Hydrogen storage in Zr0.9Ti0.1(Ni0.5Cr0.5-xVx)2 Laves phase,with x = 0, 0.125, 0.25, 0.375, 0.5. A theoretical approach

Density functional calculations were performed on Zr_0.9Ti_0.1(Ni_0.5Cr_0.5-xV_x)₂ Laves Phase, with x = 0, 0.125, 0.25, 0.375 and 0.5, in order to study its H absorption capacity. Binding energy, electronic structure and bonding were analyzed for the intermetallic compound with different V content and increasing amounts of hydrogen.The optimized geometry was found in good agreement with experimental data of the C14 Laves phase. Hydrogen locates preferentially in A₂B₂ tetrahedral sites in the AB₂ matrix (A = Zr, Ti; B = Ni, Cr, V) but AB₃ and B₄sites are also stable. The volume of the intermetallic and the H binding energy increases with vanadium content. Theoretically H absorption is possible up to 4.5 H/F.U. but the strongest binding energy is achieved with 3 H/F. U.The main contribution to density of states is due to d states of all components of the structure and an H-metal bonding is observed in the range ?10 to ?4 eV.     

FeCrAl不锈钢包壳管挤压及退火工艺优化

利用光学显微镜、扫描电镜、电子背散射衍射和万能拉伸试验机等对FeCrAl合金包壳管挤压前后的微观组织、析出相及退火后的微观组织、析出相、再结晶及力学性能进行了研究。结果表明:Nb含量对FeCrAl合金中第二相的析出影响显著,高Nb含量下Laves相的析出温度和析出数量均大大提高;降低挤压温度有助于FeCrAl合金管坯中形成细小弥散第二相;随着退火温度升高,细小弥散相的析出数量呈现先增多后减少的趋势;在相同退火工艺下,800 ℃热挤压管坯的室温力学性能比950 ℃热挤压管坯的室温力学性能要更加优异。     

Incipient melting phase and its dissolution kinetics for a new superalloy

Based on XRD, SEM and EDS analyses, the phases in GH4151 alloy were identified. Differential scanning calorimetry (DSC) experiment and metallographic method were carried out to determine the incipient melting temperature (IMT) of the alloy. The result shows that the IMT of alloy is situated between 1150 and 1160 °C. Subsequently, the dissolution process of Laves phase was carried out, and the dissolution kinetic equations were obtained at different temperatures. And then based on the verification of experiments, the model was confirmed to be credible to predict the fraction of the Laves phase dissolution. Finally, the results of diffusion coefficients indicate that the diffusion of Nb element is a critical factor for homogenization process of GH4151 alloy.     

Structure and defects evolution at temperature and activation treatments of the TiCr2 intermetallic compound of Laves phase C36-type

In this work, microstructure and defect evolution at a temperature and activation treatment of the TiCr₂ intermetallic compound of Laves phase C36-type synthesized in the abnormal glow discharge plasma were investigated. The crystalline structure of the C36TiCr₂ powder crushed by hydrogenation-dehydrogenation (HD) method is characterized by the following lattice parameters: a = 4.932 Å and c = 16.059 Å. The dilatation of the crystal lattice under the hydrogenation at the HD crushing process leads to the formation of partial dislocations. For the first time ever the experimental value of the positron lifetime of the synthesized compound of the C36TiCr₂ Laves phase, this amounted to (141 ± 2) ps, established by the positron spectroscopy. The optimal activation parameters of the HD-crushing C36TiCr₂ powder were established: the temperature should be in the range from 450 to 500 °C, the exposure time in a hydrogen atmosphere at a pressure of (1–8) atm. must be at least 10 min.     

Hydrogenation process in multiphase alloys of Ti-Zr-Mn-V system on the example of Ti42.75Zr27Mn20.25V10 alloy

The influence of phase composition and microstructure of Ti_42.75Zr₂₇Mn_20.25V₁₀ alloy on its hydrogenation kinetic and phase composition of hydrogenated product was studied. It is established that the process of dissociation of hydrogen molecules begins on the surface of Laves phase crystallites. The dissolution of atomic hydrogen in the material volume leads to the formation of cracks in the intermetallic crystallites, which further appear as additional centers of dissociation of hydrogen molecules and noticeably accelerate the diffusion of hydrogen into the bulk material. It was shown that the Laves phase acts as a donor of atomic hydrogen for the BCC solid solution during hydrogenation of two-phase structure, initiating intensive hydrogenation of the BCC phase at room temperature.     

激光熔覆FeCoCrNiNb高熵合金涂层组织及力学性能

采用激光熔覆技术在304不锈钢表面制备了FeCoCrNi、FeCoCrNiNb等摩尔比高熵合金熔覆层,研究了Nb元素对熔覆层组织及性能的影响。采用XRD、SEM、EDS、纳米压痕测试和干滑动摩擦磨损实验等方法,详细分析了2种高熵合金熔覆层的相组成、组织演变、纳米硬度及耐磨性能。结果表明：FeCoCrNiNb高熵合金熔覆层相组成为fcc固溶体及富Nb-Laves相。FeCoCrNiNb熔覆层的纳米硬度(H)、弹性模量(E)、H/E和H³/E²分别为6.066 GPa、231.54 GPa、0.0262和0.0042,远高于FeCoCr Ni熔覆层的3.456 GPa、209.48 GPa、0.0165和0.000 94。随着纳米硬度的增加,FeCoCrNiNb熔覆层的摩擦系数和比磨损率也随之降低,分别为0.519和2.54×10^-6mm³/(N·m)。综上所述,FeCoCrNiNb高熵合金熔覆层具有良好的纳米硬度和耐磨性。     

低膨胀高温合金晶粒长大规律及对其性能的影响

本工作研究了不同热处理制度对低膨胀高温合金析出相的行为以及晶粒长大的影响。实验结果表明,在Laves相析出峰温度范围（980～990℃）保温不同时间,Laves相尺寸逐渐增大,晶粒不长大。在1000～1040℃保温1 h后Laves相开始溶解,晶粒逐渐长大至4级、3.5级、3级、2级,因此在热加工过程中为避免晶粒长大,热变形加热温度不应超过1010℃,或在1000℃变形且保温时间不应超过1 h。晶界Laves相的含量对合金性能影响较小,而合金的晶粒度对其影响较大。     

Element Segregation and Solidification Behavior of a Nb,Ti, Al Co-Strengthened Superalloy ЭК151

The as-cast microstructure, element segregation and solidification behavior of a multi-alloyed superalloy ЭК151 have been investigated. The results show that the severe element segregation leads to the complicated precipitations at the inter-dendritic region, including η-Ni_3(Ti, Nb), eutectic(γ + γ') and Laves, which shows the characteristics of both Ti, Al-strengthened and Nb-strengthened alloys. Differential thermal analysis, heating and quenching tests reveal the solidification sequence as follows: Liquids →γ matrix →(Nb, Ti)C →η-Ni 3(Ti, Nb) →eutectic( γ+γ') → Laves. The melting points are between 1250 and 1260 °C for(Nb, Ti)C, between 1200 and 1210 °C for η phase, between 1180 and 1190 °C for eutectic(γ+γ') and Laves. γ' initially precipitates from matrix at 1150 °C and achieves the maximum precipitation at 1130 °C. According to the microstructure evolution captured during solidification and composition analysis by an energy dispersive spectrometer and electron probe microanalyzer,(Nb, Ti)/Al ratio is put forward to explain the formation of η-Ni_3(Ti, Nb) and eutectic( γ+γ'). The solidification of γ matrix increased the Nb, Ti concentration in the residual liquids, so the high(Nb, Ti)/Al ratio would result in the formation of η-Ni_3(Ti, Nb); the precipitation of the phase consumed Nb and Ti and decreased the(Nb, Ti)/Al ratio in the liquid, which led to the precipitation of eutectic(γ + γ'). Laves formed by the sides of η-Ni_3(Ti, Nb) and in front of the eutectic( γ + γ') after Al, Ti were further depleted by the two phases and Cr, Co, Mo were rejected to liquids.     

Cu - Mg - Si 三元系合金中 Laves 相的研究现状简

新材料的开发和研究是永恒课题,为了全面、充分地认识和了解Cu-Mg-Si三元系合金中金属间化合物Laves相的研究现状,总结了Cu-Mg-Si三元系合金中几种Laves相的国内外研究成果,旨在为该领域合金的进一步研究提供参考,并为该领域科研人员提供理论依据.