Formation And Property Of Pr (Tb)-based Metallic Glasses And Related Nanostructural Materials

This work focuses on analysis and studying of the two newly discovered RE-based bulk metallic glasses (BMGs) and related nanocrystalline materials. We report that the formation of bulk nanocrystalline alloys with tunable microstructure and properties based on the Pr₆₀Al₁₀Ni₁₀Cu₂₀ BMG-forming alloy by doping Fe. In addition, the newly developed Tb-based BMGs and Tb nanocrystalline array have also been studied. The critical section thickness of the Pr₆₀Cu₂₀Ni₁₀Al₁₀ composition is 5 mm in diameter for die cast, which exhibits a distinct glass transition and a wide supercooled liquid region (SLR). The glass transition temperature is 409 K when the scanning rate is 10K/min, and it exhibits paramagnetic in room temperature. Our work firstly presents a simple approach to obtain the bulk nanocrystalline material with controllable microstructure, by doping RE-based BMGs with Fe. We report that the formation of Pr-Al-Ni-Cu-Fe bulk nanocrystalline alloy based on the Pr₆₀Al₁₀Ni₁₀Cu₂₀ BMG-forming alloy by doping Fe,including its glass forming ability (GFA),microstructure, magnetic and mechanical properties. By varying the content of Fe, the microstructure of the Pr-based alloy changes progressively from full glassy state to composite with nanocrystalline particles embedded in the glassy matrix, and finally into nano-structured state accompanying with the gradual magnetic and mechanical property changes. The role of the addition in the control of microstructure and property, the mechanism for the nanocrystalline formation induced by addition, and the relation between the microstructure and properties are discussed. The newly developed Tb-based BMGs and nanocrystalline array have been studied, including the preparation and microstructure. The critical section thickness of the Tb_<sub>36Y₂₀Co₂₀Al₂₄ composition is 5 mm in diameter for die cast, which exhibits higher glass transition temperature and elastic moduli. A two-dimensional (2D) thin film composed of Tb nanocrystals with uniform orientations is fabricated from Tb₆₅Fe₂₅Al₁₀ alloy melt upon quenching. The Tb nanocrystals with vertical height of 15-30 nm and lateral width of 10-20 nm are assembled into the nanocrystalline array on amorphous substrate. The formation mechanism for the Tb nanocrystals is discussed. The formation method may provide a new and flexible alternative to fabricate nanostructured film or array.