W.D. Wei

Microhardness and fracture properties of nanocrystalline NiP alloy

lu, k (reprint author), acad sinica,inst met res,natl lab rsa,shenyang 110015,peoples r china

A new method for synthesizing nanocrystalline alloys

A new method to prepare nanocrystalline alloys was developed by means of crystallization from amorphous alloys. By using this method, a Ni-P alloy with 9 nm crystallites was synthesized. The structure and grain sizes of the alloy were examined by means of x-ray diffraction, transmission electron microscopy, and high resolution electron microscopy. Specific heat capacity and thermal expansion coefficient of the nanocrystalline Ni-P alloy prepared by this method were found to be greater than those of the coarse-grained crystalline alloy by 12.3% and 56.2%, respectively. A new micromechanism for nanometer-sized crystallites formation is discussed.

Structural disorder and phase transformation in graphite produced by ball milling

Nanocrystalline graphite with a crystallite size of about 2 nm is formed after 8 h of ball milling. Further milling produces a mixture of nanocrystalline and amorphous phases. The nanocrystalline graphite is relatively stable against heating when compared with some nanocrystalline metals.

GRAIN-GROWTH KINETICS AND INTERFACIAL ENERGIES IN NANOCRYSTALLINE NI-P ALLOYS

Grain growth process in nanocrystalline Ni‐P alloys was investigated by use of differential scanning calorimetry and x‐ray diffraction. Two exothermal peaks which result from grain growth processes of Ni3P and Ni crystallites, respectively, have been detected upon heating the nanocrystalline samples at constant heating rates. Activation energies for the two processes of grain growth were calculated by means of the relationship of grain growth temperature and heating rate using the Kissinger equation. Average interfacial energies of Ni3P/Ni3P grain boundary and Ni3P/Ni boundary were determined from the heat released during grain growth.

Thermal expansion and specific heat capacity of nanocrystalline NiP alloy

lu, k (reprint author), acad sinica,inst met res,natl lab rsa,shenyang 110015,peoples r china

Preparation of Al nanoparticles in a controlled environment

Abstract In the present work we have studied the preparation of Al nanoparticles by the inert gas evaporation method, with the emphasis on control of the environment. We conclude that vacuum, gas purity, and leak and outgassing rates all exert an important influence on the preparation of clean nanoparticles, and that these three factors must be controlled within a definite range in order to make nanomaterials with clear crystal habits and clean interfaces. Two criteria for matching the three factors are given in the present work.

The formation of TiFe nanoparticles by gas condensation method

Ti-Fe nanoparticles were synthesized from TixFe100-x (x=50 similar to 85) alloys in an atmosphere of helium or hydrogen by gas condensation method. XRD and TEM were employed to analyze the particle size and structure. A FCC phase was observed which is a special martensite formed only in small sized particles(<20nm). It is found that the particles are all with FCC single phase when the helium gas pressure is 0.2 kPa or below, and with increasing the gas pressure multiple-phase particles are formed. Nanoparticles formed in hydrogen are similar to those formed in helium, but the difference between the evaporation rate of Fe and Ti is more remarkable due to hydrogen reaction

Preparation of nanocrystalline CuTi by quenching the melt under high pressure

Abstract A new method of preparing a bulk nanocrystalline alloy by means of quenching a melt under high pressure has been developed. Using this method, a bulk CuTi alloy with 10–20 nm crystallites was synthesized. The structures and grain sizes of the alloy were examined by means of X-ray diffraction and TEM. We know of no precedent for using this method to directly prepare nanocrystalline alloys. The interfaces within the bulk alloys are very clean, and there is no porosity. The mechanism for nanometer-sized crystallite formation by this method is discussed.

Stability in air of ultrafine particles of chromium

Abstract In this work, the structure, morphology and oxidation behavior in air of ultrafine Cr particles prepared by the gas evaporation method are investigated, using TEM, HREM, XRD and TG. The ultrafine Cr particles are easily oxidized when directly exposed to air or even when combustion occurs. After a protective treatment, a thin oxide film is formed on the surfaces of the particles, which makes them stable in the air. The growth morphologies of the Cr particles depend on the size and intrinsic structure. The starting temperature of pronounced oxidation for ultrafine particles is much lower than that for coarse particles.

SURFACE-STATE ANALYSIS OF FE50PD50 ALLOY ULTRAFINE PARTICLES

The surface state of Fe50Pd50 alloy ultrafine particles (UFP) has been investigated by AES and XPS. The results show that the surface of Fe50Pd50 alloy UFP was oxidized. There are two kinds of oxidized Fe existing on the surface of Fe50Pd50 alloy UFP. But the element Pd in the alloy UFP was not oxidized and stabilized the UFP. The surface of the alloy UFP is a bilayered structure.