||In this dissertation, the ternary Mg-based amorphous ribbons are characterized and analyzed first. Among the three Mg65Cu25Y10, Mg65Cu25Gd10 and Mg65Ni25Gd10 amorphous ribbons, the Mg65Cu25Gd10 amorphous ribbon exhibits the best thermal properties in terms of the glass forming ability (GFA) indexes, such as 68 K of the supercooled liquid region (ΔTx), 29 K of the liquidus region (ΔTl), 0.582 of the reduced glass transition temperature (Trg), 0.427 of the γ value and 0.768 of the γm value. In spite that the Mg65Cu25Gd10 amorphous ribbons do not show the best performance in mechanical properties, such as micro-hardness value of 231 Hv (2.26 GPa), nano-hardness value is 3.24 GPa (300 Hv) and modulus from nano-indentation of 62.4 GPa, this composition is close to the two prediction compositions of Mg62Cu27Gd11 (the e/a-variant criterion) and Mg67Cu23Gd10 (the binary eutectic clusters criterion). However, among a series of ternary of Mg-Cu-Gd amorphous ribbons, the better overall thermal properties are seen in the Mg54Cu32Gd14 and Mg54Cu31Gd15 amorphous ribbons.|
In terms of the bulk Mg65Cu25Gd10 amorphous alloys, the 6 mm bulk metallic glass (BMG) rod can be fabricated successfully with minimum porosity. In order to improve the brittle properties of the Mg65Cu25Gd10 BMG rod, there are two methods applied in this study, namely, the intrinsic toughening method by heat treatment and the extrinsic toughening method of adding reinforcements.
For the heat treated Mg65Cu25Gd10 BMG rod, both of the one-step and two-steps BMG rods show no distinct plastic deformation in the engineering stress-strain curves, while the micro-hardness and compressive stress are increased from 270 Hv to higher than 300 Hv and from 804 to 830 MPa. But, for the ductile metal-reinforced Mg-based BMG rods, the brittle properties are improved. For the Nb-reinforced Mg65Cu25Gd10 BMG rods, the compressive stress decreases from 804 to 595 MPa and the plastic strain increases from 0 to 0.48% with increasing volume fraction from 0 to 17.3%. But, for Mg65Cu25Gd10 BMG rod reinforced by 21.6% porous Mo, the compressive stress and plastic strain are 821 MPa and 1.63%, respectively. Moreover, for the porous Mo-reinforced Mg58Cu28.5Gd11Ag2.5 BMG rods, the compressive stress increases from 827 to 1111 MPa and the plastic strain increases from 0 to 7.84% with increasing volume fraction from 0 to 25.4%.