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具有改进性能的新型结构mo - si -b基合金，应用温度高达1300°C。在第一个资助阶段，我们成功地开发了合金，在少量铁的Mo-Si-B-Ti体系中显著扩大了三元Moss-T1-T2相场。本文首次制备了含有（Mo,Ti）5Si3相的三元合金，在750 ~ 1300℃下具有优异的抗氧化性能。采用电弧冶金工艺可避免（Mo,Ti）3Si相的灾难性氧化。结果表明，Mo-Si-B- ti合金在力学性能（蠕变）方面优于Mo-Si-B合金和ni基单晶合金。在高温氧化行为方面，由于KIT和USiegen两个机构的富有成效的合作，获得了保护性sio2 - tio2 -双相层特异性调节的基本知识。此外，还收集了足够的实验数据，对内部和外部氧化过程进行了合理、真实的模拟，这将成为开发Mo-Si-B-Ti-Fe合金现有潜力的重要工具。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。重点将放在观察到的钛硅化物对本已优异的机械性能和固有抗氧化性的影响。这意味着微观结构的广泛表征，ti -硅化物析出物对Mo-Si-B-Ti-Fe合金固溶相变形行为的性质/影响，以及等温/循环抗氧化性。为了实现高效的开发周期，应该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更好的力学和氧化性能平衡的合金成分。对不同Mo-Si-B-Ti-Fe合金的氧化过程的评估必须根据温度、微观结构和化学成分进行，采用考虑实际微观结构的有限元模型，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。应根据预测的性能改进，生产和调查选定的组合物，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.