Microstructural evolution and dynamic recrystallization mechanisms of additively manufactured TiAl alloy with heterogeneous microstructure during hot compression

Microstructural evolution and dynamic recrystallization(DRX)mechanisms of a Ti-48Al-2Cr-2Nb(at.%)alloy prepared by selective electron beam melting(SEBM)during hot deformation at 1150℃and 0.1 s^(-1)were investigated by hot compression tests,optical microscope(OM),scanning electron microscope(SEM),electron back-scattered diffraction(EBSD)and transmission electron microscope(TEM).The results show that the initial microstructure of the as-SEBMed alloy exhibits layers of coarseγgrains and fineγ+α_(2)+(α_(2)/γ)lamellar mixture grains alternately along the building direction.During the early stage of hot deformation,deformation twins tend to form within the coarse grains,facilitating subsequent deformation,and a small number of DRX grains appear in the fine-grained regions.With the increase of strain,extensive DRX grains are formed through different DRX mechanisms in both coarse and fine-grained regions,involving discontinuous dynamic recrystallization mechanism(DDRX)in the fine-grained regions and a coexistence of DDRX and continuous dynamic recrystallization(CDRX)in the coarsegrained regions.

Xinfuli Granule improves post-myocardial infarction ventricular remodelingand myocardial fibrosis in rats by regulating TGF-β/Smads signaling pathway

Recent clinical and experimental studies have confirmed the effects of Xinfuli Granule (XG), a compound Chinese medicine in the prevention and treatment of heart failure (HF). This study aimed to investigate the effects and the mechanisms of XG on ventricular reconstruction in rats with acute myocardial infarction (AMI).MethodsSprague-Dawley rats were subjected to left anterior descending branch ligation. The rats that survived 24 h were randomly assigned to five groups: medium-dose of XG group (MI+XGM), high-dose of XG group (MI+XGH), carvedilol group (MI+C), medium-dose of XG + carvedilol group (MI+C+XGM). Fourteen rats underwent identical surgical procedures without artery ligation, serving as sham controls. At 28 days, left ventricular weight to body weight (LVW/BW) and heart weight to body weight (HW/BW) were calculated; left ventricular ejection fraction (LVEF), left ventricular shortening fraction (LVFS), left ventricular internal diameter at systole (LVIDS) were measured by ultrasound; HE staining, Masson staining, and Sirius red staining were used to assess the myocardial pathological and physiological changes as well as myocardial fibrosis area and non-infarct zone I/III collagen ratio. Expression of Smad3 were detected and analyzed by Western blot, immunohistochemistry and immunofluorescence. P-Smad3, Smad2 and Smad7 in the TGF-β/Smads signaling pathway were also analyzed by Western blot.ResultsThe LVIDS (P < 0.01), HW/BW (P < 0.05), type I/III collagen ratio (P < 0.01) and myocardial collagen (P < 0.01) decreased significantly while the LVW/BW, LVFS (P < 0.05) increased significantly in MI+XGM group as compared with those in other groups. The expression of key signal molecules of the TGF-β/Smads signaling pathway, including Smad3, P-Smad3 and Smad2 protein were decreased, while the expression of Smad7 increased in both XG and carvedilol treatment groups as compared to those of the MI group (all P < 0.01). Immunohistochemistry and immunofluorescence further confirmed the down-regulated Smad3 expression.ConclusionXG can improve ventricular reconstruction and inhibit myocardial fibrosis in rats with AMI by regulating TGF-β/Smads signaling pathway.

Characterization of hot deformation behavior of AA2014 forging aluminum alloy using processing map

The hot deformation behavior of AA2014forging aluminum alloy was investigated by isothermal compression tests attemperatures of350-480°C and strain rates of0.001-1s-1on a Gleeble-3180simulator.The corresponding microstructures of thealloys under different deformation conditions were studied using optical microscopy(OM),electron back scattered diffraction(EBSD)and transmission electron microscopy(TEM).The processing maps were constructed with strains of0.1,0.3,0.5and0.7.The results showed that the instability domain was more inclined to occur at strain rates higher than0.1s-1and manifested in theform of local non-uniform deformation.At the strain of0.7,the processing map showed two stability domains:domain I(350-430°C,0.005-0.1s-1)and domain II(450-480°C,0.001-0.05s-1).The predominant softening mechanisms in both of the twodomains were dynamic recovery.Uniform microstructures were obtained in domain I,and an extended recovery occurred in domainII,which would lead to the potential sub-grain boundaries progressively transforming into new high-angle grain boundaries.Theoptimum hot working parameters for the AA2014forging aluminum alloy were determined to be370-420°C and0.008-0.08s-1.

Isothermal oxidation behavior of TiAl intermetallics with different oxygen contents

Isothermal oxidation behaviors of Ti-45Al-2Fe-2Mo-1Cr intermetallics with different oxygen contents were studied under the condition of 950 °C, 100 h in air, and the oxidation kinetic parameters were also evaluated. The results show that the oxidation resistance of the TiAl intermetallics is negatively related to the oxygen content, and both the mass gain and thickness of oxide scale increase with the oxygen content. The sub-surface microstructure of the oxide scales varies with the oxygen content. Z phase is observed in the sub-surface area of the low-oxygen-content alloy, while the τ2(Al2FeTi) phase is found in the medium-oxygen-content and the high-oxygen-content alloys. The deterioration of oxidation resistance is due to the enhanced internal oxidation with the increase of oxygen content. It is possible to improve the oxidation resistance by controlling the oxygen content.

Dynamic tensile behavior of PM Ti-47Al-2Nb-2Cr-0.2W intermetallics at elevated temperatures

Split Hopkinson Tension Bar(SHTB) experiments were conducted to explore the dynamic mechanical behavior and deformation mechanism of powder metallurgical(PM) Ti-47 Al-2 Nb-2 Cr-0.2 W(at.%)intermetallics with near lamellar(NL) and duplex(DP)microstructures. Results show that,under dynamic loading,the high temperature strength of the PM TiAl intermetallics is higher than that under quasi-static loading, and the ductile to brittle transition temperature(DBTT) increases with the increase of strain rate. Formation of twinning and stacking faults is the main deformation mechanism during dynamic loading. The work hardening rates of the PM TiAl intermetallics are nearly insensitive to strain rate and temperature at high strain rates(800-1600 s-1)and high temperatures(650-850 ℃). Zerilli-Armstrong model is successfully used to describe the dynamic flowing behavior of the PM TiAl intermetallics. In general, the PM TiAl intermetallics are found to have promising impact properties, suitable for high-temperature and high-impact applications.

Effect of non-isothermal aging on microstructure and properties of Al−5.87Zn−2.07Mg−2.42Cu alloys

The evolution of microstructure and properties of Al−5.87Zn−2.07Mg−2.42Cu alloys during non-isothermal aging was studied.The mechanical properties of the alloy were tested by stretching at room temperature.The results show that in the non-isothermal aging process,when the alloy is cooled to 140℃,the ultimate tensile strength of the alloy reaches a maximum value of 582 MPa and the elongation is 11.9%.The microstructure was tested through a transmission electron microscope,and the experimental results show that the GP zones andη'phases are the main strengthening precipitates.At the cooling stage,when the temperature dropped to 180℃,the GP zones were precipitated again.Besides,the experimental results show that the main strengthening phase during non-isothermal aging isη'phases.

Microstructure and high-temperature mechanical properties of near net shaped Ti−45Al−7Nb−0.3W alloy by hot isostatic pressing process

Near net shaped Ti−45Al−7Nb−0.3W alloy(at.%)parts were manufactured by hot isostatic pressing(HIP).The microstructure and high-temperature mechanical properties of the alloy were investigated by X-ray diffractometry(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that at a temperature of 700℃,the peak yield stress(YS)and ultimate tensile stress(UTS)of alloy are 534 and 575 MPa,respectively,and the alloy shows satisfactory comprehensive mechanical properties at 850℃.The alloy exhibits superplastic characteristics at 1000℃ with an initial strain rate of 5×10^−5 s^−1.When the tensile temperature is below 750℃,the deformation mechanisms are dislocation movements and mechanical twinning.Increasing the tensile temperature above 800℃,grain boundary sliding and grain rotation occur more frequently due to the accumulation of dislocations at grain boundary.

Xinfuli improves cardiac function, histopathological changes and attenuate cardiomyocyte apoptosis in rats with doxorubicin-induced cardiotoxicity

Background Xinfuli Granule （XG）, a compound Chinese herbal medicine, has been effectively used in China for the treatment of heart failure for more than fifty years. This study aimed to investigate the effects and the underlying mechanisms of Xinfuli in rats with dox- orubicin-induced cardiotoxicity. Methods Sprague-Dawley rats were treated with intraperitoneal injection of Doxorubicin （DOX, 2.5 mg/kg per week） for six weeks, and then randomly divided into four groups which received intragastrically administration of normal saline （control group） or different dosage of XG （0.675 g/kg per day, 1.35 g/kg per day, and 2.7g/kg per day, respectively） for six weeks. Transtho- racic echocardiography was performed to evaluate the left ventricular fractional shortening （LVFS） and left ventricular ejection fraction （LVEF） before and after the XG treatment and histopathologic changes were also examined. Myocardial cell apoptosis was detected by TUNEL staining. The expression of related genes and proteins were analyzed using immunohistochemical staining. Results Compared to those in the control group, rats in XG treated groups showed significantly improved cardiac function and milder cardiac histopathological changes, lower cardiomyocyte apoptosis index, higher expression of Bcl-2 and lower expression of Bax. Conclusions Administration of XG improves cardiac function and histopathological changes in rats with doxorubicin-induced cardiotoxicity. These effects are associated with inhibition of cardiomyocyte apoptosis, perhaps via regulation of Bcl-2 and Bax protein expression.

Effect of aging time on discontinuous precipitates,continuous precipitates and mechanical properties of AZ80A magnesium alloy

The evolution of precipitates and mechanical properties of AZ80A magnesium alloy with aging time was studied by in situ observation with SEM,TEM and tensile testing.The results show that the continuous precipitation(CP)phases near the reaction front(RF)are replaced by the discontinuous precipitation(DP)phases at the early aging stage.In DP regions,the elliptical phases coarsen obviously with the increase of aging time,which results in a slightly slow reduction of the intracrystalline hardness of DP regions.In CP regions,some small plate phases reprecipitate simultaneously with the growth of the initial precipitates,which contributes to a slight increase in the intracrystalline hardness in CP regions at the later aging stage.The aging hardening of DP regions is faster and stronger than that of CP regions.However,the age strengthening of CP regions not only compensates for the overaging softening of DP regions but also improves the strength of the alloy.

Effect of T6-treatments on microstructure and mechanical properties of forged Al-4.4Cu-0.7Mg-0.6Si alloy

Transmission electron microscopy(TEM),scanning electron microscopy(SEM),hardness tests and tensile tests were performed to investigate the effect of aging on microstructure and mechanical properties of forged Al-4.4Cu-0.7Mg-0.6Si alloy.The results show that the alloy exhibits splendid mechanical properties with an ultimate tensile strength of504MPa and an elongation of10.1%after aging at170°C for16h.With tensile testing temperature increasing to150°C,the strength of the alloy declines slightly to483MPa.Then,the strength drops quickly when temperature reaches over200°C.The high strength of the alloy in peak-aged condition is caused by a considerable amount ofθ'and AlMgSiCu(Q)precipitates.The relatively stable mechanical properties tested below150°C are mainly ascribed to the stability ofθ'precipitates.The growth ofθ'and Q precipitates and the generation ofθphase lead to a rapid drop of the strength when temperature is over150°C.

High temperature mechanical properties and microstructure of die forged Al-5.87Zn-2.07Mg-2.42Cu alloy

The high temperature mechanical properties(250 ℃) and microstructure of a die-forged Al-5.87 Zn-2.07 Mg-2.42 Cu alloy after T6 heat treatment were investigated. High temperature tensile tests show that as the temperature increases from room temperature to 250 ℃, the ultimate tensile strength of the alloy decreases from 638 to 304 MPa, and the elongation rises from 13.6% to 20.4%. Transmission electron microscopy(TEM) and electron backscattered diffraction(EBSD) were applied for microstructure characterization, which indicates that the increase of tensile temperature can lead to the coarsening of precipitates, drop of dislocation density, and increase of dynamic recovery. After tensile testing at 250 ℃, a sub-grain structure composed of a high fraction of small-angle grain boundary is formed.