Nanocrystallization and structural correlation in quasicrystalline and crystalline phases during mechanical milling

Powder Metallurgical Processing of Sn-Reinforced Al-Cu-Fe Quasicrystals: Structure, Microstructure and Toughening Behavior

The present work deals with powder metallurgical processing of Sn-reinforced Al-Cu-Fe icosahedral quasicrystalline (IQC) composites processed through mechanical milling (MM) followed by hot pressing and pressureless sintering. The structure, microstructure and toughening behavior of the nanocomposite powders and bulk samples were investigated through X-ray diffraction (XRD), optical metallography (OM), scanning electron microscopy (SEM) and indentation techniques. The XRD pattern suggested the coexistence of IQC and λ-Al13Fe4 (mC102; a = 1.549 nm, b = 0.808 nm, c = 1.248 nm) and B2-type Al (Cu, Fe) (cP2; a = 0.29 nm) crystalline phases in milled as well as sintered samples. The face-centered icosahedral (FCI) ordering was persistent even after 40 h of milling and sintering. The structural transformation during MM influences the indentation behavior of IQC-Sn nanocomposite powders, and the microhardness was found to be in the range of ~5.3 to 7.3 GPa. Further, efforts were made to study the indentation behavior of IQC-Sn composite prepared by pressureless sintering and hot pressing. The fracture toughness of the IQC-10Sn hot-pressed sample was found to be ~1.92 MPa.√m, which is ~22% higher than that of the as-cast and annealed IQC. The enhancement in the fracture toughness resulted mainly from the inhibition of cracks by Sn reinforcement particles. This suggests that powder metallurgical processing can produce the IQC-Sn composite with an optimal combination of microhardness and fracture toughness.

Structural Characterization of Al65Cu20Fe15 Melt-Spun Alloy by X-ray, Neutron Diffraction, High-Resolution Electron Microscopy and Mössbauer Spectroscopy

The aim of the work was to characterize the structure of Al₆₅Cu₂₀Fe₁₅ alloy obtained with the use of conventional casting and rapid solidification-melt-spinning technology. Based on the literature data, the possibility of an icosahedral quasicrystalline phase forming in the Al-Cu-Fe was verified. Structure analysis was performed based on the results of X-ray diffraction, neutron diffraction, ⁵⁷Fe Mössbauer and transmission electron microscopy. Studies using differential scanning calorimetry were carried out to describe the crystallization mechanism. Additionally, electrochemical tests were performed in order to characterize the influence of the structure and cooling rate on the corrosion resistance. On the basis of the structural studies, the formation of a metastable icosahedral phase and partial amorphous state of ribbon structure were demonstrated. The possibility of the formation of icosahedral quasicrystalline phase I-AlCuFe together with the crystalline phases was indicated by X-ray diffraction (XRD), neutron diffraction (ND) patterns, Mössbauer spectroscopy, high-resolution transmission electron microscopy (HRTEM) observations and differential scanning calorimetry (DSC) curves. The beneficial effect of the application of rapid solidification on the corrosive properties was also confirmed.