含亚稳相的Ti-Al-Mo-V-Cr体系晶体结构和热力学性质研究

A quantitative description of microstructure evolution in materials is the core of materials design. However, the quantitative description of microstructure evolution for many multicomponent alloy systems is limited due to the lack of thermodynamic data of stable and metastable phases. The present proposal intends to choose the new high strength Ti-Al-Mo-V-Cr system as the target, to make substantial progress in obtaining the thermodynamic data of stable and metastable phases. (1) Adopting the experiment-simulation complementary method, preparing key experiments and obtaining phase equilibria and thermodynamic data for key ternary and quaternary systems via X-ray diffraction (XRD), scanning electron microscope (SEM), electron probe microanalysis (EPMA) and differential thermal analysis (DTA) methods; (2) Development of the crystal structure of metastable phase via an integration of first-principles calculation, XRD and transmission electron microscope (TEM); (3) Obtaining the thermodynamic properties of the metastable phase at high temperature based on the calculation of its crystal formation energy at 0K by using first-principles calculation and the calculation of the contribution of lattice vibration and electronic activation to the free energy by using statistical physics method; (4) Obtaining an optimal set of thermodynamic parameters of the stable and metastable phases in the Ti-Al-Mo-V-Cr system by means of CALPHAD method combined with the measured data. It is highly expected that the completion of the project will provide key thermodynamic data for the quantitative description of microstructure evolution and enlarge the application of the CALPAHD approach.

材料微观结构演变的定量描述是材料设计的核心。许多多元合金因缺少含亚稳相的热力学数据而使微观结构演变的定量描述受到很大限制。项目拟选择新型高强Ti-Al-Mo-V-Cr体系为研究对象，在获得含亚稳相热力学数据方面取得实质性进展：(1) 采用实验-模拟互补法，制备关键合金，借助X射线衍射、扫描电镜、电子探针和差热分析等手段获得关键三元、四元系的相平衡及热力学数据；(2) 借助第一性原理计算、X射线衍射和透射电子显微镜来确定亚稳相的晶体结构；(3) 用第一性原理计算亚稳相绝对零度时的晶体形成能，结合统计物理方法计算晶格振动、电子激活对自由能的贡献，获得亚稳相有限温度的热力学性质；(4) 结合实测数据和相图计算方法获得一套合理描述Ti-Al-Mo-V-Cr体系稳定相与亚稳相之间相关系的热力学参数。研究工作的完成可望为多元钛合金体系的微观结构演变模拟提供关键的热力学数据并扩大相图计算的应用领域。

针对Ti合金缺少稳定相和亚稳相的热力学数据及获得亚稳相晶体结构和高温热力学性质科学方法的研究现状，采用实验-模拟互补法，耦合关键实验、第一性原理计算和相图计算开展了如下研究工作：（1）基于文献报道的Ti-Al-Mo-V-Cr五元系中边际二元系的热力学参数和边际三元系的实验相平衡数据，优化计算了Ti-Mo-V，Ti-Mo-Cr，Ti-V-Cr和Al-Mo-V体系，修订了Ti-Al-Cr体系的热力参数；（2）通过配置关键合金，采用XRD、SEM、EPMA等研究了Ti-Al-Mo-V，Ti-Al-Mo-Cr和Ti-Al-V-Cr四元系20 at.% Al 700和800 oC 富Ti角的等温截面；（3）基于边际三元系的热力学参数和实验相平衡数据，优化计算了Ti-Al-Mo-V，Ti-Al-Mo-Cr，Ti-Al-V-Cr和Ti-Mo-V-Cr四元系，外推计算了Al-Mo-V-Cr体系，建立了Ti-Al-Mo-V-Cr五元系热力学数据库，利用该数据库计算了商用Ti-5553 (Ti-5Al-5Mo-5V-3Cr，质量百分数)和B120VCA (Ti-13V-11Cr-3Mo，质量百分数)合金在平衡和希尔非平衡条件下的凝固行为；（4）借助于第一性原理计算了亚稳相ω与β自由能差 Gm(ω)–Gm(β)，研究了亚稳相ω的晶体结构并对其进行了热力学建模，结合文献报道的β-αʹ/αʺ马氏体转变温度和ω形成温度，采用CALPHAD方法优化计算了Ti-M (M = Mo, V, Nb, Cr, Al)体系的T0(β/α) 和T0(β/ω)曲线和亚稳相图；（5）在完成以上研究工作之外，申请者还对Ti-RE (RE= Ce, Er, Tm, Y)、Ti-M (M = Li, Na, K)、Ni-Si-Ti、Ti-W-M (M = B, Si, Zr, Mo, Nb)、Ti-V-M (M = Nb, Ta, Si)等多个二元和三元系进行了热力学研究。以上研究工作的完成为多元多相钛合金体系的微观结构演变模拟提供关键的热力学数据并扩大相图计算的应用领域。在国内外刊物上发表本项目资助号论文12篇（其中SCI收录论文10篇），7人次参加国内外会议，培养硕士研究生4名，圆满完成了计划书的预期成果考核指标要求。