B.Z. Ding

The structure and properties of nanocrystalline Fe78B13Si9 alloy

A new method has been employed to prepare a nanocrystalline alloy from amorphous ribbons and some of the structure-dependent properties of this alloy have been studied and compared with those of coarse-grained crystalline and amorphous FeBSi alloys. The new method of preparing nanocrystalline alloys involves annealing isothermally an amorphous ribbon of the same composition. By comparing the structure-dependent properties, it can be concluded that the novel properties of the nanocrystalline alloy reflect the unusual nature of its grain boundaries.

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

The synthesis of NbSi2 by mechanical alloying

The stoichiometric intermetallic compound NbSi2 has been synthesized by mechanical alloying (MA) elemental Nb and Si powders. The alloying process has been investigated by means of x-ray diffraction (XRD) and differential scanning calorimetry (DSC). It was found that the formation of the Nb2Si intermetallic compound occurs abruptly after 65 min of milling without any interruptions during the alloying process. However, short interruptions at a 5 min interval during ball milling result in a gradual reaction for the formation of the NbSi2 compound as well as a new metastable bcc structured solid solution. We conclude that the temperature rise during mechanical alloying plays an important role in initiating the abrupt reaction after an incubation milling time.

Hall-Petch relation in nanocrystalline FeMoSiB alloys

Abstract Polycrystalline alloys with grain sizes of 15–200 nm were synthesized by crystallization of an amorphous FeMoSiB alloy. Results showed that an inverse Hall-Petch relation between the microhardness and the average grain size is observed when the average grain size D is less than 45 nm; whereas a normal one is obtained when D is larger than 45 nm. Positron lifetime results indicated that nanovoids in the interfaces greatly influence the magnitude of microhardness of nanocrystalline FeMoSiB alloys at D .

Mechanical alloying of Fe-Nb-C materials

Mechanical alloying (MA) of elemental powder mixtures of Fe50Nb35C15, Fe60Nb30C10 and Fe50Nb40C10 was performed using a high energy ball mill. In the MA processing, ball milling first leads to a Fe-Nb-C amorphous phase and nanocrystalline NbC. Further milling results in the formation of a nanocrystalline solid solution of Fe(Nb, C) and nanocrystalline NbC in Fe50Nb35C15 and Fe60Nb30C10, while the final product for Fe50Nb40C10 is a mixture of amorphous Fe-Nb-C and nanocrystalline NbC.

Influence of Mo addition on the intrinsic magnetic properties and crystallization behaviour of FeSiB glass

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

Study of SiC/Al nanocomposites under high pressure

Ceramic reinforced Aluminium matrix composites which possess high specific strength and stiffness will receive wide applications in the near future. The discontinuous-type of reinforcement, for example SiC, has been especially appealing due to its relative availability and low cost production. In this paper, pressure method has been used to make nanometer-sized SiC particle, which obtained from laser-induced vapor-phase reactions and average particle diameter is about 25 nm, in Al matrix to form SiC/Al nanocomposites. Effects of the particle size and agglomerate state of SiC on the configuration of the grain boundary, microstructural development, as well as sinterability of SiC/Al nanocomposites under different pressure and temperature conditions were studied by TEM, SEM and X-ray diffraction

In situ formation of nanometer size TiC reinforcements in Ti matrix composites

Nanometer size TiC particulate reinforcements were in situ synthesized in Ti matrix composites under high pressure and high temperature conditions. The relationship between the mean grown sizes of TiC and the processing conditions, as well as its mechanism, is discussed. The microhardness of these composites was measured.

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.

THE ACTIVATION-ENERGIES FOR NUCLEATION AND GROWTH DURING CRYSTALLIZATION IN CU40TI60 GLASS

Abstract The crystallization kinetics of as-quenched and pre-annealed Cu 40 Ti 60 glasses were studied by means of Differential Scanning Calorimetry, and the activation energy of the total crystallization process was determined by use of Kissinger peak shift method. It was found that the crystallization temperature and apparent activation energy decrease systematically as the pre-anneal time increases, and the activation energy tends to a certain value of about 198KJ/mol. The effect was explained by the pre-existing nuclei resulted from pre-annealing. The nucleation activation energy En=356KJ/mol and growth activation energy Eg=198KJ/mol were obtained.