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In this study, the exothermic DSC peaks observed in rapidly-solidified Fe-44.9at.%Al ribbons and water-quenched Fe-48.5at.%Al single crystals were analyzed by Matusita’s method in order to discuss the kinetics of the agglomeration processes of supersaturated vacancies. Both the nucleation and morphological factors, n and m, respectively were approximately 3 for the rapidly solidified ribbons and were approximately 2 for the water-quenched single crystals. Based on the Matusita’s idea, the m values suggest the growth of 3-dimensional voids in the rapidly solidified ribbons and the growth of 2-dimensional dislocations loops in the single crystals due to the agglomeration of supersaturated vacancies. In addition, the n values suggest that the nuclei of voids and dislocation loops existed in as-quenched samples. These interpretations are in good agreement with the results of TEM observations.

Three kinds of Mo-Si-B ternary alloys and a 1 at.% Al added Mo-Si-B alloy with the compositions near Mo-8.7 at.% Si-17.4 at.% B that is in the Mo5SiB2 and Mo two-phase compositional region were produced by Ar arc-melting followed by the heat treatment at 1800 °C for 24 h. These alloys have the characteristic fine microstructure composed of small Mo solid solution (Moss) particles in the Mo5SiB2 (T2) matrix with the primary phase (Moss or T2 depending on composition). The volume fraction of the Moss particles ranges from 25.5 to 30.5 % and its average size from 3.0 to 6.4 μm in the fine microstructure of the alloys. Micro cracks were introduced by Vickers hardness tests into the microstructures, and their propagation is disturbed by the small Moss particles. Thus, each hardness value seems to relate to the cracking behavior around each indent. On the other hand, Vickers hardness values do not show correlation with the volume fraction of the Moss particles, but clearly decrease with increasing the average particle size of Moss. Therefore, it should be concluded that the increase in the particle size of Moss could enhance the toughness of the Mo5SiB2/Mo-based alloys effectively by ductile phase toughening.

Nanoporous surfaces are formed in B2-type FeAl single crystals by quenching into iced water, followed by surface treatment and aging heat treatment. From our previous works, it was indicated that the nanoporous phenomenon is caused by the clustering of supersaturated thermal vacancies. In this study, the clustering process of supersaturated thermal vacancies was systematically investigated by transmission electron microscopy (TEM). An irreversible exothermic peak was detected for as-quenched specimens by differential scanning calorimetry (DSC). The isochronal changes of surface morphology and substructure around the exothermic peak temperature were clarified by TEM observation. The average size of the surface pores monotonously increased with increasing the temperature. Dislocations whose Burgerse vectors are parallel to existed in the isochronally-heated single crystals, and its density was changed with heat treatment temperature. On the other hand, there was no dislocation zone from surface to the depth of several tens nanometers. A growth model of the surface pores is discussed

ABTSRACTSeveral lamellar microstructures of a Ti-48 % Al alloy were made by changing heating rate in the α+γ dual phase field, and their creep properties were investigated at 1150 K. Average spacing and average length of α2 lamellae decrease with increasing heating rate. The decrease of α2 lamellar spacing is most effective at lower heating rate, and minimum creep rate decreases with increasing the heating rate, since a high density of γ/α2 boundaries stabilizes lamellar microstructure during creep. On the other hand creep rate increases at high heating rate, since α2 lamellar length becomes shorter with increasing heating rate. A reduction of creep rate by one order of magnitude is achieved at the optimum heating rate providing the best combination of narrow spacing and sufficiently long length of α2 lamellae.

Materials Research Society (Integrative and Interdisciplinary Aspects of Intermetallics Session) From 11/29/2004 To 12/3/2004, Boston, MA, USA, available, unclassified, unlimited

Adhesion strength in sputter-deposited Cu thin films on various types of barrier layers was investigated by scratch test. The barrier layers were Ta1-xNx with varied nitrogen concentration of 0, 0.2, 0.3, and 0.5. Microstructure observation by TEM indicated that each layer consists of mixed phases of β;-Ta, bcc-TaN0.1, hexagonal-TaN, and fcc-TaN, depending on the nitrogen concentration. A sulfur- containing amorphous phase was also present discontinuously at the Cu/barrier interfaces in all samples. Scratch test showed that delamination occurred at the Cu/barrier interface and that the overall adhesion strength increased with increasing the nitrogen concentration. A good correlation was found between the measured adhesion strength and the composing phases in the barrier layer.

Thermal cycling was performed in Al-lmo%Si thin films deposited on Si wafers. After a given number of cycling between room temperature and 723 K, residual stress was measured at room temperure. Residual stress was found to increase with increasing the cycling number up to the 4th cycle, followed by further a continuous decrease by further cycling. The intial increase was found to be related to the increase of lattice dislcocations and their tangling. The following decrease was caused by crack formation along grain boundaties or by film delamination in some cases.

Creep characteristics of polycrystalline single-phase intermetallics, α 2 -Ti 3 AI and γ-TiAl, at 1100 K have been summarized to evaluate their relative strength at elevated temperature at three strain-rate levels, 10 -1 10 −4 and 10 −8 s −1 , and are compared with those of α Ti-Al terminal solid solution alloys. The strength of these intermetallics is obviously higher than that of α, random solid solutions, especially at low strain-rates. However, the difference in high-temperature long-term strength among intermetallic alloys is not significant at any strain-rate level.