Deformation Behavior of a Quaternary Mo-Nb-Si-B Alloy
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Deformation Behavior of a Quaternary Mo-Nb-Si-B Alloy A.P. Alur1, R. Sakidja2, P. Wang1, P. Jain1, J.H. Perepezko2 and K.S. Kumar1 School of Engineering, Brown University, Providence, RI 02912 2 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, WI 53711 1
ABSTRACT The microstructure and compression response of a quaternary Mo-Nb-Si-B alloy has been examined in in the temperature interval 1200°C-1600°C and in the strain rate regime 10-4 s-1 to 10-6 s-1 and compared to earlier results on the ternary Mo-Si-B alloys The microstructure is composed of a three-phase microlamellar eutectic composed of the Mo-Nb solid solution phase, the T1 and the T2 intermetallic phases. Compression test confirm significantly superior creep resistance for the eutectic alloy compared to the ternary Mo-rich Mo-Si-B alloys with virtually no microstructural degradation. INTRODUCTION The search for candidate materials for elevated temperature applications beyond the capability of advanced Ni-base superalloys has focused on intermetallic compounds, multiphase refractory alloys and ceramics and ceramic-matrix composites. Within the realm of refractory alloys, attention has focused on Mo-based and Nb-based alloys. Scientific progress in these two areas were summarized in two overview papers in 2003 [1,2]. Within the Mo-based family of alloys, research has primarily evolved in the area of Mo-rich Mo-Si-B ternary alloys and a lengthy summary of microstructural findings, oxidation response and mechanical behavior was published in 2007 [3]. Research groups in the United States and around the world, particularly in Germany and Japan, have reported on various processing routes and resulting mechanical properties and oxidation resistance of these Mo-Si-B alloys as well as on single crystals of constitutent phases, but in the interest of brevity and space limitation, it is not possible to summarize all of the details in this section. A selected set of references on these topics is included [4-14] but is by no means exhaustive. An important attraction of Mo-rich alloys in the ternary Mo-Si-B system is the remarkable stability of the as-processed microstructure at high temperatures. While this stability is highly desirable in service, it also represents a significant challenge in developing secondary processing routes aimed at modifying/refining microstructure. As a result, current efforts are focused on innovations in processing [15] and in identifying potentially useful/novel microstructures by alloying that can change solidification pathways and modify phase equilibria. In this context, Perepezko and coworkers [16] have demonstrated that Nb, Ta and W are soluble in Mo and Mo5SiB2, but tend to destabilize the Mo3Si phase in favor of the Mo5Si3 phase. As an example, with increasing additions of Nb, a microstructure based upon Mo + T2 + T1 can be developed that is not accessible in ternary alloys.
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In this paper, we report preliminary findings on the high temperature compression behavior of such a three-phase
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