Study Of The Glass-forming Ability And Magnetic Properties Of RE(Gd, Nd)-Co-Al Amorphous Alloys

This thesis studies the RE(Gd, Nd)-Co-Al amorphous alloy materials. Accurately, the alloys which we study on are Gd55-xNdxCo2oAl25(x=0,5,10,15,20). The glass-forming ability (GFA), thermal stability (TS) and magnetic properties of Gd55Co2oAl25are studied. And the glass-forming ability and thermal stability of Nd element substitution in Gd55-xNdxCo2oAl25(x=0,5,10,15,20) amorphous ribbon samples are studied.The microstructure of the Gd55-xNdxCo2oAl25(x=0,5,10,15,20) alloys are studied by the X-ray diffraction spectrum (XRD) and differential scanning calorimetry (DSC). And the glass forming ability and thermal stability of Gd55-xNdxCo2oAl25alloys are studied by some parameters such as supercooled liquid region (△T), reduced glass transition temperature (Trg), equivalent atomic radius (δ), electronegativity difference (Ay), crystallization activation energy (Ep), and so on. The magnetic properties of the Gd55Co2oAl25alloys are evaluated by the VSM measurement.The experimental results are as followed:1. The critical diameter of Gd55Co20Al25as-cast cylindrical rod which is got by injected into a copper mold with fully amorphous structures is less than3mm. The thermal stability of Gd55Co2oAl25as-cast cylindrical rod1.5mm in diameter is better than the3mm diameter sample. The magnetization and temperature (M-T) curve of Gd55Co2oAl25as-cast cylindrical rods1.5mm and3mm in diameter are analyzed. It is found that both the curie temperature of the Gd55Co2oAl25as-cast cylindrical rods1.5mm and3mm in diameter are99K. But compared with the Gd55Co20Al25as-cast cylindrical rod3mm in diameter, the rod with1.5mm in diameter is easier to be saturated.2. The glass-forming ability of Gd55Co20Al25amorphous ribbon samples become stronger and the supercooled liquid region become larger if the rate of the single roll copper wheel increase when strip casting. There is almost no difference between the500rpm and4000rpm single-roller melt-spinning amorphous ribbon samples for their curie temperature, but compared with the500rpm ribbon, the4000rpm ribbon is easier to be saturated and the saturation magnetization is higher at the same temperature.3. The magnetic entropy change and the magnetic refrigeration capacity of the Gd55Co20Al25as-cast cylindrical rod samples and the Gd55Co20Al25strip casting samples are analyzed and calculated under30kOe. It is found that the magnetic refrigeration capacity of the Gd55Co20Al25alloy cylindrical rod with fully amorphous structure with the diameter in1.5 mm is the highest, then is4000rpm ribbon,500rpm ribbon and the Gd55Co20Al25alloy cylindrical rod with the diameter in3mm. The more quenched-in precipitates in Gd-based metallic glasses, the lower magnetic refrigeration capacity.4. The glass-forming ability of Gd55-xNdxCo2oAl25amorphous ribbon is higher with the more Nd element partly instead of Gd element in the alloy. The activation energy is analyzed by the famous Kissinger equation. It is found that the thermal stability of Gd55-xNdxCo20Al25amorphous ribbon sample show a minimum at x=10. By analyze and the Gd55Co20Al25amorphous ribbon samples to study the magnetic entropy change for the different temperature and calculate the refrigeration capacity of the samples.