Effect of lithium content on the mechanical and corrosion behaviors of HCP binary Mg–Li alloys

The microstructure,crystallographic texture,mechanical properties and corrosion resistance of as-extruded HCP Mg-x Li(x=1,3,5;in wt%)alloys were investigated.The results indicated that the HCP Mg-5 Li alloy with high lithium content exhibited a low degree of dynamic recrystallization(DRX)compared with Mg-1 Li and Mg-3 Li alloys.Besides,the 45°base(0001)texture of Mg-1 Li alloy could turn into(11–20)and(10–10)prismatic texture of Mg-3 Li and Mg-5 Li alloys with c-axis approximately parallel to transverse direction(TD).As a result,the strong prismatic texture resulted in the mechanical anisotropy of as-extruded Mg-3 Li and Mg-5 Li alloys with higher mechanical strength and low elongation along extrusion direction(ED)(reverse for TD sample).Regarding of corrosion behaviors,filiform corrosion occurred in the three Mg–Li alloys,whilst the high lithium content could mitigate the groove-like corrosion and improve the corrosion resistance of Mg-5 Li alloy,which was ascribed to the refined grains,prismatic texture and surface film.

MOFs衍生金属氧化物在催化VOCs完全氧化中的应用

大量挥发性有机化合物VOCs的排放对人类和环境造成了严重的影响。通过金属氧化物催化VOCs完全氧化为无毒害的二氧化碳和水是当前最有效的处理方式。为提高金属氧化物的催化性能,已开发了多种合成策略,如形貌工程、缺陷工程和掺杂工程等。然而,这些合成工艺不仅繁琐,而且催化性能有待提升。相比之下,金属有机框架(MOFs)衍生的金属氧化物由于其形貌可调、大比表面积、高缺陷浓度和良好的掺杂分散性等优点,被广泛应用于催化VOCs的完全氧化。由于目前缺乏针对MOFs衍生金属氧化物在VOCs完全氧化应用上的总结,本文从衍生金属氧化物的调控策略出发,对MOFs的合成条件、掺杂方式和热解条件进行了综述。总结了这些调控方法、衍生金属氧化物的物理化学性质与VOCs完全氧化性能的关系,并探讨了其未来的发展和挑战。

Effects of icosahedral phase on mechanical anisotropy of as-extruded Mg-14Li (in wt%) based alloys

Through investigating and comparing microstructure and crystallographic texture of as-extruded Mg-14Li and Mg-14Li-6Zn-1Y(in wt%)alloys,the differences in their mechanical anisotropy were investigated.It revealed that the formation of I-phase(Mg3Zn6Y,icosahedral structure)can effectively refine grain size.Moreover,compared with Mg-14Li alloy,the texture type of Mg-14Li-6Zn-1Y alloy changed slightly,but its texture intensity decreased remarkably.As a result,the stronger texture contributed to the"normal"mechanical anisotropy of Mg-14Li alloy with higher tensile strength and a lower elongation ratio along transverse direction(TD)than those along extrusion direction(ED).However,for Mg-14Li-6Zn-1Y alloy,the zonal distribution of I-phase particles along ED caused"abnormal"mechanical anisotropy,i.e.higher tensile strength and better plasticity along ED.

Biodegradation of Mg-14Li alloy in simulated body fluid: A proof-of-concept study

High corrosion kinetics and localised corrosion progress are the primary concerns arising from the clinical implementation of magnesium(Mg)based implantable devices.In this study,a binary Mglithium(Li)alloy consisting a record high Li content of 14%(in weight)was employed as model material aiming to yield homogenous and slow corrosion behaviour in a simulated body fluid,i.e.minimum essential medium(MEM),in comparison to that of generic Mg alloy AZ31 and biocompatible Mg-0.5Zn-0.5Ca counterparts.Scanning electron microscopy examination reveals single-phase microstructural characteristics of Mg-14Li(b-Li),whilst the presence of insoluble phases,cathodic to a-Mg matrix,in AZ31 and Mg-0.5Zn-0.5Ca.Though slight differences exist in the corrosion kinetics of all the specimens over a short-term time scale(no longer than 60 min),as indicated by potentiodynamic polarisation and electrochemical impedance spectroscopy,profound variations are apparent in terms of immersion tests,i.e.mass loss and hydrogen evolution measurements(up to 7 days).Cross-sectional micrographs unveil severe pitting corrosion in AZ31 and Mg-0.5Zn-0.5Ca,but not the case for Mg-14Li.X-ray diffraction patterns and X-ray photoelectron spectroscopy confirm that a compact film(25 mm in thickness)consisting of lithium carbonate(Li2CO3)and calcium hydroxide was generated on the surface of Mg-14Li in MEM,which contributes greatly to its low corrosion rate.It is proposed therefore that the single-phase structure and formation of protective and defect-free Li2CO3 film give rise to the controlled and homogenous corrosion behaviour of Mg-14Li in MEM,providing new insights for the exploration of biodegradable Mg materials.

Effects of V Addition on Microstructural Evolution and Mechanical Properties of AlCrFe_(2)Ni_(2) High‑Entropy Alloys

The effects of vanadium addition on the microstructural evolution and mechanical properties of AlCrFe_(2)Ni_(2) high-entropy alloy(HEA)were investigated.The results showed that the AlCrFe_(2)Ni_(2)V_(0.2) HEA was composed of FCC phase,disordered BCC phase,and ordered BCC(B2)phase.With the increase in vanadium content,the formation of FCC phase was inhibited,and a transition from FCC phase to BCC phase occurred.The FCC phase disappeared completely when the value of x exceeds 0.4 in AlCrFe_(2)Ni_(2)V_(x) HEAs.Besides,the amplitude-modulated microstructure morphology transformed from a B2 phase matrix with dispersed BCC nano-phase into an alternating interconnected B2 and BCC phases.Vanadium element has the function of stabilizing BCC phase and B2 phase in AlCrFe_(2)Ni_(2)V_(x) alloys.The hardness of AlCrFe_(2)Ni_(2)V_(x) alloys increased from HV 332.4 to HV 590.7,while the yield strength increased from 765 to 1744.6 MPa with increasing vanadium content,which was mainly due to the decreasing content of FCC phase and the solid solution strengthening of vanadium element.At the same time,the compression ratio of the alloys decreased with the disappearance of the FCC phase.Among the alloys,the AlCrFe_(2)Ni_(2)V_(0.2) alloy possessed the most excellent comprehensive mechanical properties with yield strength,fracture strength,and compressive ratio 1231.1,2861.9 MPa,and 44.5%,respectively.

Effects of Homogenized Treatment on Microstructure and Mechanical Properties of AlCoCrFeNi_(2.2) Near-Eutectic High-Entropy Alloy

A 4 kg AlCoCrFeNi_(2.2) near-eutectic high-entropy alloy ingot was prepared by vacuum medium frequency induction melting. The effects of homogenized treatment on microstructure and mechanical properties of AlCoCrFeNi_(2.2) were studied. The results showed that all the alloys consisted of the primary FCC phases and eutectic FCC/B2 phases. After homogenized treatment, lots of precipitated phases appeared in the primary phase. The hardness of the as-cast alloy was HV296. The hardness values of samples were decreased and were around HV250 after homogenized treatment. The tensile fracture strength of the as-cast alloy reached 900 MPa, while the elongation was 18%. After homogenized treatment at 900 ℃, the alloy showed the most excellent mechanical properties with the fracture strength 880 MPa and the elongation was 29%, respectively. All the alloys displayed a mixture fracture mechanism, including ductile fracture in primary FCC phases and eutectic FCC phases, and brittle quasi-cleavage fracture in eutectic B2 phases. Through a simple heat treatment method, the strength of the alloy was not reduced but the plasticity was greatly enhanced, which was more conducive to the industrial application prospects.