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1.
Formation and evolution details of a blocky microstructure in AISI 304 stainless steel are studied by quenching method during directional solidification. Results show that a coupled growth microstructure, consisting of lathy ferrite and austenite, forms first from the melt. At solid-state transformation stage, most lathy ferrite disappears due to the phase transformation from ferrite to austenite. With further decreasing of the temperature, plenty of fine ferrite colonies occur in the original austenite region. The formation of the blocky ferrite indicates that reverse solid-state transformation from austenite to ferrite takes place. This transformation is due to the segregation and the instability of austenite during the growth of austenite under low cooling rate. The fine ferrite colonies transform into blocky ferrite at room temperature. TEM and EDS analyses were carried out to identify the phases and determine the phase composition, respectively.  相似文献   

2.
A series of isovelocity experiments was performed to investigate the interface morphology evolution during the solid-state ferrite–austenite transformation of the Fe–Mn–Al alloy, and a quantitative relationship between cellular spacing and growth velocity had been measured. The corresponding cellular spacing of the product phase decreases with the growth velocity increasing. Theoretical model modified from directional solidification process was also applied to study the relationship between cellular spacing and growth velocity, and the theoretical prediction corresponds well with the measured results.  相似文献   

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4.
We report on a comparative investigation of the incorporation of group III, IV and V impurities in 3C–SiC heteroepitaxial layers grown by the vapour–liquid–solid (VLS) mechanism on on-axis α-SiC substrates. To this end, various Si-based melts have been used with addition of Al, Ga, Ge and Sn species. Homoepitaxial α-SiC layers grown using Al-based melts were used for comparison purposed for Al incorporation. Nitrogen incorporation depth profile systematically displays an overshoot at the substrate/epilayer interface for all the layers. Ga and Al incorporations follow the same distribution shape as N whereas this is not the case for the isoelectronic impurities Ge and Sn. This suggests some interaction between Ga/Al and N coming from the high bonding energy between the group III and V elements, which does not exist with Ge and Sn. This is why both incorporate as a cluster. A model of incorporation is proposed taking into account metal-N and metal-C bonding energies together with the solid solubility of the corresponding nitrides.  相似文献   

5.
Calorimetric, magnetic and X-ray diffraction measurements have been used to study the magnetic susceptibility and thermal stability of Co80ErxB20−x with (0 ? x ? 4) amorphous ribbons. The compounds are found to crystallize in Co2B and β-Co, after precipitation of the tetragonal Co3B phase. The addition of erbium shifts up the crystallization temperature leading to the increase in the stability of the amorphous state. Magnetic susceptibility measurements show that the addition of erbium increases the Curie temperature and induces noncollinear magnetic behavior. This latter fact is explained on the basis of random local magnetic anisotropy related to the rare earth atoms in amorphous materials.  相似文献   

6.

The possibility of formation of molybdenum and tungsten polyoxides in the Mo–W–Al2O3–H2 system at T = 2400 K and P = 1 bar in a controlled Ar + H2 atmosphere has been investigated by the method of thermodynamic analysis. The formation of polyoxides is found to occur both due to the processes involving Al2O3 melt and in the absence of the latter. It is established that metals (Mo and W) and their mono-, di-, and even trioxides (in the latter case, mediated polymerization occurs) can be used as initial components to form polyoxides. It is shown that polyoxides themselves may interact with one of their main sources: Al2O3 melt.

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7.
Crystallography Reports - The compositions of nonstoichiometric phases Pb1 – xRxF2 + x (CaF2 type, R is a rare-earth element) have been optimized with...  相似文献   

8.
Crystallography Reports - The structural features of the phases formed during crystallization of mixed copper and nickel complexes with nitrilotris(methylenephosphonic acid)...  相似文献   

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