Development of novel Ti-based alloys with improved thermal-mechanical capability

市售的高温钛基合金具有低密度、抗蠕变和抗疲劳的优点。然而，由于其有限的固有抗氧化性，这些材料只能使用到大约550°C的最高温度。在该项目中，将开发具有高达1000°C热性能的新型抗氧化钛基合金。这些新材料应表现出良好的平衡(1)室温延展性/变形性，(2)蠕变和抗氧化性，(3)低密度。抗氧化性将依赖于保护性cr - ta基氧化层的形成。在我们之前的研究中，确定了形成连续保护垢所需的Cr和Ta的最低浓度。在项目的第一步，将开发不同Mo/Ti比和单相无序bcc（A2）组织的韧性Ti基合金。适量的Ta、Mo、Cr和Ti稳定了bcc（A2）的晶体结构。在第二步中，这些延展性合金的强度将通过(i) A2基体的B2析出强化（模仿ni基合金的-’显微组织）或（ii）添加Y2O3分散体的氧化物分散强化来增强。最后，为了进一步改善合金的氧化行为，降低合金的密度，将合金中具有最佳力学性能的部分Ta替换为Nb。预计该项目开发的钛基合金的密度低于7 g/cm3。合金开发理念以基于相图计算（CALPHAD）方法的热力学建模为指导。整个合金概念的可行性将通过大量的显微组织、力学性能和氧化行为的实验研究来验证。

Commercially available high temperature Ti-based alloys possess a very attractive combination of low density, creep and fatigue resistance. These materials can, however, only be used up to a maximum temperature of approximately 550°C because of their limited intrinsic oxidation resistance. In this project, new oxidation-resistant Ti-based alloys with a thermal capability of up to 1000°C will be developed. These new materials should exhibit a favorable balance of (i) room temperature ductility/deformability, (ii) creep and oxidation resistance and (iii) low density. The oxidation resistance will rely on the formation of protective Cr-Ta-based oxide layers. In our previous studies, the minimal concentrations of Cr and Ta required for the formation of a continuous protective scale were determined. In the first step of project, ductile Ti-based alloys of different Mo/Ti ratios and a single-phase disordered bcc(A2) microstructure will be developed. The bcc(A2) crystal structure is stabilized by sufficient amounts of Ta, Mo, Cr and Ti. In the second step, the strength of these ductile alloys will be enhanced by (i) B2 precipitation strengthening of the A2 matrix (mimicking the  – ‘ microstructure of Ni-based alloys) or (ii) oxide dispersion strengthening by additions of Y2O3 dispersoids. Finally, in order to further improve the oxidation behavior and to reduce the alloy density, Ta will partially be substituted by Nb in the alloy exhibiting the best mechanical properties from previous steps. A density of below 7 g/cm3 is envisaged for the Ti-based alloys developed in this project. The alloy development concept is guided by thermodynamic modeling based on the CALPHAD (Calculation of Phase Diagram) approach. The feasibilty of the entire alloy concept will be validated by extensive experimental investigations of microstructure, mechanical properties and oxidation behavior.