B. Z. Ding

INTERFACIAL REACTIONS ON ANNEALING CU/AL MULTILAYER THIN-FILMS

Thin film reactions of Cu/Al multilayer films were investigated by differentia scanning calorimetry and transmission electron microscopy. Sequential intermetallic compound formation was found in the temperature range from 300 to 620 K. With excess copper present in the as-deposited trilayer and multilayer films, the observed sequence was CuAl2 and Cu9Al4, and the interfacial reactions were controlled by interfacial and grain boundary diffusion. The activation energies for the formation of CuAl2 and Cu9Al4 are 0.78+/-0.11 and 0.83+/-0.2 eV, respectively.

ELECTRICAL-RESISTIVITY OF NANOCRYSTALLINE FE-CU-SI-B ALLOYS OBTAINED BY CRYSTALLIZATION OF THE AMORPHOUS ALLOY

Abstract Nanocrystalline Fe-Cu-Si-B alloys, with grain sizes of 30–90 nm, were prepared by crystallization of the parent amorphous alloy. Electrical resistivity of 30 nm-grained Fe-Cu-Si-B samples measured at room temperature was found to be higher than that of the amorphous material. With increasing grain size, the resistivity declines rapidly, which is in good agreement with the theoretical analysis based on the electron scattering of interfaces.

AMORPHOUS B-C-N SEMICONDUCTOR

Amorphous BC2N powders were prepared by mechanical milling with hexagonal boron nitride and graphite as starting materials. A bulk amorphous BC2N compound was produced by sintering the as-milled amorphous BC2N powders in a vacuum of 10−5 Torr at a temperature of 1470 K. The conductivity measurement for the bulk amorphous BC2N compound showed that it behaves as a semiconductor with band gap energy of 0.11 eV for temperatures ranging from room temperature to 560 K and a semimetal for temperatures between 560 and 740 K. The mechanism of the formation of the amorphous BC2N powders is discussed.

Properties of nanocrystalline Fe-Cu-Si-B alloys generated by crystallization of the amorphous alloy

Abstract Nanocrystalline Fe-Cu-Si-B alloys with grain sizes of 30–90 nm were prepared by crystallization of the amorphous alloy. Properties including microhardness and electrical resistivity were examined in this study. Microhardness measurements showed that a normal Hall-Petch relation between the microhardness and the average grain size was obtained in nanocrystalline Fe-Cu-Si-B alloys. It was found that the electrical resistivity of a 30 nm-grained Fe-Cu-Si-B sample measured at room temperature was higher than that of the amorphous sample. With increasing grain size, the residual resistivity drops rapidly, which is in good agreement with the theoretical analysis based on the electron scattering of interfaces.

Investigation of the lattice structure of nanophases in FeCuSiB alloys

In this paper we present the first investigation on the lattice structure of nanophases, α-Fe(Si) and Fe2B, in nanostructured FeCuSiB alloys obtained via crystallization of the parent amorphous alloy. It is found that the lattice constant of α-Fe(Si) phase is increased, whereas the a-axis is elongated and the c-axis is shortened simultaneously for Fe2B phase with the decrease of grain size. The above results are attributed to a super-saturation of vacancies in the nanophases examined as a result of grain size refinement. The Mossbauer parameters are presented to support the above interpretation.

Formation kinetics of nanocrystalline FeBSi alloy by crystallization of the metallic glass

In order to clarify the formation mechanism of extremely fine-grained microstructures by crystallization of the FeBSi metallic glass, the nucleation and crystal-growth rates have been determined. The results indicate that the parabolic growth rate increases with annealing temperature, showing a maximum nucleation rate at an intermediate temperature range. Obviously it is possible to obtain nanocrystalline structures by controlling crystallization of the metallic glass on annealing at temperatures near the maximum nucleation rate.

Influence of phosphorus addition on the surface tension of liquid iron and segregation of phosphorus on the surface of Fe-P alloy

This article presents a study of the surface tension and phosphorus surface segregation in Fe-P alloys. The surface tension was measured by the sessile drop technique. The result of the dynamic surface tension for the low phosphorus content alloys shows that the alloy surface vaporization has a clear effect on the surface tension and causes a positive surface tension temperature coefficient. However, from this article, it is evident that phosphorus in liquid iron acts as a surface active element similar to arsenic. The surface segregation was determined using Auger electron spectroscopy. The result on the surface analysis of as-solidified sample indicates that the adsorption of impurity elements, such as oxygen, carbon, and nitrogen, can conceal phosphorus segregation on the free surface. Phosphorus segregation was also examined in the samples as-cleaned by Ar+ and then treated 30 minutes at 650°C. Phosphorus was found to segregate extensively on the surface of the alloys. On the basis of the analysis of the published data, the surface active intensity sequence of some nonmetallic elements was arrayed, and the surface active intensity of fluorine and boron in liquid iron was estimated.

An in situ TEM observation on the thermal stability of a nanocrystalline FeBSi alloy

The thermal stability of nanocrystalline Fe78B13Si9, prepared by crystallization, has been studied by in situ heating TEM observations at temperatures from 450 to 650-degrees-C. The nanocrystalline FeBSi alloy, with an average grain size of about 30 nm, was found to be thermally stable with nondetectable grain growth up to temperature of 450-degrees-C. The grain growth results can be discussed in terms of the mechanisms of precipitation, solute, vacancies and grain boundary triple junctions which may be operative in reducing the overall mobility of the interfaces. At the elevated temperature of about 650-degrees-C, secondary recrystallization occurred with abnormal growth of a few grains.

EFFECT OF HIGH PRESSURE ON THE PREPARATION OF PD-SI-CU BULK NANOCRYSTALLINE MATERIAL

A Pd-Si-Cu bulk nanocrystalline material was prepared by quenching the melted Pd78Si16Cu6 alloy at a cooling rate of 200 K/s under 2-6 GPa. It was found that the nanocrystalline material. consists of Pd(Cu) disordered solid solution and a metastable phase-II, Pd4Si. The grain size was found to decrease with increasing pressure. The influence of high pressure on the grain size of bull; nanocrystalline material is discussed, and a possible formation mechanism is proposed.

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.