Rare Earth Compounds in Cemented Carbides with Trace Rare Earth Additions

The morphology,structure and distribution of the rare earth compounds in the YG8R.YT5R and YT14Rcemented carbides with additions of trace light rare earths were studied with an analytical electron microscope.The particles of the rare earth compounds in these alloys are all spherical and distribute at interfaces betweenthe Co-cement phase and WC hard phase or(TiW)C solid solution,and in the(TiW)C solid solution.In theYG8R and YTI4R alloys,the rare earth compound is RE_2O_3 with a bcc structure,while in the YT5R alloy.the rare earth compound is RE_2O_2S with a hcp structure.     

稀土在铸造镁合金中的应用

综述了稀土镁合金相图、相结构及稀土在铸造镁合金中的使用 ,总结了各种系列稀土镁合金的研究应用和最新进展     

稀土在铸造镁合金中的应用

综述了稀土镁合金相图、相结构及稀土在铸造镁合金中的使用,总结了各种系列稀土镁合金的研究应用和最新进展。     

Preparing nano-crystalline rare earth doped WC/Co powder by high energy ball milling

The nano-crystalline rare earth doped WC/Co powder was prepared by high energy ball milling. The nano-crystalline powders were characterized by means of XRD (X-ray diffraction), SEM (scanning electron microscope) and DTA (differential thermal analysis). The results show that adding trace rare earth elements into carbides is effective to minish the grain size of WC/Co powder. The grain size of rare earth doped powder became two times smaller as compared with the undoped powder within ball milling times of 25–45 h. The XRD peak of Co phase disappeared after 25 h ball milling. A sharp peak of heat release at the temperature of 597 °C was emerged in DTA curve within the range of heating temperature. After consolidated the rare earth doped WC/Co alloy by high energy ball milling exhibits ultra-fine grain sizes and better mechanical properties.     

稀土Pr对Al-Cu铸造铝合金的影响

探讨了稀土Pr在Al-Cu系铸造铝合金中的作用。结果表明,稀土Pr在Al-Cu合金中主要存在于晶界处,并形成稀土化合物;同时能有效地细化晶粒、提高析出相的弥散度、改善其断口形貌,从而改变了Al-Cu合金的组织和性能。     

Phase transformation of ZrO_2 doped with CeO_2

Thermal barrier coatings(TBCs) protection is widely used to prolong the lifetime of turbine components.The outermost layer of TBCs is ceramic layer, whose function is heat insulation, and the main composition of the ceramic layer is ZrO_2. In this study, the micro-Zr02 and the nano-ZrO_2 doped with 10 wt% CeO_2 as well as microZrO_2 and nano-ZrO_2 were prepared by air plasma spraying(APS) to study the advantages of the addition of rare earth element. The effect of CeO_2 on the phase transformation of ZrO_2 was studied. The results show that there are few cracks in micro-and nano-ZrO_2 doped with 10 wt% CeO_2,and rare earth oxides can affect the phase transformation significantly. The morphologies, hardness and elastic modulus of the four ceramic layers were also discussed.     

Thermodynamic modeling of the Ce–Zn and Pr–Zn systems

In order to develop the thermodynamic database of phase equilibria in the Mg–Zn–Re (Re: rare earth element) base alloys, the thermodynamic assessments of the Ce–Zn and Pr–Zn systems were carried out by using the calculation of phase diagrams (CALPHAD) method on the basis of the experimental data including thermodynamic properties and phase equilibria. Based on the available experimental data, Gibbs free energies of the solution phases (liquid, bcc, fcc, hcp and dhcp) were modeled by the subregular solution model with the Redlich–Kister formula, and those of the intermetallic compounds were described by the sublattice model. A consistent set of thermodynamic parameters has been derived for describing the Gibbs free energies of each solution phase and intermetallic compound in the Ce–Zn and Pr–Zn binary systems. An agreement between the present calculated results and experimental data is obtained.     

Optical study of a new phase LaGa3O6:RE (RE=Pr, Nd, Eu) in the La2O3–Ga2O3 system

The absorption and emission spectroscopies of RE³⁺ ions embedded in a new phase, LaGa₃O₆, owing to the La₂O₃–Ga₂O₃ binary system (RE=Pr, Nd, Eu) are discussed. The ^2S+1L_J level degeneracies are completely lifted in accordance with the low point symmetry of the site occupied by the rare earth ion in LaGa₃O₆. The energy level schemes deduced from the data are reproduced by considering a crystal field (CF) effective Hamiltonian involving the nine real and five imaginary parameters required for the C₂ or C_s symmetry of the rare earth site. The rms deviation is satisfactory for the three simulations. However, the strong variation of the CF parameters between Pr³⁺ and Eu³⁺ in LaGa₃O₆ suggests the possible limit of existence of the phase, intimately correlated to small variations of the rare earth ionic radius.     

稀土对真空机械粉末渗锌层的组织和性能的影响

研究了不同工艺参数和添加ＲＥ对渗锌层的影响,对经了渗层厚度、金相组织、显微硬度、尺寸增厚值、单位面积的增重、Ｚｎ的浓度分布和Ｚｎ渗层的形貌、渗层和基体交界面的冶金扩散层等。渗锌层主要由ＦｅＺｎ４和ＦｅＺｎ相组成。在相同的工艺条件下,添加ＲＥ能增加渗锌层的厚度。渗层中Ｚｎ的浓度分布和显微硬度略低。但相结构与不加ＲＥ的无明显的区别。     

GCr15销轴固体渗Cr层的生长机制及孔隙成因探索

低扩渗效率和渗层孔隙是困扰着渗铬生产的两个重要难题。本文采用固体包埋法在GCr15表面制备渗Cr涂层，重点探讨了渗层的生长机制、孔隙成因及不同稀土氧化物的催渗作用。结果表明，加入稀土氧化物后渗层厚度明显提高，三种稀土氧化物的催渗效率依次为Y2O3>CeO2>La2O3。渗Cr层明显的分为双层结构，外层是以（Cr，Fe）23C6相为主的多孔层，内层为（Cr，Fe）7C3相为主的致密层。扩渗初期在基材表面首先生成的（Cr，Fe）23C6相层阻碍了表面活性Cr原子向内扩散，其自身作为Cr源向内扩散促进了致密层的生长，Cr原子扩散速度的差异及渗层中的应力是产生孔隙的主要原因。发现降低基体碳含量抑制（Cr，Fe）23C6相层的生成或细化该相层晶粒增加Cr原子扩散通道可有效降低孔隙率，这为改进渗铬层质量提供了一个重要思路。     

微量Ce对工业纯铝铸态组织的影响

研究了微量Ce对工业纯铝铸态组织的影响,分析了Ce对微观组织的细化作用及变质机理。结果表明,微量Ce会使铝熔体成分过冷和增大溶质不稳定扰动,并释放大量潜热,导致界面稳定性下降,促使组织晶粒细化;Ce具有较高的化学活性,易形成新的α相核心,促进晶粒细化;界面上形成的含稀土化合物会填补界面表面缺陷,促使杂质相转变成球粒状,并促使杂质原子在晶界富集。     

稀土元素变质A356铝合金的研究进展

总结了目前国内外采用稀土对A356铝合金变质的研究进展,归纳了稀土元素对A356铝合金的变质效果。综合目前的研究结果,结合商业化A356铝合金应用的实际情况,认为采用DOE成分设计方法对相对价廉的二元、甚至多元稀土或稀土与其他元素的复合变质体系进行成分设计是有前景且符合实际的。     

Improvement and Micro-mechanism of a Low Expansion Superalloy

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The interpolated Tm---Mg phase diagram

The alloying behavior of the different rare earths, which varies according to systematic patterns, can be used to predict constitutional properties of rare earth alloys with the same element. The applicability to prediction of the Tm---Mg phase diagram is presented here. The predicted version is compared with that determined experimentally by analyzing a few key compositions using X-ray powder diffraction, optical and scanning electron microscopy, electron probe microanalysis (EPMA) and differential thermal analysis (DTA). The following phases were identified and their crystal structures confirmed or determined: β phase, ≈Tm₂Mg (cubic, cI2, W type), TmMg (cubic, cP2, CsCl type), TmMg₂ (hexagonal, hP12, MgZn₂ type) and ≈Tm₅Mg₂₄ (cubic, cI58, -Mn type). All the phases show peritectic formation. Two other equilibria were also observed: a eutectic reaction at 575 °C and 89 at.% Mg and the eutectoid decomposition of the β phase at 670 °C and approximately 30 at.% Mg.     

碳钢填料气相稀土扩渗及其性能研究

采用化学气相扩渗法对化工用碳钢填料进行稀土多元扩渗,研究了填料的化学性能,力学性能和传质性能.结果表明,经扩渗处理后碳钢填料的耐腐蚀性能明显增强,硬度提高,同时,填料塔的等板高度有所下降,使传质性能得到改善.并初步分析了稀土发生作用的可能机理.     

稀土微合金化对Mg-9Li-1Zn合金组织性能的影响

通过复合添加0.2%的Y+0.1%的Nd+0.05%的Gd(质量分数,下同)制备了轻质高强Mg-9Li-1Zn-RE合金(LZ91-RE),随后对其进行锻造和冷轧。采用OM、SEM、EDS、XRD、TEM对锻造态和冷轧态LZ91合金和LZ91-RE合金进行组织及物相分析,同时利用拉伸试验机进行力学性能测试。结果表明,LZ91合金组织由α-Mg和β-Li两相组成,添加多元稀土元素后LZ91合金中α相体积分数减少了26.5%,晶粒得到显著细化,同时原位析出了富Y、富Nd、Mg₁₂Nd及Mg₃RE稀土强化相,但存在局部偏聚现象;LZ91-RE合金经过大应变冷轧变形,稀土强化相被破碎细化且分布更加均匀。此外,与LZ91合金相比,锻造态的LZ91-RE合金抗拉强度比LZ91合金提高了13.9%。冷轧态的LZ91-RE合金的抗拉强度比LZ91合金提高了19%,而伸长率只下降了4.4%。     

Effects of Rare Earth on Austenite-Ferrite Phase Transformation in a Low-Carbon Fe-C Alloy

The influence of rare earth (RE) elements on austenite-ferrite phase transformation in Fe-0.14%C alloy has been investigated by in situ observing the nucleation, growth and morphology of ferrite using high temperature laser scanning confocal microscopy, and controlled atmosphere decarburization experiments. It is found that under the low-oxygen condition in steel, trace RE addition can significantly influence the nucleation, morphology and growth of ferrite in Fe-0.14%C alloy by the combined effects of RE slowing down the carbon diffusion and decreasing grain boundary energy by segregating at grain boundaries. This research provides evidences of adjusting the phase transformation and improving the mechanical properties of steels by RE addition.     

Bainite isothermal transformation of Si–Mn–Mo alloy by phase structure factor calculation under different rare earth contents

The effect of rare earth(RE) on bainite transformation mechanism is not yet unified in the academia.Therefore, further studying the effect of RE on bainite transformation mechanism will have important guiding significance for the development of bainite steels. In this paper, using differential dilatometer(DIL805A/D), heat treatment was performed and C-curve was drawn. The effect of phase structure factor on bainite transformation under two different fractions of RE in Si–Mn–Mo bainite steels was investigated by the empirical electron theory(EET) of solids, molecules, dilatometry, and metallography. Experimental results show that RE makes Fe–CRE segregation structural unit of Si–Mn–Mo bainite steels increase, i.e., the values of phase structure factor(nA, FDC)increase, and delay bainite transformation due to the drag effect resulting from the segregation of RE ferrite island interphase and the retardation of RE to carbon diffusion in Si–Mn–Mo bainite steels. Beside this, C-curve is shifted to right and down, and microstructures of bainite ferrite and substructures are finer.     

Phase relationships at 500 °C in the Y---Pr---Mg system

Phase equilibria in the ternary system Y---Pr---Mg have been studied by X-ray powder diffraction analysis, optical and scanning electron microscopy, and electron probe microanalysis. The isothermal section at 500 °C has been determined in the range 50–100 at.% Mg. The phase equilibria are characterized by the formation of the following rather extended solid solutions: (Y_xPr_1−x)Mg (continuous solid solution of cP2-CsCl type) and Y_xPr_1−xMg₃ (0 x 0.5) of cF16-BiF₃ type. A cubic phase of (Y_xPr_1−x)Mg₂, (cF24-CuMg₂ type) derived from the binary PrMg₂ phase by a substitution of Pr with Y has been observed in a narrow range close to x ≈ 0.6. A solid solution based on the binary YMg₂ phase, i.e. (Y_xPr_1−x)Mg_{2 + y} of hP12-MgZn₂ type (0.79 x 1, for y = 0), extends into the ternary field. The ternary compound Y_xPr_{1 − x}Mg₅ (0.3 x 0.9) of the cF440-GdMg₅ type has been established. Finally, the Y---Pr---Mg section has been compared with the similar Y---La---Mg section studied previously and with an isothermal section predicted on the basis of the systematic trends of the rare earth alloy properties.     

含稀土镁铝系合金耐腐蚀性能的研究现状

镁铝系合金是目前最常用的商业材料之一,但由于合金的耐蚀性能较差,因此对合金的耐蚀性研究具有重要意义。本文综述了稀土在镁铝系合金中的存在形式以及含稀土镁铝系合金在国内外的研究现状,讨论了稀土对合金耐蚀性的影响机理。