储氢合金Mg2Ni的制备及其储氢性能分析

Mg-Ni基储氢合金以其比容量高、成本低而倍受关注.采用感应熔炼法,在不高于900 ℃的温度下成功制备出Mg2Ni合金,X射线衍射及金相组织分析表明,合金中主相为Mg2Ni.对制备出的Mg2Ni合金进行气态吸放氢性能测试,结果表明,经粉碎后的合金粉体经第1次活化,吸氢量为3.15 wt%,2次活化后吸氢量达到3.49 wt%,接近其理论值,而合金块体在第2次活化后的吸氢量远小于合金粉体的吸氢量,且第3次活化后未见明显增大.     

Mg+10%TiFe1-xCrx(x=0,0.3)复相合金的储氢特性

采用高能机械球磨法制备了Mg 10%TiFe1-xCrx(x=0,0.3)复相储氢合金,对比研究了球磨复相合金和球磨纯镁的微结构与储氢性能.研究结果表明:在纯Mg中添加质量分数为10%的TiFe1-xCrx(x=0,0.3)进行复合球磨,可以明显提高其吸放氢性能;在相同温度条件下,x=0.3的含铬复相合金具有最佳的吸放氢性能,其中在613 K下的吸氢容量(氢的质量分数)为7.14%,放氢容量(氢的质量分数)为6.91%;在493～573 K的较低温度下,含铬复相合金表现出更好的放氢动力学性能.通过XRD、SEM、EDS分析研究表明,TiFe1-xCrx(x=0,0.3)合金粉以细小颗粒的形式分散镶嵌在镁粉基体上成为催化活性点,改善了体系的吸放氢性能.     

基于机械形变方法的TiFe基储氢合金的研究进展

TiFe储氢合金理论储氢量为1.86 wt.%,且分解压力适中,循环稳定性好,价格便宜且资源丰富,极适于大规模工业生产和应用,被认为是一种非常有前途的固态储氢材料。但传统的TiFe储氢合金存在着活化困难、有效储氢容量较低、抗杂质气体毒化能力很差等突出问题。针对上述TiFe基储氢合金的缺点,研究人员进行了大量的改性研究。笔者总结了基于机械形变方法的TiFe基储氢合金的研究进展,对比了采用高能球磨技术、冷轧技术、孔型轧制技术及高压扭转技术处理后的TiFe基储氢合金的储氢性能,并探讨了冷锻技术、等径角挤压技术及搅拌摩擦加工技术等潜在的可用于TiFe基储氢合金的储氢性能改善的机械形变方法。     

球磨Mg17Al12纳米晶/非晶合金的微结构和储氢性能

采用镁粉和铝粉为原料,通过高能球磨方法制备了Mg17Al12纳米晶/非晶储氢合金,系统研究了球磨时间对合金微结构和储氢性能的影响.结果表明:球磨时间对Mg17Al12合金的微结构和储氢性能有显著影响,随着球磨时间t从10 h延长到100 h,合金发生从晶态(t≤50 h)到纳米晶态(t=70 h)再到非晶态(t=100 h)的结构转变;样品的平均颗粒尺寸随着球磨时间的增加先减小后增大;球磨时间为30、70和100 h后的Mg17Al12合金在350℃时的最大储氢量(氢的质量分数)分别为4.03%、4.27%和4.18%,而相同条件下铸态Mg17Al12合金的最大储氢量只有2.85%;球磨时间为70 h的Mg17Al12纳米晶合金在200、280和320℃的储氢量分别为1.07%、3.02%和4.07%;球磨时间为100 h的Mg17Al12非晶合金在200℃时30 min内的吸氢量(氢的质量分数)可达到2.84%,分别为相同条件下纳米晶合金和铸态合金的2.7倍和5.1倍.     

Mo部分替代Ti对V_(40)Ti_(50)Fe_(10)合金储氢性能的影响

为了考察Mo部分替代Ti对高容量V_(40)Ti_(50)Fe_(10)合金储氢性能的影响,采用电弧熔炼制备了V_(40)Ti_(50-x)Mo_xFe_(10)(x=0～30)合金,系统地研究了该系列合金的结构和储氢性能随Mo替代Ti含量的变化规律,并探讨合金储氢容量的衰退机制。研究表明:该系列合金均由主相体心立方(BCC)固溶体和少量的C14型Laves第2相组成;Mo取代Ti并未改变合金的主相结构,但Laves第2相的含量明显降低,合金整体均匀性增加;随着Mo含量的增加,BCC相的晶胞体积逐渐减小,合金的放氢量总体呈现下降趋势但中间出现波动状态,而放氢平台压则持续上升;在这一系列合金中,V_(40)Ti_(40)Mo_(10)Fe_(10)合金的储氢性能较优,具有相对宽泛且平坦的放氢压力平台,可逆储氢量较高,且室温下吸放氢过程均可在5 min内完成。循环测试表明,合金氢化物在吸放氢过程中会形成难以活化的TiFe相,导致合金出现成分分离,影响合金的稳定性,从而造成储氢容量衰退。     

LaNi4.25Al0.75储氢合金的改性

为了提高LaNi4．25Al0．75合金的储氢性能,采用退火、表面镀铜和表面包覆SiO2对合金进行改性,并对处理前、后合金的微观结构和吸放氢性能的变化进行研究。研究结果表明,退火消除了LaNi4．25Al0．75合金中的偏析,减少了内应力,使合金具有平坦的吸氢平台;表面镀铜处理加快了合金的吸、放氢速度,但吸氢含量略有降低,另外,镀铜合金抗粉化性能加强,经10次吸、放氢循环后没有出现粉化现象;表面包覆SiO2前、后,合金的吸氢量变化不大,抗粉化性能加强,经10次吸、放氢循环后没有出现粉化现象。     

放电等离子烧结制备Mg2-xNdxNi（x=0～0.3）储氢合金

采用放电等离子烧结(SPS)工艺制备了Mg2-xNdxNi(x=0,0.1,0.2,0.3)储氢合金.通过X射线衍射(XRD)和扫描电镜(SEM)研究了合金的相结构和表面形貌,利用等容压差法分析测试了合金的压力--组成--温度(PCT)曲线和吸放氢动力学性能,研究了烧结温度、稀土元素Nd对储氢合金微观组织结构和储氢性能的影响,比较了SPS技术与真空感应熔炼法制备的Mg基合金组织结构和储氢性能的异同.结果表明:SPS制备的Mg2-xNdxNi(x=0～0.3)系列储氢合金具有多相结构,储氢合金的吸放氢动力学性能良好;Nd元素有利于Mg合金化,不利于储氢量;烧结温度对储氢量、PCT曲线平台性能有明显影响;当Mg2-xNdxNi系合金中含有Mg和NdMg12相,PCT曲线出现双平台现象;与铸态合金相比,SPS制备的Mg1.7Nd0.3Ni储氢合金的吸放氢动力学性能较好,但储氢容量、放氢率和PCT曲线平台性能更差.     

球磨改性处理对Ti9.6Cr11V75.4Fe4合金储氢性能的影响

系统研究了机械球磨改性处理时间(t=0,1,2,4,8 h)对Ti9.6Cr11V75.4Fe4合金相结构和储氢性能的影响.XRD及扫描电镜分析表明,Ti9.6Cr11V75.4Fe4合金在球磨前后均为体心立方结构的固溶体单相,随着球磨时间的增加,合金的晶胞体积略微减小,合金颗粒逐渐细化并发生团聚.储氢性能测试表明,球磨改性处理能有效地改善合金的活化性能,随着球磨时间的增加,合金的室温可逆有效储氢量先增加后降低.其中,当球磨时间为2 h时,合金具有最佳的综合储氢性能,其室温最大吸氢量(质量分数)为3.7%,可逆有效储氢量(质量分数)为2.23%.     

Mg2Ni型镁基储氢合金研究新进展

镁基储氢合金因其具有较高的储氢容量、资源丰富和良好的吸放氢平台而被认为是最具应用价值的金属储氢材料之一.综述了镁基储氢材料尤其是Mg2Ni型镁基储氢合金材料实验和理论研究的新进展,讨论了现有的镁基储氢合金材料的优缺点,同时也提出一些尚需深入研究的问题.     

Li修饰的石墨炔纳米管储氢性能的第一性原理研究

储氢材料的性能直接影响环保能源氢的使用,基于密度泛函理论的第一性原理计算,研究了石墨炔纳米管被Li原子修饰后的储氢性能.结果表明:由γ相石墨炔片卷曲得到的石墨炔纳米管结构的稳定性高;优化结构后发现单个Li的最稳定的修饰位是在单胞石墨炔纳米管的乙炔键所围成的十二元环处;在修饰位上逐步添加氢分子进行分析后,得到最大吸附数为7个氢分子的结果,吸附氢分子的质量比达到2.34 wt%.这与之前未修饰和用其他原子修饰后的石墨炔纳米管吸氢性能相比具有明显优势,为设计和制造储氢材料提供了有力的理论依据.     

冷坩埚无玷污悬浮熔炼

作者研制了一种水冷紫铜坩埚,供熔炼过渡元素合金,稀土元素合金之用,这种坩埚具有特殊的结构,在采用高频感应加热时,可在熔料及坩埚壁上产生特殊取向的涡流,使熔化的金属液与紫铜坩埚脱离接触而悬浮在冷坩埚中,从而避免了坩埚对熔料所可能产生的污染。试验结果表明,熔料可达到的最高温度不低于2500K;坩埚的铜质对熔锭並无污染;熔锭成分均匀,配以保护气氛时,表向洁净。熔锭的典型体积为4.5cm~3。这种无玷污悬浮熔炼特别适用于精密合金材料的研制。作者曾用本法研究钕铁硼永磁,短期內即获得成功。     

Creep behavior and effect factors of a TiAl–Nb alloy at high temperature

The effect of solution treatment on the microstructure and creep properties of forged TiAl–Nb alloys was investigated. The results showed that the microstructure of forged alloy mainly consisted of γ/α₂ lamellar colonies and fine equiaxed recrystallized γ/α₂ grains. During the solution treatment the microstructure of the alloy transformed into a fully lamellar structure due to the lamellar colonies growth by consuming equiaxed grains. Compared with the forged alloy the creep life of the solution treated alloy at 800 ?°C/220 ?MPa increased from 116 ?h to 339 ?h. The better creep resistance may be attributed to the transform of fine equiaxed γ/α₂ grain to the lamellar colonies with serrated grain boundaries due to the solution treatment. The deformation mechanism of the solution treated alloy during creep is considered to be dislocation slipping within the lamellar γ/α₂ phases, and the dislocation movement may be hindered by the γ/α₂ interface and the formation of dislocation tangles. The interaction of the dislocations with the tangles may increase the resistance of the dislocation motion and hence improve the creep resistance of the alloy. It was found that during the creep of the forged alloys the cracks mainly initiated at the equiaxed grain, and in the solution treated alloy the cracks initiated at the grain boundaries. As creep continued the cracks propagated and connected to each other, leading to the damage and rupture of the forged and solution treated alloys.     

Effect of heat treatment on hydrogen storage properties and thermal stability of V68Ti20Cr12 alloy

Effect of heat treatment on the crystal structure, microstructure, hydrogen storage properties and thermal stability of V68Ti20Cr12 alloy prepared by arc-melting was studied in this work. It was found that both the as-cast and annealed (973 K/72 h) V68Ti20Cr12 alloys consisted of a single body-centered cubic (bcc) phase. After heat treatment, the hydrogen absorption/desorption kinetic characteristics of the as-cast alloy was improved greatly due to the homogeneous composition and perfect structure. The mechanism of hydrogen absorption/desorption process in the as-cast and annealed alloys was further investigated according to the Johnson-Mehl-Avrami (JMA) equation. The hydrogen absorption process of the as-cast and annealed alloys would be controlled by the one-dimensional diffusion process, while the hydrogen desorption process in the as-cast and annealed alloys was dominated by the geometrical contraction model. The pressure-composition-temperature (PCT) measurements show that the plateau pressure of the annealed alloy becomes comparatively flat. Furthermore, the activation energies of the dehydrogenation in the as-cast and annealed alloys were calculated using the Kissinger method, indicating that heat treatment is a very beneficial way to improve hydrogen absorption/desorption kinetics of the alloy.     

Microstructure and heat treatment for Ni3Al-based single crystal alloy with different crystal orientations

Ni₃Al-based single crystal alloy IC6SX with different crystal orientations were prepared by seed crystal method. The microstructure and heat treatment of the alloy were investigated. The results showed that the microstructure of the alloy was in dendrite structure, and the crystal orientation had significant effect on the dendrite morphology of this alloy. The precipitated phases of (MoNi)₆C and NiMo appeared in the microstructure of the three alloys with different crystal orientations during solidification process. Compared with other two alloys, the volume fractions of precipitated phases of both (MoNi)₆C and NiMo was the most in the alloy with [111] orientation and the least in the alloy with [001] orientation. The solidus and liquidus temperatures of the alloy IC6SX tested by differential scanning calorimetry (DSC) were 1356 °C and 1387 °C, respectively. Meanwhile, the effect of different solution temperatures on the microstructure of the alloy with different orientations was studied. The results showed that the precipitated phases of (MoNi)₆C and NiMo were eliminated with the solid solution treatment under the condition of 1300 °C/10 h. However, the incipient melting of the alloys occurred due to the dissolution of low melting point phases. As the temperature dropped to 1280 °C, the area of incipient melting in the alloy with different orientations decreased gradually. However, there was no incipient melting appearing in the three alloys with different orientations when the solution treatment temperature dropped to 1260 °C.     

原位合成TiC／Ti复合材料的微结构和力学性能

利用钛与碳之间的反应,经非自耗电弧溶炼工艺,简洁,低成本地制备了TiC增强的钛基复合材料,借助光学金相为微镜和透射电镜分析了复合材料的微结构,测定了原位合成钛基复合材料的力学性能和硬度值,结果表明,原位合成增强体TiC均匀地分布在基体钛合金中,增强体主要呈树枝晶状和等轴,近似等轴状,由于增强体TiC与基体合金的热膨胀系数存在较大的差异,在基体钛合金中形成同密度的位错,增强体与基体界面洁净,没有任何界面反应,复合材料的力学性能和硬度与基体钛合金比较有了明显的提高,铝元素的加入,不仅固溶强化了基体钛合金,同时使增强体更为细小,也有利于提高复合材料的性能。     

Microstructural characteristics and electrical resistivity of rapidly solidified Co-Sn alloys

The rapid solidification behavior of Co-Sn alloys was investigated by melt spinning method.The growth morphology of αCo phase in Co-20% Sn hypoeutectic alloy changes senistively with cooling rate.A layer of columnar αCo dendrite forms near the roller side at low colling rates.This region becomes small and disappears as the cooling rate increases and a kind of very fine homogeneous microstructure characterized by the distribution of equiaxed αCo dendrites in γCo3Sn matrix is subsequently produced.For Co-34.2% Sn eutectic alloy,anomalous eutectic forms within the whole range of cooling rates.The increase of cooling rate has two obvious effects on both alloys:one is the microstructure refinement,and the other is that it produces more crystal defects to intensify the seattering of free electrons,leading to a remarkable increase of electrical resistivity,Under the condition that the grain boundary reflection coefficient γ approaches 1,the resistivity of rapidly solidified Co-Sn alloys can be predicted theoretically.     

Al-Ti-C-B中间合金对高铝锌基合金组织和性能的影响

研究了Al-6.53Ti-0.3C-0.46B中间合金（Ti:C＞4:1）对高铝锌基合金的组织和性能的影响,结果表明,加入适量的中间合金可显著细化合金的显微组织,初生富铝α相从粗大的树枝晶转变为细小均匀等轴晶,等轴晶尺寸30~50 μm。砂型铸造条件下,合金的伸长率从1.7%提高到10.0%,拉伸强度在410 MPa左右。金属型铸造条件下, 合金的伸长率从1.0%提高到16.0%,拉伸强度约407 MPa。尽管组织显著细化,但拉伸强度并没有显著增加。高铝锌基合金组织细化的机理主要通过加入Al-Ti-C-B中间合金增加了异质形核质点。     

稀土Y对挤压态Mg-5Li合金组织及性能的影响

采用表面覆盖剂及氩气保护的熔炼方法制备了Mg-5Li-x Y(x=0,1,2,3,4)合金,研究了稀土元素Y对挤压态Mg-5Li合金的显微组织及力学性能的影响.研究结果表明,Mg-5Li合金中的Y元素主要是以稀土化合物Mg24Y5的形式存在于合金中;挤压变形后,合金发生了明显的动态再结晶,出现了大量的等轴晶,弥散分布的Mg24Y5相阻碍了动态再结晶过程中的晶粒长大,晶粒明显细化.挤压态Mg-5Li-3Y合金获得了优异的力学性能,其抗拉强度和断裂伸长率分别达到了231.63 MPa和9.35%,合金断裂方式主要为韧性断裂.     

Ni基合金-石墨自润滑材料的熔炼组织及性能

采用熔炼法制备了Ni-4.2%A1-3.5%C高温自润滑材料.结果表明,石墨在合金基体中呈高密度均匀分布;Al不仅是强化合金基体的元素,而且对结晶中的石墨有一定的球化作用,Al与氧结合成渣降低了氧在石墨表面的吸附;稀土镁球化剂对Ni-4.2%Al-3.5%C合金中的石墨生长具有更有效的球化作用,其孕育形核的作用也十分显著.石墨经球化处理后,材料的冲击韧性得到提高;该合金与45#退火钢及GCr15轴承钢在干摩擦磨损条件下,摩擦系数保持在0.12和0.15的较低水平.