添加Co对AB3.5型储氢合金结构及性能影响的理论与实验研究

基于密度泛函理论,采用总能量平面波赝势方法,设计了La0.75Mg0.25Ni3.5-xCox(x=0、0.25、0.5、0.75)系列合金,并研究了其晶体及电子结构.计算结果显示随着Co含量的增加,La原子上的电荷转移先增大后保持不变,在Co含量为0.5时达到最大;费米能级处的态密度值先增加后稍减小,Co含量在0.5时达到最大.利用悬浮感应熔炼法制备了该系列合金La0.75Mg0.25Ni3.5-xCox(x=0、0.3、0.5、0.7).对熔炼所得合金进行了结构和性能表征,XRD结果显示,随着Co含量的增加,合金的主相均为Ce2Ni7型AB3.5相;电化学测试显示,x=0.5时,合金的放电容量和循环性能均较好,为398.5 mAh/g,容量保持率S250为62%;PCT结果表明,在室温条件下合金的吸氢平台在0.04~0.09 MPa之间,当x=0.5时,吸氢平台压最低,为0.04 MPa,同时吸氢量最大,为1.587wt%.综合分析计算和实验的结果,AB3.5合金性能随Co添加量的变化趋势符合第一性原理计算的预测.     

Characterization of silicides in high-temperature titanium alloys

Different types of silicides precipitate in high-temperature titanium alloys depending upon the composition and heat treatment of the alloys. However, there are inconsistencies and lacunae with respect to the chemical and crystallographic characteristics of the silicides and these are pointed out here. Hexagonal silicides s1 (a=0.7804 nm; c=0.5447 nm) and s2 (a=0.701 nm; c=0.368 nm) coexist in the ternary alloy Ti–5Zr–Si; however, only the s2 silicide exists when the addition of stabilizing element is made. In addition, there is no common agreement about the space group of s2 silicide while the space group of s1 silicide was found to be P63/mcm (hP16). The (TiZr)6Si3 stoichiometry of s2 silicide is based on the experimental findings; however, the (TiZr)5Si3 stoichiometry of s1 silicide is simply deduced. Also the orientation relationships of silicides with and phases of the matrix are discussed.     

熔体快淬对La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1(x=0～0.2)电极合金循环稳定性的影响

为了改善La-Mg-Ni系A287型电极合金的电化学循环稳定性,用Zr部分替代合金中的La,并用熔体快淬工艺制备了La0.75-xZrxMg0.25Ni3.2Co0.2Al0.1(x=0、0.05、0.1、0.15、0.2)电极合金.用XRD、SEM、TEM分析了铸态及快淬态合金的微观结构,测试了铸态及快淬态合金的电化学循环稳定性,研究了快淬工艺及Zr替代La对合金循环稳定性的影响,探讨了电极合金的失效机理.结果表明,铸态及快淬态合金均具有多相结构,包括两个主相(La,Mg)Ni3及LaNi5和一个残余相LaNi2.快淬处理及Zr替代La可以显著的改善舍金的电化学循环稳定性.导致合金失效的主要原因是电极表面被电解液剧烈腐蚀以及合金电极在电化学循环过程中的粉化.     

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.     

快速凝固MlNi4.0CO0.2Mn0.40Al0.30Cu0.10低Co贮氢合金的相结构和电化学性能

系统研究了单辊快淬快速凝固处理对低Co贮氢合金MlNi4.0Co0.2Mn0.40Al0.30Cu0.10的相结构和电化学性能的影响.XRD分析表明,铸态和快凝合金均为单相CaCu5型结构,但快凝合金的成分和结构均匀性得到明显改善,并具有较低的吸氢体积膨胀率(△V/V).电化学测试表明,快速凝固处理后合金的活化性能不变,循环稳定性得到显著改善,但其放电容量和高倍率放电性能有所降低.研究发现,快速凝固低Co合金循环稳定性能的改善主要归结于快凝合金具有较低的吸氢体积膨胀率和较好的成分均匀性,而快凝合金电极的电催化活性以及氢在合金中的扩散速率较铸态合金有所减小是导致其高倍率放电性能降低的主要原因.     

Mg-Ti基bcc结构固溶体的制备与性能研究

采用机械合金化制备Mg70-xTi12+xNi12Mn6(x=8、16、24、32)合金,通过X射线衍射(XRD)、差热分析(DTA)、扫描电子显微镜(SEM)和压强-成分-温度(PCT)分析等方法对合金粉末进行分析和表征。结果表明,随着球磨时间的增加,合金中hcp相所对应的衍射峰减弱,衍射峰宽化,合金中固溶度以及合金化程度提高;当球磨时间为200h时,在合金Mg46Ti36Ni12Mn6和Mg38Ti44Ni12Mn6中出现具有bcc结构的固溶体,Mg70-xTi12+xNi12Mn6(x=8、16、24、32)合金的吸氢量分别为0.83%、0.68%、1.36%和0.41%(质量分数),根据DTA测试结果,Mg70-xTi12+xNi12Mn6(x=8、16、24、32)合金氢化物的第一个吸热峰位置分别为670、688、593和662K。在Mg46Ti36Ni12Mn6合金中添加5%(质量分数)的TiF3和Nb2O5混合球磨后,合金的吸氢量分别增加到了2.33%和2.36%(质量分数),TiF3和Nb2O5能有效地提高Mg-Ti基合金的贮氢性能。     

机械合金化制备Mg76-xTi12Ni12Mnx（x=2,4,6,8）合金及其贮氢性能研究

利用机械合金化法制备了Mg76-xTi12Ni12Mnx(x=2,4,6,8)合金,并研究了Mn添加量对合金贮氢性能的影响。结果表明,在Mg76-xTi12Ni12Mnx(x=2,4,6,8)合金中合金相主要由Mg2Ni和Ti2Ni相组成,合金最大贮氢量分别为3.47%、3.32%、3.60%和3.11%(质量分数,下同),合金氢化物的分解热依次为-79.2kJ/mol、-78.0kJ/mol、-73.7kJ/mol和-73.6kJ/mol,添加Mn可降低合金氢化物的稳定性,改善其热力学性能,非晶化不利于提高合金的贮氢性能。     

The behaviour of highly over-stoichiometric LaNi5 Mn2 alloy as negative electrode for Ni/MH batteries

Key electrochemical properties of highly over-stoichiometric LaNi₅Mn₂ alloy with CaCu₅-type structure have been measured and compared with those of stoichiometric LaNi₄Mn alloy. LaNi₅Mn₂ is obtained by mechanical alloying of two-phase La(Ni,Mn)₅+(Ni,Mn) alloy previously produced by induction melting. The as-milled alloy was thermally annealed at 450°C for one hour to crystallise milling-induced amorphous phase. As derived from DSC and XRD measurements, further annealing at 550°C produces segregation of minor NiMn-phase (21 wt%), which leaves stoichiometric LaNi₄Mn alloy (79 wt%) as a major phase. Electrochemical cycle-life and potential equilibrium measurements for both LaNi₅Mn₂ and LaNi₄Mn alloys show that the over-stoichiometric alloy has much lower discharge capacity than the stoichiometric one (135 mAh/g and 260 mAh/g, respectively). Conversely, the over-stoichiometric alloy exhibits much better cycle-life than the stoichiometric one (5% and 25% decay capacity after 55 cycles, respectively). These results demonstrate that stoichiometry is an effective parameter for tuning the discharge capacity and cycle-life of LaNi_5+x -type electrodes to the performances required by a particular application.     

Pr替代La对La-Mg-Ni系A_2B_7型电极合金微观结构及循环稳定性的影响

为了改善La-Mg-Ni系A2B7型电极合金的电化学循环稳定性,用Pr部分替代合金中的La,并用熔体快淬技术制备了La0.75-xPrxMg0.25Ni3.2Co0.2Al0.1(x=0、0.1、0.2、0.3、0.4)电极合金。用XRD、SEM、TEM分析了铸态及快淬态合金的微观结构,测试了铸态及快淬态合金的电化学循环稳定性,研究了Pr替代La对合金微观结构及循环稳定性的影响,探讨了合金电极在电化学循环过程中的失效机理。结果表明,铸态及快淬态合金均具有多相结构,包括2个主相(La,Mg)Ni3及LaNi5和一个残余相LaNi2。Pr替代La使(La,Mg)Ni3明显增加而LaNi5减少。电化学测试的结果表明,合金的循环稳定性随Pr替代量的增加而增加。导致合金电极失效的主要原因是电极表面被电解液剧烈腐蚀以及合金电极在电化学循环过程中的粉化。     

铸态La0.75Mg0.25Ni3.3Co0.2Six(x=0～0.2)电极合金的电化学与动力学性能

为了提高La-Mg-Ni系A2B7型贮氢合金的电化学循环稳定性,添加少量的Si,用铸造工艺制备了La0.75 Mg0.25 Ni3.3 Co0.2 Six(x＝0、0.05、0.1、0.15、0.2)贮氮合金,分析并测试了其微观结构和电化学性能,以及高倍率放电能力,交流阻杭等动力学性能.结果表明,合金具有多相结构,主相...     

Cu的添加对Mg2Ni合金储氢性能的影响

采用机械合金化法,制备了Mg2Ni1-xCux(x=0、0.1、0. 3)合金,研究了Cu对Mg2Ni储氢合金储氢性能的影响.XRD和SEM研究表明Cu的加入使合金中产生了Cu11Mg10Ni9新相.利用PCT测试仪测定了合金的储氢性能,结果表明,添加Cu元素会降低合金的吸氢量,但能有效地提高放电容量和循环稳定性.制备出的Mg2Ni0.9Cu0.1与Mg2Ni0.7Cu0.3相比,前者具有较大的吸氢量,后者的放电容量较大,循环稳定性较好.     

A new magnetic alloy of high constant permeability

Several conventional alloys of constant permeability used previously were of lower values of permeability, or they would change obviously in different intensities of magnetic field and thus could not satisfy some specific requirements of electrical application. The alloys consisted of Ni 60-70 wt%, Fe 29-39wt% and Mn 0-1 wt% were investigated. The best of those alloys for certain use is 1J66 alloy in China. It is a new alloy of high constant permeability with the chemical composition as Fe 34 wt%, Ni 65 wt% and Mn 1 wt%. Its AC induction permeabilitymu_{L}= 3400G/Oe (f=60Hz). Within the range of Bm=20-6800 G, the stability of AC induction permeability (f=60Hz)alpha_{sim} = 4.3%. The α is defined asalpha = mumax-mumin/mumin,alphamaxandmuminare the maximum and the minimum of permeability respectively in the range of given magnetic field. The temperature stability αTof μLwithin the range of temperature from -60°C to +90°C is 2.9%. The saturation magnetic induction of 1J66 alloy equals 13500 G. The remanenceB_{r} < 150G. The coercive forceH_{c} = 0.05Oe. The oxygen content of 0.015- 0.04% in the alloy is considered necessary for obtaining a good stability of permeability.     

Zr1-xTix(Ni0.6Mn0.3V 0.1Cr0.05)2(x=0～0.5)Laves相储氢合金的电化学性能

本文研究Zr1-xTix(Ni0.6 Mn0.3V0.1Cr0.05)2(x=0,0.1,0.2,0.3,0.4,0.5)系Lav es相储氢电极合金的气态P-C-T性能、晶体结构及电化学性能.XRD分析表明,Ti合金化使 Zr基储氢合金主相从C15相转变为C14相.当x>0.2时,第二相Zr7Ni10相消失, 并出现TiNi相.Ti合金化使Zr基储氢合金中C15相和C14相的晶格常数线性递减.气态P-C-T 测试表明,Ti合金化从x=0增加至x=0.5时合金的吸放氢平台压力升高约10倍,但降低了储氢合金的最大储氢容量.电化学测试表明,Ti合金化有利于改善Zr基储氢合金的活化性能, 这与Ti在KOH溶液中易于溶解有关,但过高的Ti含量降低了合金电极的循环稳定性.Zr1 -xTix(Ni0.6Mn0.3V0.1Cr0.05)2合金的电化学容量和高倍率放电性能均随合金中Ti含量的增加先上升后下降,这与合金的相结构组成有很大关系 .     

La0.7-xPrxZr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2 (x=0.00,0.05,0.10, 0.15,0.20)合金储氢及电化学性能研究

在Ar气保护下,采用高频感应悬浮炉制备La0.7-xPrxZr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2(x=0.00,0.05,0.10,0.15,0.20)合金,研究Pr替代La对合金电极电化学性能的影响。结果显示,所有合金主要由LaNi5和La2Ni7相组成,以Pr替代La后,LaNi5相和La2Ni7合金相的晶胞收缩,导致氢原子在合金电极体内扩散受限,合金电极的动力学性能下降。但由于Pr的抗腐蚀作用,合金电极循环稳定性增加,经过200次充放电循环后容量保持率分别从66.2%(x=0.00)逐渐增加到69.5%(x=0.05)、73.2%(x=0.10)、74.0%(x=0.15)和75.1%(x=0.20)。     

Effect of Niobium on Microstructure and Properties of the CoCrFeNb_xNi High Entropy Alloys

A series of CoCrFeNb_xNi(x values in molar ratio, x = 0, 0.25, 0.45, 0.5, 0.75, 1.0 and 1.2) high entropy alloys(HEAs) was prepared to investigate the alloying effect of Nb on the microstructures and mechanical properties. The results indicate that the prepared CoCrFeNb_xNi(x 0) HEAs consist of a simple FCC solid solution phase and a Laves phase. The microstructures of the alloys change from an initial single-phase FCC solid solution structure(x = 0) to a hypoeutectic microstructure(x = 0.25), then to a full eutectic microstructure(x = 0.45) and finally to a hypereutectic microstructure(0.5 x 1.2). The compressive test results show that the Nb0.45(x = 0.45) alloy with a full eutectic microstructure possesses the highest compressive fracture strength of 2558 MPa and a fracture strain of 27.9%. The CoCrFeNi alloy exhibits an excellent compressive ductility, which can reach 50% height reduction without fracture. The Nb0.25 alloy with a hypoeutectic structure exhibits a larger plastic strain of 34.8%. With the increase of Nb content, increased hard/brittle Laves phase leads to a decrease of the plasticity and increases of the Vickers hardness and the wear resistance. The wear mass loss, width and depth of wear scar of the Nb1.2(x = 1.2) alloy with a hypereutectic structure are the lowest among all alloy systems, indicating that the wear resistance of the Nb1.2 alloy is the best one.     

First-principles investigation of B2 partial disordered structure,martensitic transformation,elastic and magnetic properties of all-d-metal Ni-Mn-Ti Heusler alloys

In this work,the B2 partial disordered structure of the austenitic parent phase,martensitic transformation,elastic and magnetic properties of the Ni8 Mn4+xTi4-x(x=0,1 and 2) Heusler alloys have been systematically investigated by the first-principles calculations.The preferential atomic occupation of B2 structure is one Ti atom exchange with the nearest neighboring Mn atom from the view of lowest energy principle.This disordered exchange sites(Mn-Ti) and the excess Mn atoms occupying the Ti sites(MnTi)could reduce the nearest Mn-Mn distance,resulting in the anti ferromagnetic state in the austenitic and martensitic phases of the alloys.The total magnetic moment of the alloy decreases with the increasing Mn content;it is ascribed to the antiferromagnetic magnetic moments of the excess Mn atoms.When x=0,the alloy does not undergo martensitic transformation since the austenite has absolute phase stability.The martensitic transformation will occur during cooling process for x=1 or 2,owing to the energy difference between the austenite and the martensite could provide the driving force for the phase transformation.The elastic properties of the cubic austenitic phase for the Ni2 MnTi alloy is calculated,and the results reveal the reason why Ni-Mn-Ti alloy has excellent mechanical properties.The origin of martensitic transformation and magnetic properties was discussed based on the electronic density of states.     

Crystal defects in the laves phase TiCo∼2

Both intrinsic and extrinsic stacking faults are observed on {111} in well annealed cubic TiCo_2+x alloys (x = ?0.06, 0.0, 0.13). The faults are more profuse in the stoichiometric phase than in the off-stoichiometric ones. The intrinsic/extrinsic fault populations range from 61 pct extrinsic in the nominally stoichiometric alloy to 67 pct intrinsic in the cobalt-deficient alloy. Partial dislocations bounding all faults studied in CTEM contrast experiments are Shockley-type ($\text{b}{}_{\mathrm{p}}\text{=}\text{1}\text{6}\text{〈112〉}$).     

Co47.6Fe20.4B21.9Si5.1Nb5-xZrx(x=0~5)合金的非晶形成能力和磁性能

采用铜模吸铸法制备了直径d为2~5mm的Co_(47.6)Fe_(20.4)B_(21.9)Si_(5.1)Nb_(5-x)Zr_x(x=0~5)合金。利用X射线衍射(XRD)、差示扫描量热仪(DSC)、振动样品磁强计(VSM)和显微硬度计分析合金的非晶形成能力(GFA)、磁性能及显微硬度。结果表明:该合金体系具有较好的GFA,随着Zr含量的增加,其GFA呈逐渐降低的趋势。Zr含量为0~2%(原子分数)时,能制得d为3mm的非晶合金;Zr含量为0~3%(原子分数)时,可制得d为2mm的非晶合金。直径2mm的棒状非晶合金(Zr含量为0~3%(原子分数))表现为明显的软磁性,饱和磁化强度Ms趋于一定值。该体系非晶合金均具有很高的显微硬度,Zr含量为3%(原子分数)时达到1420HV。     

Comparison of hydrogen storage characteristics between as-cast and melt-spun TiCr1.1V0.5Fe0.1Mn0.1 alloys

Hydrogen storage characteristics of as-cast and melt-spun TiCr_1.1V_0.5Fe_0.1Mn_0.1 alloys were investigated by pressure–composition–temperature (PCT) tests, X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD showed that both the as-cast and the melt-spun alloys were similarly consisted of V based BCC phase and Ti_1.07Cr_1.93 phase. However, PCT tests showed that the melt-spun alloy, with larger hysteresis between hydrogen absorption and desorption, had higher hydrogen storage capacity than the as-cast alloy. More interestingly, the phase compositions of the two fully hydrogenated alloys were entirely different. The as-cast and the melt-spun alloys should have different atomic motion mechanisms during the course of hydrogenation.     

Er对ZrCuNiAl非晶合金结构、力学性能、热稳定性及非晶形成能力的影响

以(Zr_0.6336Cu_0.1452Ni_0.1012Al_0.12)_100-xEr_x(x=0,0.5,1,1.5,2,2.5,3,原子分数,下同)系块体非晶合金为研究对象,通过改变微量元素Er的含量来研究Er对非晶合金的结构、力学性能、热稳定性及非晶形成能力的影响。结果表明:添加Er元素所制备出的试样都是完全非晶结构的合金。随着Er含量的增加,各试样的弹性模量呈现出先增大后减小,压缩塑性应变呈台阶式上升,x=0,x=0.5,x=1试样的塑性应变在4%的范围内波动;x=1.5,x=2,x=2.5试样的塑性应变在11%的范围内波动;x=3试样的塑性应变最高,其值为23.19%,弹性模量为37.76GPa,屈服强度为1604MPa,抗压强度为2068MPa,断裂强度为2060MPa;随着Er含量的增加,锆基非晶合金的热稳定性和非晶形成能力均先减小后增大。