The effect of repeated melting of the mother ingot on the thermal stabilityof a Zr_(60)Al_+(15)Ni_(25) glassy alloy was investigated by differential scanning calorimetry(DSC). Experimental results indicate that after the repeated melting of the ingots at 1300 and 1580K, the glass transition temperature T_g increases from 686.4 to 690.7 and 696.8 K and the onsettemperature of crystallization T_x from 757.9 to 758.6 and 763.4 K, respectively, indicating thatthe thermal stability becomes higher after the repeated arc melting of the mother ingot and that itis more effective at higher temperature. Within the framework of structure heredity, the origin ofthe improvement of the thermal stability of Zr_(60)Al_+(15)Ni_(25) 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 precipitation 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 clifficult, 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 calorimetry (DSC); high-resolution transmission electron microscopy (HREM). The results show that the values of full width at half maximum (FWHM) of the XRD patterns; exothermic enthalpy ΔH of DSC plots do not monotonically change with the variation of deformation degrees . As is not large than 20%, the values of FWHM; ΔH are lower than that of the as-cast state. When reaches 30%, the values of FWHM; ΔH become larger than that of the as-cast state, while their values begin to decrease again as reaches about 85%. These results indicate that the reversible transitions between ordered; disordered atomic configurations occur during rolling, which is further verified by the HREM images. The reversible phase transition can be explained by the competition between the diffusion controlled reordering; 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
