Hiroyasu Tezuka

Solidification structure of monotectic alloys

The formation manner of the monotectic structure is shown from the observation of the evolution of crystallization and growth of CuPb and some aluminium-based monotectic alloys solidified in a free direction and unidirectionally. The morphological change of the monotectic composite structure is discussed in relation to the solid-liquid interfacial morphology at the monotectic growth front as well as the interfacial energy balance between the solid and two liquids in the monotectic reaction. In free-directional solidification, a characteristic monotectic cell with a spherical shape is formed which is unlike dendritic and lamella morphologies. The monotectic cell consists of a spherical solid and a separated L2 liquid lying along the radii of the solid sphere. In unidirectional solidification, the monotectic structure of AlPb, AlBi and AlIn alloys changes in the following sequence with decreasing growth rate under a constant temperature gradient; random dispersion of L2 droplets in the aluminium solid matrix → periodic regular array of L2 droplets → fibrous L2 composite → aluminium single-phase region without the L2 phase. In CuPb monotectic alloy the monotectic structure changes with decreasing growth rates as follows: irregularly shaped rod-like L2 composite → coalesced coarsened discontinuous L2 composite → periodic banded structure consisting of L2-rich regions and L2-poor regions. These morphological transformations of monotectic structure are strongly affected by the ratio of the temperature gradient to the growth rate, the volume fraction of liquid L2 separated through the monotectic reaction and the interfacial energies between the solid and two liquids at the monotectic growth front.

Fabrication of Al/Al3Fe composites by plasma synthesis method

Abstract The present work was undertaken to highlight a novel in-situ process in which plasma spraying techniques plus electromagnetic stirring were used to produce Al/Al 3 Fe composites consist of angular and needle-like morphology of Al 3 Fe intermetallic compounds of about 10–20 μm in size. The microstructures of fabricated materials consisted of α-Al and Al 3 Fe intermetallic compounds, and the size, volume fraction and shape of Al 3 Fe intermetallic compounds depended mainly on the temperature of the melt and the plasma spraying conditions such as input current, gas flow rate of plasma and spraying distance. The microstructural difference arose from the difference of instantaneous temperature and velocity of the iron particle on the melt surface. The temperature and velocity of the iron particles in the plasma arc were calculated and the results were compared with the fabricated microstructures. In addition, the evolution of microstructures of angular and needle-like Al 3 Fe intermetallic compounds was analyzed morphologically by spherical shell model incorporating of diffusion kinetics.

Evolution of iron aluminide in Al/Fe in situ composites fabricated by plasma synthesis method

Abstract The evolution of intermetallic compounds for Al/Fe in situ composites fabricated by the plasma synthesis method (PSM) was investigated through the microstructural analyses for the partially reacted particle region. The partially reacted particle is composed of Al/Al 13 Fe 4 /Al 5 Fe 2 /Fe layer. Based on the concept of effective free energy of formation, the first phase that nucleates on the interfacial layer of Al/Fe is determined as Al 13 Fe 4 . By the reaction of Al 13 Fe 4 and Fe, Al 5 Fe 2 forms and grows inward. Due to heat extraction by the reaction, the edge of Al 13 Fe 4 dissolves to form angular Al 13 Fe 4 in the matrix. By the reaction and decomposition of Al/Fe through the intermediate phase of Al 5 Fe 2 , the Fe particles transform to Al 13 Fe 4 in the plasma synthesis method. In addition, the differences of main intermetallic compounds between by the hot dipping process and by the plasma synthesis method were discussed.

Dispersoid Formation and Recrystallization Behavior in an Al-Mg-Si-Mn Alloy

The nucleation and precipitation of Mn-containing dispersoids in an Al-Mg-Si-Mn alloy (6082) have been studied by optical microscopy, EPMA (electron probe microanalysis) and TEM (transmission electron microscopy). The in∞uence of Mn-containing dispersoids on the recrystallization behavior was also investigated. The size and distribution of dispersoids were strongly afiected by both the homogenization process and the alloying element distribution formed in the direct chill cast procedure. The Mn-containing dispersoids were observed to nucleate preferentially on the fl 0 -Mg2Si phase and to be aligned along the direction of the matrix. After cold deformation, the morphology of dispersoids greatly in∞uences the recrystallization and grain growth behavior in the annealing process.

Interfacial bond between SiCw and Mg in squeeze cast SiCw/Mg composites

The interfacial microstructure of precipitate- and reaction-free interface in squeeze cast SiCw/AZ91 Mg matrix composites were investigated by High Resolution Electron Microscopy (HREM). Two kinds of crystalline orientation relationships between SiC whisker and Mg are observed, which resulted from the solidification of molten Mg at the different surface planes of SiCw exposed whisker. The interfaces with orientation relationships are semi-coherent interfaces and high interfacial bond strength exist in these interfaces.

Effects of particle properties on the microstructure of aluminum based metal–metal composites fabricated by plasma synthesis method

Abstract Aluminum based metal–metal composites were fabricated by the plasma synthesis method with Fe, Cr and Ni powders. The fabricated microstructures are mainly composed of α-Al and aluminide intermetallic compounds. However, the microstructural features are different with each powder. The as-cast microstructures were analyzed by the properties of powders such as temperature in the plasma arc, diffusivity and solubility in the molten aluminum.

Crystallographic orientation relationship between SiCw and Mg in squeeze-cast SiCw/Mg composites

harbin inst technol, sch mat sci & engn, harbin 150001, peoples r china. tokyo inst technol, dept met engn, tokyo 152, japan. acad sinica, inst met res, atom imaging solids lab, shenyang 110015, peoples r china.;wu, k (reprint author), harbin inst technol, sch mat sci & engn, harbin 150001, peoples r china

Effects of Sintering Conditions on Mechanical Properties of Biomedical Porous Ti Produced by Spark Plasma Sintering

Because of its excellent biocompatibility, good corrosion resistance and relatively lower Youngs modulus, Ti was suitable for biomaterial. It, however, showed still bigger Youngs modulus comparing to the living bone. It was necessary to decrease the Youngs modulus in order to avoid adversely affect to the bone, such as stress sheilding. In this study, porous Ti were fablicated to decrease the Youngs modulus by space holder method from Ti/NaCl composites sintered using spark plasma sintering (SPS) method. The sintering condition and the size of NaCl affected to the porous structure and mechanical properties. According to the scanning electron microscope (SEM) observation and the relative density measurement of specimens sintered with several sintering conditions, the desirable sintering condition was concluded as 973 K of sintering temperature and 1.2 ks of sintering time. The specimens made from NaCl powder whose size were from 106 to 214 µm showed almost opened and connected pores. The Youngs modulus was decreased with increasing the porosity.

Effects of Cu and Ag Addition on Nanocluster Formation Behavior in Al-Mg-Si Alloys

Two types of nanoclusters, termed Cluster (1) and Cluster (2) here, both play an important role in the age-hardening behavior in Al-Mg-Si alloys. Small amounts of additions of Cu and Ag affect the formation of nanoclusters. Two exothermic peaks were clearly detected in differential scanning calorimetry(DSC) curves by means of peak separation by the Gaussian method in the base, Cu-added, Ag-added and Cu-Ag-added Al-Mg-Si alloys. The formation of nanoclusters in the initial stage of natural aging was suppressed in the Ag-added and Cu-Ag-added alloys, while the formation of nanoclusters was enhanced at an aging time longer than 259.2 ks(3 days) of natural aging with the addition Cu and Ag. The formation of nanoclusters while aging at was accelerated in the Cu-added, Ag-added and Cu-Ag-added alloys due to the attractive interaction between the Cu and Ag atoms and the Mg atoms. The influence of additions of Cu and Ag on the clustering behavior during low-temperature aging was well characterized based on the interaction energies among solute atoms and on vacancies derived from the first-principle calculation of the full-potential Korrinaga-Kohn-Rostoker(FPKKR)-Green function method. The effects of low Cu and Ag additions on the formation of nanoclusters were also discussed based on the age-hardening phenomena.

A New Deformation-Semi-Solid Casting Process of Highly Concentrated Fe Containing Al-Si-Cu-Fe Cast Alloys

A newly proposed process of the deformation-semi-solid casting (D-SSC) process was applied to the highly concentrated Fe containing Al-7%Si-3%Cu-1%Fe alloys (in mass%) to eliminate the harmful influence of impurity Fe. The proposed D-SSC process consists of hot-deformation, heating to the semi-solid temperature and subsequent casting. The markedly improved microstructures and mechanical properties of the fabricated alloys by the D-SSC process were investigated. In the microstructure observation, the size and shape of the characteristic morphologies of the primary α-Al phase and the Fe containing intermetallic compound of the β-Al 5 FeSi phase were evaluated. the extremely refined β phase and the finely spheroidized α-Al phase are simultaneously achieved by the D-SSC process. The D-SSC process is found to be useful to modify the high amount of Fe into a harmless impurity.