含钛κ相的热力学建模及稳定性研究

The nano-sized κ phase can precipitate dispersively by spinodal decomposition, which improves the mechanical properties of the Fe-Al-Mn-C alloys remarkably. The present project introduces Ti element to the κ phase and studies the influence of Ti element and temperature on the precipitation behavior of the κ phase, so as to control the phase stability and spinodal microstructure rationally. Firstly, the effect of alloy elements and temperature on the atomic occupancy of the κ phase is studied by combining the experimental investigation and first principle calculations. By using the partitioning model, the κ phase is thermodynamically modelled to describe the ordering between metal atoms. The three-dimensional atom probe tomography is employed to accurately measure the carbon content in standard samples. Combining with the sensitivity curve method, the phase equilibria of the multicomponent alloys are measured. Then the thermodynamic modelling of the critical sub-systems is performed and the thermodynamic database of the Fe-Al-Mn-C-Ti quinary system is established to reproduce the phase relations over the wide composition and temperature ranges. Based on the thermodynamic database, the alloy composition and aging temperature are selected to control the phase stability of the κ phase. The spinodal decomposition of the κ phase is finally promoted to obtain the novel lightweight materials with excellent properties.

κ相通过调幅分解可实现纳米级弥散析出，对Fe-Al-Mn-C合金力学性能具有显著的提升作用。本项目将钛元素引入到κ相，研究钛元素和温度对κ相析出行为的影响规律，以实现控制其稳定性，获得调幅分解组织的理论设计。首先结合实验测定和第一性原理计算方法，探究合金元素和温度对κ相原子占位的影响，采用有序无序模型对κ相结构进行热力学建模；采用三维原子探针技术实现标准样品中碳含量的准确测定，结合灵敏度曲线法，获得多元合金的相平衡数据；然后，对关键子体系进行热力学建模优化，建立可准确描述Fe-Al-Mn-C-Ti五元系宽广成分和温度范围的热力学数据库；在自建数据库基础上，优选合金成分和时效温度，合理控制κ相稳定性，促进κ相调幅分解弥散析出，以获得性能优异的新型轻量化材料。

Fe-Al-Mn-C合金是性能优异且低密度的结构金属材料，在汽车领域具有巨大的应用潜力。合金中κ相作为强化相，通过调幅分解实现弥散析出，对力学性能具有显著的提升作用。然而，κ相在含钛轻质合金中的稳定性仍然不够清晰。本项目通过对含钛多元轻质合金关键体系进行热力学建模优化，建立可靠的相稳定性描述，并通过热力学计算分析，调控调幅分解组织，以获得具有优异力学性能的含钛轻质合金。主要研究内容包括：建立可反映κ相晶体结构和溶解度范围的热力学模型；发展微区碳含量的定量测试方法；构建Fe-Al-Mn-C四元系低温平衡相关系；建立含钛多元轻质合金关键体系的热力学模型描述；通过热力学计算，设计调控可实现κ相调幅分解的合金成分及工艺，获得理想力学性能。通过对上述内容的研究，取得的创新性成果如下：（1）建立了κ相的有序无序模型，即有序态为(M,Al)0.75(M,Al)0.25(C,Va)0.25，无序态为(M,Al)1(C,Va)0.25；（2）采用三维原子探针和电子探针，建立了微区碳测定的C-K校正曲线，从而实现微区碳含量的定量测定；（3）首次构建Fe-Al-Mn-C四元系低温相平衡关系；（4）开发了可描述宽广成分和温度范围的含钛多元轻质合金热力学数据库；（5）设计开发出具有κ相调幅分解组织的含钛轻质合金，抗拉强度和断后伸长率分别达到775MPa和40.96%，强塑积达到31744MPa∙%。