The effect of repeated melting of the mother ingot on the thermal stability of a Zr60All5Ni25 glassy alloy was investigated by differential scanning calorimetry (DSC). Experimental results indicate that after the repeated melting of the ingots at 1300 and 1580 K, the glass transition temperature Tg in.eases from 686.4 to 690.7 and 696.8 K and the onset temperature of crystallization Tx from 757.9 to 758.6 and 763.4 K, respectively, indicating that the thermal stability becomes higher after the repeated arc melting of the mother ingot and that it is more effective at higher temperature. Within the framework of structure heredity, the origin of the improvement of the thermal stability of Zr60AllsNi25 bulk glassy alloy is discussed.
YAN Zhijie , LI Jinfu WANG Honghua HE Shunrong and ZhOU Yaohe1) State Key Lab. of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200030, China2) Taiyuan Heavy Machinery Institute, Taiyuan 030024, China
Differential scanning calorimetry (DSC) shows that repeated melting of mother ingot improves the stability of icosahedral phase (I-phase) precipitated from Zr65Al7.5Ni10Cu12.5Ag5 glass. The Kissinger analysis of crystallization implies that the effective activation energies for the pre-cipitation of I-phase and its decomposition considerably increases due to the repeated melting of mother ingot. Repeated melting of mother ingot refines ingot microstructure. Because of structure heredity, the size of the short-range orders (SROs) in the glassy alloy produced from the mother ingot with finer microstructure becomes smaller, which makes the rearrangement of atoms more difficult, and the I-phase more stable.
The microstructure evolution of the Zr60Al15Ni25 metallic glass during rolling at room temperature is investigated by X-ray diffraction (XRD), differential scanning calo- rimetry (DSC) and high-resolution transmission electron microscopy (HREM). The results show that the values of full width at half maximum (FWHM) of the XRD patterns and exothermic enthalpy △H of DSC plots do not monotonically change with the variation of deformation degrees ε. As ε is not larger than 20%, the values of FWHM and △H are lower than that of the as-cast state. When ε reaches 30%, the values of FWHM and △H become larger than that of the as-cast state, while their values begin to decrease again as ε reaches about 85%. These results indicate that the reversible transitions between ordered and disordered atomic configurations occur during rolling, which is further verified by the HREM images. The reversible phase transition can be explained by the competition be- tween the diffusion controlled reordering and shear-induced disordering during rolling.
YAN Zhijie1, 2, LI Jinfu1, ZHOU Yaohe1 & WU Yanqing3 1. State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200030, China
