【作者】 杭州明；

【导师】 陈立新； 陈长聘；

【作者基本信息】 浙江大学 ， 材料学， 2010， 博士

【摘要】 本文在对国内外体心立方(BCC)结构的钒基固溶体储氢合金的研究进展进行全面综述的基础上,为了探索以低成本V-Fe替代高纯V的可行性,确定以高V含量和中V含量的Ti-V-Fe系BCC储氢合金为研究对象,采用XRD、SEM、EDS、AES、TG/DSC等材料分析方法以及吸放氢性能测试手段,比较系统地研究了多元合金化和热处理改性对Ti-V-Fe系储氢合金的微观结构和储氢性能的影响规律；同时,探究了影响该类合金活化的主要因素并提出相应的活化机理,为进一步改善此类合金的综合储氢性能提供重要依据。本文首先研究了Fe部分替代V对Ti10V90-xFex(x=3-9)系合金微观结构和储氢性能的影响。结果表明,该系列合金均由单一的BCC固溶体相(体心立方结构,空间群为Im3m)组成,晶胞体积随着x的增加而减小。随着Fe含量的增加,合金的活化性能变差,室温吸氢容量逐渐降低。在x≤6时,合金的放氢动力学随着x的增加得到明显改善。随着Fe含量的增加,合金的333 K放氢平台压力先增后减,在x=7时达到最大值0.65 MPa；333 K的有效放氢容量亦先增后减,在x=6时达到最大值2.36wt.%。在所研究的合金中,Ti10V84Fe6合金具有较佳的综合储氢性能。为了改善合金的活化性能,采用Zr部分替代V,系统地研究了Ti10V84-xFe6Zrx(x=1-8)系合金的微观结构和储氢性能。结果表明,当x=l时,合金基本由单一的BCC固溶体相组成；而当x≥2时,合金均由BCC主相和C14相Laves第二相(六方结构,空间群为P63/mmc)组成,且第二相含量随着Zr含量的增加而明显增多。Zr部分替代V后,合金的活化性能得到显著改善；随着Zr含量的增加,合金的放氢平台压逐渐降低,吸放氢容量逐渐减小。研究表明,Zr部分替代V可有效减弱p单氢化物相的稳定性,降低其放氢温度,但过量Zr会引起合金吸氢容量明显下降。为了探究此类含Zr的钒基双相储氢合金的活化机理,作者选择活化性能最佳的Ti10V76Fe6Zr8合金作为研究对象,根据该合金中所含两相(BCC相和C14相)的相成分分别炼制了两个合金样品。XRD分析表明,两个样品均为单相合金。AES深度分析表明,BCC相合金的表面氧化膜的厚度远高于C14相合金。作者进一步分析提出了钒基双相合金的微区活化模型,即在室温抽真空的温和预处理条件下,由于合金表面氧化膜没有破坏,氢穿透C14相表面氧化膜的几率以及C14相吸氢后产生微裂纹和新鲜表面的能力远远高于BCC相,所以C14相含量越低的钒基合金需要的活化孕育时间越长；在高温抽真空的激烈预处理条件下,由于合金表面氧化膜已被破坏消除,氢气与合金的新鲜表面直接接触,故合金的活化变得比较容易。为了提高合金的放氢平台压力,从而提高有效放氢容量,本文进一步研究了Cr部分替代V对Ti10V80-xCrxFe6Zr4(x=0-14)系合金微观结构和储氢性能的影响。结果表明,所有合金均由BCC主相和少量的C14型Laves第二相组成,两相的晶胞体积均随着Cr含量的增加而逐渐减小。该系列合金在室温下首次吸氢就能活化；吸氢容量随Cr含量的增加而递减,尤其当x≥10时,吸氢量递减幅度较大。随着Cr含量的增加,合金的放氢速率明显增大,333 K放氢P-C-T平台压力逐渐增加,平台斜率因子减小；有效放氢容量则先增后减,在x=6时达到最大值1.50wt.%。添加过量的Cr含量会导致高温放氢峰值温度增加。在上述研究基础上,本文优化设计了成分为Ti10V77Cr6Fe6Zr的合金,研究了两种热处理工艺(1373 K下保温8h淬冷、1523 K下保温5 min淬冷)对合金微观结构的影响和对合金吸放氢平台特性的改善作用。结果表明,热处理前后合金均由BCC主相和C14型Laves第二相组成；热处理后合金中第二相含量有所减少,且呈点状弥散分布。热处理使得合金的吸氢容量有所下降,但明显改善了合金放氢平台的平坦度。其中,经1523 K保温5 min淬冷的合金具有较好的综合储氢性能,其333 K放氢平台压力为0.75 MPa,放氢平台斜率因子仅为0.1,有效放氢容量为1.82wt.%。为了考察Mn元素对合金吸放氢平台特性的改善作用,本文采用Mn部分替代Ti10V83Fe6Zr合金中V的方法,系统地研究了Ti10V83-xFe 6ZrMnx(x=0-6)合金的微观结构和储氢性能。结果表明,无Mn合金(x=0)具有BCC单相组织,而含Mn合金(x=2-6)均由BCC主相和C14型Laves第二相组成,且主相晶胞体积随着Mn含量的增加而逐渐减小。该系列合金的吸氢动力学性能较好,其中含Mn合金无需氢化孕育期就能快速吸氢。Mn部分替代V后,合金的P-C-T放氢平台特性得到明显改善,放氢平台斜率因子逐渐减小；333 K的放氢平台压力先增后减,在x=4时达到最大值0.58 MPa。合金的室温吸氢容量和有效放氢容量随着x的增加而递减,尤其当x≥4时合金的吸放氢容量降幅较大。本文进一步选择具有较高储氢容量的中V合金Ti16Zr5Cr22V57Fe为研究对象,系统研究了Fe部分替代V对Ti16Zr5Cr22V57-xFex(x=2-8)系合金微观结构和储氢性能的影响。结果表明,所有合金均由BCC主相和少量的C14型Laves第二相组成,且主相晶胞体积随着x的增加而递减。该系列合金都具有较好的活化性能,室温下首次吸氢即能活化。随着Fe含量的增加,合金样品的放氢平台压逐渐升高,但吸氢容量和有效放氢容量逐渐减小。适量的Fe替代V可以有效降低β氢化物相的热稳定性。对其中综合性能较好的Ti16Zr5Cr22V55Fe2合金的热处理(1553 K保温5min淬冷)改性研究表明,热处理后合金的两相结构基本没变,但主相晶胞体积增大,且主相晶粒长大。热处理后合金的活化孕育期缩短,吸氢容量和有效放氢容量得到提高。热处理降低了合金的P-C-T放氢平台压力和平台斜率因子,特别是放氢平台的平坦度有了明显改善。本文采用Mn部分替代Ti16Cr22Zr5V55Fe2合金中V的方法,进一步研究了Ti16Cr22Zr5V55-xFe2Mnx(x=0-3)合金的微观结构和储氢性能。结果表明,所有合金均由BCC主相和C14型Laves第二相组成,且主相晶胞体积随着x的增加而逐渐减小。该系列合金的活化性能优良,但室温吸氢容量则随着x的增加而明显下降。该系列合金的室温放氢容量普遍较低,且随着Mn含量的增加而逐渐减少。随着Mn含量的增加,合金的298 K放氢平台压力显著增高,平台宽度缩短,平台斜率明显减小,平台的平坦度得到改善。更多还原

【Abstract】 In this thesis, based on an overall review of the research and development of V-based solid solution hydrogen storage alloys with body-centered cubic (BCC) structure, Ti-V-Fe based hydrogen storage alloys with high and medium V content were developed and studied for the purpose of lowering cost and improving the overall hydrogen storage properties. By means of XRD, SEM, EDS, AES, TG/DSC analysis and hydriding/dehydriding characteristic measurements, the effects of multi-component alloying and heat treatment modification on the microstructures and hydrogen storage properties of the studied Ti-V-Fe-based alloys were investigated systematically. Moreover, the activation mechanism of this series alloys was also discussed and deduced.The effects of Fe content on the microstructures and hydrogen storage properties of Ti10V90-xFer(x=3-9) alloys have been investigated. The results show that all alloys have a single solid solution phase with BCC structure (Space group:Im3m), and the increase of Fe content leads to a decrease of the lattice parameter and unit cell volume. It is found that with the increase of Fe content in the alloy, the activation behavior deteriorated and hydrogen absorption capacity at room temperature decreased. In the range of x<6, the hydriding kinetics is noticeably improved with increasing x. As the Fe content increases, the P-C-T desorption plateau pressure at 333 K increases first and then decrease, reaching its maximum value of 0.65 MPa at x=7; And the hydrogen desorption capacities at 333 K against 0.1 MPa also increase first and then decrease, reaching their maximum values of 2.36 wt.%at x=6. In the studied alloys, Ti10V84Fe6 has a better overall hydrogen storage performance.In order to improve the activation behavior, by the partial substitution of Zr for V, the microstructure and hydrogen storage properties of Ti10V84Fe6Zrx (x=1-8) alloys have been investigated. The results show that the alloy with x=l still has a single solid solution phase with BCC structure, while the alloys with x=2-8 consist of a main phase with BCC structure and a secondary phase with C14 type Laves structure (Space group: P63/mmc)and the abundance ratio of the secondary phase increases with increasing Zr content. As the Zr content in the alloys increases, the activation behavior is markedly improved, but the hydrogen absorption and desorption capacities decrease gradually. The partial substitution of Zr for V can distinctly lower the stability ofβmono-hydride phase and decrease its dehydrogenation temperature. However, excessive Zr leads to a notable decrease of hydrogen absorption capacity.To explore the activation mechanism of this series Zr-contained alloys with a dual-phase, Ti10V76Fe6Zr8 alloy with excellent activation behavior was chosen as the research object. Based on the chemical components of the BCC phase and C14 phase in Ti10V76Fe6Zr8 alloy, the BCC alloy of Ti7.7V87.5Fe4.8 and C14 alloy of Ti10.2V42.4Fe11 6Zr35.8 were prepared respectively. The XRD analysis shows that above two alloys are both single phase alloys. The AES analysis shows that the thickness of the surface oxide film of BCC alloy is much bigger than that of C14 alloy. The micro-area activation model of the V-based alloy with dual-phase structure is put forward, namely:after evacuation at room temperature, due to the non-destruction of surface oxide film on the alloy, the possibility of the penetration of hydrogen through the surface oxide film of C14 phase and the occurring probability of micro-cracks and fresh surface by the hydrogenation are much higher than that of BCC phase. Hence, the less C14 phase the alloy contains, the longer incubation time the activation needs. After evacuation at high-temperature, the refresh surface can contact with hydrogen directly and the activation becomes much easier owing to the partial or entire demolishment of the surface oxide film on the alloy.Aiming at the improvement of hydrogen desorption plateau pressure and effective hydrogen capacity mainly, the partial substitution of Cr for V in Ti10V8o-xFe6Zr4Crx (x=0, 6,10 and 14) alloys is employed. It is found that all alloys consist of a main phase with BCC structure and a secondary phase with C14 type Laves structure. The Cr addition leads to a contraction of the unit cells of both phases. These alloys have good activation behavior. As the Cr content increases, the hydrogen absorption capacity decreases, especially for the alloys with x>10, while the hydrogen desorption capacity increases first and then decreases, reaching the highest value of 1.50 wt.%at x=6. With increasing the Cr content, the dehydriding rate and the hydrogen desorption plateau pressure at 333K are remarkably enhanced, moreover the slope factor of the plateau is reduced. The excessive Cr addition would result in the increase of peak temperature for the dehydrogenation ofβphase.Based on the optimally prepared Ti10V77Cr6Fe6Zr, the effects of heat treatment (1373 K for 8 h,1523 K for 5 min) on the microstructures and hydrogen storage properties were investigated systematically. The results show that all alloys consist of a BCC main phase and a secondary C14 Laves phase. After heat treatments, the content of C14 Laves phase decreases and the hydrogen absorption capacity decreases, while the hydrogen desorption plateau is flattened distinctly. The sample treated at 1523 K for 5 min and followed by quenching in cold water has the best overall hydrogen storage properties, with the dehydrogenation plateau pressure of 0.75 MPa at 333 K, plateau sloping factor of 0.1, and the effective hydrogen desorption capacity of 1.82 wt.%.Mn element has been introduced into Ti10V83Fe6Zr alloy for its positive effect of flattening the dehydrogenation plateau, the microstructure and hydrogen storage properties of Ti10V83-Fe6ZrMnx (x=0-6) alloys have been investigated. It is found that the Mn-free alloy with x=0 has a single solid solution phase with BCC structure, while other alloys with x=2-6 consist of a BCC main phase and a small fraction of C14 type Laves secondary phase. The cell volume of the BCC main phase decreases with the increase of x. All of these alloys have good activation behaviors and hydriding kinetics. With increasing the Mn content in the alloys, the plateau pressure at 333 K increases first and then drops, reaching the maximum value of 0.58 MPa atx=4, and the hydrogen desorption plateau is remarkably flattened, showing slope factor of 0.09 at x=6. However, the maximum hydrogen absorption capacity at 298 K and the effective hydrogen desorption capacity at 333 K decrease gradually with the increase of the Mn content, especially for the alloys with x> 4.In order to further lowering the cost of V-based hydrogen storage alloys, the microstructure and hydrogen storage properties of Ti16Zr5Cr22V57-xFex (x=2-8) alloys with medium V content have been investigated systematically. The results show that all alloys are composed of a main phase with BCC structure and a secondary phase with C14 type Laves structure. By addition of Fe, the unit cell of the BCC main phase decreases. All of the studied alloys have good activation behavior and hydriding/dehydriding kinetics. As the Fe content increases, the hydrogen desorption plateau pressure of the alloy increases gradually, however, the hydrogen absorption and effective desorption capacities decrease. The appropriate Fe addition can also decrease the decomposition enthalpy ofβphase. The effect of heat treatment (1553 K for 5 min) on the microstructure and hydrogen storage properties of Ti16Zr5Cr22V55Fe2 alloy has been systematically studied. The results show that after heat treatment, the two-phase structure of sample has not changed, however, the lattice parameter of BCC main phase is increased and its grain grows. Compared to the as-cast alloy, the heat treated alloy has shorter activation incubation time and higher hydrogen absorption/desorption capacities. The hydrogen desorption plateau pressure is reduced and the plateau is remarkably flattened by the heat treatment.The influence of partial substitution of Mn for V on the microstructure and hydrogen storage properties of Ti16Cr22Zr5V55-xFe2Mnx(x=0-3) has been systematically investigated. The results show that all alloys are composed of a BCC main phase and a C14 Laves secondary phase. With increasing Mn content, the lattice parameter of BCC main phase decreases gradually. This series alloys have good activation behavior, however, the hydrogen absorption/desorption capacities decrease with increasing Mn content. By Mn addition, desorption plateau pressure is increased and the plateau width is decreased. Furthermore, the flatness of the plateau is noticeably improved.更多还原