Characterization of Crack Nucleation in Titanium Alloys with Metastable Microstructures

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Definitive evidence for the nanostructured process within FGA is provided by a multi-scale characterization of the nanograin orientation, grain rotation, and the lattice strain up to atom scale by utilizing the transmission Kikuchi diffraction (TKD) and aberration-corrected scanning transmission electron microscope. Direct aging treatment can be used to optimize the mechanical properties of the weldment by decomposition of the thermal martensites and precipitation of the nano lamellar alpha structure within the coarse beta grain, thereby enhancing the crack nucleation resistance. Cracking interfaces of the oxidation domain and topmost nanograins facilitate surface degradation, thereby promoting the stress mismatch along the contact area boundary and giving rise to the formation of macrocrack thereafter with the assistance of oxygen pick-up at the crack tip.