Microstructure and mechanical properties of Cu54Ni6Zr22Ti18 bulk amorphous alloy fabricated by warm extrusion

초록

In this study, the microstructure and the mechanical properties of Cu54Ni6Zr22Ti18 bulk amorphous alloys fabricated by warm extrusion of amorphous powders were investigated. The Cu54Ni6Zr22Ti18 bulk amorphous powders which has particle size below 63㎛ and wide supercooled liquid region of 53K were prepared by a high-pressure gas atomization method. The powders were filled in a Cu can with an inner dimension 20x2x50mm in air, evacuated, sealed and then pre-compacted in the press. The billet heating rate was 50K/min and the holding time was about 5min. The extrusion temperature range was from 723K to 743K, and the extrusion ratio was from 2 to 5. By warm extrusion of amorphous powders in the supercooled liquid state, a fully amorphous Cu54Ni6Zr22Ti18 alloys is successfully synthesized. The conditions for extrusion are obtained from the time-temperature-transformation curve by measuring the time for the onset of crystallization during isothermal annealing in DSC. Phase analysis wad performed by XRD and TEM. The result of phase analysis indicate that Cu54Ni6Zr22Ti18 BMGs having fully amorphous phase could be obtained until exclusion ratio of 4 at extrusion temperature 733K but partial crystalline phase was observed in the bulk alloy extruded at extrusion ratio of 5. The size of crystalline phase is about 20nm. As a result of compressive test, the extruded Cu54Ni6Zr22Ti18 bulk amorphous alloys exhibited high strength about 1.8GPa and in the in the partial crystalline bulk alloy exhibited strength about 1.2GPa.