Microstructure and Compressive Behavior of Al Based Amorphous/ Nanocrystalline Alloys Fabricated by a Powder Forging

초록

Al based bulk hybrid alloys composed of amorphous Al-10Ni-6Ce (at%) matrix alloy and nano-crystalline Al-8Fe-2Mo-2V-1Zr alloy (Vf=0.3) were fabricated by a powder forging process. The starting materials were rapidly quenched, powder-shaped amorphous Al-10Ni-6Ce alloy and nano-crystalline Al-8Fe-2Mo-2V-1Zr alloy. The amorphous alloy powders were prepared by the pulverization of melt-spun ribbons, and the nano-crystalline powders were fabricated by using a gas atomization technique. The powder forging process involved pre-compaction of amorphous/crystalline powder mixtures by cold pressing and subsequent isothermal forging at temperatures from 523K to 723K with the pressure of 660MPa and the strain rate of 10-2 s-1 to achieve the rod-shaped bulk hybrid alloys having 10 mm diameter. Similar process was used to obtain the same shaped bulk monolithic alloy to the hybrid alloy. The porosity decreased rapidly with increasing forging temperature up to 648K for both the monolithic and hybrid alloys. Fully dense bulk specimens with the porosity less than 1.5% were achieved when the forging was carried out at and above 648K. Noticeably high compressive fracture strength of 1.2GPa with the compressive plastic strain of 1% was obtained at room temperature for the fully dense bulk hybrid specimen forged at 648K. In contrast, the fully dense bulk monolithic specimen forged at 648K did not exhibit any compressive plastic strain although it possessed the very high compressive fracture strength of 1.4GPa.