On investigating the soda-lime shot blasting of AZ31 alloy:Effects on surface roughness,material removal rate,corrosion resistance,and bioactivity

In the present study,a novel method of surface finish improvement is proposed using shot blasting of soda lime(SBSL)beads on the Mg-AZ31 alloy.The effect of the soda blasting process parameters,such as blast pressure,stand-off distance,and blast duration,have been studied in-response of material removal rate(MRR)and surface roughness(SR)and corresponding statistical models have been obtained.The multi-objective optimization has also been performed to obtain parameters for maximum MRR and minimum SR.The corrosion behavior of the treated specimens has been performed to study their in-vitro biodegradability in simulated body fluid(SBF)for 1,3,7,10,15,and 21 days.The wettability study of the SBSL treated samples has been investigated using sessile drop methodology.Further,cell adhesion test has also been performed to study the biocompatibility characteristics of the SBSL treated samples using Huh7 liver cell lines.Based on obtained quantitative data as well as scanning electron microscopy analysis of treated samples,the SBSL treatment of the AZ31 alloy has been found highly useful in producing biocompatibility surfaces along with desirable morphological features.

Influence of extrusion temperature on microstructure and mechanical properties of Mg-4Y-4Sm-0.5Zr alloy

The solution-treated Mg-4Y-4Sm-0.5Zr alloy was extruded at temperatures from 325℃ to 500℃.Dynamic recrystallization(DRX) completely occurs when the alloy is extruded at 350℃and above.The grains of the extruded alloy are obviously refined by the occurrence of DRX.The average grain size of the extruded alloy increases with increasing the extrusion temperature,leading to a slight decrease of the ultimate tensile strength(UTS) and the yield strength(YS) .On the contrary,the UTS and YS of the extruded and aged alloy increase with increasing the extrusion temperature.Values of UTS of 400 MPa,YS larger than 300 MPa and elongation(EL) of 7%are achieved after extrusion at 400℃ and ageing at 200℃ for 16 h.Both grain refinement and precipitation are efficient strengthening mechanisms for the Mg-4Y-4Sm-0.5Zr alloy.

Cu-WC复合材料涂层的受限烧结和磨损性能（英文）

采用固态烧结法制备Cu-WC金属基复合材料涂层。将不同体积分数(5%-30%)的WC增强颗粒与Cu颗粒混合,然后在还原性气氛和垂直膨胀计中于1000°C进行烧结。结果表明,复合材料涂层的烧结动力学受基体材料和WC颗粒的影响,WC颗粒能减缓粉末径向和轴向的致密化。复合材料涂层紧实地粘附于基体上,而WC颗粒随机分布在基体中。与未添加增强剂的样品相比,添加了WC增强剂的样品的显微硬度增加,磨损量降低至原来的1/17。样品在载荷为5 N条件下的主要磨损机理为磨粒磨损,当WC增强剂的体积分数为20%时复合涂层的性能最优。

Sintering study of Ti6Al4V powders with different particle sizes and their mechanical properties

Ti6Al4V powders with three different particle size distributions(0–20, 20–45, and 45–75 μm) were used to evaluate the effect of the particle size distribution on the solid-state sintering and their mechanical properties. The sintering kinetics was determined by dilatometry at temperatures from 900 to 1260°C. The mechanical properties of the sintered samples were evaluated by microhardness and compression tests. The sintering kinetics indicated that the predominant mechanism depends on the relative density irrespective of the particle size used. The mechanical properties of the sintered samples are adversely affected by increasing pore volume fraction. The elastic Young's modulus and yield stress follow a power law function of the relative density. The fracture behavior after compression is linked to the neck size developed during sintering, exhibiting two different mechanisms of failure: interparticle neck breaking and intergranular cracking in samples with relative densities below and above of 90%, respectively. The main conclusion is that relative density is responsible for the kinetics, mechanical properties, and failure behavior of Ti6 Al4 V powders.

一种兼具高强度、高应变硬化率和高塑性的新型钛合金

本研究设计了一种三元亚稳β钛合金Ti-9Mo-6W(质量百分数)。由于该合金变形时会联合出现相变诱发塑性效应和孪晶诱发塑性效应,使该合金的加工硬化速率可以接近2 100MPa,均匀变形能力高于35%。为了深入了解Ti-9Mo-6W合金的变形过程,对其变形过程中的显微组织进行了详细分析。结果表明,Ti-9Mo-6W合金变形过程中存在{332}<113>机械孪晶、应力诱发ω相、应力诱发α"马氏体等不同的变形机制,综合作用使合金内部最终形成了具有高度协合性的复杂网络变形组织。

Thin Oxide Film Growth during Final Annealing of Stainless Steels

After the cold rolling sequence of the production line,stainless steels strips present highly disordered structure and have to be annealed to recover their crystalline structure.This operation takes place by passing the moving strip through a furnace heated by combustion of natural gas with little air excess.Although the time at high temperature is short(<1 min),the formed surface oxide is thick enough to modify the surface aspect of the steel,making necessary subsequent chemical pickling.The present work explores the oxidation step of various stainless steels during final annealing in order to better understand the mechanisms involved and make further improvements in the pickling sequence.

Modeling and numerical investigation of slow crack growth and crack arrest in ceramic polycrystals

ntergranular slow crack growth in zirconia polycrystal is described with a cohesive zone model that simulate mechanically the reaction-rupture mechanism underlying stress and environ- mentally assisted failure. A 2D polycrystal is considered with cohesive surfaces inserted along the grain boundaries. The anisotropic elastic modulus and grain-to-grain misorientation are accounted for together with an initial stress state related to the processing. A minimum load threshold is shown to originate from the onset of the reaction-rupture mechanism to proceed where a minimum traction is reached locally and from the magnitude of the initial compression stresses. This work aims at providing reliable predictions in long lasting applications of ceramics.

A Double-Phase High-Frequency Traveling Magnetic Field Developed for Contactless Stirring of Low-Conducting Liquid Materials

The use of low electrically conducting liquids is more and more widespread.This is the case for molten glass,salt or slag processing,ionic liquids used in biotechnology,batteries in energy storage and metallurgy.The present paper deals with the design of a new electromagnetic induction device that can heat and stir low electricallyconducting liquids.It consists of a resistance-capacity-inductance circuit coupled with a low-conducting liquid load.The device is supplied by a unique electric power source delivering a single-phase high frequency electric current.The main working principle of the circuit is based on a double oscillating circuit inductor connected to the solid-state transistor generator.This technique,which yields a set of coupled oscillating circuits,consists of coupling a forced phase and an induced phase,neglecting the influence of the electric parameters of the loading part(i.e.,the low-conductivity liquid).It is shown that such an inductor is capable to provide a two-phase AC traveling magnetic field at high frequency.To better understand the working principle,the present work improves a previous existing simplified theory by taking into account a complex electrical equivalent diagram due to the different mutual couplings between the two inductors and the two corresponding induced current sets.A more detailed theoretical model is provided,and the key and sensitive elements are elaborated.Based on this theory,equipment is designed to provide a stirring effect on sodium chloride-salted water at 40 S/m.It is shown that such a device fed by several hundred kiloHertz electric currents is able to mimic a linear motor.A set of optimized operating parameters are proposed to guide the experiment.A pure electromagnetic numerical model is presented.Numerical modelling of the load is performed in order to assess the efficiency of the stirrer with a salt water load.Such a device can generate a significant liquid motion with both controlled flow patterns and adjustable amplitude.Based on the magnetohydrodynamic theory,numerical modeling of the salt water flow generated by the stirrer confirms its feasibility.

Strain Capacities Limits of Wrought Magnesium Alloys: Tension vs. Expansion

Lightening structure is one of the goals of many fields of research. As a result, magnesium alloys are studied due to their low density. However, one drawback of these alloys is their low formability at room temperature due to their hexagonal closed-packed structure. In the present work, the forming capacity of an AZ31 Mg alloys has been studied using a mini deep-drawing device, image correlation techniques and tests (tension and expansion) at temperatures contained between 20°C and 200°C. To investigate formability limits of Mg alloys in expansion, major and minor strains data were generated using hemispherical punch tests and analyzed with 3D digital images correlation techniques. Thanks to images correlation, strains on the surface of the samples were observed by means of a double digitization of the sample in three dimensions before and after deformation by using stereoscopic vision and triangulation. Image correlations have also been used in 2D to measure strains on the surface of the tensile test samples. These tests gave interesting information on the evolution of various parameters such as hardening coefficient, strain rate sensitivity parameter, and Lankford coefficient, which may affect the behavior of the alloys. Finally, the forming limits in both configurations (tension and expansion) were compared and discussed.

Strong dependency of the tribological behavior of CuZr-based bulk metallic glasses on relative humidity in ambient air

Thanks to their outstanding mechanical properties,Bulk Metallic Glasses(BMGs)are new alternatives to traditional crystalline metals for mechanical and micromechanical applications including power transmission.However,the tribological properties of BMGs are still poorly understood,mostly because their amorphous nature induces counter intuitive responses to friction and wear.In the present study,four different BMGs(Cu_(47)Zr_(46)Al_(7),Zr_(46)Cu_(45)Al_(7)Nb_(2),Zr_(60)Cu_(28)Al_(12),and Zr_(61)Cu_(25)Al_(12)Ti_(2))underwent ball-on-disc friction tests against 100Cr6 steel balls(American Iron and Steel Institute(AISI)52100)at different relative humidities(RHs)ranging from 20%to 80%.Controlling humidity enabled to observe a high repeatability of the friction and wear responses of the BMG.Interestingly,the friction coefficient decreased by a factor of 2 when the humidity was increased,and the wear rate of BMGs was particularly low thanks to a 3rd-body tribolayer that forms on the BMG surface,composed of oxidized wear particles originating from the ball.The morphology of this tribolayer is highly correlated to humidity.The study also identifies how the tribolayer is built up from the initial contact until the steady state is achieved.

Additive manufacturing of tungsten,tungsten-based alloys,and tungsten matrix composites

Tungsten(W) materials are gaining more and more attention due to the extended applications of metallic systems in the extreme environments.Given W’s unique characteristics like room-temperature brittleness,additive manufacturing(AM)techniques could give them a higher design flexibility and manufacturability.With the growing focus and thriving development of W-faced AM techniques,since the mechanical performance of additively manufactured W parts is still unsatisfactory,a critical review to further explore the possibilities of combining W and AM processes is urgently needed.In this review,we systematically explain the fundamentals of AM processes for W materials.Following the traditional classification,we further discuss the widely used AM processes including wire arc additive manufacturing(WAAM),electron beam melting(EBM),laser powder bed fusion(LPBF),laser direct energy deposition(laser DED),and other modified yet emergent AM techniques.Accordingly,since additively manufacturing W materials is processing parameter-sensitive,we illustrated the effects of various important processing parameters on the AM process control and final parts’ quality.With this detailed understanding,various categories of AM-compatible W materials(i.e.,pure W,W alloys,and W composites) were presented,and their general mechanical performance,distinct role(particularly the role of different alloying elements and added secondary-phase particles in W),and application-oriented benefits have been summarized.After clarifying the current status,main challenges,and triumphant successes for additively manufacturing W materials,we further provide a concise prospect into the development of additively manufactured(AMed) W materials by integrating potential fabrication,measurement,alloy design,and application’s considerations.In summary,this critical review investigates the fundamental and practical problems crucially limiting the applications of AMed W materials,and the comprehensive discussion concentrates the history of the development and combination between AM techniques and W design.All the understanding is of great importance to achieving foreseeable successful future applications of AMed W materials.

Impact of the Travelling Magnetic Field on the Metallic Impurities During the Crystallization of Photovoltaic Silicon

Silicon is the most extensively studied semiconductor mainly owing to its wide applicability in the photovoltaic solar cell industry.However the qualily of Si photovoltaic cells depends on the purity of the material and on the grain structure of the ingot from which the wafers are cutting.The electrical performance of such materials,i.e. mainly their minority carrier lifetime,is closely related to metal impurities present in the feedstock or introduced during crystal growth.These impurities strongly interact with existing crystal defects to form complexes,accumulate at dislocations or grain boundaries in different forms,or even form silieide precipitates,which simultaneously contain several metal impurities.In such a context,it is necessary to control the segregation of impurities especially metallic in the grown ingot in order to optimize the cell properties as a function of the raw material purity.A new Bridgman set-up is developed in order to study the crystallization of photovoltaic Si under independently controlled solidification parameters growth rate,thermal gradient,purity and convection.Convection,either natural or forced,plays a very important role during the crystallization.Its intensity and flow pattern affect heat and mass transfer and,consequently,macrostructure and segregation in a solidified ingot.Here the convection can be controlled by a travelling magnetic field in order to homogenize or segregate the rejected impurities such as metallic elements.The effects of the magnetic field intensity and frequency on the segregation and crystalline structure will be presented.

Modelling the Segregation of Impurities During Solidification With Turbulent Electromagnetic Stirring

This paper proposes an estimate of the stirring intensity needed to maintain an efficient segregation of impurities towards the liquid when crystallizing semiconductors such as silicon,with rapid solidification rates(several cm/h).The method,valid far from stagnation points or detachments,is based on the properties of turbulent boundary layers,with a normal velocity of the liquid towards the solid/liquid interface due to solidification,that has the same effect as boundary layer suction in aeronautics.The transition between the diffusive regime(no segregation),and the convective regime(efficient segregation)occurs if the friction at the wall is greater than a threshold depending on the solidification rate.A chart is given to estimate the convecto-diffusive parameter from the ratio between stirring and solidification velocity,and the Reynolds number.

Atomic-scale structural signature of dynamic heterogeneities in metallic liquids

With sufficiently high cooling rates,liquids will cross their equilibrium melting temperatures and can be maintained in a metastable undercooled state before solidifying.Studies of undercooled liquids reveal several intriguing dynamic phenomena and because explicit connections between liquid structure and liquids dynamics are difficult to identify,it remains a major challenge to capture the underlying structural link to these phenomena.Ab initio molecular dynamics(AIMD)simulations are yet especially powerful in providing atomic-scale details otherwise not accessible in experiments.Through the AIMD-based study of Cr additions in Al-based liquids,we evidence for the first time a close relationship between the decoupling of component diffusion and the emergence of dynamic heterogeneities in the undercooling regime.In addition,we demonstrate that the origin of both phenomena is related to a structural heterogeneity caused by a strong interplay between chemical short-range order(CSRO)and local fivefold topology(ISRO)at the short-range scale in the liquid phase that develops into an icosahedral-based medium-range order(IMRO)upon undercooling.Finally,our findings reveal that this structural signature is also captured in the temperature dependence of partial pair-distribution functions which opens up the route to more elaborated experimental studies.

Study of the Influence of Traveling Field Frequency and Wave Length on Pressure-Flow Rate Characteristic and Modeling of MHD Coupling in Annular Linear Induction Pump

The paper studies specific pumping characteristics of the annular linear pumps with travelling field(ALIP)for liquid sodium.This research represents a preliminary step in the study and development of very large electromagnetic pumps able to provide high flow rates.Since in such cases the magnetic Reynolds number are quite large,it is necessary to take into account the full magnetohydrodynamic interaction between the electromagnetic field and the liquid metal flow inside the pumping channel.The case where the velocity field is uniform in the channel cross section is firstly considered. Then,the coupling between the electromagnetic aspects with the hydrodynamic ones in a 2D axisyrnmetric fmite element model is studied,in order to compare the magnetic convection and the magnetic diffusion.

Vickers and Knoop Micro-hardness Behavior of Coarse-and Ultrafine-grained Titanium

The present study focuses on the relationship of hardness with grain size for commercially pure titanium （CpTi） and ultra fine grained titanium （UFG-Ti） produced by equal channel angular process （ECAP） of Cp-Ti）.Vickers and Knoop indentations of UFG-Ti at different loads was ～2.5 times harder than those of Cp-Ti.Xray diffraction （XRD） analysis showed peak broadening in UFG-Ti due to reduced grain size and micro-lattice strains.Scanning electron microscopy （SEM） revealed that ECAP had reduced the grain size of Cp-Ti by ～10 times.Weibull statistics showed UFG-Ti with lower dispersion in hardness values compare to Cp-Ti indicating a more uniform microstructure.

Effect of vertical electromagnetic stirring on solute distribution in billet continuous casting process

A volume averaged columnar solidification model,which couples the flow,temperature and solute concentration fields,is applied to simulate experimental continuous casting cases with and without vertical electromagnetic stirring(V-EMS).The calculated distribution of magnetic induction intensity and final macrosegregation maps are consistent with the experimental results.Calculation results reveal that the V-EMS promotes longitudinal melt flow,accelerates heat dissipation and solidification and finally reduces the central segregation of carbon.However,when V-EMS is applied,the solute distribution becomes asymmetric because the melt flow shows opposite directions between the near and far sides from stirrer.An obvious positive segregation band is observed at about 1/4 width of the billet near the stirrer in both calculated and experimental results.The position and degree of such positive segregation could be affected by installation height of stirrer,as demonstrated by additional simulation cases.

Serrated plastic flow behavior and microstructure in a Zr-based bulk metallic glass processed by surface mechanical attrition treatment

The serrated plastic flow,microstructure and residual stress of a Zr_（55）Cu_（30）Ni_5Al_（10） bulk metallic glass（BMG）undergone surface mechanical attrition treatment（SMAT）have been investigated by a combination of compression tests with scanning electron microscopy（SEM）,high resolution transmission electron microscopy（HRTEM）and the incremental hole-drilling strain-gage method.It is found that SMAT leads to various microstructural modifications and residual stress distribution in the surface layers of the Zrbased BMG due to the mechanically-induced nanocrystallization and generation of shear bands.As a result,the BMG alloy exhibits a remarkable work-hardening like behavior and significant increase of plastic strain from less than 1%to 15%,and its plastic deformation dynamics yields a power-law distribution of shear avalanches.Based upon the analysis of the experimental results,it is indicated that this can be connected to the SMAT-induced microstructural modifications and the resulting residual compressive stress in the Zr-based BMG.

In-Situ Analysis of Bulk Solidifying the Hyper-Monotectic Alloy Under a Compound Electric-Magnetic Field by Physical Simulation

A physical simulation was carried out to investigate the realistic experiment of bulk solidifying the Zn-Bi hyper-monotectic alloy under various compound electric-magnetic fields(CEMF).For this experiment,two crucial parameters determinate the cast microstructure,the one is electric-magnetic force(EMF)and the other is the frequency of AC current.Results show that the minor phase could be mixed in the other phase from the initial layered structure when the EMF above a specific value under fixed frequency,and the average diameter of minor phase droplet decreases with increasing EMF.The evolution of the liquid phases structure is reasonable agree with the realistic experiment of Zn-Bi hyper-monotectic alloy,which suggests that the mechanism revealed by the physical simulation could represent the one in the realistic experiment.