Biomedical rare-earth magnesium alloy:Current status and future prospects

Biomedical magnesium(Mg)alloys have garnered significant attention because of their unique biodegradability,favorable biocompatibility,and suitable mechanical properties.The incorporation of rare earth(RE)elements,with their distinct physical and chemical properties,has greatly contributed to enhancing the mechanical performance,degradation behavior,and biological performance of biomedical Mg alloys.Currently,a series of RE-Mg alloys are being designed and investigated for orthopedic implants and cardiovascular stents,achieving substantial and encouraging research progress.In this work,a comprehensive summary of the state-of-the-art in biomedical RE-Mg alloys is provided.The physiological effects and design standards of RE elements in biomedical Mg alloys are discussed.Particularly,the degradation behavior and mechanical properties,including their underlying action are studied in-depth.Furthermore,the preparation techniques and current application status of RE-Mg alloys are reviewed.Finally,we address the ongoing challenges and propose future prospects to guide the development of high-performance biomedical Mg-RE alloys.

Role of multi-microalloying by rare earth elements in ductilization of magnesium alloys

The present work investigates the influences of microalloying with rare earths on the mechanical properties of magnesium alloys.The amount of each rare earth element is controlled below 0.4 wt.%in order not to increase the cost of alloy largely.The synergic effects from the multi-microalloying with rare earths on the mechanical properties are explored.The obtained results show that the as-cast magnesium alloys multi-microalloying with rare earths possesses a quite high ductility with a tensile strain up to 25-30%at room temperature.Moreover,these alloys exhibit much better corrosion resistance than AZ31 alloy.The preliminary in situ neutron diffractions on the deformation of these alloys indicate that the multi-microalloying with rare earths seems to be beneficial for the activation of more slip systems.The deformation becomes more homogeneous and the resultant textures after deformation are weakened.

THE EFFECT OF RARE EARTH ELEMENTS ON THE SOLIDIFICATION BEHAVIOR OF Al-Mg ALLOYS

The effect of rare earth element on the solidification behavior of Al-Mg alloy was investigated in a directional solidification apparatus.It was found that during the solidification process.the rare earth element segregated in the liquid at sold-liquid interface,changed the solidification morphology and reduced the secondary arm spacing markedly.

Study of the Coarse Blocky Compounds in the As－cast 7075 Aluminium Alloys Containing Rare Earth Elements

The coarse blocky compounds in the as-cast 7075 aluminium alloys containing rare earth elements, neodymium, cerium or mischmetal were investigated by means of transmission electron microscope with EDX and scanning electron microscope. The blocky compounds in these alloys were identified as rare earth compounds, (Cr, Ti)2 RE (Al, X)20 (X is magnesium, copper and zinc),body-centred cubic, with 184 atoms to the unit cell , lattice parameter 1.453￣1. 458 nm, Vickers hardness 4000￣5600 MPa and calculated density 3400 kg/m3. The results show that the amount of blocky compounds in the alloys decreases with decreasing of Ti and Cr content or with increasing of cooling rate during solidification.

Multiplex modification with rare earth elements and P for hypereutectic A1-Si alloys

The effect of rare earth （RE） elements on the morphologies and sizes of Si phases in the hypereutectic A1-Si alloys modified with P was investigated. The results show that the addition of La element to the hypereutectic A1-Si alloys can enhance the effect of P element on the modification of the primary Si phases. In the multiplex modification of RE-P, the primary Si phase is refiner and the shape of the eutectic Si is changed from long needle-like to short rod-like. Moreover, the agglomeration rate of the primary Si phase is slowed greatly. Even the melt is held for 6 h, the average size of the primary Si phase is still satisfied. The results analyzed by scanning electron microscope （SEM） indicate that La is richer at A1-Si interface than that in α-A1 or primary Si phase. The higher the La content in the A1-Si interface, the smaller the primary Si phase.

Effect of rare earth elements addition on thermal fatigue behaviors of AZ91 magnesium alloy

Influences of rare earth （RE） elements addition on thermal fatigue behaviors of AZ91 alloy were studied. Repeated heating and cooling cycles were applied on the samples at 170 and 210℃ to develop thermal fatigue cracks. Crack growth mechanisms and microstructural influences were investigated by optical and scanning electron microscopy （SEM） as well as energy dispersive X-ray spectroscopy （EDS）. Thermal fatigue behaviors were observed to improve successively by addition of the RE up to 2wt.%. This improvement was attributed to the consummation of aluminum in melt by precipitation of the needle shaped AII1RE3 phases. This process was attributed to the reduction of MglTAl12 phase volume fraction and consequent decrease of the brittle Mg/MglTAl12 interface which was the main reason for weak thermal properties of the alloy at rather high temperatures. Further additions of RE, however, reduced the thermal shock resistance of the samples by increasing the mean length of the brittle needle shaped phases.

Effect of rare earth and alloying elements on the thermal conductivity of austenitic medium manganese steel

The influence of different contents of Cr, Mo, and rare earth element(RE) additives on the thermal conductivity of austenitic medium manganese steel was studied and discussed. The results show that the addition of Cr in medium manganese steel can improved the ordering of C–Mn atomic clusters, so as to improve the steel's thermal conductivity. However, Cr will lead to precipitation of a great deal of carbides in medium manganese steel when its content is greater than 4wt%. These carbides would aggregate around the grain boundary, and as a result, the thermal conductivity is decreased. By the addition of Mo whose content is about 2wt%, spherical carbides will be formed, thus improving the thermal conductivity of the medium manganese steel. The interaction between rare earth elements and alloying elements will raise both the thermal conductivity and the wear-resisting property of medium manganese steel.

Improvement of Ductility of Powder Metallurgy Titanium Alloys by Addition of Rare Earth Element

Ti-4.5Al-6.0Mo-1.5Fe, Ti-6Al-1Mo-1Fe and Ti-6Al-4V alloys were prepared by blended elemental powder metallurgy （PM） process, and the effects of Nd on the microstructures and mechanical properties were investigated by scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and X-ray diffraction （XRD）. It was found out that the addition of Nd increased the density of sintered titanium alloys slightly by a maximum increment of 1% because small amount of liquid phase occurred during sintering. The addition of Nd shows little effect on the improvement of tensile strength, while the elongation is significantly improved. For example, the elongation of Ti-4.SAl-6.0Mo-1.5Fe can be increased from 1% without addition of Nd to 13% at a Nd content of 1.2 wt pct.

Effect of Rare Earth Elements on Anisotropy and Microstructure of Al-Li Alloy 2195 Sheets

For the purpose of decreasing the applied limitation resulting from the anisotropic mechanical property of Al-Li alloy 2195, this study employed a complex heat treatment process, involving the pre-tension, thermo-infiltration of the rare earth element Ce, solution treatment, and artificial aging technology. The results indicate that the infiltration of rare earth element Ce benefits the abatement of anisotropy of Al-Li alloy 2195 sheet, in contrast with that of the normal heat treatment process. The gradient of the Vickers-hardness decreases at least 50% through the thickness, and the tensile strength in the rolling direction also increases significantly. If Ce was infiltrated into the alloy under the optimum pre-deformation, the yield strength （σ0.2） increased by 30 MPa while the tensile strength （σb） enhanced by 25 MPa compared to the rare earth free samples. Meanwhile, the fractography illustrated that the fracture surface of the sample became more desirable.

Effects of rare earth elements on the microstructure and properties of magnesium alloy AZ91D

The effects of rare earth elements on the microstructure andproperties of magnesium alloy AZ91D alloy were studied. The differentproportion of rare earth elements was added to the AZ91D and thetensile tests were carried out at different temperatures. Theexperimental results show that at room temperature or at 120 deg. Cthe AZ91D's strength decrease with the increasing amount of the rareearth elements. However, the ductility is improved. The influence of0.14/100Sb(mass fraction)on the AZ91D's strength is like that of rareearth elements(0.2/100-0.4/100)(mass fraction). Microstructure graphsdemonstrate that appropriate amount of rare earth elements(0.1/100-0.2/100)can fine AZ91D's grain and improve its ductility.

Effect of rare earth elements on the microstructure and property for magnesium alloy AM60B

The effects of rare earth elements on the microstructure and properties ofmagnesium alloy AM60B alloy were studied. Different proportions of rare earth elements were added toAM60B and the tensile tests were carried out under different temperatures. The experimental resultsshow that at room temperature the tensile strength of AM60B can be improved with the addition ofrare earth elements. The ductility of which at room or elevated temperature (120 deg C) can also beimproved, and the ductility is to some extent in proportion with the amount of rare earth elements.The ductility at 120 deg C is better than that at room temperature. The microstructure graphsdemonstrate that appropriate amount of rare earth elements (0.1 percent-0.2 percent, mass fraction)can fine AM60B's grain and improve its ductility.

Effect of combinative addition of strontium and rare earth elements on corrosion resistance of AZ91D magnesium alloy

The influence of strontium(Sr) and rare earth(RE) elements on the corrosion behavior of AZ91D magnesium alloy was investigated by conventional corrosion testing and electrochemical measurements in 3.5% NaCl solution.After comparing the mass loss and hydrogen evolution of the samples,the microstructures of the alloys and the morphologies of their corrosion product films were characterized by electron probe microanalysis-energy dispersive spectrometry(EPMA-EDS) and Auger electron spectroscopy(AES).Compared with individual addition of Sr or RE to AZ91D,the combinative addition of 0.5% Sr and 1% RE to AZ91D successfully decreases the corrosion rate further,which can be attributed to the depression of micro-galvanic couples,as well as the formation of more protective film due to aluminum enrichment.The combinative addition of strontium and rare earth elements to AZ91D magnesium alloy appears to be a promising approach to increase its corrosion resistance.

Corrosion behaviour and cytocompatibility of selected binary magnesium-rare earth alloys

The corrosion behaviour of as-cast binary Mg–0.3 Ce,Mg–1.44 Nd,Mg–0.63 Gd and Mg–0.41 Dy(wt%)alloys was investigated in DMEM+10%FBS solution using electrochemical and weight loss tests.The results revealed that the alloys with heavy RE elements(Gd and Dy)exhibited the lowest corrosion rate compared to the alloys with light RE elements(Ce and Nd).The cytocompatibility of the Mg–RE alloys was assessed via live/dead straining after 3 and 7 days.The results show that Mg–0.63 Gd alloy is a suitable candidate for biomedical applications.

Effects of Copper-Zinc Alloy Doped with Rare Earth Elements on Crystal of Calcium Carbonate

A copper-zinc alloy doped with rare earth elements was prepared and the mechanism was demonstrated in a simulating boiler and circulating cooling water with rigidity 1 mmol·L-1. The polar curve and scale inhibiting ability of the alloy was tested by a corrosion measurement system and a scale inhibition evaluation system, respectively. Scale samples were characterized with SEM and XRD. It is found that the transfer of cations could be promoted by doping with proper rare earth elements, and the corrosion potentials descend by 25～126 mV. The results indicated that the copper-zinc alloy doped with rare earth elements has higher scale inhibiting ability of CaCO3. The growth of calcite was affected by zinc ions dissolved because of primary battery reaction, and the transition of calcium carbonate from aragonite to calcite was hampered resulting in the proportion of aragonite to calcite is changed from 1.7∶1 to 2.7∶1.

Impact of scandium and terbium on the mechanical properties,corrosion behavior,and biocompatibility of biodegradable Mg-Zn-Zr-Mn alloys

Magnesium(Mg)-based bone implants degrade rapidly in the physiological environment of the human body which affects their structural integrity and biocompatibility before adequate bone repair.Rare earth elements(REEs)have demonstrated their effectiveness in tailoring the corrosion and mechanical behavior of Mg alloys.This study methodically investigated the impacts of scandium(Sc)and terbium(Tb)in tailoring the corrosion resistance,mechanical properties,and biocompatibility of Mg–0.5Zn–0.35Zr–0.15Mn(MZZM)alloys fabricated via casting and hot extrusion.Results indicate that addition of Sc and Tb improved the strength of MZZM alloys via grain size reduction and solid solution strengthening mechanisms.The extruded MZZM–(1–2)Sc–(1–2)Tb(wt.%)alloys exhibit compressive strengths within the range of 336–405 MPa,surpassing the minimum required strength of 200 MPa for bone implants by a significant margin.Potentiodynamic polarization tests revealed low corrosion rates of as–cast MZZM(0.25 mm/y),MZZM–2Tb(0.45 mm/y),MZZM–1Sc–1Tb(0.18 mm/y),and MZZM–1Sc–2Tb(0.64 mm/y),and extruded MZZM(0.17 mm/y),MZZM–1Sc(0.15 mm/y),MZZM-2Sc(0.45 mm/y),MZZM-1Tb(0.17 mm/y),MZZM-2Tb(0.10 mm/y),MZZM–1Sc-1Tb(0.14 mm/y),MZZM-1Sc-2Tb(0.40 mm/y),and MZZM–2Sc–2Tb(0.51 mm/y)alloys,which were found lower compared to corrosion rate of high-purity Mg(~1.0 mm/y)reported in the literature.Furthermore,addition of Sc,or Tb,or Sc and Tb to MZZM alloys did not adversely affect the viability of SaOS2 cells,but enhanced their initial cell attachment,proliferation,and spreading shown via polygonal shapes and filipodia.This study emphasizes the benefits of incorporating Sc and Tb elements in MZZM alloys,as they effectively enhance corrosion resistance,mechanical properties,and biocompatibility simultaneously.

Investigation on Behavior of Rare Earth Element Cerium in Aluminum-Lithium Alloys by Internal Friction Method

The behavior of rare earth element Ce in 2090 Al Li alloys was studied by the method of low frequency internal friction.The results showed that rare earth element Ce can increase the activation energy of grain boundary and improve the grain boundary strength of alloys.Rare earth element Ce can decrease the tendency of softening of elastic modulus of 2090 Al Li alloys after heat cycle and keep high elastic modulus of initial state.

INFLUENCE OF RARE-EARTH ELEMENTS ON THERMAL STABILITY OF PdSi_(16.5)GLASS

The influence of rare-earth elements,La,Ce,Pr,Nd,Sm,Eu,Gd,Dy,Ho,Er and Yb on the thermal stability of PdSi_(16.5) glass was studied systematically by means of DSC.All rare-earth elements,especially heavy ones,increase obviously the thermal stability parameters,including T_θ(T_g ,T_x ,T_g),T_(rg) and ΔE etc.The crystallization temperatures T_(p1) and T_(p2) increase linearly with the lanthanide constriction increasing,but Eu shows an anomalous influence:Pd-Si-Eu metallic glass possesses the highest thermal stability and the lowest concentration limit of glass forming among Pd-Si-R glasses.

Effects of rare earth elements on properties of AB_5-type electrode materials at different temperature

Discharge property is an important factor to evaluate electrode materials. The discharge capacity of the hydrogen-storing alloys are not only influenced by its thermodynamic property but also closely related to its dynamic property. When the temperature changes, the degrees of influence of the above-mentioned two factors on the discharge performance vary accordingly. As a consequence, adjusting compositions of the alloys to make them have good discharge performance under a relatively wide range of temperature is of great significance. On the basis of great deal of experimental investigation, the optimum combination of rare earth elements in hydrogen-storing electrode materials using at-30-55℃ is determined and the relationships between the cell parameters and discharge performance of alloys at -30℃ are discussed. Additionally, the DFEC calculation method has been improved to predict the discharge capacities, which is in good agreement with the experimental ones. This is of theoretical significance in investigating new hydrogen-storing alloys of the AB5 type.

Research progress,doping strategies and dielectric-ferroelectric anomalies of rare earth-based Bi_(0.5)Na_(0.5)TiO_(3) perovskites

Rare earth-based functional perovskites have received significant attention due to increasing energy crisis problems and environmental pollution.Many non-toxic,lead-free materials have been investigated;bismuth sodium titanate(Bi_(0.5)Na_(0.5)TiO_(3)) has gotten significant attention because of its unique morphological,structural,and electrical properties.Also,the emergence of bismuth sodium titanate with a high remnant polarization has revived the application of inorganic materials in electronic devices.This type of ferroelectrics is known to display new functionalities coupled with ferroic orders.In recent years,research in the field of inorganic-based ferroelectrics,mainly Bi_(0.5)Na_(0.5)TiO_(3)(BNT),has been thriving toward enhanced electronic device performance.Doping rare earth elements in BNT compounds has achieved significant electrical properties.This article summarizes prominent theories associated with ferroelectric-dielectric mechanisms and provides the most recent progress in rare earth-based BNT systems.Emphasis is placed on design of principles toward tailoring the crystal structure via doping effect and oxygen vacancies,as well as domain engineering.Finally,the critical investigation is accompanied by future perspectives,including integrating rare earth BNT perovskites for high-performance ferroelectric devices.

Study of rare earth element effect on microstructures and mechanical properties of an Al-Cu-Mg-Si cast alloy

The improvements of microstructures and properties of a high strength aluminum cast alloy were studied. The effects of rare earth elements on the microstructures and mechanical properties of the high strength cast alloy Al-Cu-Mg-Si were investigated. The result shows that the addition of rare earth elements can change the microstructures in refining the grain size of the alloy and making the needle-like and laminar eutectic Si to a granular Si. With the increase of the rare earth, the tensile strength and elongation of the alloy increase first and then fall down. The mechanical properties of the alloy will reach the highest value when the content of rare earth elements is about 0.7%.