Particle modification of niobium MASC alloys by processing under semi-levitation in a cold wall induction crucible

以难熔金属为基础的合金系统提供了一种有吸引力的替代商用镍基高温合金的方法。Nb-MASC系统(金属和硅化物复合材料)在高温元件中具有重要的应用价值。由于其良好的性能，Nb-MASC系统得到了广泛的研究，目前已进入第四代开发阶段。在本研究项目的范围内，将首次研究现有Nb-MASC系统的颗粒改性潜力。除了通过弥散硬化或沉淀直接强化外，单个相成分的形态和尺寸还需要通过颗粒来调整，以改善合金的性能。因此，颗粒变质将为NbMASC合金提供新的发展前景。使用冷壁感应坩埚加工可以提高强度和更高效的生产路线，这将扩大商业应用的范围，并改善特定的材料性能。第一个任务将是确定合适的颗粒系统。研究了Nb-MASC合金体系受颗粒影响的机理、后续热处理的影响及其对颗粒稳定性的影响。在选择合适的合金和颗粒体系后，材料在冷壁坩埚中进行半悬浮加工，并利用工艺固有的搅拌作用来确保颗粒分布均匀。在冷壁感应坩埚中几乎无接触地熔化Nb基合金，可获得极高的纯度和很高的工艺稳定性。最后，对改性Nb-MASC合金进行力学性能测试，并根据其在相应温度范围内的力学性能评价其高温应用的适宜性。对调整后的显微组织与获得的(热)强度之间的机理进行了分析和描述。

Alloy systems based on refractory metals offer an attractive alternative to commercially available nickel-base superalloys. Niobium-MASC systems (Metal And Silicide Composites) are of interest for application in high-temperature components. Due to their promising properties, niobium silicide systems are widely researched and are now in their fourth development generation.Within the scope of this research project, the potential of a particle modification of existing Nb-MASC systems will be investigated for the first time. In addition to a direct strengthening by dispersion hardening or precipitations, the morphology and size of the individual phase components are to be adjusted by the particles to improve the alloys' properties. Thus, the particle modification will offer new perspectives for the niobium MASC alloys. Increased strength and a more efficient production route using cold wall induction crucible processing will expand the spectrum of commercial applications and improve the specific material properties.The first task will be to identify a suitable particle system. The mechanisms by which the Nb-MASC alloy system is affected by the particles, the influence of a subsequent heat treatment, and its influence on the stability of the particles will be investigated. After selecting a suitable alloy and particle system, the material is processed under semi-levitation in a cold wall crucible and the process inherent stirring effect will be exploited to ensure a homogeneous particle distribution. The almost contactless melting of the niobium-based alloy in the cold wall induction crucible results in an extremely high purity and offers a high process stability. Finally, the modified Nb-MASC alloy will be mechanically tested and the suitability for high temperature application will be assessed based on the mechanical properties in the relevant temperature range. The mechanisms between adjusted microstructure and achieved (hot) strength will be analysed and described.