Scripta Metallurgica et Materialia最新文献

$\text{〈}\text{1}\text{01〉>}$ superdislocations in TiAl can dissociate on discrete segments of the dislocation line and generate trailing $\text{±}\text{1}\text{6}\text{〈}\text{11}\text{2〉}$ or $\text{±}\text{1}\text{3}\text{〈}\text{2}\text{11〉}$ dipoles. A mechanism for $\text{±}\text{1}\text{3}\text{〈}\text{2}\text{11〉}$ dipole formation from a $\text{〈}\text{1}\text{01〉}$ superdislocation dissociated on two adjacent (111) planes is discussed. The non-coplanar $\text{〈}\text{1}\text{01〉}$ core structure may arise either from direct dissociation by the cross-slip of a $\text{1}\text{2}\text{〈}\text{1}\text{01〉}$ superpartial, or by an initial $\text{〈}\text{1}\text{01〉 →}\text{1}\text{2}\text{〈}\text{1}\text{10〉 +}\text{1}\text{2}\text{〈}\text{11}\text{2〉}$ decomposition of the superdislocation and the subsequent pinning of the $\text{1}\text{2}\text{〈}\text{1}\text{10〉}$ perfect dislocation by an immobile $\text{1}\text{6}\text{〈}\text{11}\text{2〉}$ delocalised partial associated with a non-coplanar $\text{1}\text{2}\text{〈}\text{11}\text{2〉}$ superdislocation core.

We have studied the crystallization, crystal structure, microstructure, and magnetic properties of melt-spun ribbons of R₆(Fe-Nb)₈₈B₆ with RNd, Pr, Dy, Tb and Nd_3.5(Fe-Nb)₉₃B_3.5 consisting of a mixture of exchange-coupled magnetically hard R₂Fe₁₄B and soft α-Fe phases. The as-spun ribbons of R-rich composition crystallize in two steps; for RNd, Pr, and Dy at first the Y₃Fe₆₂B₁₄-type + α-Fe phases and subsequently they transform to 2:14:1 and α-Fe upon heating above 700 °C. The intermediate phase in the case of Tb₆(Fe-Nb)₈₈B₆ is of the TbCu₇-type. Very high remanences up to 145 emu/g with reduced remanences ranging from 0.6 to 0.7 were observed. The coercivity of the samples was found to vary with the R element and the hard phase content. The highest room temperature coercivity of 4.5 kOe was obtained in a Nd₄Tb₂(Fe-Nb)₈₈B₆ sample. The observed reversible demagnetization curves are characteristic of exchange-spring magnets.

A two-phase microstructure was also obtained in Sm-Fe-Ga-C ribbons consisting of exchange-coupled 2:17 and α-Fe phases after annealing in the temperature range of 700–800 °C. The highest coercive force (12.8 kOe) was obtained in samples annealed at 800 °C. Annealing at 700 °C led to finer grains with lower coercivities (5kOe) but higher remanences.

Correlation between magnetic and structural properties of electroless-deposited CoNiP films for the use of perpendicular magnetic recording media was studied, focusing upon their phase-separated structure in nanometer scale. The media with various perpendicular coercivity, Hc(⊥), were examined and it was clarified that higher Hc(⊥) medium showed a clearer phase-separated condition, which was confirmed by the selective chemical-etching technique. It was strongly indicated that such a structure plays an important role in attaining a high Hc(⊥) and in forming an hcp structure in a film with a Ni-rich average composition.

Previous nanostructural and nanocompositional studies performed on the boundaries of deformed grains in two die-upset rare earth magnets with bulk compositions Nd_13.75Fe_80.25B₆ and Pr_13.75Fe_80.25B₆ indicate that the intergranular phase in many grain boundaries is enriched in iron relative to the bulk. We present here preliminary magnetic data that provide further evidence that this grain boundary phase is indeed iron-rich, and in fact appears to be ferromagnetic. Hysteresis loops were performed at 800 K on die-upset magnets with the above compositions. Each sample showed a clear hysteresis with coercivities between 34 and 40 Oe and an average remanence 4πB_R of 6.8 G for the Nd-based sample and 10.3 G for the Pr-based sample. The ferromagnetic signals measured at high temperature in these magnets are attributed to the iron-rich grain boundary phase. The implications of this conclusion with respect to coercivity are discussed.