Cu-Ni-Sn三元系相平衡的热力学计算

基于Cu-Ni-Sn三元系的相平衡和热力学的实验信息,采用亚正规溶体模型描述液相和fcc相的Gibbs自由能,为了预测该体系中bcc相的A2 B2有序无序转变,bcc相的Gibbs自由能采用双亚点阵模型进行描述。利用CALPHAD(相图计算)方法评估了Cu-Ni-Sn三元系各相的热力学参数,计算的富Cu侧相图和热力学性质与实验数据比较一致。并对该三元系中bcc相的A2 B2有序无序转变及fcc相的溶解度间隙进行了计算。这些计算结果对利用析出强化以及Spinodal分解开发高强度和高导电性的新型Cu基合金的组织设计具有一定的指导意义。

Zr-X(X=Li,Na,K,Sc,Hf)体系的二元相图理论研究

采用相图计算(CALPHAD:Calculation of phase diagrams)方法对Zr-X(X=Li,Na,K,Sc,Hf)5个二元体系进行了相图热力学研究.基于实验数据,通过热力学优化计算获得了一套描述液相及(αZr),(βZr),(Li),(Na),(K),(αSc),(βSc),(αHf)和(βHf)相的热力学参数.Zr-Li,Zr-Na和Zr-K体系中的气相视为理想气体.与实验相图数据对比发现,本文获得的热力学参数能够准确地描述实验相平衡数据.

基于Ti-Nb-Zr三元系合金的相图优化

利用Pandat软件优化和计算了Ti-Nb-Zr三元系相图。采用SGTE(scientific group thermodata Europe)数据库中的表达式描述纯组元的吉布斯能,选取置换溶体模型和双亚点阵模型来描述液相和固溶体相。利用Pandat软件的PanOptimizer模块并结合文献中相平衡和热力学性质的实验数据,重新评估了Ti-Nb和Ti-Zr二元系的热力学参数以改善Ti-Nb-Zr三元系的热力学描述。利用优化得到的热力学参数进行相平衡和热力学性质的计算,计算结果与文献实验结果吻合较好,该结果对Ti-Nb-Zr三元系生物医学材料的开发有重要的指导意义。

基于CALPHAD的高温高压相图建模

高温高压相图在物理化学、矿物学、地球科学和极端条件下的材料科学中都具有重要的地位和应用价值,相图计算方法(alculation of phase diagram,CALPHAD)是建立温度-压强热力学相图和热力学数据库的主要方法,可以计算材料体系的相平衡、组成相的相分数和相成分、热力学性质,一定程度上解决单一实验建立高温高压相图的困难。本文对基于CALPHAD的高温高压相图建模方法进行了详细介绍,并总结其当前面临的问题和下一步研究方向,为极端条件下材料设计和性能评估奠定基础。

V掺杂对CoCrFeNiV_(x)高熵合金相结构的影响

采用相图计算方法(CALPHAD),应用热力学计算模型对高熵合金CoCrFeNiV_(x)(x=0.0~1.0)的相图进行模拟,并用分子动力学方法对V掺杂的高熵合金CoCrFeNiV_(0.2)的强度和温度的关系以及变形机制进行研究.结果发现,未掺V时,室温下体系有4种相,分别为BCC-A2、BCC-A2#2、FCC-A1和SIGMA相,SIGMA相含量最高,随着温度升高到550 K,BCC-A2和BCC-A2#2相消失,FCC-A1成分下降,SIGMA相成分达到极大值.当V含量为0.2时,室温下体系有3种相,分别为BCC-A2、FCC-A1和BCC-A2#2相,随着温度升高到600 K,BCC-A2和BCC-A2#2相含量减少,FCC-A1相增加,同时SIGMA相出现.在600~620 K区间发生BCC-A+BCC-A2#2→SIGMA转变,并在990 K时,SIGMA相完全消失.当V含量为0.4~1.0时,600~800 K区间SIGMA相含量均高于V含量为0.2时的相图.因此,V元素的掺入有助于抑制高熵合金CoCrFeNiV_(x)脆性SIGMA相出现.此外,通过分子动力学模拟发现,高熵合金CoCrFeNiV_(0.2)的变形机制主要为晶粒旋转、晶内层错以及非晶化.

Thermodynamic modeling of ZrO_(2)−CaO−TiO_(2)system

The phase diagram of ZrO_(2)−CaO−TiO_(2)system was essential for the development of photocatalytic materials and refractory materials.In this work,the ZrO_(2)−CaO−TiO_(2)system was accessed by using the CALPHAD method.The substitutional solution models were used to describe liquid and solid solution phases,the sub-lattice models were used to describe ternary compounds,and then the thermodynamic parameters were obtained by the least square method combined with literature experiment results.The acquired thermodynamic parameters were used to calculate the isothermal sections of the ZrO_(2)−CaO−TiO_(2)system at 1473 and 1673 K.There existed a good agreement between experimental and predicted phase relationships,the experimental points which were inconsistent with calculated results may be attributed to experimental errors and the sluggish kinetics of cations for ZrO_(2)-based materials.In order to further verify the validity of the database,the thermodynamic parameters were also used to simulate the thermodynamic properties(specific heat capacity,enthalpy,and entropy)of CaZrTi_(2)O_(7) within 5%errors.Good consistency demonstrated that the present thermodynamic database was self-consistent and credible.

First-principles lattice stability of Fe, Ru and Os

Lattice constants, total energies and densities of states of transition metals Fe, Ru and Os with BCC, FCC and HCP structures were calculated by the GGA+PBE functional and the ultrasoft pseudo-potential plane wave method, and compared with those of the first-principles projector augmented wave (PAW) method, CALPHAD method and experimental data. The results show that the lattice stability of this work is △GBCC-HCP>△GFCC-HCP>0, agreeing well with those of PAW method in the first-principles and CALPHAD method except for BCC-Fe. And the densities of state of HCP-Ru and Os have an obvious character of stable phase, agreeing completely with the results of the total energy calculations. Further analyses of atomic population show that the transition rate of electrons from s to p state for HCP, FCC and BCC crystals increases from Fe to Os, and a stronger cohesion, a higher cohesive energy or a more stable lattice between atoms of heavier metals are formed.

关于材料基因组的基本观点及展望

通过几个相关的研究项目,展示了作者关于材料基因组(Materials Genome)的基本观点.目前多组元材料的热力学和动力学数据库包含有单个相的吉布斯自由能函数和原子迁移率,它们是温度、成分以及压力(某些情况下)的函数.这种数据库的构建方式是把基于不同晶体结构的单个相作为材料的基因组(组成模块).作者认为,如果单个相其内在的特定构型,比如磁自旋构型和铁电极化,随着温度、应力和磁场、电场而显著改变,那么这些具体的构型反而应该被看做是单个相的基因组.一个特定相的"变异"是受这个相稳定和亚稳组态之间的混合熵,即"结构组态熵"(structural configurational entropy,SCE)所控制的.这种不同组态之间的混合也是导致单个相异常行为的内在原因.通过改变材料成分来控制不同单个组态的性质的能力是实现材料设计的关键所在.