The influence of pre-annealing on thermal stability of the amorphousZr_(70)Cu_(20)Ni_(10) alloy was reported by employing the differential scanning calorimetry (DSC)and high-resolution transmission electron microscopy (HRTEM) techniques. It has been observed thatthe supercooled liquid region decreases with increasing the annealing time under isothermalconditions, indicating that the thermal stability of the amorphous Zr_(70)Cu_(20)Ni_(10) alloydecreases gradually. HRTEM observations reveal that there exist some ordered atomic clusters in theamorphous matrix at the relaxation stage. These ordered atomic clusters can be regarded asprecursors for the precipitation of the crystalline phases in the subsequent crystal-lizationprocess. The reasons resulting in the decrease in thermal stability of the amorphousZr_(70)Cu_(20)Ni_(10) alloy with annealing time are discussed through the Gaussian decomposition forthe radial distribution function of the amorphous Zr_(70)Cu_(20)Ni_(10) alloy.
The liquid structure of Fe-4.30C and Fe-4.30C-0.21Ce alloys was studied by high temperature X-ray diffractometer. The results show that for Fe-C alloy the nearest neighbor distance of the eutectic alloy is 0.259-0.260 nm at the temperature range of 1200-1400℃, which increases to 0.269-0.271 nm with the addition of 0.21% (mass fraction) Ce in the Fe-C alloy at the same temperature range. There is a pre-peak at Q = 15.5 nm-1 on the original intensity curve and structure factor S(Q) of the liquid Fe-4.30C-0.21Ce alloy, which was caused by the Ce atoms in the C-Ce clusters. Combined with the shared face, the tetragonal structure can meet the requirement for the distance of Ce-Ce atoms. It also shows that the cluster size in the liquid Fe-4.30C-0.21Ce alloy increases with the decreasing temperature.
X-ray diffraction (XRD) and differential scanning calorimetry (DSC) wereemployed to investigate the influence of Ni content on the crystallization of amorphousZr_(70)Cu_(30-x)Ni_x (atom fraction in percent) alloys. Experimental results show that with the Nicontent increasing the activation energies for crystallization of amorphous Zr_(70)Cu_(30-x)Ni_xalloys increase correspondingly, indicating that the thermal stability is greatly improved. All theDSC traces of amorphous Zr_(70)Cu_(30-x)Ni_x alloys exhibit two exothermic peaks, suggesting thatthe crystallization process proceeds via a double-stage mode. The first exothermic peak at lowertemperature mainly corresponds to the precipitation and growth of Zr_2Cu particles, while the secondone corresponds to the precipitation of nano-scale Zr_2Ni phase and crystallization of residualamorphous phase. The mechanism on the crystallization of amorphous Zr_(70)Cu_(30-x)Ni_x alloys wasdiscussed.
The valence electron structure of TiC was calculated by using the empirical electron theory of solids and molecules. The calculated results show that with the increase of temperature the number of common electrons of TiC increases, which indicates that TiC has a good thermal stability; and there exists a close relationship between hardness and brittleness of TiC. According to the number of lattice electrons, the differences among the crystals with different structures can be explained qualitatively. Using the 'bond-strengthening factor', the differences of hardness among the crystals with different structures can also be qualitatively explained to some extent.
