Modification of the Ti40Cu36Zr10Pd14 BMG Crystallization Mechanism with Heating Rates 10-140 K/min

Abstract

The article presents investigations of Ti 40 Cu 36 Zr 10 Pd 14 bulk metallic glass crystallization process heated with the rates of 10, 60, 100 and 140 K/min. High heating rates experiments were performed in a new type of differential scanning calorimeter equipped with a fast responding thermal sensor. Phase composition and microstructure were studied with x-ray diffraction and transmission electron microscopy. The observed crystallization proceeded in two separate steps. Applied high rates of heating/cooling resulted in the crystallization of only one CuTi phase, replacing typical multi-phase crystallization. The microstructure after crystallization was polycrystalline with some amount of amorphous phase retained. Kinetic parameters were determined with the use of the Kissinger and Friedman iso-conversional analysis and MatusitaSakka iso-kinetic model. The kinetic analysis supplies results concerning autocatalytically activated mechanism of primary crystallization with decreasing activation energy and small density of quenched-in nuclei, in good agreement with previous structural investigations. The mechanism of secondary crystallization required dense nuclei site, increasing activation energy and large nucleation frequency. The amorphous phase of Ti 40 Cu 36 Zr 10 Pd 14 BMG revealed high thermal stability against crystallization. Application of high heating rates in DSC experiments might be useful for the determination of mechanism and kinetic parameters in investigations of metallic glasses crystallization, giving reasonable results.

Spherulitic growth process in Ti-based metallic glass: Microstructure, phase identification, and growth mechanism

“…According to Sypien et al [9], the differential scanning calorimetry (DSC) curves for this alloy (initial amorphous state) revealed several crystallisation peaks, indicating the presence of different phases. The phases identified in [10] were all from the CuTi binary phase diagram, under the assumption that Zr atoms substitute at Ti sites and Pd atoms substitute at Cu sites. This strong assumption allowed Sypien et al to reveal the presence of the (Ti,Zr) 3 (Cu,Pd), Ti 2 (Cu,Pd,*), and (Ti,Zr) 2 (Cu,Pd) phases from scanning electron microscopy (SEM)-energy-dispersive X-ray spectroscopy (EDS) measurements.…”