R_2PdSi_3（R=Pr,Tb和Gd）单晶生长沉淀

利用具有无坩埚、高稳定性等特性的光辐射悬浮区熔法,制备R2PdSi3（R=Pr,Tb和Gd）单晶。从原材料和试样制备过程、单晶生长过程、熔体内部以及单晶基体4个方面研究单晶制备过程中一个很重要的现象,第二相沉淀。采用退火热处理方法以及给料棒成分微调法可以有效减少凝固后期冷却过程中由于Si溶解度降低析出的条纹状RSi（R=Pr,Tb和Gd）沉淀。     

含有易挥发元素的Eu_2PdSi_3光辐射悬浮区熔法晶体生长

新型磁盘存储材料Eu_2PdSi_3单晶制备由于Eu的挥发问题一直是一个难点。本文采用光辐射加热悬浮区熔法尝试制备了Eu_2PdSi_3单晶。采用标准化学成分配比制备给料棒,制备出的Eu_2PdSi_3晶体为胞状晶,分析是由于熔区成分发生变化,发生成分过冷导致胞状组织;采用给料棒成分调整法成功生长出大块Eu_2PdSi_3晶体。研究发现,采用3 MPa循环Ar气并不能完全抑制Eu在高温下的挥发,继续增大保护气体的压强配合给料棒成分调整,有利于解决Eu元素的挥发问题。     

光辐射悬浮区熔法Tb_2PdSi_3单晶生长及磁性能

采用光辐射加热悬浮区熔法以3 mm/h的生长速度成功制备了Tb2PdSi3单晶。通过分析得知,该化合物为同成分熔融化合物,熔点约为1700℃。和其它R2PdSi3型化合物(R为稀土元素)不同,在单晶基体中没有发现TbSi沉淀,分析原因可能是因为晶体中Tb含量略高于化学计量比。采用X射线Laue背散射实验对晶体的晶格结构和高完整性进行了验证,并对定向单晶的a和c方向磁化率-温度曲线进行了测定。     

稀土硅化物Nd_2PdSi_3晶体生长及磁性能研究

采用高射频感应加热法以及光辐射加热悬浮区熔法分别制备了Nd2PdSi3多晶和单晶样品,并对比研究了它们的磁性能。研究得出:多晶样品和单晶样品的磁性能完全不同。多晶样品居里温度为15.9 K,单晶样品居里温度为15.1 K;而[001]方向为Nd2PdSi3单晶的易磁化轴,单晶各向异性在0~150 K范围内明显。     

移动溶液浮区法Nd_2Fe_(14)B单晶生长

由于Nd2Fe14B为异成分熔融化合物,同时Nd极易和氧发生反应使得其单晶制备异常困难。通过研究伪二元相图,针对Nd2Fe14B的自身特点,采用移动溶液浮区法制备了Nd2Fe14B单晶。对单晶制备过程中熔区的温度进行了研究,并对所制备单晶的淬硬熔区以及晶体生长的完整性同样进行了分析。     

悬浮区熔法生长Tb_5Si_3晶体完整性研究

通过采用光辐射加热悬浮区熔法制备了Tb5Si3单晶。得出的结论为:3 mm/h的生长速度,0.1 MPa的循环氩气比较适合Tb5Si3单晶体的生长;Tb5Si3单晶基体内容易产生定向Tb5Si4脱溶沉淀相。调整材料成分可明显减少Tb5Si3相沉淀的尺寸和数量,提高制备晶体的完整性。     

Ag-Pd-5Ru-Gd四元系部分相图的700℃等温截面

在Ag Pd Gd ,Ag Pd Ru ,Ag Ru Gd和Pd Ru Gd三元系合金相图的基础上 ,采用X射线衍射 ,差热分析、扫描电镜和显微金相分析等方法研究了Ag Pd Ru Gd(x(Ru) =5 % ,x(Gd) <2 5 % )四元系相图的 70 0℃等温截面。结果表明 :该截面上包含有 2个单相区 ,即Pd(Ag)和Pd3 Gd ;4个两相区 ,即Pd(Ag) (Ru) ,Pd(Ag) Pd3 Gd ,(Ru) Ag51Gd14 ,(Ru) Pd3 Gd ;3个三相区 ,即Pd(Ag) Pd3 Gd (Ru) ,Pd(Ag) Ag51Gd14 (Ru) ,Pd3 Gd Ag51Gd14 (Ru) ;1个四相区 ,即Pd(Ag) Pd3 Gd Ag51Gd14 (Ru)。未发现新的四元中间相     

Ag-Pd-Gd-20Ru和Ag-Pd-Gd-50Ru四元系部分相图研究

采用X -射线衍射、扫描电镜和显微金相分析等方法研究了Ag -Pd -Ru -Gd四元系相图的富Ag -Pd -Ru区域 (Gd <2 5at% )。测定了Ag -Pd -Gd - 2 0Ru和Ag -Pd -Gd- 5 0Ru四元系相图的 70 0℃部分等温截面。这两个等温截面上都分别含有 3个二相区 :Pd(Ag) + (Ru) ,(Ru) +Ag51 Gd1 4 ,(Ru) +Pd3Gd ;3个三相区 :Pd(Ag) +Pd3Gd + (Ru) ,Pd(Ag) +Ag51 Gd1 4 + (Ru) ,Pd3Gd +Ag51 Gd1 4 + (Ru) ;1个四相区 :Pd(Ag) +Pd3Gd +Ag51 Gd1 4+ (Ru)。这 2个截面上都不含有单相固溶区 ,也未发现新的四元中间相     

Al2O3的W金属化及其与Nb的Pd钎焊研究

在考察Al2O3(95%Al2O3瓷和Al2O3单晶)的W-Y2O3金属化工艺的基础上,制备Al2O3单晶/Pd/Nb的高温钎焊接头,分析Al2O3的W-Y2O3金属化和Al2O3 /Nb的Pd钎焊机制.结果表明:在Al2O3基体和金属化层界面附近存在Y元素的偏聚行为,同时伴随着Al含量的下降.这是由于金属化过程中陶瓷/金属化层界面新生固相产物扩散的结果,且其扩散主要为朝金属化层方向.高温钎焊过程中,金属化层中的W元素和金属Nb扩散进入几乎整个Pd焊料层,这使得在Nb/Pd界面附近及焊料层内形成脆性固溶体或金属间化合物,从而导致微裂纹产生.     

定向凝固铁磁形状记忆合金Ni2MnGa的固-液界面形态

采用超高温度梯度真空区熔法定向凝固制备了Ni2MnGa晶体,改变晶体生长速度、温度梯度和熔区长度,获得了平直的固-液生长界面,制备出Ni2MnGa单晶．用光学显微镜观察了Ni50Mn29Ga21晶粒的竞争生长过程,制备的定向凝固试样无宏观成分偏析．X射线衍射分析仅显示四方结构马氏体Ni2MnGa400峰和004峰,晶体生长轴向择优取向为立方奥氏体(100)方向．采用差式扫描量热分析(DSC)和热重法(TG)分别测定试样中不同部位的相转变温度和Curie温度．在稳定生长区,沿轴向马氏体相变温度在10℃左右变化,而Curie温度几乎没有变化．这进一步表明采用该方法制备的Ni2MnGa晶体沿轴向成分均匀,且马氏体相变温度一致。     

Alloy Casting by the Horizontal Ohno Continuous Casting System

Abstract

Sn-Pb alloys in the compositional range 2.5–22.5% Pb have been continuously cast using the horizontal Ohno Continuous Casting (OCC) process. The effects of alloy composition and process variables on the location and size of the liquid-solid zone were investigated and information obtained was examined in order to establish the breakout point. It was found that the liquid-solid zone existed partly or entirely within the mould during casting, depending on casting conditions. The liquid-solid zone expanded with increasing mould-cooler distance and also with decreasing mould exit temperature, whereas it remained constant with the casting speed within the range investigated. As the composition approaches the eutectic point, the L+S zone shifted into the mould, and existed entirely within the mould at 22.5% Pb. It was also found that breakout occurred when the rod temperature at the mould exit exceeded a critical temperature which can be expressed as Tc=228–2A, where Tc is the critical rod temperature in Celsius and A is wt% Pb (<22.5% Pb). It was confirmed that the mould exit temperature must be kept above the liquidus temperature of the alloy to be cast in order to obtained unidirectional or single crystal materials.     

白光LED用新型Eu或Gd共掺杂的Ce:YAG单晶荧光材料的光谱性能研究

开展了白光LED用新型YAG单晶荧光材料的制备和光谱性能研究,采用提拉法生长Eu,Ce:YAG及Gd,Ce:YAG晶体,并通过吸收光谱,激发、发射光谱及电光性能等对晶体材料的光谱特性进行表征。结果表明,Eu或Gd共掺杂的Ce:YAG单晶荧光材料均可以被波长460nm左右的蓝光芯片有效激发,产生一个范围为480～650nm的宽峰发射。Eu3+或Gd3+共掺杂会对Ce3+离子的发光产生影响:Eu3+离子的掺杂,会对Ce3+离子的发光产生淬灭效应;而Gd3+离子取代基质Y3+离子可以使Ce3+离子的发射峰发生红移。     

Bonding interface zone of Mg-Gd-Y/Mg-Zn-Gd laminated composite fabricated by equal channel angular extrusion

In order to improve the mechanical properties and corrosion resistance of Mg alloys, the equal channel angular extrusion (ECAE) was employed to fabricate the Mg-5Gd-5Y/Mg-2Zn-1Gd (GW55/ZG21) laminated composites. After fabrication and annealing treatment, the microstructural evolution, phase constitution, microhardness, and bonding strength were investigated on the bonding interface zone of GW55/ZG21 laminated composites. The bonding interface zone of GW55/ZG21 laminated composites comprises a lot of Mg3(Y, Gd)2Zn3 particles along the bonding interface, some rod Mg24(Y, Gd)5 phases on GW55 side, and a precipitation free zone (PFZ) on ZG21 side. After annealing treatment, Mg3(Y, Gd)2Zn3 particles along the bonding interface increase, rod Mg24(Y, Gd)5 phases on GW55 side decrease, and PFZ is broadened. Meanwhile, the hardness on the bonding interface zone decreases and the bonding strength increases from 126 MPa to 162 MPa.     

Experimental parameters during optical floating zone crystal growth of rare earth silicides

Optical floating zone（FZ） crystal growth involving growth stability and as-grown crystal perfection is affected by experimental conditions and the specific material. Referring to rare earth silicides, high purity of raw rare earth elements and ambient argon atmosphere are crucial to grow high-quality crystals; the maximum zone height is determined by equating the capillary forces of the surface tension; and asymmetric counter rotation of crystal and feed rod with convex（toward the melt） interfaces are favored to reach single crystals. Influences of several other growth parameters were also discussed in detail in this paper.     

双合金工艺制备钕铁硼永磁体的性能和显微组织的研究

用双合金工艺在Nd13.05Dy0.23Fe80.12B6.5铸片主合金中添加质量分数为3%~20%的富稀土铸锭辅合金Nd38.2Gd11.8Fe44.88Al4.12B,研究稀土元素Gd部分取代Nd时对钕铁硼永磁体的磁性能和显微组织的变化规律。结果表明,Gd的加入不仅可改善钕铁硼磁体性能,也可节约Nd和Dy的用量。从显微结构可看出,组织中细小的颗粒状富稀土相增多,元素Gd主要富集于晶界处,形成了更多的对矫顽力有贡献的富稀土相。     

Cu-Gd_2O_3复合材料界面与性能研究

采用放电等离子烧结工艺制备Cu-Gd_2O_3复合材料,主要研究该复合材料内部Cu/Gd_2O_3界面结合情况及物理性能。增强相Gd_2O_3在复合材料中弥散分布,随含量增多在基体中呈现出立体网格状分布结构。X射线衍射分析有少量新相Gd_2CuO_4形成,透射电镜分析发现Gd_2O_3和铜基体发生部分界面反应形成Gd_2CuO_4,且过渡区反应层的厚度随温度的增加而加厚,通过有效控制界面反应层的厚度可以提高材料的力学性能。     

Defects in La2CuO4 and La1.86Sr0.14CuO4 single crystals

La2CuO4 and La1.86Sr0.14CuO4 single crystals were obtained by traveling solvent floating zone method. There were five kinds of defects in these single crystals: cracks, inclusions, gas bubbles, unhomogeneous distribution of Sr^2 , and substructures. CH3COOH aqueous solution was used to etch these single crystals, and the etch-pit density was calculated.The formation mechanism of these defects was discussed. It is suggested that the good preparation of raw materials and the stringent growth conditions play an important role in growing high quality single crystals.     

Enrichment of Gd and Al atoms in the quadruple close packed planes and their in-plane long-range ordering in the long period stacking-ordered phase in the Mg–Al–Gd system

The crystal structure of a long period stacking-ordered (LPSO) phase newly found in the Mg–Al–Gd ternary system has been investigated by scanning transmission and transmission electron microscopy. The LPSO phase in the Mg–Al–Gd system is found to form by stacking structural blocks, each of which consists of six close-packed atomic planes. In each of the structural blocks long-range ordering occurs for the constituent Mg, Al and Gd atoms, with enrichment of Gd atoms occurring in four consecutive planes of the six close-packed atomic planes. The ideal chemical composition of the structural block is determined to be Mg₂₉Al₃Gd₄ (Mg–8.3 at.% Al–11.1 at.% Gd). However, the stacking of structural blocks is largely disordered. Strictly speaking, the technical term LPSO cannot be used to describe this phase because of the long-range ordering of the constituent atoms in each structural block. The crystal structure of the LPSO phase can thus be crystallographically described as one of the order–disorder structures, and either the C2/m, P3₁12 or P3₂12 space group is assigned when the simplest stacking of structural blocks is assumed.     

Microstructure evolution of Cu-Pb monotectic alloys during directional solidification

1 Introduction Monotectic alloy is an important class of alloy whose binary phase diagram has a miscibility gap, in which the original single liquid will decompose into two distinct immiscible liquids within a few seconds. In the normal gravity field, a …