Evaluation of thermally degraded rapidly solidified iron-base and nickel-base alloys

The extent of thermal degradation of two rapidly solidified alloys (RSA) Type 304 and Ni{dollar}sb{lcub}53{rcub}{dollar}Mo{dollar}sb{lcub}35{rcub}{dollar}Fe{dollar}sb9{dollar}B{dollar}sb2{dollar} was evaluated at room temperature. The RSA 304 containing helium was compared with IM 304, which was conventionally prepared by ingot metallurgy.; Grain growth retardation was evident on annealed RSA 304 at 1000C for up to 24h. Annealed RSA 304 and IM 304 showed a similar strengthening mechanism, which was apparently due to matrix hardening and dislocation interaction since the dislocation locking term K{dollar}sb{lcub}rm y{rcub}sim{dollar} 0 and the friction stress {dollar}sigmasb{lcub}rm ys{rcub}simsigmasb{lcub}rm o{rcub}{dollar} in the Hall-Petch equation. The dislocation locking term K{dollar}sb{lcub}rm y{rcub}{dollar} was derived using a proposed analytical model. The strengthening of the Ni{dollar}sb{lcub}53{rcub}{dollar}Mo{dollar}sb{lcub}35{rcub}{dollar}Fe{dollar}sb9{dollar}B{dollar}sb2{dollar} was due to a uniform dispersion of boride particles and to matrix hardening. An analytical model of the Hall-Petch type equation was derived by modifying the Cottrell and Orowan theories. Particle coarsening occurred upon annealing at 1100C for 24, 48, and 240h. This alloy showed limited ductility related to particle fracture apparently at the onset of triaxial stresses.; RSA 304 showed better polarization behavior than IM 304 in 0.1N H{dollar}sb2{dollar}SO{dollar}sb4{dollar} due to the homogenous microstructure induced by rapid solidification processing (RSP). However, stress corrosion cracking (SCC) studies indicated a different trend. SCC attack was intergranular (IG) in RSA 304 apparently due to hydrogen-induced cracking (cathodic SCC). IM 304 showed anodic IGSCC accompanied with the film-rupture mechanism. In any case, the IGSCC fracture mode was associated with dimple rupture and occasionally particle-matrix separation was observed.; The Ni{dollar}sb{lcub}53{rcub}{dollar}Mo{dollar}sb{lcub}35{rcub}{dollar}Fe{dollar}sb9{dollar}B{dollar}sb2{dollar} showed good polarization behavior in 0.1N H{dollar}sb2{dollar}SO{dollar}sb4{dollar} and it was better than RSA 304 near the corrosion potential. Fractography showed dimple rupture and limited secondary cracks along the gage length. High strength and limited ductility were evident.; RSA 304 and the IM 304 showed similar damping behavior. The internal friction in both alloys was apparently due to dislocation damping and grain boundary damping mechanisms. The internal friction in the Ni{dollar}sb{lcub}53{rcub}{dollar}Mo{dollar}sb{lcub}35{rcub}{dollar}Fe{dollar}sb9{dollar}B{dollar}sb2{dollar} was due to interfacial effects. Complex moduli notation was used to derive the shear loss factor, which was greater than the extensional loss factor. Finally, it was concluded that internal friction can be used to detect microstructural changes and to predict mechanical properties.