High temperature deformation and recrystallization behavior of magnesium bicrystals with 90°<1010>and 90°<1120>tilt grain boundaries

The deformation mechanisms and dynamic recrystallization(DRX)behavior of specifically grown bicrystals with a symmetric 90°<1010>and 90°<1120>tilt grain boundary,respectively,were investigated under deformation in plane strain compression at 200℃and 400℃.The microstructures were analyzed by panoramic optical microscopy and large-area electron backscatter diffraction(EBSD)orientation mapping.The analysis employed a meticulous approach utilizing hundreds of individual,small EBSD maps with a small step size that were stitched together to provide comprehensive access to orientation and misorientation data on a macroscopic scale.Basal slip primarily governed the early stages of deformation at the two temperatures,and the resulting shear induced lattice rotation around the transverse direction(TD)of the sample.The existence of the grain boundary gave rise to dislocation pile-up in its vicinity,leading to much larger TD-lattice rotations within the boundary region compared to the bulk.With increasing temperature,the deformation was generally more uniform towards the bulk due to enhanced dislocation mobility and more uniform stress distribution.Dynamic recrystallization at 200℃was initiated in{1011}-compression twins at strains of 40%and higher.At 400℃,DRX consumed the entire grain boundary region and gradually replaced the deformed microstructure with progressing deformation.The recrystallized grains displayed characteristic orientations,such that their c-axes were perpendicular to the TD and additionally scattered between 0°and 60°from the loading axis.These recrystallized grains displayed mutual rotations of up to 30°around the c-axes of the initial grains,forming a discernible basal fiber texture component,prominently visible in the{1120}pole figure.It is noteworthy that the deformation and DRX behaviors of the two analyzed bicrystals exhibited marginal variations in response to strain and deformation temperature.

Effect of surface retaining elements on rock stability:laboratory investigation with sand powder 3D printing

This study aims to investigate the benefcial efects of surface retaining elements (SREs) on the mechanical behaviors of bolted rock and roadway stability. 3D printing (3DP) technology is utilized to create rock analogue prismatic specimens for conducting this investigation. Uniaxial compression tests with acoustic emission (AE) and digital image correlation techniques have been conducted on 3DP specimens bolted with diferent SREs. The results demonstrate that the strength and modulus of elasticity of the bolted specimens show a positive correlation with the area of the SRE;the AE characteristics of the bolted specimens are higher than those of the unbolted specimen, but they decrease with an increase in SRE area, thus further improving the integrity of the bolted specimens. The reinforcement efect of SREs on the surrounding rock of roadways is further analyzed using numerical modelling and feld test. The results provide a better understanding of the role of SREs in rock bolting and the optimization of rock bolting design. Furthermore, they verify the feasibility of 3DP for rock analogues in rock mechanics tests.

Deformation behaviour of magnesium bicrystals with symmetrical 90°<1120>tilt grain boundaries analysed by large area EBSD mapping

Grain boundaries play a significant role in the deformation of polycrystals.Their response to deformation is however not completely understood,particularly with respect to how they accommodate lattice rotation of adjoining crystallites by changing their structure and geometry.The current study thus investigates the deformation behaviour of Mg bicrystals with 90°<1120>symmetric tilt boundary strained in plane-strain compression up to different final strains.Due to the initial soft orientation of the two crystals,activation of basal slip in each crystal gave rise to lattice rotation around the transverse direction towards the compression direction of the channel-die.Hundreds of single EBSD maps with a small step size were obtained from the GB region and stitched together to produce large panoramic maps of a macroscopic scale.Although very time-consuming,this technique has proven useful in clarifying the origin of the non-uniform deformation zones in the vicinity of the grain boundary and explains the mechanisms,by which the grain boundary was able to cope with the imposed strain before fracture.Interestingly,several variants of extension twins were observed as an additional deformation mechanism despite having negative Schmid factors.Systematic investigation of their resulting combined shear components with respect to the sample coordinate system revealed an alignment along the longitudinal direction of the channel-die,therefore justifying their nucleation.

A promoting nitric oxide-releasing coating containing copper ion on ZE21B alloy for potential vascular stent application

Magnesium-based biodegradable metals as cardiovascular stents have shown a lot of excellent performance, which have been used to treat coronary artery diseases. However, the excessive degradation rate, imperfect biocompatibility and delayed re-endothelialization still lead to a considerable challenge for its application. In this work, to overcome these shortcomings, a compound of catalyzing nitric oxide(NO) generation containing copper ions(Cu^(2+)) and hyaluronic acid(HA), an important component of the extracellular matrix, were covalently immobilized on a hydrofluoric acid(HF)-pretreated ZE21B alloy via amination layer for improving its corrosion resistance and endothelialization. Specifically,the Cu^(2+) chelated firmly with a cyclen 1,4,7,10-tetraazacyclododecane-N’, N’’, N’’’, N-tetraacetic acid(DOTA) could form a stability of hybrid coating, avoiding the explosion of Cu^(2+). The chelated Cu^(2+) enabled the catalytic generation of NO and promoted the adhesion and proliferation of endothelial cells(ECs) in vascular micro-environment. In this case, the synergistic effect of NO-generation and endothelial glycocalyx molecules of HA lead to efficient ECs promotion and smooth muscle cells(SMCs) inhibition. Meanwhile, the blood compatibility also had achieved a marked improvement. Moreover, the standard electrochemical measurements indicated that the functionalized ZE21B alloy had better anti-corrosion ability. In a conclusion, the dual-functional coating displays a great potential in the field of biodegradable magnesium-based implantable cardiovascular stents.

Serum zinc levels and multiple health outcomes: Implications for zinc-based biomaterials

Background:Zinc-based biomaterials,including biodegradable metal,nanoparticles,and coatings used in medical implants release zinc ions that may increase the whole-body and serum zinc concentrations.The impact of serum zinc concentrations on major health outcomes can provide insights for device design and clinical transformation of zinc-based biomaterials.Methods:This nationally representative cross-sectional study enrolled participants from the National Health and Nutrition Examination Survey(NHANES,2011-2014)including 3607 participants.Using unadjusted and multivariate-adjusted logistic regression analyses,two-piecewise linear regression model with a smoothing function and threshold level analysis,we evaluated the associations between elevated serum zinc levels and major health outcomes.Results:Elevated serum zinc levels were significantly associated with an increase in total spine and total femur bone mineral density(BMD).Every 10μg/dL increase was associated with a 1.12-fold increase in diabetes mellitus(DM)and 1.23-fold and 1.29-fold increase in cardiovascular diseases(CVD)and coronary heart disease(CHD),in participants with serum zinc levels≥100μg/dL.It had no significant linear or nonlinear associations with risk of fractures,congestive heart failure,heart attack,thyroid disease,arthritis,osteoarthritis,rheumatoid arthritis,dyslipidemia and cancer.Conclusion:Serum zinc levels are significantly associated with increased BMD in the total spine and total femur,and risk of DM,and CVD/CHD among participants with serum zinc levels≥100μg/dL.

Quantitative analysis with plastic strain indicators to estimate damage induced by fault-slip

In the present study, methodologies to evaluate damage around an underground opening due to seismic waves arising from mining-induced fault-slip are examined. First, expressions for an associated flow rule with a failure criterion are developed for biaxial stress conditions, which are implemented into FLAC3D code. A three-dimensional(3D) mine model encompassing a fault running parallel to a steeply dipping orebody is constructed, whereby static and dynamic analyses are performed to extract stopes and simulate fault-slip in dynamic condition, respectively. In the analysis, the developed biaxial model is applied to the stope wall. The fault-slip simulation is performed, considering shearing of fault surface asperities and resultant stress drop driving the fault-slip. Two methodologies to evaluate damage caused by seismic waves arising from the simulated fault-slip are examined:(i) the ratio of dynamic plastic strain increment to elastic strain limit and(ii) plastic strain energy density. For the former one, two types of strain increments are tested, namely effective shear strain increment and volumetric strain increment.The results indicate that volumetric strain increment is a suitable index for detecting damage near the stope wall, while effective shear strain increment is appropriate for evaluating damage in backfill. The evaluation method with plastic strain energy density is found to be capable of assessing damage accumulated in an extensive area caused by rock mass oscillation due to seismic wave propagation. Possible damage to mine developments in the proximity of a stope is clearly described with the index. The comparison of the two methods clarifies that the former one assesses "instantaneous" damage, which is found to be different from "accumulated" damage calculated using plastic strain energy density, in terms of damage area and its location. It is thus concluded that the combination of the two methodologies leads to more accurate damage assessment as a proper measure against rockburst.

Moving research direction in the field of metallic bioresorbable stents-A mini-review

In contrast to polymer bioresorbable stents(BRS)that exhibited suboptimal performance in clinical trials due to their deficient mechanical properties,metallic BRS with improved mechanical strength have made their way into the clinic and have demonstrated more promising results.In the roadmap of research and development of metallic BRS,magnesium and iron based biodegradable metal stents had been clinically used,and the zinc based biodegradable metal stents had been trailed in Mini-Pigs.In this mini-review paper,we demonstrate the current technology levels and point out the future R&D direction of metallic BRS.Magnesium based BRS should target for decreasing struct thickness meanwhile balancing with enough supporting strength.Iron based BRS should move towards high efficient absorption,conversion,metabolism,elimination of its degradation products.Zn based BRS should strive to improve mechanical stability,creep resistance and biocompatibility.Future R&D directions of metallic BRS should move towards new materials such as Molybdenum,intelligent stent integrated with degradable biosensors,and new stent with multiple biofunctions,such as NO release.

Perceiving the connection between the bone healing process and biodegradation of biodegradable metal implants through precise bioadaptability principle

The implants made of metallic biomaterials help healing the bone fracture but also affect the bone repair process.As proposed in Matter 4(2021)2548–2650 by Wang et al.,a precisely adaptable biomaterial ought to recapitulate the targeted tissue with spatiotemporal precision and hierarchical accuracy,ranging from atoms and molecules(genes,proteins,etc.)to cells(including organelles)and to tissues and organs.In comparison to traditional bio-inert metallic bone implants such as Co-based alloys and Ti alloys,biodegradable metal(Mg and Zn alloys)bone implants had been developed and might arise many unexpected variables in the bone repair,due to their bioactive nature.In this paper,the bone repair without and with the presence of metallic implants is compared.Thereafter,the perspectives concerning the interactions between the bone tissues and biodegradable metal implants are put forward,and how to better mimic in vivo biodegradation by in vitro experiments is proposed for further research and development of biodegradable metals.

Comparison of microstructure,mechanical property,and degradation rate of Mg-1Li-1Ca and Mg-4Li-1Ca alloys

Mg-1 wt.%Li-1 wt.%Ca(LX11)and Mg-4 wt.%Li-1 wt.%Ca(LX41)alloys share the same hexagonal closed-packed crystalline structure.However,the differences in microstructure,mechanical properties,and degradation rates between the two alloys are not well understood.Hereby,the above three aspects of LX11 and LX41 alloys were studied via optical microscopy,tensile tests,and electrochemical polarization and electrochemical impedance spectroscopy,together with hydrogen evolution.The concentration of the released Mg^(2+),Ca^(2+),and Li+ions was analyzed using a flame atomic absorption spectrophotometer.Results demonstrated that the LX11 alloy was composed of finerα-Mg grains,fewer twins,and smaller volume fractions of the intermetallic phases Mg_(2)Ca than the LX41 alloy.The increasing Li concentration generated a weak decrease in the yield strength of the Mg-Li-Ca alloys,a remarkable increase in elongation to failure,and a stable ultimate tensile strength.The LX11 alloy had better corrosion resistance than the LX41 alloy.The release rate of the cations(Mg^(2+),Ca^(2+),and Li+)varied significantly with time.The release rate of metallic ions in Hank’s solution cannot reflect the true corrosion rate of Mg-Li-Ca alloys due to the formation of the precipitated corrosion products and their difference in solubility.The dealloying corrosion mechanism of the Mg_(2)Ca phase in Mg-Li-Ca alloys was proposed.

Investigating the stress corrosion cracking of a biodegradable Zn-0.8 wt%Li alloy in simulated body fluid

Stress corrosion cracking(SCC)may lead to brittle,unexpected failure of medical devices.However,available researches are limited to Mg-based biodegradable metals(BM)and pure Zn.The stress corrosion behaviors of newly-developed Zn alloys remain unclear.In the present work,we conducted slow strain rate testing(SSRT)and constant-load immersion test on a promising Zn-0.8 wt%Li alloy in order to investigate its SCC susceptibility and examine its feasibility as BM with pure Zn as control group.We observed that Zn-0.8 wt%Li alloy exhibited low SCC susceptibility.This was attributed to variations in microstructure and deformation mechanism after alloying with Li.In addition,both pure Zn and Zn-0.8 wt%Li alloy did not fracture over a period of 28 days during constant-load immersion test.The magnitude of applied stress was close to physiological condition and thus,we proved the feasibility of both materials as BM.