Slight Co-doping tuned magnetic and electric properties on cubic BaFeO_(3) single crystal

The single crystal of cubic perovskite BaFeO3 shows multiple magnetic transitions and external stimulus sensitive magnetism.In this paper,a 5%-Co-doped BaFeO_(3)(i.e.BaFe_(0.95)Co_(0.05)O_(3))single crystal was grown by combining floating zone methods with high-pressure techniques.Such a slight Co doping has little effect on crystal structure,but significantly changes the magnetism from the parent antiferromagnetic ground state to a ferromagnetic one with the Curie temperature TC≈120 K.Compared with the parent BaFeO3 at the induced ferromagnetic state,the saturated magnetic moment of the doped BaFe_(0.95)Co_(0.05)O_(3) increases by about 10%and reaches 3.64μB/f.u.Resistivity and specific heat measurements show that the ferromagnetic ordering favors metallic-like electrical transport behavior for BaFe_(0.95)Co_(0.05)O_(3).The present work indicates that Co-doping is an effective method to tune the magnetic and electric properties for the cubic perovskite phase of BaFeO_(3).

Effects of Cr content on microstructure and mechanical properties of single crystal superalloy

Two experimental single crystal superalloys with 2% Cr and 4% Cr (mass fraction) were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Cr content on the microstructure, phase stability, tensile properties at 1100 °C and stress rupture properties at 1070 °C and 160 MPa of the single crystal superalloy were investigated. The results show that the size ofγ′ phase particles become small and uniform, and the cubic shape turns a little regular with the increase of Cr content. Theγ′ directional coarsening and rafting were observed in the 2% Cr and 4% Cr alloys after long term aging (LTA) at 1100 °C. The rafting rate ofγ′ phase increased with increasing Cr content. Needle-shaped topologically close packed (TCP) phases precipitated and grew along fixed direction in both alloys. The precipitating rate and volume fraction of TCP phases significantly increased with the increase of Cr content. The tensile property of the alloy increased and the stress rupture properties of the alloy decreased with the increase of Cr content at high temperature. The increase of Cr content increased the partition ratio of TCP forming elements, Re, W, and Mo, and the saturation degrees of these elements inγ phases increased. Therefore, the high temperature phase stability of the alloy decreased with the increase of Cr content.

Mechanical properties of self-irradiated single-crystal copper

Molecular dynamics simulations are performed to investigate the influence of irradiation damage on the mechanical properties of copper. In the simulation, the energy of primary knocked-on atoms （PKAs） ranges from 1 to 10 keV, and the results indicate that the number of point defects （vacancies and interstitials） increases linearly with the PKA energy. We choose three kinds of simulation samples： un-irradiated and irradiated samples, and comparison samples. The un-irradiated samples are defect-free, while irradiation induces vacancies and interstitials in the irradiated samples. It is found that due to the presence of the irradiation-induced defects, the compressive Young modulus of the single-crystal Cu increases, while the tensile Young modulus decreases, and that both the tensile and compressive yield stresses experience a dramatic decrease. To analyze the effects of vacancies and interstitials independently, the mechanical properties of the comparison samples, which only contain randomly distributed vacancies, are investigated. The results indicate that the vacancies are responsible for the change of Young modulus, while the interstitials determine the yield strain.

Temperature dependence of anisotropic stress-rupture properties of nickel-based single crystal superalloy SRR99

In order to reveal the temperature dependence of anisotropic stress？rupture behavior of SRR99 single crystal superalloys under conditions of temperature ranging from 650 to 1 040 °C and typical stresses,fracture morphologies and microstructure evolution were investigated by SEM and TEM.From the Larson-Miller curves,it is found that single crystal with [001] orientation has the optimum stress rupture property in comparison with [011] and [111] orientations at lower and intermediate temperature.With increasing temperature to 1 040 °C,stress-rupture properties of single crystals with three principal orientations tend to be equivalent.Based on the fracture surface and microstructural observations,superior stress？rupture behavior of single crystal with [001] orientation was rationalized and the effect of misorientation of single crystal on stress rupture property was also discussed.

CONTINUOUS CASTING TECHNOLOGY OF SINGLE CRYSTAL COPPER ROD

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Effect of carbon on microstructure and mechanical properties of DD99 single crystal superalloy

The effects of carbon on the microstructure and mechanical properties of DD99 single crystal superalloy were investigated. The results show that stress rupture life of DD99 alloy possesses peak value at carbon content of 0.03%(mass fraction). As carbon addition is greater than 0.03%, the stress-rupture life decreases with the increase of carbon content. The tensile strength and yield strength of DD99 alloy reach peak value at 0.08% carbon and 760℃. On the contrary, the tensile strength and yield strength have minimal values at 0.08% carbon and 900℃. The tensile ductility of DD99 alloy basically decreases with the increase of carbon content at 760℃or 900℃. The amount of carbides greatly increases with the addition of carbon content. Dislocation moving is retarded by carbides so that dislocation networks are apt to form, which has an important role on the mechanical properties in DD99 single crystal superalloy.

Study on Strength and Life of Anisotropic Single Crystal Blade - Part Ⅱ: Experimental Research

The single crystal blade is one of the key technologies for improving the performance, durability and reliability of aero-engines and ground gas-turbine engines. However, the anisotropic mechanical properties of the single crystal material makes a great deal of difficulties on the development and the application of the single crystal blade, which is a challenge for the engineering application of the single crystal superalloy and the theoretic bases of the application. Some researches on the strength analysis and the life prediction of the anisotropic single crystal blade were carried out by the authors' research team. They are as follows. The crystallographic constitutive models for the plastic and the creep behaviors and the method of the rupture life prediction were established and verified. The tensile or the creep experiments for DD3 single crystal alloy with different orientations under different temperatures and different tensile rates or under different temperatures and different stress levels were carried out. The experimental data and the anisotropic properties at intermediate and high temperatures revealed by the experiments are significant for the application of the single crystal alloy. In addition, the experimental research for a kind of single crystal blade was also made. As the application of the researches the strength analysis and the life prediction were carried out for the single crystal blade of a certain aeroengine. In this part, the experimental research work is describled, and the constitutive models and applications have been described in part I.

A 2D Cobalt(Ⅱ) Coordination Polymer [Co(iqnc)_2]_n: Synthesis, Crystal Structure and Characterization

A new cobalt（Ⅱ） coordination polymer with the formula of [Co（iqnc）2]n（1, iqnc = l-isoquinolinecarboxylate） has been synthesized through hydrothermal synthesis and structurally characterized by single-crystal X-ray diffraction method. The title coordination polymer represents a two-dimensional layer structure featuring adjacent one-dimensional [Co（iqnc）2]n chains connected with each other by uncoordinated oxygen atoms of carboxylate. Crystal data： monoclinic, space group P21/c, a = 15.4302（2）, b = 5.6743（7）, c = 9.2307（1） A, β = 98.459（2）o, V = 799.41（2） A3, Z = 2, S = 1.019, the final R = 0.0346, w R = 0.0876（I 2σ（I）） and R = 0.0477 and wR = 0.1159 for all reflections. In addition, elemental analysis, IR, and magnetism properties are presented.

单分子磁体[Mn_4(CF_3COO)_4(hmp)_6]的合成、晶体结构及磁学性质

以[Mn12O12(CF3COO)16(H2O)4]·2CF3COOH·4H2O和2-羟甲基吡啶(hmpH)为起始物,在四氢呋喃溶液中合成了一种新的四核锰配合物[Mn4(CF3COO)4(hmp)6].X射线单晶衍射结果表明,该配合物属于单斜晶系,P21/c空间群,晶胞参数a=1.3663(3)nm,b=1.4705(3)nm,c=1.4734(3)nm,β=98.51(3)°,V=2.9276nm3,Z=2.配合物中有两个CF3COO-基团与七配位Mn2中心相连,其中一个为单齿配体,另一个是双齿配体.直流磁化率研究结果表明,该配合物具有较高的自旋基态,而交流磁化率依赖于外场频率变化极值的出现表明该配合物是一种单分子磁体.

MICRO/NANO-MACHINING ON SILICON SURFACE WITH A MODIFIED ATOMIC FORCE MICROSCOPE

To understand the deformation and removal mechanism of material on nano-scale at ultralow loads,a systemic study on AFM micro/nano-machining on single crystal ailicon is conducted. The results indicate that AFM nano- machining has a precisely dimensional controllability and a good surface quality on nanometer scale.A SEM is adopted to observe nano-machined region and chips,the results indicate that the material removal mechanisms change with the applied normal load. An XPS is used to analyze the changes of chemical composition inside and outside the nano-machined region respectively.The nano-indentation which is conducted with the same AFM diamond tip on the machined region shows a big discrepancy compared with that on the macro-scale. The calculated results show higher nano-hardness and elastic modulus than normal values .This phenomenon on be regarded as the indentation size effect(ISE).

Effect of solution cooling rate on the microstructure and creep deformation mechanism of a rhenium-free second-generation single crystal superalloy

Various cooling scenarios(water,oil,air and furnace)were employed to study the impacts of the solution cooling rate(SCR)on the microstructure and creep behavior of a novel single-crystal(SX)superalloy.The results showed that the cubic degree and size of theγphases were inversely proportional to the SCR.The creep life first increased and then dropped dramatically with a reduction in the SCR.The creep life of the sample cooled with air cooling(AC)was the highest,up to 144.90 h at 800℃/750 MPa and160.15 h at 1100℃/137 MPa.During creep at 800℃/750 MPa,the improved creep life of the AC sample was mainly attributed to the fine cubicγphases,which decreased the rate ofγ-phase coarsening and favoured plastic deformation by promoting the active movement of dislocations.The AC helped theγphases become rich in Al,Ti and Ta while depleted in Co and Cr,which enhanced its stacking fault energy,thus promoting the formation of dislocation locks.Meanwhile,the largest negative lattice misfit caused by AC induced denserγ/γinterface dislocation networks at 1100℃/137 MPa,which efficiently reduced the minimum creep rate.The calculated average dislocation spacing results indicated that the smallest density of excess dislocations corresponded to the AC sample,proving its greatest creep resistance.Interestingly,the size of the secondaryγphases first decreased and then increased sharply with decreasing SCR during creep at 1100℃/137 MPa,when fine secondaryγphases had a positive role in the blockage of dislocation movement in the matrix.Eventually,the comprehensive SCR effect was explored to provide more guidance in the design of Re-free SX superalloys.

Mg掺杂对[NH2(CH3)2]Mn1-xMgx(HCOO)3单晶性能的影响

通过水热法合成一系列不同掺杂浓度晶体[NH_2(CH_3)_2]Mn_(1-x)Mg_x(HCOO)_3(0≤x≤0.5),并对其进行X射线粉末衍射、紫外可见光谱、傅里叶变化红外光谱(FTIR)、热重等表征分析。结果表明:制备晶体的结晶性能好,透明度高,晶体为三方晶系,空间群为R-3c(167);Mg^(2+)的掺入加剧了Mn-O_6八面体的畸变,导致晶体的晶格参数发生明显变化;晶体结构框架在120℃时开始坍塌,在230℃时,甲酸根分解挥发。光学测试结果表明:晶体的禁带宽度为3.73 eV,Mg掺杂对禁带宽度没有影响。磁性测试结果表明:当测试温度范围为5~300K时,随着掺杂量增加,样品的奈耳温度(T_N)变小,当掺杂量为0.5,反铁磁转变消失。

Magnetic and magnetotransport properties of single-crystalline R2PdGe6（R = Pr, Gd and Tb）

Single crystals of R2PdGe6 (R=Pr, Gd and Tb) compounds were grown by the Bi-flux method. Pr2PdGe6 is an antiferromagnetic compound with Neel temperature Tn=15K, in which a field-induced magnetic transition (spin flip) occurs when a magnetic field is applied along either a or b axis;a small magnetization and hysteresis loop were observed when a field is applied along c axis. Gd2PdGe6 is a colli near antiferromagnetic compound with Tn=37K along b axis. Tb2PdGe6 is an antiferromagnetic compound with Tn =48 K and its hard magnetization direction is along b axis. The temperature dependences of the resista nee of the entire three compounds prese nt inflection points at the respective Tn-A large resista nee (as well as magnetoresistance) change can be found at the spin flip transition of Pr2 PdGe6, but the change is not obvious at the spin flop transition of Gd2PdGe6.

Synthesis,Structure and Polymorphism of a Novel Two-dimensional Cobalt(Ⅱ)Coordination Polymer Constructed from Citrazinate Ligand

The polymeric Co（Ⅱ） complex[Co（Hdhpc）（py）]n（1）（py = pyridine,H3dhpc =2,6-dihydroxypyridine-4-carboxyl acid） was prepared and characterized.X-ray diffraction data revealed that the compound crystallizes in dimorphic 1α and 1β forms at room and low temperature,respectively.The former crystallizes in the orthorhombic crystal system,space group Pbcm with a =7.209（1）,b = 14.834（3）,c = 15.376（3） A°,V= 1644.3（5）A°3,Z = 4,C（16）H（13）CoN3O4,Mr = 370.22,Dc= 1.496 g/cm^3,F（000） = 756,μ = 1.068 mm^-1,R = 0.0633 and wR = 0.1192.While 1β is attributed to the monoclinic space group C2/c with a = 32.102（4）,b = 7.022,c = 14.945（2）A°,β = 109.052（5）°,V= 3184.4（6） A°3,Z= 8,Dc= 1.544 g/cm^3,F（000） = 1512,μ = 1.103 mm^-1,R = 0.0428 and wR =0.0797.The conformation changes of pyridines between Co-citrazinate planes leading to a reversible single-crystal to single-crystal transformation.The variable temperature magnetic data indicate a weak ferrimagnetism.

基于选区激光熔化镍基单晶高温合金的修复

选区激光熔化技术光斑和热影响区小,成形精度高,可对镍基单晶高温合金叶片进行有效的修复以延长使用寿命。本工作选用了一种具有中等体积分数γ′相的合金粉末,研究了在单晶CM247LC基板上进行外延生长过程中该合金粉末的显微组织演变规律以及力学性能。结果表明:修复界面的熔池宽深比大于4时,沉积区与基体能形成良好的结合界面以及较小的晶粒取向差。通过增大扫描速率和降低激光功率可以有效减小沉积区裂纹密度,沉积组织以沿沉积方向生长的柱状枝晶为主,沉积层越高,冷却速率越小,枝晶间距和晶粒取向差越大。通过打印参数优化,最终得到了裂纹密度低、晶粒取向单一、且与单晶基板结合优异的镍基单晶高温合金沉积层,其抗拉强度为1094 MPa,伸长率为21%。

激光冲击强化对镍基单晶高温合金SRR99组织及性能的影响

目的解决镍基单晶高温合金航空发动机涡轮叶片在服役时发生表面损伤的问题,探究激光冲击强化对镍基单晶高温合金SRR99的强化变形机制。方法采用高功率(8J)短脉冲激光分别对试样进行1、2、3次表面强化,使用白光干涉仪、显微硬度仪、X射线分析仪对强化前后的镍基单晶高温合金试样表面形貌、粗糙度、显微硬度、残余应力进行测试,通过扫描电子显微镜、透射电子显微镜和X射线衍射仪分析激光冲击强化对镍基单晶高温合金微观组织和物相组成的影响。结果经过1、2、3次激光冲击后,单晶高温合金试样表面发生了塑性变形,表面凹坑随着冲击次数的增加逐渐加深,表面粗糙度分别为1.566、1.868、2.265μm,显微硬度分别增加了15.3%、25.8%、32.1%,表面残余压应力分别提高为–790、–870、–917MPa。经强化后,试样表层形成了畸变层,γ′相的面积和体积分数均增大,合金未发生相变,但两相发生了严重的晶格畸变,晶格常数和晶面间距的变化导致两相晶格发生失配,经强化后在试样表层γ′强化相、γ通道、γ/γ′界面观察到大量位错结构,此外还观察到贯穿γ′相、γ相的位错滑移带和致密的位错网络。结论激光冲击强化技术可使镍基单晶高温合金SRR99发生塑性变形,在其表层内部形成高密度位错网络结构,加工硬化效果显著,提高了基体表面的显微硬度和残余应力。

不同取向镍基单晶高温合金650℃原位拉伸

镍基单晶高温合金作为飞机涡轮发动机叶片的主要使用材料,其在服役过程中受到各向应力作用产生变形导致材料失效,因此本文基于课题组自主研发的原位拉伸设备对[140]取向、[340]取向、[122]取向的镍基单晶高温样品进行了650℃原位拉伸。其中[140]取向样品在屈服阶段后样品硬化到塑性变形后期出现了幅度较小的应力下降,最后样品在应力作用下滑移迹线所在的基体发生开裂,裂纹沿着滑移迹线所在方向扩展至样品断裂。[340]取向样品在整个塑性变形阶段,样品的应力持续下降,孔洞缺陷处形成缺陷导致材料失效。[122]取向样品一直处于硬化阶段,到塑性变形后期样品出现了应力的下降,跟[340]取向样品失效方式相同,孔洞开裂形成裂纹源导致材料失效。本文针对三种取向样品的力学性能,塑性变形过程中的滑移情况以及对应的施密特因子变化、样品失效的方式进行了分析,对合金在真实服役过程中提高其服役寿命具有重要意义。

单晶合金激光增材修复接头组织和性能研究

采用激光熔化沉积技术对DD6单晶高温合金进行修复,利用光学显微镜、扫描电镜和显微硬度仪对单晶母材和增材修复接头的组织特征和力学性能进行对比研究。结果表明:激光熔化沉积修复组织为外延生长的定向凝固柱状晶组织,由γ相基体和少量晶间MC型碳化物组成;DD6单晶合金基体热影响区微观形貌和物相组成与母材相似,但其γ′相的尺寸(≤0.2μm)更小,且γ′/γ的比例明显降低。经激光熔化沉积修复后,增材修复区的显微硬度可达450~470 HV,显著高于DD6单晶基体,具有更优异的耐磨损性能。

TiAl金属间化合物定向技术研究进展

TiAl合金具有低密度和良好的高温性能,被视为航空航天领域极具应用潜力的一类新型结构材料。具有柱晶/单晶组织特征的全片层结构TiAl合金展现出极为优异的高温综合力学性能。本文首先介绍了定向TiAl合金的发展背景、定向组织、力学性能各向异性等基本概念;然后,基于工作原理、关键技术、组织特征三个层面,对传统Bridgman法、光学浮区法、电磁约束以及电磁冷坩埚等定向技术进行了论述;进一步,结合最新研究成果,对定向退火制备TiAl合金的工作进行了阐述;最后,展望了TiAl合金定向技术的研究方向,指出需要从优化成分设计、组织/相变可控、大尺度定向晶稳定制备等方面发展新原理与新技术。

皮秒激光烧蚀碳化硅的改性机理研究

碳化硅材料因其优良的综合性能而广泛应用于高温、高频、高功率的电子器件领域。然而,碳化硅的高硬度和化学惰性给目前的抛光技术带来诸多挑战。使用不同激光注量、扫描速度的激光对碳化硅晶片进行扫描,SEM结果显示随着能量注量的增加,材料的表面形貌历经了纳米颗粒形成到颗粒变得无序再到颗粒融化的状态。EDS和纳米压痕分析结果表明:氧气参与了激光对碳化硅的光致化学反应,辐照表面的弹性模量从347 GPa降低至103.82 GPa,剪切强度由20.90 GPa降低至17.25 GPa。这项研究对于深入理解皮秒激光对碳化硅的改性过程具有重要的探索意义。