Effect of LiF as Sintering Agent on the Densification and Phase Formation in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-4 Wt Pct Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> Ceramic Compound

Different amounts of LiF were added to an Al₂O₃-4 pct Nb₂O₅ basic ceramic, as sintering agent. Improved new ceramics were obtained with LiF concentrations varying from 0.25 to 1.50 wt pct and three sintering temperatures of 1573 K, 1623 K, and 1673 K (1300 °C, 1350 °C, and 1400 °C). The addition of 0.5 wt pct LiF yielded the highest densification, 94 pct of the theoretical density, in association with a sintering temperature of 1673 K (1400 °C). Based on X-ray diffraction (XRD), this improvement was due not only to the presence of transformed phases, more precisely Nb₃O₇F, but also to the absence of LiAl₅O₈. The preferential interaction of LiF with Nb₂O₅, instead of Al₂O₃, contributed to increase the alumina sintering ability by liquid phase formation. Scanning electron microscopy (SEM) results revealed well-connected grains and isolated pores, whereas the chemical composition analysis by energy dispersive energy (EDX) indicated a preferential interaction of fluorine with niobium, in agreement with the results of XRD. It was also observed from thermal analysis that the polyethylene glycol binder burnout temperature increased for all LiF concentrations. This may be related to the formation of hydrogen bridge bonds.     

Effect of Planar Flow Melt Spinning Parameters on Ribbon Formation in Soft Magnetic Fe<Subscript>68.5</Subscript>Si<Subscript>18.5</Subscript>B<Subscript>9</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> Alloy

The effect of planar flow melt spinning (PFMS) parameters on the continuity, surface quality, and structure of 10-mm-wide Fe_68.5Si_18.5B₉Nb₃Cu₁ ribbons has been investigated. The change in shape and stability of the melt puddle as a function of the processing parameter was studied using a high-speed imaging system and was correlated to ribbon formation. A window of process parameters for obtaining continuous ribbons with good surface quality has been evaluated. It has been observed that thinner ribbons are found to be more continuous because of higher ductility. The higher melt temperature leads to the formation of crystalline phase in as-spun ribbons, and this deteriorates the soft magnetic properties on annealing. The experimental results are corroborated with the numerical estimates, which suggest that the critical thickness for amorphous phase formation decreases with increasing initial melt temperature.     

Effect of Superficially Applied Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating on High-Temperature Corrosion Behavior of Ni-Base Superalloys

Inhibitors and oxide additives have been investigated with varying success to control high-temperature corrosion. Effect of Y₂O₃ on high-temperature corrosion of Superni 718 and Superni 601 superalloys was investigated in the Na₂SO₄-60 pct V₂O₅ environment at 1173 K (900 °C) for 50 cycles. Y₂O₃ was applied as a coating on the surfaces of the specimens. Superni 601 was found to have better corrosion resistance in comparison with Superni 718 in the Na₂SO₄-60 pct V₂O₅ environment. The Y₂O₃ superficial coating was successful in decreasing the reaction rate for both the superalloys. In the oxide scale of the alloy Superni 601, Y and V were observed to coexist, thereby indicating the formation of a protective YVO₄ phase. There was a distinct presence of a protective Cr₂O₃-rich layer just above the substrate/scale interface in the alloy. Whereas Cr₂O₃ was present with Fe and Ni in the scale of Superni 718. Y₂O₃ seemed to be contributing to better adhesion of the scale, as comparatively lesser spalling was noticed in the presence of Y₂O₃.     

Influence of heat treatment on the efficiency of impact fragmentation of amorphous alloy Fe<Subscript>73.5</Subscript>Cu<Subscript>1</Subscript>Nb<Subscript>3</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript> ribbons

The mechanism of impact fracture of soft magnetic amorphous alloy Fe_73.5Cu₁Nb₃Si_13.5B₉ ribbons in a disintegrator after heat treatment at a temperature from the range 300–700°C and the fractional composition of the formed powder are studied. The temperature ranges of a change in the mechanism of ribbon fracture are determined. The particle size distribution is shown to change weakly within the revealed temperature ranges.