Fundamental characterization of novel Mo-Si-B-Ti-alloys at ultra-high temperatures

预期研究项目的目的是开发新型的、结构良好的Mo-Si-B基合金，其应用温度可提高到1300°C。在第一个资助期中，我们成功地开发了合金，显著拓宽了含少量Fe的Mo-Si-B-Ti系统中的三元MoSS-T1-T2相场。我们首次制备了含有(Mo，Ti)5Si3相的三元合金，该合金在750-1300℃具有良好的抗氧化性。采用电弧冶金工艺可以避免(Mo，Ti)3Si相的灾难性氧化。结果表明，在力学性能方面，Mo-Si-B-Ti合金优于Mo-Si-B合金和镍基单晶合金。关于高温氧化行为，由于两个机构的工具包和USiegen的卓有成效的合作，已经获得了具体调整保护的SiO_2-TiO_2-双层的基本知识。此外，还收集了足够的实验数据，用于合理、真实地模拟内、外氧化过程，这将为挖掘Mo-Si-B-Ti-Fe合金的现有潜力提供重要工具。本建议的最大努力将是确定技术上适用的Mo-Si-B-Ti-Fe合金的化学成分。主要的重点将放在观察到的钛硅化物对已经很好的机械性能和内在抗氧化性的影响上。这意味着对Mo-Si-B-Ti-Fe合金的微观结构、钛硅化物析出物的性质和对固溶体相变形行为的影响以及抗等温/循环氧化性能的广泛表征。为了实现有效的开发周期，应通过基于机理的模拟和实验结果之间的相互作用来评估具有改进的机械和氧化性能平衡的合金成分。对不同的Mo-Si-B-Ti-Fe合金的氧化过程的评估必须依赖于温度、组织和化学成分，使用考虑真实组织的有限元模型，通过嵌入空间和时间分辨的动力学计算以及局部热力学平衡计算。应生产和研究具有基于模拟的预测性能改进的选定组合物，以验证模拟模型。

The aim of the intended research project is the development of new, structural Mo-Si-B-based alloys with improved properties for application temperatures up to 1300°C. In the course of the first funding period we succeeded in the alloy development to broaden significantly the ternary Moss-T1-T2 phase field in the Mo-Si-B-Ti system with small amounts of Fe. We produced for the first time ternary alloys containing the (Mo,Ti)5Si3 phase with excellent oxidation resistance at 750-1300°C. The catastrophically oxidizing (Mo,Ti)3Si phase could be avoided utilizing the arc-metallurgical processing route. It was found that Mo-Si-B-Ti-alloys outplay both the Mo-Si-B alloys and the Ni-based singly crystal alloys with respect to mechanical, i.e. creep, properties. Regarding the high temperature oxidation behaviour fundamental knowledge for the specific adjustment of a protective SiO2-TiO2-duplex layer has been gained due to the fruitful cooperation of the both institutions KIT and USiegen. In addition, sufficient experimental data have been collected for a sound, realistic simulation of inner and outer oxidation processes which will serve as an important tool for the exploitation of the existing potential of Mo-Si-B-Ti-Fe alloys. Greatest endeavor of the present proposal will be the determination of the chemical composition of technically applicable Mo-Si-B-Ti-Fe alloys. Main emphasis will be placed on the impact of the observed Ti-silicides on the already excellent mechanical properties and the intrinsic oxidation resistance. This implies the extensive characterization of the microstructure, the nature/effect of the Ti-silicide precipitates on the deformation behaviour of the solid solution phase and the isothermal/cyclic oxidation resistance of Mo-Si-B-Ti-Fe alloys. To enable an efficient development cycle, the evaluation of the alloy compositions with an improved balance of mechanical and oxidative properties should occur by the interplay between mechanism-based simulation and experimental results. The assessment of the oxidation process of different Mo-Si-B-Ti-Fe alloys has to be performed dependent on the temperature, the microstructure and the chemical composition using a FEM model considering the real microstructure by embedding spatially- and time-resolved kinetic calculations as well as local thermodynamic equilibrium calculations. Selected compositions with simulation based predicted property improvement shall be produced and investigated to verify the simulation model.