Min Guanghui

Short-Range and Medium-Range Order in Liquid Cu-Ni Alloy

The liquid structure of the Cu70Ni30 alloy has been investigated using a θ-θ high-temperature x-ray diffractometer. At all temperatures above its liquidus, a distinct pre-peak has been found around a scattering vector magnitude of 13.5nm-1. The height of the pre-peak decreases gradually with increasing temperature but it clearly exists up to a temperature of 1400°C. This behaviour indicates that stable medium-range order atomic clusters exist in the melt. It is concluded that the short-range order atomic clusters of the liquid Cu70Ni30 alloy mainly consist of Cu atoms with centred Ni atoms. The appearance of the pre-peak in the structure factor of the liquid Cu70Ni30 alloy is caused by the interaction between centred Ni atoms locating in the neighbouring atomic clusters.

Effects of nickel on the crystallization of Zr70Cu20Ni10 amorphous alloy

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) are employed to investigate the effects of nickel on the crystallization of the amorphous Zr70Cu20Ni10 alloy. We have found that the crystallization process of the amorphous Zr70Cu20Ni10 alloy is strongly influenced by the addition of nickel. Addition of 10 at% Ni to the Zr70Cu30 amorphous alloy makes the crystallization process proceed from a single-stage mode to a double-stage mode. The activation energy for crystallization of the amorphous Zr70Cu20Ni10 alloy is calculated to be about 388kJmol-1 on the basis of the Kissinger equation. The effects of nickel on the crystallization of the amorphous Zr70Cu20Ni10 alloy are discussed in terms of the genetics of metals.

Anomalous change in nanocrystallization of amorphous Zr-Cu-Ni alloy

Employing X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), an anomalous change in the nanocrystallization of metallic Zr70Cu20Ni10 glass under two different conditions, i.e., continuous heating and isothermal annealing, has been observed. Both TEM observations and XRD results confirm that the first exothermic reaction in the continuous heating DSC traces of metallic Zr70Cu20Ni10 glass mainly corresponds to the precipitation of the Zr2Cu phase, while the second one mainly corresponds to the precipitation of the Zr2Ni nanoparticles. In contrast to this, when annealed in the supercooled liquid region the preferential precipitation phase of metallic Zr70Cu20Ni10 glass mainly corresponds of the Zr2Ni nanocrystals instead of the Zr2Cu phase. The origin of such an anomalous change can be explained by the Kirkendall effect between Cu and Ni atoms for the former and the difference in heat of mixing between Zr-Ni and Zr-Cu atomic pairs. Crystallization of amorphous alloys has been extensively studied because of practical and theoretical interest in crystal nucleation and growth in a high undercooling regime [1]. Two methods are often utilized to investigate the crystallization process of amorphous alloys, i.e. the continuous heating and isothermal annealing processes. For the continuous heating process, we can obtain the apparent activation energy for crystallization of an amorphous alloy by means of

Features of the Real Structure of Lanthanum Hexaboride Polycrystalline

The microstructure of lanthanum hexaboride (LaB6) polycrystalline has been studied by using transmission electron microscopy. This shows that the ideal LaB6 polycrystalline can be obtained by sintering ingots at the temperature of 2273 K for a holding time of 120 min in Ar pressure of 800 Torr, where the ingots are formed by pressing LaB6 powder at room temperature at a pressure of 0.4-0.5 GPa. The particles in LaB6 polycrystalline hardly bind; there are only a few pores at the joint parts of three particles and a few impurities exist in some pores. The sintering process for fabricating LaB6 polycrystalline is analysed and the formation of the pore and the impurities are studied from the point of surface tension.