Establishing various processing routes and their effect on microstructure and high temperature properties for alloys with melting temperatures >1900°C

难熔金属基合金一般采用粉末冶金法生产。迄今为止，对于熔点超过1900°C的铸锭冶金材料所知甚少。已知的方法只适用于小样本量的制造，或者具有非常有限的几何自由度。因此，本提案的目的是改进各种铸锭冶金路线，以制造熔点为>1900°C的合金。​在这项联合工作中，感兴趣的材料包括Mo-9Si-8B-2Al (at。%), Cr-7Si-2Ge-2Mo (at。%)和mo - al - ti基合金。拜罗伊特大学与清华大学的合作内容如下：拜罗伊特大学将负责(1)对上述合金的真空感应熔炼工艺进行优化，样品量可达2.5公斤。重点是实现孔隙度< 1.0 vol.%，并避免分离。(2)合金/坩埚界面和合金中心的显微组织观察。(3)在真空拉伸蠕变试验装置中对温度高达1700℃的VIM和浮区（FZ）试样的蠕变性能进行比较。国立清华大学将负责(1)为获得直径> 9 mm、长度> 40 mm的单晶而优化浮区技术。(2)研究元素偏析、相变。(3)测定在1700℃以下的氧化行为，作为真空感应和浮区熔化两种生产路线的函数。

Refractory metal based alloys are generally produced by powder metallurgy. Up to now, little is known about ingot metallurgy produced materials with melting points exceeding 1900°C. The already known methods are only suitable for the fabrication of small sample quantities, or have very limited geometric freedom. Therefore, the aim of this proposal is to improve various ingot metallurgy routes to fabricate alloys with melting points >1900°C. This project will be carried out in close collaboration with Prof. An-Chou Yeh of National Tsing Hua University, Taiwan. In this joint work, the materials of interest include Mo-9Si-8B-2Al (at.%), Cr-7Si-2Ge-2Mo (at.%), and Mo-Al-Ti-based alloys. The work-shares between University Bayreuth and National Tsing Hua University are as follows:University Bayreuth will be responsible of (1) Optimization of the vacuum induction melting process for casting the above mentioned alloys, for sample quantities of up to 2.5 kg. The focus is to achieve a porosity < 1.0 vol.% and to avoid segregations. (2) Microstructural observations at the alloy/crucible interface and alloy center. (3) Comparison of the creep properties of VIM and floating zone (FZ) produced samples at temperatures up to 1700°C in a vacuum tensile creep testing device.National Tsing Hua University will take charge of (1) Optimization of floating zone technique for achieving single crystals with sizes of > 9 mm in diameter and > 40 mm in length. (2) Study the elemental segregations, phase transformations. (3) Determination of oxidation behaviors up to 1700 °C as function of the two production routes, vacuum induction and floating zone melting.