Effects ofslip mode on microstructure evolution and compressive flow behavior of extruded dilute Mg−0.5Bi−0.5Sn−0.5Mn alloy

The influence of the slip mode on the microstructure evolution and compressive flow behavior at different strains in an extruded dilute Mg−0.5Bi−0.5Sn−0.5Mn alloy was analyzed through electron backscatter diffraction,X-ray diffraction,transmission electron microscopy,and hot compression tests.The results showed that at a low strain of 0.05,the basal,pyramidaland<c+a>slip modes were simultaneously activated.Nevertheless,at the middle stage of deformation(strain of 0.1,0.2 and 0.5),theslip mode was difficult to be activated and<c+a>slip mode became dominant.The deformation process between strains of 0.2 and 0.5 was primarily characterized by the softening effect resulting from the simultaneous occurrence of continuous dynamic recrystallization and discontinuous dynamic recrystallization.Ultimately,at strain of 0.8,a dynamic equilibrium was established,with the flow stress remaining constant due to the interplay between the dynamic softening brought about by discontinuous dynamic recrystallization and the work-hardening effect induced by the activation of the basalslip mode.

光子晶体提高GaN基LED出光效率的研究进展

光子晶体作为有效提高LED出光效率的手段之一,在过去的十多年受到了广泛的关注。简述了光子晶体提高LED出光效率的物理原理。从GaN基LED不同光子晶体的结构、晶格常数和高度等参数的影响出发,通过几种新型光子晶体发光二级管的介绍,总结了近年来利用光子晶体提高LED出光效率所取得的研究进展。

Microstructure,anticorrosion,biocompatibility and antibacterial activities of extruded Mg−Zn−Mn strengthened with Ca

To find suitable biodegradable materials for implant applications,Mg−6Zn−0.3Mn−xCa(x=0,0.2 and 0.5,wt.%)alloys were prepared by semi-continuous casting followed by hot-extrusion technique.The microstructure and mechanical properties of Mg−6Zn−0.3Mn−xCa alloys were investigated using the optical microscope,scanning electron microscope and tensile testing.Results indicated that minor Ca addition can slightly refine grains of the extruded Mg−6Zn−0.3Mn alloy and improve its strength.When 0.2 wt.%and 0.5 wt.%Ca were added,the grain sizes of the as-extruded alloys were refined from 4.8 to 4.6 and 4.2μm,respectively.Of the three alloys studied,the alloy with 0.5 wt.%Ca exhibits better combined mechanical properties with the ultimate tensile strength and elongation of 334 MPa and 20.3%.The corrosion behaviour,cell viability and antibacterial activities of alloys studied were also evaluated.Increasing Ca content deteriorates the corrosion resistance of alloys due to the increase of amount of effective cathodic sites caused by the formation of more Ca2Mg6Zn3 phases.Cytotoxicity evaluation with L929 cells shows higher cell viability of the Mg−6Zn−0.3Mn−0.5Ca alloy compared to Mg−6Zn−0.3Mn and Mg−6Zn−0.3Mn−0.2Ca alloys.The antibacterial activity against Staphylococcus aureus is enhanced with increasing the Ca content due to its physicochemical and biological performance in bone repairing process.

In-situ investigation of deformation behavior and fracture forms of Ti/Al/Mg/Al/Ti laminates

In-situ bending and stretching were conducted on hot-rolled and annealed Ti/Al/Mg/Al/Ti laminates,with a focus on crack initiation and propagation of intermetallics and component layers,which helps to clarify their deformation behavior and fracture forms.The results show that delamination is the early fracture form of laminate with or without intermetallics at Al/Mg interface,so Al/Mg interfacial bonding strength determines the mechanical properties of laminate.Various and irregular intermetallics cracks lead to Al/Mg interface delamination in annealed laminate and help to release stress.Necking and fracture of component layers are observed at the late deformation stage,and the sequence is Al,Mg and Ti layers,resulting from their strength.Angle between crack propagation direction and stretching direction of Mg layer both in rolled and annealed laminates is around 45°due to the effect of shear deformation,and crack convergence leads to final complete fracture of Mg layer.

Electroplated super-hydrophobic Zn−Fe coating for corrosion protection on magnesium alloy

A superhydrophobic Zn−Fe alloy coating was prepared on the surface of a reactive magnesium alloy using a simple,low-cost,eco-friendly method.Firstly,the Zn−Fe coating was obtained in a neutral glycerol Zn−Fe plating solution,which is green,compositionally stable,and non-corrosive to the equipment.And then the superhydrophobic surface with a flower-like microstructure was obtained by grafting myristic acid onto the Zn−Fe coating via a chelation reaction.The water contact angle was>150°and the rolling angle was 3°−4°.The corrosion rate of the two groups of superhydrophobic magnesium alloy samples with electrodeposition time of 30 and 50 min,respectively,was reduced by about 87%compared to that of the bare magnesium alloy.The prepared superhydrophobic coatings exhibit high performance in self-cleaning,abrasion resistance,and corrosion resistance.

Microstructure and mechanical properties of Ti−6Al−4V/Ti−22Al−25Nb joint formed by diffusion bonding

Ti-6Al-4V(wt.%) and Ti-22Al-25Nb(at.%) were joined by diffusion bonding at 950 ℃ and 15 MPa for 100 min, and the microstructure and mechanical properties of the resulting joints were investigated. The composition of the diffusion layer is B2/discontinuous α/α2 layer/necklace-shaped β+α’ layer, where the content of any element at a given point mainly depends on the distance of the point from the interface and the phase type at the point. The tensile strength of the joint is 894 MPa, which is almost the same as that of the Ti-22Al-25Nb base alloy. The fracture surfaces on both sides of the joint are composed of two main regions. One region displays a relatively flat surface and fractures along the bonding interface. The other is composed of a moderate number of irregularly-shaped cavities on the Ti-6Al-4V side and many irregularly-shaped bulges on the Ti-22Al-25Nb side. Both regions result from fracture along the boundaries between β+α’ layers and αp grains or from the transcrystalline fracture of αp grains.

Microstructure and mechanical properties of TiC nanoparticle-reinforced Mg−Zn−Ca matrix nanocomposites processed by combining multidirectional forging and extrusion

TiC nanoparticle-reinforced Mg−4Zn−0.5Ca matrix nanocomposites were processed by combining multidirectional forging(MDF)and extrusion(EX).The grain size of the nanocomposite after MDF+EX multi-step deformation was significantly decreased compared with that processed only by MDF.The average size of the recrystallized grains gradually increased after EX with increasing the number of MDF passes at 270℃.However,the grain size significantly decreased by MDF processing at 310℃.Both fine and coarse MgZn2 phases appeared in the(MDF+EX)-processed nanocomposites,and their volume fractions gradually increased with increasing the number of MDF passes before EX.Ultrahigh tensile properties(yield strength of^404 MPa,ultimate tensile strength of^450.3 MPa and elongation of^5.2%)were obtained in the nanocomposite after three MDF passes at 310℃ followed by EX.This was attributed to the refinement of the recrystallized grains,together with the improved Orowan strengthening provided by the precipitated MgZn2 particles that were generated by MDF+EX multi-step deformation.

Effect of duplex aging on microstructure and mechanical properties of near-βtitanium alloy processed by isothermal multidirectional forging

The effects of sub-transus(α+β)annealing treatment(ST),followed by single aging(SA)or duplex aging(DA)on the microstructural evolution and mechanical properties of near-βTi-4Al-1Sn-2Zr-5Mo-8V-2.5Cr(mass fraction,%)alloy were investigated using optical microscopy,scanning electron microscopy,and transmission electron microscopy.The results show that the finer secondaryαphase precipitates in the alloy after DA than SA(e.g.,149 nm for SA and 69 nm for DA,both after ST at 720℃).The main reason is that the pre-aging step(300℃)in the DA process leads to the formation of intermediateωphase nanoparticles,which assist in the nucleation of the acicular secondaryαphase precipitates.In addition,the strength of the alloy after DA is higher than that of SA at the specific ST temperature.A good combination is achieved in the alloy subjected to ST at 750℃,followed by DA(UTS:1450 MPa,EL:3.87%),which is due to the precipitation of nanoscale secondaryαphase by DA.In conclusion,DA is a feasible process for this new near-βtitanium alloy.

Effect of Ti content on corrosion behavior of Cu-Ti alloys in 3.5% NaCl solution

The corrosion behavior of the Cu-Ti alloys with different Ti contents in 3.5%(mass fraction)NaCl solution was investigated using electrochemical measurements,immersion tests,mass loss measurements and SEM observation.The results show that Ti dissolved in the Cu matrix changes the corrosion process of the alloys.Pure Cu sample exhibits a typical active–passive-transpassive corrosion behavior.The anodic polarization current densities of the Cu-Ti alloys steadily increase with increasing applied potential,indicating that active dissolution of copper proceeds due to the potential difference in the galvanic coupling of Cu and Ti.The increase of Ti content decreases the corrosion resistance of the Cu-Ti alloys.

Static coarsening behavior of equiaxed α phase in Ti-8Al-1Mo-1V alloy

To get a deep understanding of the evolution behavior of equiaxedαphase in Ti−8Al−1Mo−1V alloy during annealing,its static coarsening mechanism was studied based on the calculations of coarsening exponent n and the activation energy forαboundary migration.The result of n=6 indicates a special coarsening mechanism of equiaxedαphase.The activation energy forαboundary migration is calculated to be 138 kJ/mol,which is close to the activation energy for grain growth of pureα-Ti.It is revealed that the coarsening of equiaxedαcan be mainly attributed to the self-diffusion of Ti atoms across theα/αboundaries.Based on the experimental findings,a static coarsening kinetics model of equiaxedαgrains in theα+βfield is established.At last,the effects of the coarsening behavior of equiaxedαon tensile properties were studied.

Precipitation location of secondary phase and microstructural evolution during static recrystallization of as-cast Ti-25V-15Cr-0.3Si titanium alloy

The microstructural evolution and precipitation location of the secondary phase of an as-cast Ti-25 V-15 Cr-0.3 Si titanium alloy were investigated via isothermal compression experiments and heat treatment. The average aspect（length-to-width） ratio, average area and size of the grains at different heat treatment temperatures and holding time were analyzed and the effects of deformation and annealing time on the grain area and size were considered. It was found that the grain size was strongly influenced by the height reduction and holding time. Grain growth was significant when annealing time increased from 10 min to 2 h at 950 °C and height reduction of 30%; however, grain growth was minimal at annealing time between 2 and 4 h. Many dispersion particles were observed to form in continuous chains; the precipitation location was confirmed to be along initial grain boundaries, and the dispersion particles were identified to be Ti5 Si3 phase by TEM.