Abstract
Nb - xSi ( x =3,9,16)-22 Ti -3 Cr -3 Al -2 Hf (at.%) have been successfully prepared by directional solidification in an optical floating zone furnace. Microstructure analysis and phases identification of the alloys were examined by X-ray diffraction (XRD), Electro Probe Micro Analyzer (EPMA) and Energy Disperse Spectroscopy (EDS). Fracture toughness specimens without pre-crack were prepared, room temperature fracture toughness of alloys was tested by three-point bending method, and fracture mechanism was studied. The results showed that with increasing Si content, Nb 5 Si 3 phase gradually increased and the phase transformed from γ- Nb 5 Si 3 to the stable α- Nb 5 Si 3 phase and β- Nb 5 Si 3 phase. There appeared the Ti -rich Nb 5 Si 3 phase when the Si content is 16 at%. In addition, more micro-cracks generated in the Ti -rich Nb 5 Si 3 phase, which seriously affected room temperature fracture toughness of the alloys.
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