Rheological properties, gel network structures, and scaling laws for κ-carrageenan in aqueous solution were studied by rheology and field emission scanning electron microscopy (FESEM). The FESEM micrographs verified that the κ-carrageenan gels were formed by the formation of fibrils. The critical gel concentration, c g, obtained using the Winter–Chambon criterion, was found to be proportional to temperature as expressed by c g ∼ T 0.85 where T is the temperature in °C. At the gel point, the critical relaxation exponent n obtained was a constant (n = 0.62) and independent of temperature. The critical gel strength S g increased with increasing c g. A constant gel strength S g/c g was obtained by normalizing S g with c g to eliminate the effect of temperature, showing a unique character of κ-carrageenan in aqueous solution during gelation. The molecular structure of the junctions at the gel point was analyzed using the modified Eldridge–Ferry model, which supported the similarity of the fractal structure in the κ-carrageenan gels. Before the gel point, the zero shear viscosity η0 of κ-carrageenan solutions diverged as the gelling system approached to the gel point, and a scaling law, η0 ∼ ε–γ, was established, where ε is the relative distance of κ-carrageenan concentration c from c g and γ is the scaling exponent that was found to be 1.6. Beyond the gel point, the plateau modulus G e of κ-carrageenan gels depended on the polymer concentration according to a power law, G e ∼ ε z , where z was found to be 2.7. The critical gel exponent n evaluated from γ and z agreed well with the value of n determined from the Winter–Chambon criterion, further indicating that the characteristic relaxation time of the pregel and the postgel follows the same power law (symmetry at c = c g) for κ-carrageenan in aqueous solution.

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Vibropeening is a surface treatment process, which combines the peening effect of introducing residual stress with the polishing effect of reducing surface roughness in one single process step. Vibropeening equipment induces vibrations into the media to impart residual compressive stresses in sub-surface layers, as well as polishing on the surface of the work piece. In addition to process parameters, such as vibration frequency, amplitude, and media mass, which are well known in literature, this paper will focus on the study of two additional parameters: immersion depth and process time. It was found that the lower-middle section of the vibratory trough produced the highest Almen deflection. Different continuous treatment times were also studied to explore the maximum introducible residual compressive stress state, and it was concluded that an optimal time range is required to achieve the best residual stress profile. The study demonstrates that different process parameters can influence the effectiveness of the vibropeening process, and that these can be potentially optimized for higher treatment capability.

BALASUBRAMANIAN NAGARAJAN, SYLVIE CASTAGNE, SWAMINATHAN ANNAMALAI, ZHENG FAN, and WAI LUEN CHAN Eddy current spectroscopy is one of the promising non-destructive methods for residual stress evaluation along the depth of subsurface-treated nickel-base superalloys, but it is limited by its sensitivity to microstructure. This paper studies the influence of microstructure on the electrical conductivity of two nickel-base alloys, RR1000 and IN100. Different microstructures were attained using heat treatment cycles ranging from solution annealing to aging, with varying aging time and temperature. Eddy current conductivity was measured using conductivity probes of frequencies ranging between 1 and 5 MHz. Qualitative and quantitative characterization of the microstructure was performed using optical and scanning electron microscopes. For the heat treatment conditions between the solution annealing and the peak aging, the electrical conductivity of RR1000 increased by 6.5 pct, which is duly substantiated by the corresponding increase in hardness (12 pct) and the volume fraction of c¢ precipitates (41 pct). A similar conductivity rise of 2.6 pct for IN100 is in agreement with the increased volume fraction of c¢ precipitates (12.5 pct) despite an insignificant hardening between the heat treatment conditions. The observed results with RR1000 and IN100 highlight the sensitivity of electrical conductivity to the minor microstructure variations, especially the volume fraction of c¢ precipitates, within the materials.