The Effects of Substitutional Additions on Tensile Behavior of Nb-Silicide Based Composites
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S2.10.1
The Effects of Substitutional Additions on Tensile Behavior of Nb-Silicide Based Composites
Laurent Cretegny, Bernard P. Bewlay, Ann M. Ritter, and Melvin R. Jackson GE Global Research, Schenectady, NY 12301, USA. ABSTRACT Nb-silicide based in-situ composites consist of a ductile Nb-based solid solution with highstrength silicides, and they show excellent promise for aircraft engine applications. The Nbsilicide controls the high-temperature tensile behavior of the composite, and the Nb solid solution controls the low and intermediate temperature capability. The aim of the present study was to understand the effects of substitutional elements on the room temperature tensile behavior and identify the principal microstructural features contributing to strengthening mechanisms. INTRODUCTION Nb-silicide composites combine a ductile Nb phase with high-strength silicides and Laves phases; they show great promise for high-temperature structural applications [1-4]. These composites consist of Nb5Si3 and Nb3Si type silicides toughened with a Nb solid solution (substitution of Nb by Ti and Hf is abbreviated by (Nb)). The most recent Nb-silicide based insitu composites, alloyed with elements such as Cr, Ti, Hf, and Al, have demonstrated a promising combination of high-temperature strength, creep resistance, and fracture toughness. The Nb5Si3 and Nb3Si have the tI32 and tP32 ordered tetragonal structures with 32 atoms per unit cell. When Nb5Si3 is alloyed with Ti and Hf, the less complex hP16 (Nb)5Si3 structure can also be stabilized [5, 6]. The effect of substitutional elements on the mechanical behavior of the tI32, tP32, and hP16 silicides has not been investigated previously. An improved understanding of the mechanisms that control low- and high-temperature deformation of Nb-silicides is required to improve the strength of Nb-silicide based composites. The aim of the present study was to characterize the room temperature tensile behavior of quaternary and more complex engineering Nb-silicide based alloys and to correlate measured strength with microstructure and fracture surface features. Table 1: Compositions and room-temperature tensile strength data for quaternary and MASC-type alloys. Ti [at%]
Si [at%]
Cr [at%]
Hf [at%]
Al [at%]
Nb [at%]
25.0% 25.0% 25.0% 25.0% 25.0% 24.7% 24.7% 24.0% 24.0%
20.0% 18.0% 18.0% 16.0% 14.0% 16.0% 16.0% 16.0% 13.0%
2.0% 2.0% 2.0% 2.0%
8.0% 8.0% 8.0% 8.0% 8.0% 8.2% 8.2%
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