In-situ Calorimetry Study on Cooling of the Metallic-Glass Forming Melts

Optimizing the microchannel design of the next generation of chips requires an understanding of the in-situ property evolution of the chip-based materials under fast cooling. This work overcomes the conventional reliance on reheating data of the melt-quenched glasses by demonstrating direct observations of glass transition on cooling curves utilizing the most-advanced fast differential scanning calorimetry. By leveraging an MEMS chip sensor that allows for rapid heat extraction from microgram-sized samples to a purged gas coolant, the device is able to reach ultra-fast cooling rates of up to 40,000 K s^-1. Four thermal regions are identified by examining the cooling behaviors of two metallic glasses. This is because the actual cooling-rate of the specimen can differ from the programmed rate, especially at high setting-rates when the actual rates decrease before the glass transition is completed. We define the operational window for reliable cooling-curve analysis, build models with empirical and theoretical analyses to determine the maximum feasible cooling-rate, and demonstrate how optimizing sample mass and environment temperature broaden this window. The method avoids deceptive structural relaxation effects verified by fictive-temperature analysis and permits the capturing of a full glass-transition during cooling.