X.D. Liu

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.

PREPARATION AND PROPERTIES OF NANOCRYSTALLINE (FE0.99MO0.01)78SI9B13 ALLOYS

liu, xd (reprint author), acad sinica,inst met res,state key lab rsa,shenyang 110015,peoples r china

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.

Effect of Xe+ ion bombardment during titanium deposition in nitrogen atmosphere

Abstract Bombardment of evaporated titanium films with energetic Xe + ions deposition in nitrogen atmosphere has a marked effect on film properties. In comparison with evaporated titanium films, the Xe + ion-bombarded films contained more nitrogen and thus TiN films, instead of titanium films, have been formed. There were very small amounts of oxygen and xenon retained in the film. We also observed compressive stress in the Xe + -ion-bombarded films, whereas the evaporated films were nearly stressless. The critical load, determined by the scratch test, to damage the Xe + -ion-bombarded TiN films on steel and silicon substrates was twice that for evaporated films, which indicated that the adhesion of the film to the substrates was greatly promoted by Xe + ion bombardment. The hardness of the TiN films formed by Xe + ion bombardment reached 2200 kgf mm −2 , which was not only much higher than that of the evaporated films, but also higher than those of films formed by bombardment with N + ions in the same condition. The results are explained from the viewpoint of the difference in energy deposited in the films by incident ions.

SYNTHESIS OF TITANIUM NITRIDE FILMS BY ION-BEAM-ENHANCED-DEPOSITION

Abstract Titanium nitride films have been prepared by simultaneous vacuum deposition of titanium from an electron gun evaporation source and nitrogen ion beam bombardment with an ion energy of 40 keV. The pressure of the target chamber during processing was 6.5 × 10-4 Pa. The atomic arrival ratio of implanted nitrogen ions to deposited titanium atoms varied from 0 to 0.5. Rutherford backscattering analysis showed that nitrogen ion bombardment can apparently reduce the oxygen concentration in films. The component ratio N:Ti in films prepared at low temperature was greater than that in films prepared at high temperature. At the same atomic arrival ratio, the component ratio N:Ti in the film decreased with increasing titanium deposition rate. These facts are considered to arise from the situation that the composition in the films is strongly affected by the adsorption of nitrogen. X-ray diffraction analysis showed that films formed by ion-beam- enhanced deposition (IBED) were mainly composed of titanium nitride of NaCl- type structure. The mechanical properties of the films have been investigated. The titanium nitride films prepared by IBED exhibited high hardness on improved wear resistance. The adhesion of IBED titanium nitride films to the substrate was superior to that of films obtained by chemical or physical vapour deposition.

Synthesis of the NiZr2 intermetallic compound nanophase materials

The NiZr2 intermetallic compound nanocrystalline materials were synthesized by completely crystallizing an amorphous NiZr2 alloy under proper annealing conditions. The microstructure of the NiZr2 nanophase was characterized by means of transmission electron microscopy (TEM), high resolution electron microscopy (HREM), and X-ray diffraction (XRD), respectively. It was found that the NiZr2 nanophase sample consists of ultrafine lamellae with thicknesses of a few nanometers and there are well-defined twin boundaries between the neighboring lamellae. The dependence of the annealing temperature on the mean grain size was determined. The formation process of the NiZr2 nanophase during a polymorphous crystallization of the amorphous phase was monitored by a differential scanning calorimeter (DSC) and its kinetics was analyzed.

TRANSMISSION MOSSBAUER-SPECTROSCOPY AND X-RAY-DIFFRACTION STUDIES ON THE STRUCTURE OF NANOCRYSTALLINE FE-CU-SI-B ALLOYS

Nanocrystalline Fe-Cu-Si-B alloys with grain sizes of 25-90 nm were synthesized by crystallization of the amorphous alloy. Two nanocrystalline phases of alpha-Fe(Si) and Fe2B were observed in all tested samples. Transmission Mossbauer spectroscopy investigation on the structure of nanocrystalline Fe-Cu-Si-B alloys showed that Si atoms are completely and substitutionally dissolved in Fe bcc lattice and the arrangement of the Si atoms in the alpha-Fe(Si) phase shows short range order (SRO), whereas 8.5-9.7 at.% of the B atoms were found as Fe2B and the remainder were located in the interfaces. When grains grow larger, the arrangement of the Si atoms in the alpha-Fe(Si) phase changes. Interestingly, x-ray diffraction results reveal that the lattice constant of alpha-Fe(Si) phase decreases rapidly with grain coarsening. Based on the thermodynamic analysis, the changes in the lattice constant of the alpha-Fe(Si) phase and SRO of Si atoms in bcc Fe lattices were attributed to the lattice expansion as a result of the variation of vacancy concentration in alpha-Fe(Si) solid solution. Meanwhile, owing to the interface contribution, the alloy with small grain size is found to exhibit large values of half linewidth (HLW) and isomer shift (IS) in the Mossbauer spectra. The results from electrical resistivity measurements agree and confirm the strong effects of the lattice distortion and interfaces.

Structure and properties of Fe-based nanocrystalline alloys containing a small amount of transition elements

Abstract Polycrystalline FeTMSiB alloys (TM = Cu, Mo) with grain sizes of 15–250 nm were synthesized by means of the amorphous crystallization method. Results show that in Cu-doped alloys with reduced grain size microhardness (HV) increases rapidly; while in Mo-doped alloys the variation of microhardness (HV) is obviously a critical phenomenon. The critical average grain size is 45 nm. The above results were interpreted by use of X-ray diffraction, positron annihilation and transmission Mossbauer spectroscopy.

COMPOSITION AND STRUCTURE OF TITANIUM NITRIDE FILMS PREPARED BY ION-BEAM ENHANCED DEPOSITION

Abstract Titanium nitride films have been prepared by simultaneous vacuum deposition of titanium and nitrogen ion beams with ion energy of 40 keV. The atomic arrival ratio of implanted ions to deposited atoms was varied from 0 to 0.5. The film composition and structure were analyzed by RBS, AES, TEM and XRD. The results show that nitrogen ion bombardment can clearly reduce the oxygen concentration in the film. The component ratio (N/Ti) in films prepared at low temperature was greater than that in the films prepared at high temperature. At the same atomic arrival ratio, the component ratio (N/Ti) in the films decreased with increasing titanium deposition rate. These results are considered to occur since the film composition is strongly affected by the adsorption of nitrogen, which depends sensitively on the substrate temperature, titanium deposition rate and pressure of nitrogen gas in the target chamber. The films were mainly TiN polycrystals, whereas only amorphous structures have been observed in films prepared under the same condition but without nitrogen ion bombardment. The preferred crystalline orientation of the film changed from 〈111〉 to 〈200〉 with an increase of the atomic arrival ratio (N/Ti). Such a variation is due to the difference in energy deposition on each titanium atom from the nitrogen ion beam during the ion beam enhanced deposition (IBED) process.