镁合金微弧氧化涂层上化学镀铜层的显微组织和导电性

为了赋予镁合金微弧氧化(MAO)涂层以导电特性,对MAO涂层进行化学镀铜处理。通过测试镀层的显微组织、耐蚀性和导电性,研究镀覆温度和络合剂浓度对化学镀铜层性能的影响。结果表明,最优镀覆温度为60℃,最佳络合剂浓度为30 g/L。在此条件下,可获得完整、致密的镀层。分析镀层在镁合金MAO涂层上的形成机制,提出镀覆过程的三阶段模型。镀后试样的表面方阻在经历第三阶段后降低至0.03Ω/。通过化学镀铜,MAO样品在未明显降低耐蚀性的同时获得了良好的导电性。

Preoperative differential diagnosis between intrahepatic biliary cystadenoma and cystadenocarcinoma:A single-center experience

AIM:To investigate preoperative differential diagnoses made between intrahepatic biliary cystadenoma and intrahepatic biliary cystadenocarcinoma.METHODS:A retrospective analysis of patient data was performed,which included 21 cases of intrahepatic biliary cystadenoma and 25 cases of intrahepatic biliary cystadenocarcinoma diagnosed between April 2003and April 2013 at the General Hospital of PLA.Potential patients were excluded whose diagnoses were not confirmed pathologically.Basic information(including patient age and gender),clinical manifestation,duration of symptoms,serum assay results(including tumor markers and the results of liver function tests),radiological features and pathological results were collected.All patients were followed up.RESULTS:Preoperative levels of cancer antigen 125(12.51±9.31 vs 23.20±21.86,P<0.05)and carbohydrate antigen 19-9(22.56±26.30 vs 72.55±115.99,P<0.05)were higher in the cystadenocarcinoma subgroup than in the cystadenoma subgroup.There were no statistically significant differences in age or gender between the two groups,or in pre-or post-operative levels of alanine aminotransferase,aspartate aminotransferase,total bilirubin(TBIL),and direct bilirubin(DBIL)between the two groups.However,eight of the 21 patients with cystadenoma and six of the 25 patients with cystadenocarcinoma had elevated levels of TBIL and DBIL.There were three cases in the cystadenoma subgroup and six cases in the cystadenocarcinoma subgroup with postoperative complications.CONCLUSION:Preoperative differential diagnosis relies on the integration of information,including clinical symptoms,laboratory findings and imaging results.

Auxiliary partial liver transplantation for acute liver failure using "high risk" grafts: Case report

Acute liver failure(ALF) is a reversible disorder that is associated with an abrupt loss of hepatic mass, rapidly progressive encephalopathy and devastating complications. Despite its high mortality, an emergency liver transplantation nowadays forms an integral part in ALF management and has substantially improved the outcomes of ALF. Here, we report the case of a 32-year-old female patient who was admitted with grade Ⅳ hepatic encephalopathy(coma) following drug-induced ALF. We performed an emergency auxiliary partial orthotopic liver transplantation with a "high risk" graft(liver macrovesicular steatosis approximately 40%) from a living donor. The patient was discharged on postoperative day 57 with normal liver function. Weaning from immunosuppression was achieved 9 mo after transplantation. A follow-up using CT scan showed a remarkable increase in native liver volume and gradual loss of the graft. More than 6 years after the transplantation, the female now has a 4-year-old child and has returned to work full-time without any neurological sequelae.

Corrosion behavior of Zr–Nb–Cr cladding alloys

Zr-Nb-Cr alloys were used to evaluate the effects of alloying elements Nb and Cr on corrosion behavior of zirconium alloys. The microstructures of both Zr substrates and oxide films formed on zirconium alloys were characterized. Corrosion tests reveal that the corro- sion resistance of ZrxNb0.1Cr （x = 0.2, 0.5, 0.8, 1.1; wt%） alloys is first improved and then decreased with the increase of the Nb content. The best corrosion resistance can be obtained when the Nb concentration in the Zr matrix is nearly at the equilibrium solution, which is closely responsible for the formation of columnar oxide grains with protective characteristics. The Cr addition degrades the corrosion resistance of the Zrl.lNb alloy, which is ascribed to Zr（Cr,Fe,Nb）2 precipitates with a much larger size than β-Nb.

Efects of thermal aging temperature and Cr content on phase separ-ation kinetics in Fe-Cr alloys simulated by the phase feld method

Phase field simulations of phase separation in Fe-Cr binary alloys were performed by using the Cahn-Hilliard diffusion function. A new mobility model in relation to aging temperature and Cr content was used in the simulations. Two alloys of Fe-30at%Cr and Fe-35at%Cr were investigated at two different aging temperatures of 573 and 673 K. The phase separation kinetics was found to consist of three stages： wavelength modulation, amplitude increase, and coarsening of Cr-enriched regions. A higher thermal aging temperature accelerated the phase separation and increased the wavelength of concentration fluctuation. While the effect of Cr content on the phase separation kinetics was slight, Fe-Cr alloys with a higher Cr content were found to generate a larger number and a finer size of Cr-enriched regions. The simulation results provide consultation for design and safe operation of duplex stainless steel pipes in nuclear power plants.

Effect of thermal aging on the fatigue crack growth behavior of cast duplex stainless steels

The effect of thermal aging on the fatigue crack growth（FCG） behavior of Z3CN20？09M cast duplex stainless steel with low ferrite content was investigated in this study. The crack surfaces and crack growth paths were analyzed to clarify the FCG mechanisms. The microstructure and micromechanical properties before and after thermal aging were also studied. Spinodal decomposition in the aged ferrite phase led to an increase in the hardness and a decrease in the plastic deformation capacity, whereas the hardness and plastic deformation capacity of the austenite phase were almost unchanged after thermal aging. The aged material exhibited a better FCG resistance than the unaged material in the near-threshold regime because of the increased roughness-induced crack closure associated with the tortuous crack path and rougher fracture surface; however, the tendency was reversed in the Paris regime because of the cleavage fracture in the aged ferrite phases.

Static recrystallization behaviors and mechanisms of 7Mo super-austenitic stainless steel with undissolved sigma precipitates during double-stage hot deformation

Static recrystallization(SRX)behaviors and corresponding recrystallization mechanisms of 7Mo super-austenitic stainless steel were studied under different deformation conditions.The order of influence of deformation parameters on static recrystallization behaviors,from high to low,is followed by temperature,first-stage strain and strain rate.Meanwhile,the effect of holding time on static recrystallization behaviors is significantly controlled by temperature.In addition,with the increase in temperature from 1000 to 1200°C,the static recrystallization mechanism evolves from discontinuous static recrystallization and continuous static recrystallization(cSRX)to metadynamic recrystallization and cSRX,and finally to cSRX.The cSRX exists at all temperatures.This is because high stacking fault energy(56 mJ m−2)promotes the movement of dislocations,making the deformation mechanism of this steel is dominated by planar slip of dislocation.Large undissolved sigma precipitates promote static recrystallization through particle-stimulated nucleation.However,small strain-induced precipitates at grain boundaries hinder the nucleation of conventional SRX and the growth of recrystallized grains,while the hindering effect decreases with the increase in temperature.

Modified Arrhenius-type Constitutive Model and Artificial Neural Network-based Model for Constitutive Relationship of 316LN Stainless Steel during Hot Deformation

Hot compression experiments of 316LN stainless steel were carried out on Gleeble-3500 thermo-simulator in deforma- tion temperature range of 1 223-1 423 K and strain rate range of 0.001-1 s 1. The flow behavior was investigated to evaluate the workability and optimize the hot forging process of 316LN stainless steel pipes. Constitutive relationship of 316LN stainless steel was comparatively studied by a modified Arrhenius-type analytical constitutive model considering the effect of strain and by an ar- tificial neural network model. The accuracy and effectiveness of two models were respectively quantified by the correlation coeffi- cient and absolute average relative error. The results show that both models have high reliabilities and could meet the requirements of engineering calculation. Compared with the analytical constitutive model, the artificial neural network model has a relatively higher predictability and is easier to work in cooperation with finite element analysis software.

Characterization of Impact Deformation Behavior of a Thermally Aged Duplex Stainless Steel by EBSD

The effect of thermal aging on phase transformation and impact toughness of an as-cast duplex stainless steel was investigated at room temperature. After long-term thermal aging, the impact toughness decreases significantly and the cracks initiate and propagate more easily. The plastic deformation ability of the ferrite phase decreases after thermal aging,which leads to the degradation of impact toughness. High stress concentration occurs on the grain boundaries of the austenite phase in the aged materials. Meanwhile, high-stress concentration areas are also observed in the austenite phase near the grain boundaries. After long-term thermal aging, pinned dislocations in ferrite and along phase boundaries lead to the high stress concentration. Micro-cracks preferentially initiate in the ferrite phase and propagate via separation of phase boundaries. The blocking influences of spinodal decomposition precipitates and G-phase precipitates are stronger than the effect of grain boundaries and phase boundaries on the dislocation movement.

Effect of milling duration on hydrogen storage thermodynamics and kinetics of ball-milled Ce-Mg-Ni-based alloy powders

To improve the hydrogen storage performance of CeMg12-type alloys, partially substituting Mg with Ni in the alloy was conducted. The way to synthesize the target alloy powders was the mechanical milling method, by which the CeMg11-Ni ＋ x wt% Ni （x = 100, 200） alloy powders with nanocrystalline and amorphous structure were obtained. The influence of the milling time and Ni content on the hydrogen storage properties of the alloys was discussed. The X-ray diffractometer and high-resolution transmission electron microscope were used to investigate the microstructures of the ball-milled alloys. The hydrogenation/dehydrogenation dynamics were studied using a Sievert instrument and a differential scanning calorimeter which was linked with a H2 detector. The hydrogen desorption activation energies of the alloy hydrides were evaluated by Arrhenius and Kissinger equations. From the results point of views, there is a little decline in the thermo- dynamic parameters （enthalpy and entropy changes） with the increase in Ni content. However, the alloys desorption and absorption dynamics are improved distinctly. What is more, the variation of milling time results in a dramatic influence on the hydrogen storage performances of alloys. Various maximum values of the hydrogen capacities correspond to different milling time, which are 5.805 and 6.016 wt% for the CeMgllNi ＋ x wt% Ni （x = 100, 200） alloys, respectively. The kinetics tests suggest that the hydrogen absorption rates increase firstly and then decrease with prolonging the milling time. The improvement of the gaseous hydrogen storage kinetics results from the decrease in the activation energy caused by the increase in Ni content and milling time.

Effect of cooling rate on microstructure, hardness, and residual stress of 0.28C-0.22Ti wear-resistant steel

The microstructure, hardness, and residual stress of 0.28C-0.22Ti wear-resistant steel produced with cooling rates varying from 80.0 to 0.3℃/s were determined using a dilatometer, scanning electron microscope, Vickers hardness tester, and nanoindentation tester. The results showed that the hardness of martensite decreased at a rate of approximately 0.935 HV/s with carbon diffusion time (the cooldown time required to transition from Ar3, 635-100℃). The range of the residual stress caused by the hard particles decreased with decreasing cooling rate, from - 400-300 MPa (cooling rate 40℃/s) to - 200-100 MPa (cooling rate 0.5℃/s), proving that the TiC particles significantly contributed to the residual stress in the high-titanium steels.

Highly ameliorated gaseous and electrochemical hydrogen storage dynamics of nanocrystalline and amorphous LaMg_(12)-type alloys prepared by mechanical milling

Nanocrystalline and amorphous LaMg12-type alloy-Ni composites with a nominal composition of LaMg11Ni＋x wt.% Ni（x=100,200）were synthesized via ball milling.The influences of ball milling duration and Ni adding amount xon the gaseous and electrochemical hydrogen storage dynamics of the alloys were systematically studied.Gaseous hydrogen storage performances were studied by a differential scanning calorimeter and a Sievert apparatus.The dehydrogenation activation energy of the alloy hydrides was evaluated by Kissinger method.The electrochemical hydrogen storage dynamics of the alloys was investigated by an automatic galvanostatic system.The H atom diffusion and apparent activation enthalpy of the alloys were calculated.The results demonstrate that a variation in Ni content remarkably enhances the gaseous and electrochemical hydrogen storage dynamics performance of the alloys.The gaseous hydriding rate and high-rate discharge（HRD）ability of the alloys exhibit maximum values with varying milling duration.However,the dehydriding kinetics of the alloys is always accelerated by prolonging milling duration.Specifically,rising milling time from 5to 60 h makes the hydrogen desorption ratio（a ratio of the dehydrogenation amount in 20 min to the saturated hydrogenation amount）increase from 57%to 66%for x=100alloy and from 57%to 70%for x=200.Moreover,the improvement of gaseous hydrogen storage kinetics is attributed to the descending of dehydrogenation activation energy caused by the prolonging of milling duration and growing of Ni content.

Improved wear resistance of biodegradable Mg-1.5Zn-0.6Zr alloy by Sc addition

Magnesium alloys exhibit significant potential for use in next-generation biodegradable materials.Implanted magnesium alloys are expected to exhibit good wear resistance.In this work,the effects of rare earth metal Sc on the wear resistance of biodegradable magnesium alloys were studied.The average grain sizes of Mg-1.5 Zn-0.6 Zr-x Sc(ZK21-x Sc,x=0,0.2,0.5,1.0;wt%)alloys decreased with Sc content increasing.Unlike other rare earth metals,the grain refinement mechanism of Sc belongs to the heterogeneous nucleation mechanism.The yield tensile strengths and Vickers hardness of the ZK21-x Sc alloys markedly improved with the addition of Sc increasing.This could be due to the grain refinement and enhanced bond energy resulting from Sc addition.Moreover,the friction and wear tests showed that the friction coefficient of the alloys decreased and the weight loss reduced with Sc addition increasing.This implies that Sc addition could enhance the wear resistance of magnesium alloys.With the addition of Sc increasing,the peeling phenomenon weakened gradually and the worn surfaces of samples became smoother.The major wear mechanisms of the as-cast ZK21-x Sc alloys were abrasion wear and delamination wear.

Enhanced mechanical properties in Al/diamond composites by Si addition

Diamond particles reinforced aluminum–silicon matrix composites,abbreviated as Al（Si）/diamond composites,were fabricated by squeeze casting.The effect of Si content on the microstructure and mechanical properties of the composites were investigated.The mechanical properties are found to increase monotonically with Si content increasing up to 7.0 wt%.The Al-7.0 wt% Si/diamond composite exhibits tensile strength of 78 MPa,bending strength of 230 MPa,and compressive strength of426 MPa.Al–Si eutectic phases are shown to connect with Al matrix and diamond particles tightly,which is responsible for the enhancement of mechanical properties in the Al（Si）/diamond composites.

Microstructure and properties of 1100 MPa grade low-carbon hot-rolled steel by laser welding

The microstructure and mechanical properties of the butt joint of 1100 MPa grade hot-rolled low-carbon steel by laser welding were investigated by scanning electron microscopy, micro-hardness and tensile tests. The yield strength and tensile strength of the laser welded joint reached 100.2 and 99.5% of the base material （BM）, respectively. However, the elongation of the welded joint only reached about 60% of BM. The lowest and highest hardness areas both existed in the incomplete recrystallization zone. The width of the softened area of the welded joint is about 240-260 pro. The element distribution has no obvious change for C, Cr, Si, Mn, Ti, etc.

A Physically Based Dynamic Recrystallization Model Considering Orientation Effects for a Nitrogen Alloyed Ultralow Carbon Stainless Steel during Hot Forging

The nitrogen alloyed ultralow carbon stainless steel is a good candidate material for primary loop pipes of AP1000 nuclear power plant. These pipes arc manufactured by hot forging, during which dynamic recrystallization acts as the most important microstructural evolution mechanism. A physically based model was proposed to describe and predict the microstructural evolution in the hot forging process of those pipes. In this model, the coupled effects of dislocation density change, dynamic recovery, dynamic recrystallization and grain orientation function were con sidered. Besides, physically based simulation experiments were conducted on a Gleeble 3500 thermo-mcchanical sire ulator, and the specimens after deformation were observed by optical metallography （OM） and clectron back scat toted diffraction （EBSD） method. The results confirm that dynamic recrystallization is easy to occur with increasing deformation temperature or strain rate. The grains become much finer after full dynamic recrystallization. The model shows a good agreement with experimental results obtained by OM and EBSD in terms of stress strain curves, grain size, and recrystallization kinetics. Besides, this model obtains an acceptable accuracy and a wide applying scope for engineering calculation.

Microstructure and impact toughness of 16MND5 reactor pressure vessel steel manufactured by electrical additive manufacturing

Electrical additive manufacturing can improve manufacturing efficiency and reduce the cost of 16MND5 reactor pres-sure vessel steel. Impact tests were conducted to compare the impact toughness of 16MND5 steels manufactured by the electrical additive manufacturing and conventional forging, respectively. It is found that the impact toughness of electrical additive manufacturing specimen was slightly higher than that of conventional forging specimen. The characterizations of microstructure show that there were large ferrites and carbides in electrical additive manufacturing specimen. The fracture mechanisms of electrical additive manufacturing specimen were that microvoids or microcracks were prone to nucleate at the large ferrite/bainite interface and large carbide/bainitic ferrite interface, where the stress concentration was high. In addi-tion, the block size and high-angle grain boundaries played a vital role in hindering crack propagation of electrical additive manufacturing specimen, helping to improve the impact energy and leading to a low ductile–brittle transition temperature. The results suggest that the electrical additive manufacturing technology was an effective method to enhance the impact toughness of 16MND5 steel.

Hot deformation behavior of a heat-resistant alloy without γ′-phase

The hot compression behavior of the nickel-based heat-resistant alloy C-HRA-2®was investigated by a Gleeble-1500 thermo-mechanical simulator with the deformation temperature range of 950-1150℃and the strain rate of 0.001-10 s^−1.The constitutive equation of the alloy was established by using a hyperbolic sine function,and the peak stress followed a power law relationship with the Zener-Hollomon parameter(Z).The activation energy was about 446 kJ mol^−1 for the whole hot deformation domain in this alloy.The optimum hot deformation condition was obtained in the temperature range of 1050-1150℃and the strain rate range of 0.005-0.1 s^−1.Unsafe domains during the hot deformation would occur in the strain rate range of 0.1-10 s^−1 with inhomogeneous microstructure and high-density twins in the alloy.The dominant nucleation mechanism of dynamic recrystallization(DRX)was continuous dynamic recrystallization with sub-grain rotation at high strain rate,while DRX at low strain rate was discontinuous dynamic recrystallization with original grain boundaries bulging.