Degradation of differently processed Mg-based implants leads to distinct foreign body reactions(FBRs)through dissimilar signaling pathways

Mg alloys have mechanical properties compatible with human bones.However,their rapid degradation and associated foreign body reactions in vivo significantly limit their application for human implants.In this study,three differently processed Mg alloys,pure Mg(PM),cold extruded Mg alloy AZ31(CE AZ31),and fully annealed AZ31 Mg alloy(FA AZ31)were comparatively investigated for their potential as implants using a rat model.All three implanted Mg alloys do not show any impact on hepato-and renal function,nor any signs of observable changes to vital organs.Proteomics analysis of tissues directly contacting the implants 2.5 months post implantation revealed that FA AZ31 activates very few inflammation and immune associated signaling pathways;while the CE AZ31 and PM produce more significant inflammatory responses as confirmed by cytokine array analyses.Further,FA AZ31 activated pathways for cell organization and development that may improve the recovery of injured tissues.Structurally,EBSD analysis reveals that the FA AZ31 alloy has a higher ratio of first-order pyramidal orientated(10–11){10–1–2}grain texture with a value of 0.25,while PM and CE AZ31 alloys have lower ratios of first-order pyramidal orientated texture with the values of 0.16 and 0.17,respectively.This is associated with recovery and recrystallisation during annealing which promotes grain texture which exhibits enhanced degradation behaviours and induces a more limited immune response in vivo.In conclusion,the FA AZ31 demonstrated better biocompatibility and corrosion resistance and is a promising candidate for metal-based degradable implants which warrants further investigation.

Deformation behavior of explosive detonation in electroformed nickel liner of shaped charge with nano-sized grains

Nickel liner of shaped charge with nano-sized grains was prepared by electroforming technique and the ultra-highstrain-rate deformation was performed by explosive detonation.The as-electroformed and post-deformed microstructures of electroformed nickel liner of shaped charge were observed by optical metallography(OM),scanning electron microscopy(SEM) and transmission electron microscopy(TEM) and the orientation distribution of the grains was analyzed by electron backscattering pattern(EBSP) technique.Both melting phenomenon in the jet fragment and recovery and recrystallization in the slug after ultra-high-strain-rate deformation were observed.The research evidence shows that dynamic recovery and recrystallization play an important role in ultra-high-strain-rate deformation for electroformed nickel liner of shaped charge with nano-sized grain.

Evolution of microstructure, phase composition, and tensile properties of severely cold deformed titanium metastable β alloy in rapid continuous heating

Influence of severe cold deformation of titanium alloy Ti-1.5%A1-6.8%Mo-4.5%Fe in metastable β condition on the evolution of phase composition, microstructure, and tensile properties during continuous rapid heating was studied. As-deformed alloy was characterized by quasi-amorphous single-phase β condition with an abnormal temperature dependence of electric resistance that was normalized after 48 h exposure at room temperature as a result of isothermal ω phase precipitation. Subsequent rapid heating with a rate of 5 ℃/s caused recovery and recrystallization. Tensile properties of the alloy after different treatments were determined and discussed.

Microstructure and Deformation Behavior of Ti-10V-2Fe-3Al Alloy during Hot Forming Process

The microstructure evolution and formability of Ti-10V-2Fe-3Al alloy related to the initial microstructures and processing variables were investigated during hot forming process. The experimental results show that the α-phase growth is controlled by solute diffusion during the heat treatment processes. Four different microstructures were established by combinations of several heat treatments, and Ti-10V-2Fe-3Al alloy shows excellent formability both above and below the β transus temperature. The alloy possesses low deformation resistance and active restoration mechanism during the deformation. A constitutive equation describing the hot deformation behavior of Ti-10V-2Fe-3Al alloy was obtained. Higher fl ow stress was observed for the acicular morphology of α phase in microstructures with large aspect ratios as compared with that of small aspect ratios. Due to the dynamic recovery in soft β phase, and the dynamic recrystallization and breakage of acicular α-phase, fl ow softening occurred signifi cantly during deformation. Dynamic recrystallization also occurred especially in the severely deformed regions of forged parts.

Microstructural evolution in electroformed nickel shaped-charge liners with nano-sized grains undergone deformation at ultrahigh strain rate

Nickel shaped-charge liners with nano-sized grains were prepared by the electroforming technique, and the deformation at ultrahigh strain rate was performed by explosive detonation. The as-formed and post-deformed microstructures of electroformed nickel shaped-charge liners with nano-sized grains were observed by means of transmission electron microscopy, and the orientation distribution of the grains was analyzed by the electron backscattering pattern （EBSP） technique. The melting phenomenon in the jet fragment and the recovery and recrystallization in the slug after plastic deformation at ultrahigh-strain rate were observed in the ultrafine-grained nickel shaped-charge liners. The research evidence shows that dynamic recovery and recrystallization play an important role in plastic deformation at ultrahigh strain rate.

PLASTIC DEFORMATION BEHAVIOR OF ELECTROFORMED COPPER LINER OF SHAPED CHARGE AT DIFFERENT STRAIN RATES

The paper deals with different plastic deformation behavior of electroformed copper liner of shaped charge, deformed at high strain rate (about 1×107s-1) and normal strain rate (4×10-4s-1). The crystallographic orientation distribution of grains in recovered slugs which had undergone high-strain-rate plastic deformation during explosive detonation was investigated by electron backscattering Kikuchi pattern technique. Cellular structures formed by tangled dislocations and sub-grain boundaries consisting of dislocation arrays were detected in the recovered slugs. Some twins and slip dislocations were observed in specimen deformed at normal strain rate. It was found that dynamic recovery and recrystallization take place during high-strain-rate deformation due to the temperature rising, whereas the conventional slip mechanism operates during deformation at normal strain rate.

ON THE SWERVING OF STRENGTH CURVE FOR STEEL 20Cr11MoVNbNB

Study was made on the swerving of the curves of strength and hardness vs L-M parameter P=T(20+lgt)for steel 20Crl 1MoVNbNB aged at 550.600 and 650℃ for 0—5000 h,T being aging temperature in K and taging time in h.The swerving seems to be due to:(1)the coarsening of the mean size of principal precipitate M_(23)C_6,(2)the precipitation of Laves phase MoFe_2;(3)the decrease of Mo content in matrix and(4)the recovery and recrystallization of the matrix phase.

Microstructure Evolution of AZ31 Mg Alloy during Change Channel Angular Extrusion

Microstructure evolution of AZ31 Mg alloy during change-channel angular extrusion （CCAE） was investigated. The grains of AZ31 Mg alloy were refined significantly from 500 mm to 15 mm after CCAE deformed at 523 K. Dislocations were induced at the initial stage of extrusion and they rearranged themselves to form dislocation boundaries and sub-grain boundaries during deformation. When the specimen through the horizontal change channel with the strain increased, the sub-boundaries evolved to high angle grain boundaries （HAGB）. The process of grain refinement can be described as continuous dynamic recovery and recrystallization （CDRR）.

Processing maps and microstructural evolution of Al-Cu-Li alloy during hot deformation

The hot deformation behavior of Al-Cu-Li alloy was investigated by hot compression tests in the temperature range of 340-500℃ with strain rate of 0.001-10.000 s^(-1).Based on the dynamic materials model(DMM),processing maps of the test alloy were developed for optimizing hot processing parameters.The optimum parameters of hot deformation for Al-Cu-Li alloy are at temperature of 400-430℃and strain rate of about 0.100 s^(-1),with efficiency of power dissipation of around 30%.The microstructural manifestation of the alloy deformed in instability domains is flow localization,and dynamic softening first occurs in flow localizations structure.In stable domains,dynamic recovery(DRV) and dynamic recrystallization(DRX) are the main microstructural evolution mechanism.DRX is gradually strengthened with the increase in deformation temperature and the decrease in strain rate.During hot deformation,the DRX mechanism of Al-Cu-Li alloy is dominated by continuous DRX(CDRX).A DRX model of Al-Cu-Li alloy is proposed based on the microstructural evolution process of the test alloy.