Influence of Rare-Earth Elements on ElectricalProperties of Pd

The influence of RE (RE = La, Ce. Pr. Nd, Sm, Eu, Gd. Tb. Dy, Er, Yb) additives with dilute concentrations on the electrical properties of Pd has been studied. All RE elements increase the specific resistivity (ρ) and decrease the resistance temperature coefficient (α) of Pd. and (ρ.α) Pd-RE ls equal to (ρ· α)Pd.The RE elements before Gd reduce the thermo-emf of Pd on Cu. other heavy RE enhance the thermo-emf.The experimental data of normalized Pd-0.1 at.-%RE alloys indicate that the effect of light RE additives on the specific resistivity of Pd is larger than that of heavy RE and Ce. Eu and Yb show anomalous strong effect. The valence and atomic size are main factors influencing the electrical properties.     

Ce对铸态5356铝合金组织性能的影响

为探索稀土元素Ce对5356铝合金组织性能的影响,本文采用气泡浮游法,通过添加不同成分微量的稀土元素Ce精炼制备出含Ce不同含量的5356铝合金,通过显微组织观察、室温拉伸试验、密度测试等方法研究了在5356铝合金基体中添加稀土元素Ce对其组织性能的影响.实验结果表明:合金的力学性能及密度随着Ce添加量的增加而得到改善;稀土元素Ce既能够提高合金的抗拉强度、断后伸长率及硬度等力学性能,又能够提高合金的致密度使得铸锭中的气孔或疏松减少;添加Ce质量分数为0.4%时,其力学性能改善效果最佳,抗拉强度达到245.8 MPa,屈服强度为101.24 MPa,断后伸长率增加至29.05%,其密度也达到最大,相对提高了0.67%.     

稀土元素对富Ni的Ti-Ni形状记忆合金马氏体相变的影响

在本文中,向Ti-50.7at.%Ni合金分别加入1at.%的稀土元素Ce、Dy、Gd和Y,并利用X射线和示差扫描热分析研究了稀土掺杂对富Ni的Ti-Ni合金马氏体相变行为的影响.结果表明:向富Ni的Ti-Ni合金中添加稀土元素能使合金的马氏体相变温度显著增加,且添加稀土Ce使合金相变温度的增幅最大.此外,Ti-50.2Ni-1Gd和Ti-50.2Ni-1Y合金中发生两步马氏体相变,而添加Ce和Dy的Ti-Ni合金中仍只发生一步马氏体相变.     

Explaining texture weakening and improved formability in magnesium rare earth alloys

Wrought magnesium alloys are rarely used due to their poor formability which is caused by strong textures created during processing. Addition of rare earth (RE) elements including Y, Ce, La, Gd and Nd weakens these strong basal textures and significantly improves formability. Developing a mechanistic understanding of this effect is critical in leading alloy design towards a new class of highly formable magnesium alloys. This fall in texture intensity occurs during recrystallisation and only requires very low solute RE additions, 0·01 at.-% in the magnesium–Ce case. These additions retard dynamic recrystallisation and increase non-basal slip; however, a full understanding of the RE effect has yet to be obtained, with a variety of mechanisms proposed. Recent research in these areas is critically reviewed.     

Role of rare earth oxide coatings on oxidation resistance of chromia-forming alloys

Rare earths (RE) have been used to increase high temperature oxidation resistance of chromia and alumina forming alloys. The RE can be added as elements (or oxides) to the alloys or applied as oxide coatings to the alloy surface. This paper presents the effect of different RE oxide coatings and lanthanum chromite coatings on the high temperature oxidation behavior of Fe20Cr and Fe20Cr4Al alloys. The oxidation resistance of the Fe20Cr alloy increased with increase in ionic radius of the RE element in the coating. The RE oxides decreased chromia growth rate more than alumina growth rate. In extended cyclic oxidation tests that were carried out from peak temperatures of 900 °C, 1,000 °C and 1,100 °C to room temperature at cooling rates of 300 °C/s and 1,000 °C/s, the La₂O₃ coating increased cyclic oxidation resistance of the Fe20Cr alloy significantly more than the Pr₂O₃ coating. The role of RE in increasing overall oxidation resistance of chromia forming alloys is discussed.     

Effects of neodymium rich rare earth elements on microstructure and mechanical properties of as cast AZ31 magnesium alloy

Abstract

The effects of neodymium rich rare earth elements [RE(Nd)] on microstructure and mechanical properties of as cast AZ31 magnesium alloy were investigated. The microstructures of as cast AZ31–xRE(Nd) alloys display a dendrite configuration, and the secondary dendrite spacing of the α-Mg phase was decreased with the increasing Nd content. The addition of RE(Nd) resulted in the formation of Al₂Nd and Mg₁₂Nd phases. Mechanical properties were improved significantly due to grain refinement and precipitation of intermetallic phases. When the amount of RE is 1·0 wt-%,The as cast AZ31 alloy reached its maximum tensile strength of 249 MPa at room temperature, yield strength of 169 MPa and elongation of 9·0%.     

Combined effects of cerium and boron on the mechanical properties and oxidation behaviour of Ni3Al alloy

The combined effects of cerium and boron additions on the room-temperature tensile properties and high-temperature oxidation behaviour of Ni3Al alloys: alloy 1 doped with cerium, alloy 2 doped with boron, and alloy 3 doped with both cerium and boron. The strength, ductility and oxidation behaviour of the alloy are more effectively improved by combined cerium and boron additions than by cerium or by boron addition alone. Of the three alloys, alloy 3 exhibits comprehensively the best mechanical properties and oxidation resistance. Alloy 2 presents the better mechanical properties than alloy 1; nevertheless, alloy 1 has the better oxidation resistance than alloy 2.     

Fe和Ce 含量对Galfan合金力学性能及耐蚀性的影响

将真空熔炼的Zn-Fe-Ce中间合金加入到Zn-Al熔池中,制备Zn-5Al-0.1Ce-xFe和Zn-5Al-yCe-0.1Fe合金,分析了Fe和Ce含量对合金显微组织及力学性能的影响,并使用电化学工作站测试了合金的电化学性能。结果表明,在Zn-5Al-0.1Ce合金中Fe含量大于0.02%后会形成颗粒状的FeAl3Znx相。随着Fe含量的增加,FeAl3Znx相和先共晶的η-Zn相增加,Zn-Al共晶组织由层片状向点状转变。添加0.1%以下的Fe可提高Galfan合金的抗拉强度。但随着Fe含量的增加,合金的抗拉强度略有降低,Zn-5Al-0.1Ce-0.02Fe合金的综合力学性能最好。添加0.04%以下的Fe会提升合金耐蚀性。此外,随着Ce含量的增加,Zn-5Al-yCe-0.1Fe合金的抗拉强度有所降低,耐蚀性变化不明显。因此,在生产中需要根据镀层性能要求,严格控制合金液中的Fe和Ce含量。     

低温对时效态TC4合金拉伸性能的影响

在77－300K温度范围内对不同时6效状态TC4合金进行拉伸试验，研究了低温对时效态合金拉伸性能的影响。时效温度取813天，时效时间分别为0．5h、7h、60h。试验结果表明：在室温下，时效0．5h合金与退火态合金相比强度明显提高，延伸率略有降低；时效时间大于0．5h，随时效时间的延长，合金的强度与延伸率均下降。随试验温度的降低，3种时效态合金的强度都单调增加，延伸率先是下降，但在77K时又略有升高，TEM观察表明，随着试验温度的降低，拉伸断口附近位错分布不均匀性增大。     

The influences of rare earth content on the microstructure and mechanical properties of Mg–7Zn–5Al alloy

The influences of rare earth (RE) on the microstructure and mechanical properties of Mg–7Zn–5Al alloy were studied. The results indicate that both the dendrite and grain size of the alloy can be refined by low RE addition. The Al₂REZn₂ phase will be formed with increasing the RE content, however the high RE addition results in the grain coarsening in the alloy due to the decrease of the contribution of Al and Zn solutes on the grain refinement. The strengthening and weakening mechanisms caused by RE addition only lead to the obviously improve on the room temperature ultimate tensile strength. The mechanical properties of the studied alloys can be improved by aging treatment, and the aged Mg–7Zn–5Al–2RE alloy exhibits optimal mechanical properties at room temperature.     

Tensile properties and transformation temperatures of Pd added Ti-Ni alloy dental castings

The effect of palladium (Pd) addition to Ti-Ni alloy as the third element was investigated to improve the super-elasticity of the alloy castings at body temperature for dental application. Ti-50.8Ni (at %) alloy, which exhibited super-elasticity at 310 K in castings, was used for comparison. 5.0, 7.5, 10.0 and 15.0 at % Pd was added to Ti-50.0Ni alloy by the substitution for Ni. The change in the proportion of Ti and Ni was also examined at the fixed Pd addition of 7.5 at %. The properties of the alloys were investigated in tensile test and differential scanning calorimetry (DSC). Ti-42.5Ni-7.5Pd alloy castings showed good super-elasticity among the examined alloys from the viewpoint of residual strain and elongation. Moreover, apparent proof stress could be changeable by the proportion of Ti and Ni with residual strain being kept low. Ti-42.5Ni-7.5Pd alloy castings exhibited better super-elastic flexibility than Ti-50.8Ni alloy, which is proven by lower apparent proof stress and larger elongation. This flexibility appears to be caused by its relatively high martensitic transformation starting temperature point. It is suggested that this flexibility with super-elasticity could widen the clinical application of the alloy casting in dentistry. © 2000 Kluwer Academic Publishers     

Mg-Al Alloys Manufactured by Casting and Hot Working Process

Mechanical properties of Mg-Al based alloys at different fabrication state,namely as-cast,hot rolled,and annealed,were investigated to develop the alloys that are suitable for the casting/hot working process.Exper- imental results indicated that the castability such as hot cracking resistance tends to improve with increasing the aluminum content.However,the elongation at elevated temperatures was observed to decrease as the AI content increases,implying difficulties in hot forming.A small amount of Zr additions could significantly enhance the room temperature mechanical properties of hot-rolled Mg-6%Al-1%Zn alloy.The tendency of remarkable grain coarsening at high temperatures was effectively reduced by the Zr additions.TEM analyses suggested that very fine Al-3Zr precipitates formed in the Zr-added alloy are responsible for the obtained results.     

The use of two reactive elements to optimize oxidation performance of alumina-forming alloys

Abstract

Standard reactive element (RE) studies have characterized the behavior of single RE additions such as Y, La or Hf. However, several commercial alumina-forming alloys are “co-doped” with two or more RE additions which allows the total amount of RE dopant in the alloy to be reduced. The oxidation performance of both commercial and laboratory-made co-doped alloys shows better scale adhesion and/or slower scale growth rates than comparable alloys with one RE addition. Characterization of the alumina scales showed no significant change in the grain structure with co-doping; however, as the total RE addition was reduced in co-doped alloys, a smaller volume of RE-rich oxides was observed within the scale. Quantification of the amount of RE ionic segregation on alumina scale grain boundaries formed on single doped and co-doped alloys showed similar amounts of segregation.     

Comparison of the effects of La- and Ce-rich rare earth additions on the microstructure, creep resistance, and high-temperature mechanical properties of Mg-6Zn-3Cu cast alloy

The effect of 1 wt.% La- and Ce-rich rare earth (RE) additions on the microstructure, creep resistance, and high temperature mechanical properties of the Mg-6Zn-3Cu alloy (ZC63) was investigated by impression creep and shear punch tests (SPT). Impression creep tests were performed in the temperature range 423-498 K and under punching stress in the range 150-700 MPa for dwell times up to 3600 s. The ultimate shear strength (USS) was measured by the SPT in the temperature range 298-498 K. The results showed that Ce-rich RE was more effective than the La-rich RE in refining the as-cast microstructure, increasing the number density of eutectic phases at grain boundaries, and producing thermally stable Mg₁₂RE and MgRE compounds. The creep strength of the base alloy was remarkably improved by addition of both types of RE elements, although the Ce-rich RE-containing alloy showed better creep resistance. The addition of La-rich RE increased the shear strength of the base alloy, whereas Ce-rich RE addition had detrimental effects on the shear strength. This was attributed to the formation of a grain boundary network of Mg(Zn,Cu) Laves phases in Ce-rich RE-containing alloy. This grain boundary network with a bulky morphology promoted the initiation and propagation of cracks, leading to an adverse effect on the strength. This was in contrast with its positive influence on inhibiting grain boundary sliding and migration, which enhanced the creep strength of the alloy.     

Ductility improvement in iron aluminides

Excellent high temperature properties of intermetallic aluminides recommend their use for structural applications in sulphurous atmospheres. Interest was not sustained in them because of their brittleness at ambient temperatures. Fe₃Al based alloys (air induction melted) were taken up to study the effect of deviations from stoichiometry (both sub and super), third and fourth alloy additions, B, Ti (micro as well as macro), on physical and mechanical properties (at ambient temperatures). The columnar grains observed in sub and stoichiometric compositions were found to become equiaxed on additions of alloy. The microstructures became finer on hot forging and rolling. The hot workability of these alloys increased from 65 to 85% at 973 K on B, Ti additions. The ultimate tensile strength (UTS) and per cent, elongation E increased to 80 kg mm^–2, 3.0% and 94 kg mm^–2, 5%, respectively, for sub and stoichiometric alloys on B and Ti additions. The superstoichiometric alloys displayed dendritic structure and could not be hot worked due to cracking during forging, even after additions of alloys. The stoichiometric Fe₃Al alloy with B and Ti additions exhibited the best properties under the experimental conditions.     

Control of mechanical and wear properties of a commercial Al-Si eutectic alloy

The properties examined as a function of microstructural modification were ultimate tensile strength, fracture elongation, Vickers hardness and wear resistance. The microstructural modification was achieved by rapid cooling and additions of small amounts of strontium and lithium master alloys into the eutectic melt. In all experiments the commercial ETIAL 140 alloy was cast instead of a high-purity aluminium-silicon eutectic. This allowed determination of the effect of modification treatment, both on silicon and intermetallic phases. It was found that the slowly cooled and unalloyed castings which contained coarse silicon flakes showed highest wear resistance and lowest ultimate tensile strength, fracture elongation and Vickers hardness values. Rapid cooling and also additions of strontium and lithium master alloys reduced the eutectic interphase spacing and refined the silicon phase. This usually corresponded to a significant increase in all properties except the wear resistance. It was noted, however, that the size of the intermetallic phase particles increased abruptly above 0.04% Sr content which resulted in a sharp reduction in all mechanical properties. Unlike the strontium effect, the lithium addition did not influence the intermetallic size significantly and, therefore, the mechanical properties were not impaired. In addition, the wear resistance also remained relatively unaffected because lithium solid solution hardened the primary aluminium dendrites appeared in the modified alloys.     

Microstructure and Mechanical Properties of Mg-3Al-1Zn-xRE Alloys

In this work, the influence of element RE on the microstructures and mechanical properties of the hot extuded Mg-3Al-1Zn-xRE alloys (with element RE content of 0.05, 0.1 and 0.2 wt pct) has been investigated and compared.It was found that RE can bring about precipitations phase that is identified as Al11 RE3 by X-ray diffraction and transmission electron microscopy (TEM).The grain sizes would not be refined after adding RE element.Al11 RE3 phase would increase strength and decrease the ductility.The addition of RE element affects dynamic recrystallized process and even reorientation of recrystallized grains.The results showed that the mechanical properties of AZ31+RE alloy are affected by combination of Al atoms, Mn atoms, Al11RE3phase and grains orientation.It is important to consider the ratio of RE/Al when designing new Mg-Al-RE alloys.     

Effects of rare-earth element substitution on magnetostrictive properties of polycrystalline Tb-Dy-Fe alloys

Magnetostrictive properties of (Tb/sub 0.5/Dy/sub 0.5/)/sub 1-x/RE/sub x/Fe/sub 1.9/ (x=0-0.05, RE=Y, Ce, Sm, Gd, Ho, Yb) polycrystalline compounds were studied. Each rare-earth element formed a RE-Fe/sub 2/ Laves compound with a different lattice spacing. Corresponding to this difference, (Tb/sub 0.5/Dy/sub 0.5/)/sub 0.95/RE/sub 0.05/Fe/sub 1.9/ alloys showed a variation in lattice spacing as a result of the substitution of rare-earth elements and the prestress dependence of magnetostriction changed noticeably. In the case of Y, Sm, and Gd substitution, which showed greater lattice spacing than that of the Tb/sub 0.5/Dy/sub 0.5/Fe/sub 1.9/ alloy, the prestress dependence and maximum magnetostriction decreased. On the other hand, in the case of Ce, Ho, and Yb substitution, which showed a decrease in lattice spacing, the conspicuous prestress dependence was the same as that of the Tb/sub 0.5/Dy/sub 0.5/Fe/sub 1.9/ alloy and the maximum magnetostriction was greater than that of the latter alloy.     

Rare-earth additions to lead-free electronic solders

The research in lead(Pb)-free solder alloy has been a popular topic in recent years, and has led to commercially available Pb-free alloys. Further research in certain properties to improve aspects such as manufacturability and long term reliability in many Pb-free alloys are currently undertaken. It was found by researchers that popular Pb-free solders such as Sn–Ag, Sn–Cu, Sn–Zn and Sn–Ag–Cu had improved their properties by doping with trace amounts of rare earth (RE) elements. The improvements include better wettability, creep strength and tensile strength. In particular, the increase in creep rupture time in Sn–Ag–Cu–RE was 7 times, when the RE elements were primarily Ce and La. Apart from these studies, other studies have also shown that the addition of RE elements to existing Pb-free could make it solderable to substrates such as semiconductors and optical materials. This paper summarizes the effect of RE elements on the microstructure, mechanical properties and wetting behavior of certain Pb-free solder alloys. It also demonstrates that the addition of RE elements would improve the reliability of the interconnections in electronic packaging. For example, when Pb-free-RE alloys were used as solder balls in a ball grid array (BGA) package, the intermetallic compound layer thickness and the amount of interfacial reaction were reduced.     

Superelasticity of TiPdNi Alloys with and without Rare Earth Ce Addition

Ti50.6Pd30Ni19.4 and Ti51Pd28Ni21 (Ce) alloys have been prepared under various temperatures for long time annealing. Differential scanning calorimetery (DSC), X-ray diffraction (XRD) and tensile test were employed to investigate the phase transformation behavior and superelasticity of the alloys. It has been found that the phase transformation temperature of Ti50.6Pd30Ni19.4 is about 40C higher than that of Ti51Pd28Ni21(Ce), and do not change much with different annealed temperature. Obvious superelasticity is retained in Ti50.6Pd30Ni19.4 alloy annealed at 400C for 18 h, and annealing at higher temperature shows a deterioration of this property. The Ce addition in TisiPd28Ni2i alloy significantly delays recrystallization, increases yied strength and elastic modulus, but the superelasticity is poor.