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Recognition of the role of extended defects on local phase transitions has led to the conceptualization of the defect phase, localized thermodynamically stable interfacial states that have since been applied in a myriad of material systems to realize significant enhancements in material properties. Here, we explore the kinetics of grain boundary confined amorphous defect phases, utilizing the high temperature and scanning rates afforded by ultrafast differential scanning calorimetry to apply targeted annealing/quenching treatments at high rates capable of capturing the kinetic behavior. Four Al-based nanocrystalline alloys, including two binary systems, Al–Ni and Al–Y, and two ternary systems, Al–Mg–Y and Al–Ni–Y, are selected to probe the materials design space (enthalpy of mixing, enthalpy of segregation, chemical complexity) for amorphous defect phase formation and stability, with correlative transmission electron microscopy applied to link phase evolution and grain stability to nanocalorimetry signatures. A series of targeted isothermal annealing heat treatments is utilized to construct a Time–Temperature-Transformation curve for the Al–Ni system, from which a critical cooling rate of 2400 °C/s was determined for the grain boundary confined disordered-to-ordered transition. Finally, a thermal profile consisting of 1000 repeated annealing sequences was created to quantify the recovery of the amorphous defect phase following sequential annealing treatments, with results indicating remarkable microstructural stability after annealing at temperatures above 90% of the melting temperature. This work contributes to a deeper understanding of grain boundary localized thermodynamics and kinetics, with potential implications for the design and optimization of advanced materials with enhanced stability and performance. 

There is emerging recognition that crystalline defects such as grain boundaries and dislocations can host structural and chemical environments of their own, which reside in local equilibrium with the bulk material. Targeting these defect phases as objects for materials design would promise new avenues to maximize property gains. Here, we provide experimental proof of a dislocation-templated defect phase using a processing strategy designed to engender defect phase transitions in a nickel-based alloy and demonstrate dramatic effects on strengthening. Following heat treatments designed to encourage solute segregation to dislocations, regions with introduced dislocation populations show evidence of nanoscale ordered domains with a L1 structure, whereas dislocation-free regions remain as a solid solution. Site-specific spherical nanoindentation in regions hosting dislocations and their associated ordered nanodomains exhibit a 40% increase in mean pop-in load compared to similar regions prior to the segregation heat treatment. Strength estimates based on random solute atmospheres around dislocations are not sufficient to predict our measured strengths. Our mechanical measurements, in tandem with detailed electron microscopy and diffraction of the ordered domains, as well as characterization of dislocations in the vicinity of the nanodomains, establish the defect phase framework via direct observations of chemical and structural ordering near dislocations and its potential for offering favorable properties not achievable through conventional materials design.