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

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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.