Rare Earth Addition Research Articles

Effects of rare earth elements (Ce, La) on microstructure and mechanical properties in compacted graphite iron

ABSTRACT Microstructure and mechanical properties of compacted graphite iron (CGI) alloyed with different additions of rare earth (RE) elements are analysed in this paper. Experimental results show that graphite presents mostly vermicular shape when the content of RE is less than 0.041%. The shape of graphite becomes spherical after more RE is added. Tensile strength is improved significantly with the increase of RE content at room temperature and 400°C. Growth rate of main crack decreases obviously after RE alloying during thermal fatigue tests at 600°C. RE elements tend to segregate towards the interface between graphite and matrix, which leads to the change of graphite morphology. Auger electron spectroscopy (AES) results also show that Ce atoms will concentrate towards fracture surface, thus improving the oxidation resistance of the fracture surface at high temperature and crack propagation is inhibited.

Towards developing Mg alloys with simultaneously improved strength and corrosion resistance via RE alloying

Magnesium (Mg) alloys have received an increasing interest in the past two decades for their tremendous application potential. The strength and corrosion resistance levels of common Mg alloys are still relativity low, and especially they are to be improved simultaneously. The addition of rare earth (RE) to Mg alloys is believed to be beneficial for both the strength and corrosion resistance, and some RE-modified traditional Mg alloys have been studied and some new RE-containing Mg alloys have been developed by now. However, further simultaneous improvements in both strength and anti-corrosion require a better understanding of the behavior and mechanism of RE in Mg alloys. In this review, the common influence mechanisms of RE on mechanical and anti-corrosion properties of Mg alloys are summarized, and the latest research progress of RE-containing Mg alloys with simultaneously improved strength and corrosion resistance are introduced. It is demonstrated that the research on high-strength and high corrosion resistant RE-containing Mg alloys is still immature, and some opinions and suggestions are put forward for the synergetic improvement of the strength and corrosion resistance of Mg alloys, so as to contribute to the further development of Mg alloys with higher performance.

Hot Deformation Behavior and Microstructure Evolution of 6063 Aluminum Alloy Modified by Rare Earth Y and Al-Ti-B Master Alloy.

The hot deformation behaviors of the new 6063 aluminum alloy modified by rare earth Y and Al-Ti-B master alloy were studied through isothermal hot compression experiments on the Gleeble-3800 thermal simulator. By characterizing the flow curves, constitutive models, hot processing maps, and microstructures, we can see from the true stress–true strain curves that the flow stress decreases with the increase of deformation temperature and the decrease of strain rate. Through the calculation of the constitutive equation, we derived that the activation energy of the new composite modified 6063 aluminum alloy is 224.570 KJ/mol. we roughly obtained its excellent hot processing range of temperatures between 470–540 °C and the strain rates of 0.01–0.1 s−1. The verification of the deformed microstructure shows that with the decrease of lnZ, the grain boundary changes from a low-angle one to a high-angle one and the dynamic recrystallization is dominated by geometric dynamic recrystallization and continuous dynamic recrystallization. Analysis of typical samples at 480 °C/0.01 s−1 shows that the addition of rare earth Y mainly helps form Al3Y5 and AlFeSiY phases, thus making the alloy have the performance of high-temperature recrystallization, which is beneficial to the hot workability of the alloy.

Effect of rare earth oxide addition on microstructure and mechanical properties of Ni-based alloy

Oxide dispersion-strengthened (ODS) alloys possess several advantages such as excellent high-temperature creep strength and oxidation/irradiation resistance. Lanthanide oxides as well as yttria (Y2O3) have been proven to act as efficient additives in Fe-based ODS alloys; however, their potential for addition to Ni-based alloys has been limited. In this study, we fabricated four types of Ni-based ODS alloys with the combined addition of Ti and either Y2O3, cerium dioxide (CeO2), lanthanum oxide (La2O3), or gadolinium (III) oxide (Gd2O3) by mechanical alloying (MA) and hot isostatic pressing (HIP). We characterized both MA powders and HIPed samples of each alloy to compare the effect of oxide addition on the microstructure evolution. The results indicated that the addition of La2O3 had the most significant influence on refining oxide dispersoids and delaying recrystallization, resulting in a uniformly distributed ultra-fine grain structure. Based on further investigation of the contributions of various strengthening mechanisms, it was also found that the refinement of both oxide particles and grain size with the addition of La2O3 contributed to significant dispersion strengthening and grain boundary strengthening, leading to the highest Vickers hardness among the present alloys. When CeO2 and Gd2O3 were added, the mechanical properties were comparable, but better than those when Y2O3 was added. This demonstrates that all of the selected lanthanide oxides have practical potential as alternative additives to develop Ni-based ODS alloys, among which La2O3 would be the most advantageous in improving the mechanical properties.

Assessment of magnesium calcium alloys improved by rare earths addition for medical implants

Biodegradable materials are used as alternative implants for orthopedic applications due suitable strength, fatigue resistance, ductility and biocorrosion resistance which are features for biodegradable implants. Mechanical properties can be improved by adding alloying elements. The decrease of the corrosion rate of Mg can be induced by modifying the structure and phase distribution. Thus, Mg alloys have been designed to meet the requirements of bone repair implant materials by adding = Calcium and Yttrium or Gadolinium. Mg based alloy with Ca and Y/Gd had been proved to be a biocompatible material, osteoconductive and biodegradable and can be used in bone repairs. The system is defined as Mg100-(n+x) Ca(n) RE(x), varying the RE concentration in order to slow the degradation process. Beside morphological combining characterization SEM, EDX, with non-invasive testing is required to be carried out the determination of mechanical characteristics. The interest in this study is to analyze the influence of RE over elastic properties of these alloys in order to choose the best values appropriate with human bones, using Resonant Ultrasound Spectroscopy and ultrasound method.

Enhanced oxygen reduction reaction performance of ReOx/NC (Re = La, Ce, Pr, Sm, Eu, Tb, Er, Tm and Yb)-especially Pr6O11/NC via accommodating oxygen vacancies and its application for Zn-air battery

Rare earth metals have been widely investigated for oxygen reduction reaction (ORR) owing to their special 4f shell electronic configurations. However, the systematic comparisons of ORR activity with different rare earth have yet rarely studied. Herein, a series of rare earth (La, Ce, Pr, Sm, Eu, Tb, Er, Tm and Yb) oxides electrocatalysts were prepared with ketjin black EC300J as carbon support, in which the addition of rare earth is optimized. The ORR activities of different rare earth were evaluated by rotating disk electrode technology. The ORR performance of rare earth oxides composited carbon catalysts can be enhanced through accommodating oxygen vacancies. Then, the rare earth composite catalyst with the best ORR activities was chosen to detailed exploration. For practical application, the performance of rechargeable Zn-air battery was also researched. We believe that our work lay a good foundation to further explore rare earth based ORR catalyst with higher ORR performance.

The corrosion behavior of Mg-9Al-xRE magnesium alloys modified by friction stir processing

The combination of rare earth (RE) alloying and friction stir processing (FSP) was demonstrated to be favorable in improving the corrosion resistance of Mg-9Al alloys. The microstructure and corrosion behavior of the modified Mg-9Al-xRE alloys were documented in this paper. Electrochemical measurements revealed that the corrosion resistance of as-cast Mg-9Al-xRE alloys in 3.5 wt% NaCl solution was weaken with the addition of RE elements. It is found that the formation of a large amount of coarse strip-like Al-RE precipitates is responsible for the accelerated dissolution of anodic magnesium matrix. However, the corrosion resistance of FSPed Mg-9Al-xRE alloys was improved when the RE element was added and the improvement was further enhanced with the increasing amount of RE addition. This is mainly attributed to the alternation in the corrosion behavior of magnesium alloys owing to the refined and redistributed precipitates in α-Mg matrix. The refinement of cathodic precipitates enlarges the local area ratio of anode and cathode and retards the severe galvanic corrosion tendency in magnesium alloys. In addition, the presence of a large amount of fine Al-RE precipitates is favorable in accumulative growing of the corrosion product layer during the corrosion propagation, and thus improves the stability and compactness of this protective layer.

The martensitic crystallography and strengthening mechanisms of ultra-high strength rare earth H13 steel

Advanced die manufacture demands hot work die steels with superior strength. Unfortunately, due to the rare understanding of the crystallographic structures and strengthening mechanisms of H13 steel, the contradictory between ultra-high strength and low ductility remains inevitably as far as authors known. In this work, we developed a strategy combining rare earth addition, electroslag remelting and pre-tempering treatment, and prepared rare earth (Re) H13 steel with ultra-high ultimate tensile strength up to 2 gigapascals (GPa) and good ductility. The Re H13 steel underwent pre-tempering treatment exhibited hardness of ca. 53.6 HRC, ultimate tensile strength of ca. 2029 MPa, yield strength of ca. 1654 MPa, total elongation of ca. 9.3% and impact energy of ca. 16.0 J (superior grade of NADCA#207–2003 standard), respectively. The good ductility of Re H13 steel mainly attributed to high density of high angle grain boundaries (45° <) of ca. 1.45 μm−1, which derived from high length fraction of V1/V2 inter-variant boundaries (66.9%) by quenching, as well as coarsen sub-grains and variants refinement by subsequent tempering. The dislocation and carbide precipitates have the dominant role in controlling the strengthening of tempered Re H13 steel. The ultra-high strength of Re H13 steel mainly attributed to its high dislocation density (5.72 × 1014 m−2) and high carbide precipitates density (10.1 μm−2), which raised by 73.3% and 21.7% compared to Re H13 steel treated by conventional twice tempering (600 °C) process. The present work not only reveals the strengthening mechanisms of ultra-high strength Re H13 steel, but also characterizes the contributing microstructure feature to its good ductility.

Microstructure and texture evolution of fine-grained Mg-Zn-Y-Nd alloy micro-tubes for biodegradable vascular stents processed by hot extrusion and rapid cooling

Abstract Magnesium alloys have narrow available slip result from close-packed hexagonal structure that limit their processing properties. In the recent work, the Mg-2Zn-0.46Y-0.5Nd, as materials for degradable stents, was applied to produce as-extruded micro-tube with an outer diameter of 3.0 mm and a wall thickness of 0.35 mm by hot extrusion with an extrusion ratio of 105:1 at 653 K and rapid cooling. The fine microstructure of the dynamic recrystallization of as-extruded micro-tube could be preserved by rapid cooling such as water-cooled, resulting in more excellent mechanical properties relative to air-cooled micro-tube. The addition of rare earth elements Y and Nd results in continuous dynamic recrystallization dominated the dynamic recrystallization mechanism. During the hot extrusion process, the activation of the non-basal slip system, especially the pyramidal 〈c + a〉 slip, could significantly weaken the texture strength, and the as-extruded micro-tube exhibits weak “RE” texture components 〈 01 1 ¯ 1 〉 ∥ ED and 〈 1 ¯ 2 1 ¯ 1 〉 ∥ ED. Hence, the magnesium alloy micro-tube prepared by the rapid cooling has fine microstructure and weak texture, which is favorable for further process and governance.

Defect characteristics, local electron density, and magnetic properties of rare Earth-doped CuFeO2 ceramics

Polycrystalline CuFeO2 (CFO) and CuFe0.99R0.01O2 (R–CFO, R = La, Sm, Eu, Gd, Dy, and Ho) were prepared via solid-phase synthesis to investigate the effects of rare-earth (R) ion addition on the microstructures and magnetism. Positron annihilation lifetime spectroscopy (PALS) experimental results demonstrated that the size, concentration, and defect types were altered by R substitution due to the competition between the agglomeration of small-sized defects and the decomposition of vacancy clusters, which resulted in the redistribution of electrons around annihilation sites. The magnetic measurements revealed that the antiferromagnetic stability was influenced by R substitution, which was ascribed to the effect of magnetic moments, variations in exchange interactions, and the partial reduction of spin frustration. The magnetization behaviors of the R–CFO samples were also influenced by doping ions, which was mainly explained by the different magnitudes of the R ions’ magnetic moments. Ferromagnetism and antiferromagnetism were present in all of the samples. The local electron density ne was associated with the maximum magnetization (Mm). The correlative physical mechanisms are discussed in detail. The results demonstrated that the ne plays an important role in regulating the magnetic properties of CFO ceramics.

Microstructure and tensile properties of A356 alloy with different Sc/Zr additions

Addition of rare earth elements for improving the tensile properties of aluminum alloys has attracted great attention. In this study, a systematic analysis on the microstructure and tensile properties of A356–0.13Ti alloys with different contents of scandium (Sc) and scandium/zirconium (Sc/Zr) after solution and aging treatment process was carried out. The addition of Sc/Zr into A356–0.13Ti alloys can greatly refine the grain size and modify the deleterious coarse eutectic Si structure and harmful acicular iron-containing phase morphology. As a result, the maximum value of strength (298 MPa) and ductility (elongation of 8.4%) are acquired by co-addition of Sc/Zr after solution and aging treatment process, which indicates that the tensile properties of A356 alloy are greatly enhanced by the synergistic effect of co-addition of Sc/Zr.

Evaluation of the Effect of Rare Earth Alloying Additions on the Hot Tearing Susceptibility of Aluminum Alloy 7150 During Rapid Solidification

Additive manufacturing of the high-strength 7xxx Al alloy series is limited due to the susceptibility of these alloys to hot tearing. The objective of the current study is to determine the effect of rare earth (RE) element additions on the hot tearing susceptibility of Al alloy 7150 during rapid solidification conditions characteristic of additive manufacturing processes. Cast 7150-xRE (x = 0, 3, 6 wt pct) samples were remelted using a number of laser power-scan speed combinations. Cracks were observed in melt pools for 6 out of 12 processing conditions for 7150, but in all 12 conditions for the RE-containing alloys. Electron backscatter diffraction of the melt pool revealed the melt pool boundary grain size increased with RE additions, and cracks occurred along the grain boundaries. RE-containing intermetallics were observed on the crack surfaces, and were noted to possibly impede the interdendritic flow of eutectic liquids. A smaller amount of eutectic was observed in the thermal data for the RE alloys compared to 7150. Hot tearing indicators were useful in understanding the effect of RE additions when coupled with the experimental results. It is concluded that the addition of 3 to 6 wt pct RE elements increases hot tearing in 7150.

A novel ultra-high temperature Pt–Rh alloy with balanced tensile strength and creep resistance achieved by rare-earth intermetallics

A novel ultra-high temperature Pt–25Rh (wt.%) alloy with a minor addition of rare-earth (RE) elements (0.2 wt% La and 0.2 wt% Ce) was developed for the first time which exhibits the capability to withstand aggressive environment with a high operating temperature of >1500 °C. Tensile creep tests of the alloy were carried out at 1500 °C under a load of 5 MPa, the high tensile strength (σb) was up to 47.8 MPa, the creep rate (ε) as low as 0.008%/h and a rupture time (τ) more than 53 h, respectively. Detailed microstructure characterization revealed that there exist two balanced phases in the alloy, a ductile (Pt, Rh) solid solution phase with a face-centered cubic structure and a strengthening Pt5RE (RE = La, Ce) intermetallic phase with a hexagonal structure. The Pt5RE phases present three types of forms in the alloy, precipitates in the (Pt, Rh)ss matrix, an intergranular phase along the grain boundaries and a eutectic mixture in the matrix. Composition analysis showed that RE elements almost completely exist in the Pt5RE intermetallic phase but rarely in the (Pt, Rh)ss phase. It is interesting to note that the Pt5RE intermetallic phase is a RE-poor phase in which the content of RE elements is less than 5 wt%, much lower than the stoichiometric ratio (12.46 wt%). Compared with the reported Pt–Rh binary alloys, a minor additions of La and Ce in the new alloy effectively improves its high-temperature mechanical properties, which can be attributed to the formation of the strengthening Pt5RE intermetallic phase. By the way, an orientation relationship was identified between the Pt5RE and (Pt, Rh)ss phases in the eutectic structure for the first time.

Effects of Rare Earth Elements on Microstructure and Mechanical Properties of H13 Die Steel

The effects of rare earth (RE) elements on the carbide distribution, transformation temperature, and mechanical properties of H13 die steels after annealing were systematically investigated by scanning electron microscopy, electron probe microanalysis, and transmission electron microscopy. The results indicated that the addition of RE elements is helpful in increasing the fraction of the disrupted M23C6 carbide along the grain boundaries, hindering the migration of grain boundaries and improving the crack-formation and expansion resistance of the carbides in the tensile process. With the addition of RE, the Ac3 temperature increased by 11.4 °C and the diffusion of carbon atoms was pinned during the austenitizing process. Moreover, the carbides were modified by rare earth elements, and RE-inclusion promoted the transition of brittle-type failure to ductile-type failure. Therefore, the impact energy, hardness, and ultimate tensile strength improved significantly in the RE-modified H13 die steels.

Enhanced mechanical properties of as-cast AZ91 magnesium alloy by combined RE-Sr addition and hot extrusion

The synergetic effects of strontium (Sr) and rare earth elements (RE) on the modification of the microstructure and enhancement of the mechanical properties of as-cast Mg–9Al–1Zn alloy were studied. Based on the microstructural analysis, phase identification, and tensile tests, it was revealed that the combined RE and Sr addition results in superior mechanical properties compared to those of solo additions of RE or Sr. This was related to both morphological enhancement of the β-Mg17Al12 intermetallics notably by RE towards the disappearance of the intergranular network and modification of the Al11RE3 particles by Sr. The enhancement of tensile properties was achieved by increasing the RE/Sr ratio in the Sr-RE containing alloys and the best combination of mechanical properties was observed for the Mg–9Al–1Zn-0.9RE-0.1Sr alloy. Owing to the dissolution of the β phase and solid solution strengthening effect of Al, the tensile properties of the Mg–9Al–1Zn-0.9RE-0.1Sr alloy were enhanced by homogenization treatment. Moreover, the hot extrusion process remarkably augmented the tensile properties by combined effects of grain refinement and fracturing and distributing the intermetallic particles.

Impacts of yttrium on microstructure and tensile properties of biomedical β Ti-Nb-Zr fabricated by metal injection molding

Impurities, particularly oxygen, are a critical issue to address in metal-injection-molding (MIM) processed Ti-Nb-Zr biomaterials. The addition of rare earth (RE) elements such as yttrium is a possible solution to the impurity problem due to their potential for scavenging oxygen. The impacts of added Y on the sinterability, microstructure and mechanical properties of the MIMed Ti-Nb-Zr, however, largely remain unclear. In this study, different sized Y particles with varying weight fractions have been added to the β Ti-Nb-Zr alloy in order to elucidate the aforementioned aspects. It has been found that, although the added Y has an obvious β grain refinement effect, its impacts on the residual porosity, ultimate tensile strength and tensile toughness can be significantly negative, particularly if using large sized Y particles. Small sized (<15 μm), moderate amount (e.g. 0.3 wt%) of Y addition, however, proved to be beneficial, in terms of scavenging oxygen and promoting fracture toughness. Characterization techniques and mechanical testing are employed to understand the above experimental findings with the assistance of sintering theory and existing literature. It is hoped that the present study can provide an important guidance for using Y as an oxygen scavenger to develop low-cost, high-performance MIMed Ti alloys.

Experimental and theoretical study on the effect of different rare-earth oxides on the high-temperature stability of SiO2 glass at 1973K

The effect of different rare-earth oxides additives (La2O3, Nd2O3, Y2O3, Sm2O3, Yb2O3 and Lu2O3) on the stability of SiO2 glass at 1973 K was systematically studied employing volatility test and first-principles calculations. Both experimental and theoretical results show that the introduction of rare-earth oxides plays an active role in developing the stability of SiO2 glass at 1973 K due to the presence of Re2Si2O7 (Re= La, Nd, Y, Sm, Yb, Lu) phase. SiO2 glass samples doped with rare-earth oxide owning smaller cationic radius show better stability at 1973 K. Re atoms in Re2Si2O7 can diffuse into SiO2, which tends to occupy the interstitial site of SiO2 network. The influence of various interstitial Re atoms on SiO2 network are different and the inLu-SiO2 structure is the most stable. Meanwhile, the diffusion of Re atoms enhances the interface bonding between SiO2 (0 1 0) and inRe-SiO2 (1 1 2) and the inLu-SiO2 (1 1 2)/SiO2 (0 1 0) interface owns the highest binding energy, which is profitable to develop the thermal stability of SiO2 glass at 1973 K.

The Regularities in Constitution of the Ternary Phase Diagrams of Magnesium Alloys with Two Rare-Earth Metals Belonging to Different Groups (Yttrium Group or Cerium Group)

Investigations of the ternary phase diagrams of magnesium with two rare-earth metals from different groups (the yttrium group or the cerium group) are described with the main attention being paid to regions near the Mg corner. In these parts of the ternary phase diagrams, it was found that the magnesium solid solution was in equilibrium with only two binary compounds of magnesium with both rare-earth metals, and in addition, a significant solubility of each rare-earth metal in the most magnesium rich compound of the second rare-earth metal. In ternary Mg-systems involving rare-earth metals of different groups, trends in changes in the constitution in the Mg-region of the diagram as a function of the atomic number of the rare-earth additions were noted. These trends were established by comparing ternary phase diagrams of Mg-containing systems comprising yttrium and a rare-earth metal from the cerium group, and systems comprising samarium (from the cerium group) and a rare-earth metal from the yttrium group.

Recrystallization texture development in rare-earth (RE)-doped non-oriented silicon steel

High-grade non-oriented silicon steel with higher permeability and lower core loss has become the pursed target with the rapid development of electrical machines. The effects of rare-earth (RE) element on recrystallization texture in RE-doped Fe-3.1 wt.% Si-1.2 wt.% Al non-oriented silicon steel were investigated by macro- and micro-texture analyses. Nonlinear variation of recrystallization texture with RE element content was observed. In the competition among main recrystallization texture components, favorable {113} and λ fiber ( //ND) are strengthened and unfavorable γ fiber is evidently decreased by the addition of RE element, whereas the effect of RE element is reversed by excess RE element. The recrystallization texture development is determined by RE-affected nucleation and grain growth in terms of grain boundary migration related to segregation and inclusion. The properly inhibited grain boundary mobility can promote favorable recrystallization texture by the improved nucleation and efficient grain growth.

Effect of Heterogeneous Nucleation on Removal of Arsenic from Molten Steel by Rare Earth Addition

Cleanliness control is an eternal theme to improve the properties of steel products. With the increasing recycling rates of scrap steel, the removal and stabilization of residual elements have become a vital issue for improving the performance of steel products. Thermodynamic and mismatch calculations plus laboratory experiments were carried out to study the heterogeneous nucleation phenomena of inclusions when lanthanum was employed to remove arsenic from molten steel and stabilize arsenic in solid steel. The effect of heterogeneous nucleation on the mechanism of arsenic removal was discussed. A series of heterogeneous nucleation phenomena of inclusions in the La-O-S-As system were discovered, and the heterogeneous nucleation among the inclusions turned out to be selective. As the vital product of arsenic removal, La-S-As is most likely to generate with LaS as heterogeneous nucleation cores, and its possible chemical formula turned out to be 3LaS⸱LaAs. Sulfur plays an essential role in removing arsenic from molten steel by adding lanthanum. It needs to control the initial sulfur content in an appropriate range, because the high initial content causes too much loss of rare earth, and the low initial content cannot produce LaS and La-S-As.