Ti合金化Mg2Ni氢化物能量和电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法,计算Ti掺杂Mg2Ni储氢合金及其氢化物的能量和电子结构。计算结果表明:在掺杂浓度为0≤x≤0.5的情况下,Ti优先占据Mg(II)位,Ti的掺杂使Mg2Ni合金稳定性降低,且随着掺杂浓度的升高,对稳定性的削弱效果逐渐增强。六方结构的固溶体合金Mg(2-x)TixNi(0≤x≤0.5)相对于立方结构的Mg3TiNi2化合物呈现热力学不稳定性,极易分解为Mg3TiNi2和Mg2Ni组成的复合相。Ti的掺杂使低能级区域的成键电子数减少,削弱了H-Ni的成键作用,提高了Mg2Ni氢化物的解氢能力。     

Mg3MNi2（M=Ti，Al）的晶体结构

Al和Ti对Mg2Ni结构中部分Mg的取代,得到与Mg2Ni晶体结构不同的新型合金．多晶X射线结构分析表明,其化学式为Mg3MNi2(M=Ti,Al),立方晶系,空间群Fd3m,Z=16,48个Mg坐落在48(y),16个M(M=Al,Ti)坐落在16(d)位,32个Ni坐落在32(e)位,Mg3AlNi2的晶胞参数a=1．15474(2)nm,Mg3TiNi2的a=1．16178(2)nm．与Mg2Ni相比,Mg3MNi2合金的晶体密度更大,Mg-Ni键长更长,吸放氢温度降低,循环寿命延长．     

钛合金化对Mg_2Ni储氢性能的影响

采用第一性原理方法研究了钛合金化对Mg_2Ni及其氢化物储氢性能的影响。计算结果表明,在掺杂浓度为0~0.5的范围内,Ti优先占据Mg(6i)位,六方结构的固溶体合金Mg_((2-x))TixNi极易分解为立方结构的Mg3TiNi2和六方结构的Mg_2Ni组成的复合相。Ti的掺杂削弱了H原子和Ni原子间的相互作用,降低了其合金体系的吸氢反应焓,提高了Mg2Ni氢化物的解氢能力。     

Mg1.7M0.3(M＝Mg,Ti,Al)Ni贮氢合金结构及性能研究

采用固态烧结法制备了Mg1 7M0 3(M =Mg、Ti、Al)Ni贮氢合金 ,X射线衍射分析结果表明 ,适当提高烧结温度有利于Mg2 Ni相的形成 ;Ti对Mg的取代未引起合金相结构的明显变化 ,而Al取代Mg除有Mg2 Ni相外 ,还有一呈立方晶体结构的新相生成。Ti、Al对Mg的取代 ,不仅提高了Mg2 Ni合金的放电容量 ,同时也提高了合金的循环寿命。     

Mgl．7M0．3（M＝Mg，Ti，Al）Ni贮氢合金结构及性能研究

采用固态烧结法制备了Mg1．7M0．3(M＝Mg、Ti、A1)Ni贮氢合金，X射线衍射分析结果表明，适当提高烧结温度有利于Mg2Ni相的形成；Ti对Mg的取代未引起合金相结构的明显变化，而A1取代Mg除有Mg2Ni相外，还有一呈立方晶体结构的新相生成。Ti、A1对Mg的取代，不仅提高了Mg2Ni合金的放电容量，同时也提高了合金的循环寿命。     

Mg(2-x)AlxNi的燃烧合成及其电极性能

采用燃烧合成法合成了三元镁基储氢合金Mg2-xAlxNi(x=0.1~0.5),XRD衍射研究表明合成产物中出现了具有Ti2Ni型立方结构的新相,SEM结果显示合金表面存在大量缺陷.Al元素部分替代Mg对Mg2Ni电化学性能影响的研究表明:Mg2-xAlxNi合金的电化学容量和循环寿命明显优于无Al的Mg2Ni,这归因于新相Mg3AlNi2的结构特点及形成的Al2O3保护层.此外,对合成产物的进一步的机械研磨有助于改进合金的活化行为及电极容量,但无助于循环能力的提高.     

Ti-V基固溶体/La-Mg基合金复合储氢材料的结构与电化学性能

两步电弧熔炼法制备Ti0.10Zr0.15V0.35Cr0.10Ni0.30+1%La0.85Mg0.25Ni4.5Co0.35Al0.15复合储氢合金,XRD、SEM、EDS分析结果表明,复合储氢合金的主相是体心立方结构的钒基固溶体相和六方结构的C14Laves相。电化学研究表明:复合过程中存在明显的协同效应;与母体合金电极相比,复合合金电极的P-C-T特性、活化性能、最大放电容量、循环稳定性、低温放电能力和高倍率放电性能均有了显著改善;复合合金电极的电荷转移电阻较小,交换电流密度和氢的扩散系数较大,这些改善可能与第二相的形成有关。     

Ti3Al基合金(0001)α2∥(110)β界面价电子结构分析

基于固体与分子经验电子理论,以改进的TFD理论提出的电子密度连续的量子力学条件为判据,计算了Ti3Al基合金中(0001)a∥(110)β界面的价电子结构.对比分析了单相Ti3Al基合金(0001)a2-Ti3Al∥(0001)a2-(TiMy)Al界面与多相Ti3Al基合金(0001)a2-Ti3Al∥(110)β-Ti0.5xAl0.5M0.5y,(0001)a2-(TixMy)Al∥(110)β-Ti0.5xAl0.5M0.5y界面电子结构.从电子结构层次上初步解释了延性β相改善合金薄弱的相界面电子结构与键结合,增加界面稳定性与连续性,提高合金强韧性的微观本质.     

Ti3B4表面修饰对Mg45Ti3V2Ni50合金电极循环稳定性的影响

用机械合金化法合成不同组成的Ti-B系列的复合物与Mg45Ti3V2Ni50储氢合金.探索Ti、B复合修饰对Mg45Ti3V2Ni50合金循环稳定性的影响,筛选出对Mg45Ti3V2Ni50合金电极综合修饰效果较好的Ti3B4.将Ti3B4以不同质量比对Mg45Ti3V2Ni50合金电极球磨修饰.结果表明:不同比例的修饰,对储氢合金电极循环稳定性的提高程度不同,持久性不同,Ti与B复合修饰提高镁基储氢合金的循环寿命存在一个最佳组成和最佳比例.     

快速凝固制备La0.83Mg0.17Ni3.25Al0.15Mn0.1储氢合金的相结构和电化学性能

采用感应熔铸+退火处理(常规冷速)及快速凝固方法制备了La0.83Mg0.17Ni3.25Al0.15Mn0.1储氢合金.系统研究了快速凝固对合金的相结构、微观组织及电化学性能的影响.X射线衍射分析表明,冷却速率对合金的相组成影响不大,但对各相丰度影响明显.随着冷却速率的增加,合金中的LaNi5相(CaCu5型结构)丰度增加,LaNi3相(PuNi3型结构)丰度减少.EPMA分析表明,快速凝固方法制备的La0.83Mg0.17Ni3.25Al0.15Mn0.1储氢合金为扁平状晶粒组织.合金电极的电化学测试表明,冷却速率对合金的活化性能影响不大.随冷速的增加,合金的最大放电容量减小,合金电极的循环稳定性改善明显,铜辊线速度为15 m/s时容量保持率达到97.03%.     

Synthesis and grain growth kinetics of in-situ FeAl matrix nanocomposites（ Ⅰ ）： Mechanical alloying of Fe-A1-Ti-B composite powder

Three nanocrystalline alloys, FesoAlso, Fe42.5Al42.5Ti5B10 and Fe35Al35Ti10B20 （molar fraction, %）, were synthesized from elemental powders by high-energy ball milling. The structural evolutions and morphological changes of the milled powders were characterized by X-ray diffractometry（XRD）, transmission electron microscopy（TEM） and scanning electron microscopy（SEM）. The effects of different Ti, B additions on the structure and phase transformation in these alloys were also discussed. It is observed that the diffusion of AI, Ti, B atoms into Fe lattice occurs during milling, leading to the formation of a BCC phase identified as Fe（Al） or Fe（Al, Ti, B） supersaturated solid solution. Fe-based solid solution with nanocrystalline structure is observed to be present as the only phase in all the alloy compositions after milling. Furthermore, the contents of Ti, B affect the formation of mechanical alloying products, changes in the lattice parameter as well as the grain size.     

MICROSTRUCTURE AND COMPRESSIVE PROPERTIES OFTi_(50)Al_(48)Mn_2 AND Ti_(50)Al_(48)Cr_2

The microstructure and compressive properties of Ti_(500Al_(48)Mn_2and Ti_(50)Al_(48)Cr_2 alloys are studied in this paper Existence of αx y transforntation in TiAl alloys is confirnted by metallographic examincttion,the transformation temperatuses of Ti_(50)Al_(48)Mn_2 and Ti_(500Al_(48)Cr_2,are 1375and 1373C respeclively,After treating withic x y phase field,themicrostructure of alloys consists of lamellar zones(L)and bulk y_p.,The vohme ratio of L/y_p inctrases with increasing solution treatnient temperature.The third alloying ele-ments of Mn and Cr distribute perfentially over αphase at solution treatment tempera-tures and result in that α_2 and γ lamellae become thicker.The yield strength of Ti_(50)Al_(48)Mn_2 and Ti_(500Al_(48)Cr_2 alloys decreases and the compressibllity increases with in-creasing γ_p volume fraction.     

Gd对Mg9AlZnY镁合金消失模组织和性能的影响

在Mg9AlZnY合金基础上添加不同含量Gd元素,采用消失模铸造成形,研究其组织性能变化。结果发现,随着Gd含量的增加,Mg9AlZnY合金中的β-Mg17Al12相形成数量显著减少,并由连续网状结构转变为断续状和颗粒状结构。含Gd的Mg9AlZnY合金组织主要由α-Mg固溶体、β-Mg17Al12相和分布在α-Mg晶界的少量棒状Al2Y相和块状Al2Gd相组成。Al2Y和Al2Gd相热稳定性好,在高温下对晶界具有钉扎作用,防止晶界滑移,提高了晶界的高温强度。当Gd含量在0.9%(质量分数)左右时,经T6热处理后室温的抗拉强度为235MPa,200℃高温抗拉强度为156MPa,分别比Mg9AlZnY合金提高了11.9%和28.9%。     

Effect of mischmetal and yttrium on microstructures and mechanical properties of Mg-Al alloy

The effect of yttrium and mischmetal(MMs)on the as-cast and solid solution treated structures of Mg-Al alloys with different Al-contents was investigated.The results show that the MMs in Mg-Al alloy existed in rod Al4(Ce,La)compound while Y in Mg-Al alloy in polygonal Al2Y compound.The amount of Mg17Al12 in Mg-Al alloy is decreased with increasing Y or MMs addition,and Mg17 Al12 intermetallic compound is changed from continuous network to discontinuous one.The Al4(Ce,La)and Al2Y compounds are not dissolved into Mg-Al alloy matrix during solid solution treatment so that their high heat stability can be exhibited.The experiment of mechanical properties indicate that elongation and impact toughness of the Mg-Al-Y alloy with polygonal Al2Y compound are higher than those of Mg-Al-MMs alloy with rod A4(Ce,La) compound.     

Tix(AlNbZr)100-x系多主元合金力学性能的第一性原理研究

通过对合金的固溶体参数以及相比例图进行计算,研究了Ti_x(AlNbZr)_100-x系多主元合金的固溶体相形成规律,运用基于密度泛函理论的第一性原理方法研究了Ti含量变化对Ti_x(AlNbZr)_100-x系多主元合金结构稳定性以及力学性能的影响。结果表明,Ti_x(AlNbZr)_100-x系多主元合金可以形成稳定的固溶体相,且合金主要由BCC相和Al₃Zr₅相组成,随Ti含量增加,合金的液相线降低,Al₃Zr₅相的相形成温度减小,直到Ti含量为60%~70%时,Al₃Zr₅相消失,合金由单一BCC相组成;Ti含量增加可以提高合金的结构稳定性,当Ti含量为25%~70%时,合金具有良好的力学稳定性,合金的体积模量、剪切模量以及杨氏模量随着Ti含量的增加呈上升趋势。Ti_x(AlNbZr)_100-x系多主元合金的基态能量和形成热随着Ti含量的增加而降低,表明增加Ti含量可以增加该合金系的热力学稳定性,使合金更易形成固溶体相。     

TAMZ合金在人工唾液中的电化学行为

运用电化学方法对工业纯Ti，Ti6Al4V合金和TAMZ合金在人工唾液中的电化学行为进行了研究，探讨了溶液pH值对Ti合金电化学性能的影响。结果表明，在人工唾液中，TAMZ合金具有最佳电化学稳定性，腐蚀速率最低。Ti合金在人工唾液中存在较大的钝化区间，电化学稳定性按工业纯Ti，Ti6Al4V合金和TAMZ合金的顺序依次增强。随溶液pH值升高，试样的热力学稳定性增强。交流阻抗结果显示，3种实验材料在人工唾液中具有优异的耐蚀性能，腐蚀速率均在10^-2μm／a数量级，小于医用级标准0．25μm／a。     

Mechanical properties of Al(Mg) solid solution prepared by solidification under high pressures

Mechanical properties of Al(Mg) solid solution with different Mg solubility prepared by solidification under high pressure were investigated in the present study. The results show that the tensile strength of solid solution increases first, and then decreases with increasing Mg solubility. Fractographic examination reveals that the fracture characteristic transforms from dimple-like fracture to combination of quasi-cleavage plus intergranular fracture with increasing Mg solubility. This trend is believed not only limited to Al(Mg) solid solution, but also to other solute-strengthened alloys.     

Formation of Al2Ca Phase in as-Extruded X20 Magnesium Alloy by Solution Treatment

对Ca含量为2wt%的挤压态X20镁合金在410 ℃固溶处理20 h,采用光学显微镜 (OM)、扫描电镜 (SEM) 结合能谱分析 (EDS)以及透射电镜 (TEM) 对固溶处理前后的组织进行了表征,利用XRD衍射仪考察了固溶处理前后合金的相组成。结果表明,经固溶处理后,合金初始组织中β-Mg17Al12相的数量明显减少,同时析出新相Al2Ca。Al2Ca的形成可归结于残余β-Mg17Al12中高的Ca原子所造成的Mg原子被Ca原子取代,同时Al2Ca相自身高的结构稳定性也是其在Mg-Ca和Al-Ca系竞争析出中胜出的原因。     

The solidification path related columnar-to-equiaxed transition in Ti–Al alloys

Columnar-to-Equiaxed Transition (CET) of binary Ti–Al alloys and multi-component Ti–48Al–2Cr–2Nb alloys is studied using Bridgman solidification technique. The effect of aluminum concentration and growth rate on CET is determined. It is found in Ti–46Al and Ti–50Al alloy ingots equiaxed grains develop ahead of the moving solid–liquid interface with a growth rate of 500 μm/s; microstructures in Ti–49Al alloy stay columnar dendrites with the same growth rate. CET in Ti–Al alloys are not only influenced by growth rate, but also by the solidification path that is related to alloying composition. CET in Ti–Al alloys is predicted using the dendritic growth model based on the criterion of growth at marginal stability. According to the calculated results and directionally solidified microstructures, values of the nucleation undercooling for α and β phases are given. The growth rates to avoid CET in Ti–48Al–2Cr–2Nb alloy are suggested.