Speaker
Description
Contemporary alloys for gas turbines operate at 90% of their melting point, necessitating the development of novel materials that withstand higher temperatures. Promising possibilities are alloys located in the system MoSiTiB, which have been under investigation for several years and show viable properties in terms of high-temperature mechanical properties and corrosion resistance.
The group of Chang [1] developed a thermodynamic database, which is widely used for CALPHAD analyses to guide the development of the materials system. Based on new results, some areas of the phase diagram warrant further investigation. This contribution aims to refine the thermodynamic phase modelling in the metal-rich area of the MoSiTi diagram, which is important for future applications. For this reason, several additional alloys with varying compositions were produced by vacuum arc melting from high-purity raw materials. After annealing for 330 h at 1425 °C, the samples were characterized via SEM, EDX, WDX and XRD to compare experimental and calculated results.
While several regions could be verified, the technologically relevant three-phase regions β(Mo,Si,Ti)-Mo3Si-Mo5Si3 as well as β(Mo,Si,Ti)-Mo5Si3-Ti5Si3 could not be completely reconfirmed. Instead, the three-phase regions Mo3Si-Ti5Si3-β(Mo,Si,Ti) and Mo3Si-Ti5Si3-Mo5Si3, respectively, with a small two-phase field of Mo3Si-Ti5Si3 between them, were found. Additionally, there are strong indications for the existence of an invariant transition reaction Mo3Si + Ti5Si3 ⇄ β(Mo,Si,Ti) + Mo5Si3 near the annealing temperature of 1425 °C, which is far lower than the earlier reported temperature of 1870 °C. Those results suggest that the thermodynamic database should be refined, as the area under investigation in this work have direct consequences for the application of the material.
[1] Y. Yang, Y. A. Chang, L. Tan, Y. Du, Materials Science and Engineering A361, pp. 281-293, 2003
| Speaker Country | Germany |
|---|