Numerical and experimental studies on solidification of AZ80 magnesium alloy under out-of-phase pulsed magnetic field

For obtaining the finer grains of magnesium alloy,a novel combined pulsed magnetic field with different initial phases,also called out-ofphase pulsed magnetic field(OPPMF),was applied to study the solidification structure of AZ80 magnesium alloy.The numerical simulation was simultaneously conducted to investigate the refinement mechanisms.The experimental results showed that the macrostructure could be effectively refined by applying external magnetic field.Meanwhile,finer grains were obtained with the higher current intensity.However,the increase of current intensity could only refine the grains to about 0.5 mm.Furthermore,compared to a single pulsed magnetic field(PMF)and alternating series of OPPMF(Connection II),a finer structure was observed when the consecutive series of OPPMF(Connection I)was imposed.In contrast with a single PMF and Connection II,the numerical results showed that the greater axial Lorentz force was obtained under the Connection I,generating the stronger forced flow in the melt.It is believed that abundant nuclei could detach from the mold wall and move faster into the interior melt due to the stronger forced flow;besides,the lower superheat and greater temperature uniformity in bulk melt were realized,accounting for the finest structures under the Connection I.

Characteristic Surface Oxide Film Cracking Behavior of a Fe-Ni-Cr Alloy under In-phase and Out-of-phase Thermo-mechanical Fatigue

The surface oxide film cracking behavior of Fe-30Ni-20Cr alloy under in-phase and out-of-phase synchronizing thermal cycling with mechanical cycling was studied.Surface oxide film cracking along the grain boundary under in-phase overlapping was creep predominant fracture mechanisms.Strongly induced slip lines preceding were accompanied by the surface oxide film cracking under Out-of phase,and the shear cracking was dominant mode.Negative mean stress could counteract a part of the tensile component of alternative stress,so as to delay the cracking process under in-phase,but positive mean stress overlapping the tensile alternative stress could accelerate the cycling cracking process under out-of-phase.

Conversion of out-of-phase to in-phase order in coupled laser arrays with second harmonics

A novel method for converting an array of out-of-phase lasers into one of in-phase lasers that can be tightly focused is presented.The method exploits second-harmonic generation and can be adapted for different laser arrays geometries.Experimental and calculated results,presented for negatively coupled lasers formed in a square,honeycomb,and triangular geometries are in good agreement.

A new model for life prediction of GH4133 under TMF conditions

Thermal mechanical cyclic strain tests were carried out under in-phase andout-of-phase conditions on a Nickel-base Superalloy GH4133 in the temperature range of 571-823 degC. Based on analyzing the present models of TMF (thermal mechanical fatigue) life prediction, a newmodel for predicting nickel-base superalloy TMF lifetime was proposed. TMF life of superalloy GH4133was calculated accurately based on the new model. Experimental TMF life has been compared with thecalculated results and all results fall in the scatter band of 1.5. The calculating results showthat the new model is not only simple, but also precise. This model will play great roles as lifeprediction of the metal materials and the engineering components subjected to non-isothermal serviceconditions.

EFFECTS OF STRAIN RATIO ON THERMAL-MECHANICAL CYCLIC STRESS-STRAIN RESPONSE AND FATIGUE LIFE IN DS SUPERALLOY DZ125

The effects of strain ratio on thermal-mechanical cyclic stress-strain response and fatigue life in DS superalloy DZ125 have been studied by performing tests at various strain ratio experiments, under strain-controlled and temperature cycling from 550 to 1000℃. It is shown that thermal-mechanical cyclic stress-strain response behavior not only depend on magnitude of strain, and temperature-loading phase angle, but also strain ratio. Fatigue life at strain ratio Rε=-0.3 is longer than that of strain ratio Rε=-1.0, under in-phase thermal-mechanical loading. However, Fatigue life at strain ratio Rε=-0.3 is shorter than that of strain ratio Rε=-1.0, under out-of-phase thermal-mechanical loading. The thermal-mechanical fatigue (TMF) damage model was discussed. Results of fractography show that fatigue, creep and oxidation damage always occur during TMF. The main damage mode depends on loading wave, strain ratio and magnitude of strain.

Hepatic steatosis with mass effect:A case report

BACKGROUND Hepatic steatosis is a common radiologic finding.Some imaging inklings are the absence of a mass effect,and there is currently no report of hepatic steatosis with mass effect.CASE SUMMARY A 23-year-old female was admitted due to a liver mass for half a month.No obvious abnormalities were found in physical and laboratory examinations.Ultrasound,computed tomography,and magnetic resonance imaging showed a huge mass between the liver and stomach with a significant mass effect,and the caudate lobe and left lobe of the liver were involved.The signal on T2-and T1-weighted fat-saturated images of the mass was significantly reduced,and the enhanced scan showed inhomogeneous enhancement.Surgical and pathological findings indicated the diagnosis of hepatic steatosis.The operation and re-review of the patient’s images showed that the lesion was supplied by the branch of the hepatic artery.The signal on T1-weighted out-of-phase images of the lesion was lower than on in-phase images,and there was no black rim cancellation artifact around the hepatic steatosis area on T1-weighted out-of-phase images.The dynamic enhancement pattern of the lesion was similar to that of the adjacent normal liver parenchyma.The above characteristics suggested that the lesion was hepatic steatosis.However,in this case,the lesion showed exogenous growth and was mass-like,with an obvious mass effect,which has not been reported previously.CONCLUSION Hepatic steatosis could grow exogenously and has an obvious mass effect.It needs to be distinguished from fat-rich tumors.The T1-weighted in-and out-of-phase images and dynamic enhanced scanning are valuable for differential diagnosis of this lesion.

非比例加载下电镀铜箔的晶粒长大行为(英文)

Grain growth behavior in a copper foil under nonproportional loading was investigated. The grain growth density decreased with increasing phase shift between normal stress and shear stress. Moreover, under this condition, grains tended to grow in various directions. However, the relative frequency of the grain growth direction was slightly large in the maximum shear stress direction. Therefore, grain growth density is mainly dominated by the equivalent shear stress in Tresca theory in the case of nonproportional loading as well as proportional loading.