phase on creep behavior for nickel-based superalloy K439B

The synergy of γ′ phase, MC carbide and grain boundary phase on 815 °C/379 MPa creep behavior for nickel-based superalloy K439B was investigated by adjusting the time and temperature of the first-stage aging treatment. Increasing aging time from 4 h to 6 h, the total creep life is reduced by 35.8% due to the increased bimodal γ′ phase size. The bimodal γ′ phase transforms into small unimodal γ′ phase when increasing aging temperature from 1000 °C to 1080 °C. In addition, the content of M23C6 carbide increases, and the total creep life is increased by about 1.3 times. Small-size γ′ phase with bimodal distribution redissolves into γ matrix during creep deformation. Dislocations pile up at the γ/γ′ interface, and partial dislocations enter into large-size γ′ phase, mainly forming isolated parallel stacking faults. By comparison, the crossed stacking faults within small unimodal γʹ phase form Lomer-Cottrell locks, APB coupled dislocation pairs shear into γʹ phase, and more granular M23C6 carbide precipitates at the grain boundary, which further decreases the minimum steady creep rate and improves the creep life. At the beginning of creep deformation, MC carbide prevents the movement of dislocations. MC carbide formed at grain boundaries can delay crack propagation to a certain extent. MC carbide debonds from γ matrix subsequently due to the dislocation accumulation and higher interface energy, which provides a pathway for crack initiation and propagation. Moreover, the fragmentation and degeneration inside MC carbide promote crack initiation.