Multiphase Mo-Si-B alloys processed by directional solidification
- PDF / 307,520 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 51 Downloads / 251 Views
Multiphase Mo-Si-B alloys processed by directional solidification Manja Krüger1, Georg Hasemann1, Iurii Bogomol2, Petr I. Loboda2 1 2
Otto-von-Guericke University Magdeburg, Institute for Materials and Joining Technology, P.O. Box 4120, D-39016 Magdeburg, Germany National Technical University of Ukraine “Kiyv Polytechnic Institute”, Kiev, Ukraine
ABSTRACT Multiphase Mo-Si-B alloys are potential candidates for applications in the aerospace and power generation industry due to their enhanced creep and oxidation resistance at ultra-high temperatures. It is documented that the microstructure and the resulting properties of Mo-based alloys are heavily influenced by their fabrication procedure. In this study we investigate different multiphase Mo-Si-B alloys processed by zone melting (ZM) starting from cold pressed elemental powders. Microstructural characterization of zone melted alloys based on SEM investigations shows elongated arrangements of phases parallel to the growing direction as well as homogeneously distributed phases in the cross-section for some of the alloys investigated. First compression creep tests were performed at about 1100°C. In comparison to the creep resistance of powder metallurgically (PM) processed alloys the behaviour of ZM materials was found to be substantially improved. Hence, targeted application temperatures of around 1200°C to 1300°C may become feasible. Furthermore, the oxidation behaviour was found to be influenced by the volume fraction of the Mo solid solution phase since the volatilization of the Mo solid solution phase leads to a mass loss of the compound. INTRODUCTION While Ni-based superalloy turbine blade materials already operate at very high homologous temperatures, new metallic materials that can withstand surface temperatures higher than 1100°C would be desirable in order to increase the thermodynamic efficiency of gas turbines. Three phase Mo-Si-B alloys, consisting of Mo solid solution ( -Mo) and the intermetallic phases Mo3Si and Mo5SiB2, have been the subject of intensive research because of both promising mechanical properties at ambient as well as at high temperatures and oxidation resistance. Previous research clarified that ingot metallurgical processes like arc-casting lead to inhomogeneous and coarse grained microstructures with intermetallic matrices. Materials processed in this manner show brittle behaviour at low temperatures [1,2]. On the other hand, processes like He gas atomization [3] or mechanical alloying [4] and subsequent consolidation of the powders result in fine-grained microstructures with a Mo solid solution matrix and a homogeneous distribution of the individual intermetallic phases. These materials provide decreased brittle-to-ductile-transition temperatures (DBTT) and, therefore, a good balance of the properties at ambient and elevated temperatures. However, the ultra-fine grained microstructure of powder metallurgically (PM) processed materials was superplastically deformed at temperatures in excess of 1300°C [5]. This limits the application to
Data Loading...
