In-Situ Visualization of Long-Range Defect Interactions at the Edge of Melting

Connecting a bulk material's microscopic defects to its macroscopic properties is an age-old problem in materials science. Long-range interactions between dislocations (line defects) are known to play a key role in how materials deform or melt, but we lack the tools to connect these dynamics to the macroscopic properties. We introduce time-resolved dark-field X-ray microscopy to directly visualize how dislocations move and interact over hundreds of micrometers, deep inside bulk aluminum. With real-time movies, we reveal the thermally-activated motion and interactions of dislocations that comprise a boundary, and show how weakened binding forces inhomogeneously destabilize the structure at 99% of the melting temperature. Connecting dynamics of the microstructure to its stability, we provide important opportunities to guide and validate multiscale models that are yet untested

Alüminyum-nadir toprak elementi amorf/nanokristal hacimli kompozitlerin üretimi ve karakterizasyonu.

The structure, production and consolidation of binary Al-RE (RE=Sm, Tb) and multicomponent Al-RE-TM (TM= Fe, Ni, Cu) metallic glasses were studied mainly in two parts. In the first part, solid-state amorphous structures of melt-spun and magnetron sputtered thin films of Al90Tb10 were investigated with high energy X-ray diffraction (HEXRD) constrained reverse Monte Carlo (RMC) simulations. The experimental findings and calculated models had shown that amorphous alloys having the same composition comprises the same atomic arrangement in short-range order (SRO) scale, yet have distinctly differing structures in medium-range (MRO) scale. In the second part of the study, amorphization of Al-RE and Al-RE-TM based alloys with mechanical milling and alloying were studied. It was found that binary and quaternary compositions of Al-RE systems had strong resistance against vitrification through mechanical milling. However, partial amorphization in Al-RE-TM and Al-RE-TM1-TM2 systems were achieved with mechanical alloying. Characterization of mechanically alloyed Al85Sm7Fe5Ni3 powders had revealed the structure is not fully disordered but comprise an amorphous/nanocrystalline structure, consisting of amorphous phase, fcc-Al nanocrystals and unknown intermetallic phase with spherical morphology. Consolidation of mechanically alloyed Al85Sm7Fe5Ni3 powders were studied with pressing and sintering, and warm pressing. The effect of ex-situ composite formation with the mechanically alloyed powders mixed with pure Al powders on mechanical properties of the bulk structures were also investigated. Mechanical characterization of the bulk amorphous/nanocrystalline and ex-situ composite consolidates were performed, together with their post-mortem failure analyses.M.S. - Master of Scienc

FEN BİLİMLERİ ENSTİTÜSÜ/LİSANSÜSTÜ TEZ PROJESİ

A1-NTE BAZLI HACİMLİ AMORF/NANOKRİSTAL KOMPOZİT YAPILARIN ÜRETİMİ VE KARAKTERİZASYON

AL-NTE METALİK CAM ALAŞIMLARINDA KISA VE ORTA ERİM DÜZENİNİN İNCELENMESİ

AL-NTE METALİK CAM ALAŞIMLARINDA KISA VE ORTA ERİM DÜZENİNİN İNCELENMES