Search

Aluminum matrix composites (AMCs) reinforced with graphene nanoplatelets (GNPs) were fabricated by using an accumulative roll-compositing (ARC) process. Microstructure, mechanical and electrical properties of the nanostructured AMCs were characterized. The results showed that small addition (0.2 vol% and 0.5 vol%) of GNPs can lead to a simultaneous increase in the tensile strength and ductility of the GNPs/Al nanocomposites, as compared with the same processed pure Al. With increasing GNPs content, the tensile strength of the GNPs/Al nanocomposites can be enhanced to 387 MPa with retained elongation of 15%. Meanwhile, the GNPs/Al nanocomposites exhibited a good electrical conductivity of 77.8%–86.1% that of annealed pure Al. The excellent properties (high strength, high ductility and high conductivity) of the GNPs/Al are associated with the particular ARC process, which facilitates the uniform dispersion of GNPs in the matrix and formation of ultrafine-grained Al matrix. The strengthening and toughening of the GNPs/Al nanocomposites were discussed considering different mechanisms and the unique effect of GNPs.

The present work investigates the thermal stability and mechanical properties of a Co–20Cr–15W–10Ni (wt%) alloy with a bimodal grain (BG) structure. The BG structure consisting of fine grains (FGs) and coarse grains (CGs) is thermally stable under high-temperature exposure treatments of 760 °C for 100 h and 870 °C for 100–1000 h. The size of both FGs and CGs remains no significant changes after thermal exposure treatments. The microstructural stability is associated with the slow kinetics of grain growth and the pinning of carbides. The thermal stability enables to maintain the BG structures, leading to the same mechanical properties as the sample without thermal exposure treatment. In particular, the BG alloy samples after thermal exposure treatment exhibit superior mechanical properties of both high strength and high ductility compared to the unimodal grain (UG) structured ones. The BG structure of the alloy samples after thermal exposure is capable of avoiding severe loss of ductility and retaining high strength. More specifically, the ductility of the BG alloy samples after thermal exposure treatments of 870 °C for 500–1000 h is ten times higher (44.6% vs. 3.5% and 52.6% vs. 5.0%) than that of the UG ones. The finding in the present work may give new insights into high-temperature applications of the Co–20Cr–15W–10Ni alloy and other metallic materials with a BG structure.

The influence of pre-strain on the formation of bimodal grain structures and tensile properties of a Co–20Cr–15W–10Ni alloy was investigated. The bimodal grain structures consist of fine grains (FGs; 2–3 μm in diameter) and coarse grains (CGs; 8–16 μm in diameter), which can be manipulated by changing the pre-strain (ɛ = 0.3–0.7) and annealing temperatures (1000–1100 °C). High pre-strain applied in the samples can intensify the plasticity heterogeneity through increasing the total dislocation density and the local volumes of high-density dislocations. This can essentially result in finer FGs, a higher FG volume fraction, and overall grain refinement in the samples after annealing. High-temperature essentially increases both the size and volume fraction of CGs, leading to an increase in the average grain size. The tensile test suggests that the bimodal grain structured samples exhibited both high strength and ductility, yield strengths of 621–877 MPa and ultimate tensile strengths of 1187–1367 MPa with uniform elongations of 55.0%–71.4%. The superior strength-ductility combination of the samples arises from the specific deformation mechanisms of the bimodal grain structures. The tensile properties strongly depend on the size ratio and volume fraction of FGs/CGs in addition to the average grain size in the bimodal grain structures. The grain structures can be modified via changing the pre-strain and annealing temperature.

The isothermal compression tests were carried out to study the hot deformation behavior and microstructure evolution of Ti–19Al–22Mo alloy. The samples were deformed in the temperature range from 1100 to 1250 °C with an interval of 50 °C, strain rate ranging from 0.01 to 1 s−1 and the height reduction of 50% using Gleeble-3800 thermal–mechanical simulator. By using this experimental data an artificial neural network (ANN) model was developed and evaluated with unseen data. Further, the developed ANN model was used to predict flow stress correction from adiabatic heating at finer intervals of strain rates and temperatures. The predicted isothermal flow stress values were utilized to construct processing maps for Ti–19Al–22Mo alloy at true strain of 0.4 and 0.6. The maximum efficiency was noticed at 1100 °C with the strain rate of 0.01 s−1 associated with dynamic recrystallization and dynamic recovery. The deformation conditions of the instability domains in processing map showed wedge cracking and flow localization. Using the processing maps safe working parameters for hot deformation of Ti–19Al–22Mo alloy was identified.

We have studied {332} detwinning mechanism in a bcc-Ti–10Mo–xFe (x = 1–3 wt%) multilayered alloy upon annealing treatment at 900 °C by electron backscatter diffraction and electron channeling contrast imaging. Our analysis reveals that in the present material the detwinning process consists of two independent detwinning events that occur at two different microstructural regions, namely twin tips located at grain interiors and grain boundaries. Boundary dissociation reactions and mobilities were analyzed by tracking the evolution of the twin structure upon thermal annealing. We find that the first detwinning process is characterized by the evolution of incoherent twin boundaries into a Σ3 boundary and its subsequent migration. The second detwinning event is characterized by the detachment of the twin crystal from a grain boundary by the formation and migration of Σ11 {113} incoherent twin boundaries. Both detwinning modes can be explained from a thermodynamic standpoint where the boundary dissociation processes minimize the boundary free energy.

In order to develop a new titanium alloy with a good combination of strength–ductility–toughness, a near-beta titanium alloy was designed based on the already widely used Ti-1023 alloy. To avoid beta fleck occurring in the microstructure, the new Ti–Al–Fe–V (Cr, Zr) alloy has been made through decreasing the content of Fe, based on molybdenum equivalency and Bo–Md molecular orbital method (a method for new alloy designing based on the molecular orbital calculating). After primary design computation, Ti–Al–Fe–V (Cr, Zr) alloy was optimized as Ti–3Al–4.5Cr–1Fe–4V–1Zr finally. The microstructure and tensile properties of this alloy subjected to several commonly used heat treatments were investigated. The results show that the tensile strength of the alloy after solution treated below the β-transus temperature comes between 850 and 1100 MPa, with elongation in the range of 12.5 %–17.0 %. In solution-treated and solution-aged samples, a low-temperature aging at 500 °C results in the precipitation of finer α phase. With the increase in aging temperature, the secondary α phase becomes coarser and decreases in amount. Thus, it will lead to the increase in tensile ductility, but reduction in strength. Eventually, after modulated aging treatment, the alloy can obtain high-strength level with acceptable ductility. The tensile strength of the alloy can achieve 1273 MPa, with an elongation of 11.0 %. At the same time, the fracture toughness (K IC) of the alloy achieves 83.8 MPa·m1/2. It is obvious that the newly designed alloy has achieved a good blend of strength–ductility–toughness.

The effect of Al addition on ω precipitation and age-hardening behavior of Ti-9.2Mo-2Fe and Ti-2Al-9.2Mo-2Fe alloy during aging treatment was investigated. The results showed that athermal and isothermal ω phase formation in Ti-2Al-9.2Mo-2Fe alloy was suppressed to a certain extent due to Al addition. In addition, a small amount of athermal ω phase was observed in the β matrix with a size of about ~5 nm during water quenching from above the β transus temperature for both alloys. Isothermal ω formation was also found during aging at temperatures ranging from 573 K to 773 K (300 °C to 500 °C) in both alloys, although it had a limited time of stability at 773 K (500 °C). The hardening due to isothermal ω precipitation exhibited no over-aging as long as ω phase existed in both alloys, and ω phase played a more important role in hardening than α phase. And the ω phase in 50 to 100 nm size exhibited the best hardening effect in Ti-9.2Mo-2Fe alloy. Similarly, α phase with 100 to 200 nm in length showed better hardening effects in Ti-2Al-9.2Mo-2Fe alloy. Both the alloys showed stronger age hardening at an intermediate temperature of 673 K (400 °C) and in the first aging stage at a higher temperature of 773 K (500 °C) due to the sufficiently fine size (50 nm), while they exhibited weaker age hardening at a lower temperature of 573 K (300 °C) and long period aging at a higher temperature of 773 K (500 °C) due to incomplete ω formation and/or coarsening of α phase. No over or peak aging stage was found at 573 K and 673 K (300 °C and 400 °C) during the aging for 72 hours, while the peak hardness values of both alloys aged at 773 K (500 °C) were obtained in the first stage of aging. The hardness of the alloys was very sensitive to size and volume fraction of ω phase, which depends on aging temperature, time, and composition of the involved alloys.

Unfortunately, the acknowledgements were incomplete in the original version of this article.

A series of Ti–Al–V titanium alloy bars with nominal composition Ti–7Al–5V ELI, Ti–5Al–3V ELI, commercial Ti–6Al–4V ELI and commercial Ti–6Al–4V were prepared. These alloys were then heat treated to obtain bimodal or equiaxed microstructures with various contents of primary α phase. Dynamic compression properties of the alloys above were studied by split Hopkinson pressure bar system at strain rates from 2,000 to 4,000 s−1. The results show that Ti–6Al–4V alloy with equiaxed primary α (αp) volume fraction of 45 vol% or 67 vol% exhibits good dynamic properties with high dynamic strength and absorbed energy, as well as an acceptable dynamic plasticity. However, all the Ti53ELI specimens and Ti64ELI specimens with αp of 65 vol% were not fractured at a strain rate of 4,000 s−1. It appears that the undamaged specimens still have load-bearing capability. Dynamic strength of Ti–Al–V alloy can be improved as the contents of elements Al, V, Fe, and O increase, while dynamic strain is not sensitive to the composition in the appropriate range. The effects of primary alpha volume fraction on the dynamic properties are dependent on the compositions of Ti–Al–V alloys.

Radiotherapy is an effective treatment for some esophageal cancers, but the molecular mechanisms of radiosensitivity remain unknown. Ubiquitin-like with PHD and ring finger domains 1 (UHRF1) is a novel nuclear protein which is overexpressed in various cancers but not yet examined in esophageal squamous cell carcinoma (ESCC). The correlation between UHRF1 and the radioresistance in ESCC is still unclear. In the present study, the expression of UHRF1 was examined by immunohistochemistry in specimens of ESCC patients treated with radiotherapy. The results showed that UHRF1 was significantly overexpressed in ESCC specimens. Overexpression of UHRF1 correlated significantly with advanced T-stage, positive lymph node metastasis and poor differentiation. In addition, UHRF1 was associated with radiotherapy response, in which overexpression of UHRF1 was observed more frequently in the radioresistant group than in the effective group. At the molecular level, inhibition of UHRF1 by lentivirus-mediated shRNA targeting UHRF1 increased the radiosensitivity and apoptosis, while decreased radiation-induced G2/M phase arrest in TE-1 cells. Moreover, inhibition of UHRF1 resulted in higher residual γH2AX expression after irradiation, but not initial γH2AX. Further study showed that inhibition of UHRF1 down-regulated the endogenous expressions of DNA repair protein Ku70 and Ku80 in TE-1 cells, and significantly inhibited the increase of these proteins after irradiation. Above all, our data suggested that UHRF1 might play an important role in radioresistance of ESCC, and inhibition of UHRF1 can increase the radiosensitivity of TE-1 cells by altering cell cycle progression, enhancing apoptosis, and decreasing DNA damage repair capacity.