Single-phase metal alloys

In most materials selection processes, it is virtually impossible to make materials choices independent of the product shape. This includes not only the macroscopic, or bulk, shape of the object such as hammer or pressure relief valve, but also the internal or microscopic shape, such as a honeycomb structure or a continuous-fiber-reinforced composite. Shape is so important because in order to achieve it, the material must be subjected to a specific processing step. In Chapter 7, we saw how even simple objects made from a single-phase metal alloy could be formed by multiple processes such as casting or forging, and how these processing steps can affect the ultimate properties of the material. As illustrated in Figure 8.6, function dictates the choice of... 

Three techniques have been described in the literature to prepare combinatorial libraries of fuel cell electrocatalysts solution-based methods [8, 10-14], electrodeposition methods [15-17] and thin film, vacuum deposition methods [18-21]. Vacuum deposition methods were chosen herein for electrocatalyst libraries in order to focus on the intrinsic activity of the materials, e.g., for ordered or disordered single-phase, metal alloys. 

We will now present two methods for measuring the activities which are more specifically designed for solid solutions. The first method, involving the solid solution in a reaction which does not involve any other solution. Note that this method could be applied to liquid solutions but usable reactions are then very rare. The second method is an electrochemical method designed for single-phase metal alloys. 

In summary, we have discussed the three mechanisms that may be used to strengthen and harden single-phase metal alloys strengthening by grain size reduction, solid-solution strengthening, and strain hardening. Of course, they may be used in conjunction with one another for example, a solid-solution strengthened alloy may also be strain hardened. 

For a single-phase binary alloy A-B, the two anodic partial reactions of metal dissolution are... 

We will study and follow only single-phase binary alloys (with two components) for which it was possible to set up some models, which already show the complication of the phenomena compared to oxidation of pirre metals. 

Consider a single-phase binary alloy (Al, A2) forming a sohd solution of substitution of two metals Al and A2. One carries out the oxidation of this alloy by a gas G2 under conditions such as only the Al element is oxidized to form on the surface of alloy a layer of the oxidized compound AIG. It is said that Al tmdergoes a selective oxidation. That will be, for example, the case of nickel-platimtm alloys with selective oxidation of nickel into NiO, example of which is used [KUB 49], [LAL 73], [THO 49], [WAG 52] to model selective oxidation as we will see further. We suppose that the gas imdergoes a dissociative adsorption. 

In the previous chapter the solidification of single-phase metals and alloys was considered with regard to both the constitutional and structural effects which occurred. In this chapter more complex alloys are treated in which two or more phases are present. Eutectics, peritectics and monotectics are considered first. Particles in melts and gases in melts are dealt with subsequently. 

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