Microstructural Evolution and Mechanical Behaviors of an Nb-16Si-22Ti-2Al-2Hf Alloy with 2 and 17 at. pct Cr Additions at Room and/or High Temperatures

Abstract

X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy were used to investigate the microstructures and orientation relationships (ORs) of Nb-16Si-22Ti-2Al-2Hf-(2,17)Cr alloys (hereafter referred to as 2Cr and 17Cr alloys, respectively). The mechanical properties of the two alloys at room and/or high temperatures were compared. The 2Cr alloy comprised Nb_SS and (α + β)-Nb₅Si₃ phases, while the 17Cr alloy consisted of Nb_SS, (α + β)-Nb₅Si₃ and Laves Cr₂Nb phases with a C15 structure. The β-Nb₅Si₃ and Laves Cr₂Nb phases exhibited variable ORs with respect to the Nb_SS phase. The Laves Cr₂Nb phase was found to play a negative role on the fracture toughness at room temperature and on the compressive strength at temperatures from 1523 K to 1623 K (1250 °C to 1350 °C). The fracture toughness and the compressive yield strength at 1623 K (1350 °C) both decreased from 14.4 to 10.3 MPa m^1/2 and from 300 to 85 MPa, respectively, when the nominal Cr content increased from 2 to 17 at. pct. Finally, the fracture modes of these typical Nb_SS/Nb₅Si₃ and Nb_SS/Nb₅Si₃/Cr₂Nb microstructures under bending and compression conditions at room and high temperatures were investigated and discussed.