Duplex microstructures

The difficulty of obtaining pure / "-material for the electrolyte has been tackled in many production processes worked out in the past. Unless precautions are taken, sintering of a -alumina-derived / "-alumina compositions invariably results in the duplex microstructure and a low-strength ceramic. Therefore a balance has to be struck between conductivity and strength. The problem arises because the conversion from —alumina to / " -alumina is slow... 

The results of development work on processes indicate that the two main methods of preventing the duplex microstructure from forming appear to be fast-firing, or increasing the amount of / "-alumina at low temperatures. Based on these results, Duncan et al. [20] and Zyl et al. [21] have described production processes starting from aluminum oxy-hydroxides or aluminum hydroxides as precursors for the synthesis of the solid electrolyte "-alumina. Duncan et al. described an alumina precursor which substitutes in part or wholly for or-alumina in an established... 

High toughness Duplex microstructure with high aspect ratios... 

Comparing the requirements for high strength (uniform, fine microstructure) to those needed to improve toughness (nonhomo-geneous, duplex microstructure) reveals the problem in achieving both simultaneously. 

When using the creep model for duplex microstructure, as developed by French et al. [98], it is possible to fabricate a composite with a defined creep resistance that will control the grain size, the width of the layers, and the compression axis. In the case of isostrain, where the strain and strain rate are the same for each phase, and assuming the creep equation in a compact form as, e = Ajo the stress for this configuration, o, is given as ... 

Almost no engineering material is safe from or immune to microbial corrosion. In Chapter 8 the vulnerability and susceptibility of copper and cupronickels, duplex stainless steels and concrete will be discussed in a brief and informative manner. I had my reasons for picking these materials copper and its alloys have the reputation of being poisonous to micro-organisms, duplex stainless steels are known for their high resistance to corrosion thanks to their duplex microstructures of ferrite and austenite, and concrete is widely used in both the marine and water industries because of its good performance and cost effectiveness. 

Figure 10.8 Metallographic views of 9Cr, llCr-ODS steel having duplex microstructure consisting of tempered martensite and residual-a ferrite.

The materials under study are uncoated and aluminized 12% chromium steels. The 12% chromium steel reported in this chapter was a ferritic alloy steel HCM12A, prepared by Sumitomo, Japan, of nominal composition 12.22 wt.% Cr, 1.88 wt.% W, 0.86 wt.% Cu, 0.53 wt.% Mn, 0.36 wt.% Mo, 0.35 wt.% Ni, 0.31 wt.% Si, 0.20 wt.% V, 0.10 wt.% C, 0.052 wt.% N, 0.05 wt.% Nb, 0.014 wt.% P, 0.001 wt.% S, 0.0008 wt.% A1 and Fe (balance). This is a so-called third generation ferritic steel for power plants, with improved weldability and creep strength compared to prior ferritic steel versions. It has a duplex microstructure of tempered martensite and 6-ferrite [2]. The uncoated steel samples were ground to 320 grit finish using SiC grinding paper. Prior to the experiments, the samples were washed ultrasonicaUy in acetone and then in ethanol. 

Such a duplex microstructure is commonly observed for NiO scales grown at a temperature lower than 1000°C (Peraldi et al., 2002 Haugsrud, 2003). For such duplex scales, inert marker location, 0 experiments and careful analysis of NiO scale microstructure show that the growth of the external columnar subscale is associated with the outward diffusion of Ni cations and occurs at the scale-gas interface, while the inward diffusion of oxygen is involved in the growth of the inner equiaxed subscale. Therefore, the internal interface between the equiaxed and columnar sublayers marks the initial location of the Ni surface before the formation and growth of NiO scales. 

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