Alloy design

Alloy Design and Fabrication Considerationsfor Pone lain Enameling Aluminum, Bulletin P-402(69), Porcelain Enamel Institute, Washington, D.C., 1969. 

Alloy Designation UNS Composition, Condition Yield strength, Idp/in (MPa) Tensile strength, Idp/in (MPa) Elongation, % Hardness, HB... 

As Fig. 20.7 shows, if DS eutectics ( DSEs ) prove successful, they will allow the metal temperature to be increased by =100°C above conventional DS nickel alloys, and the inlet temperature by =200°C (because of a temperature scaling effect caused by the blade cooling). Further improvements in alloy design are under way in which existing nickel alloys and DS eutectics are being blended to give a fibre-reinforced structure with precipitates in the matrix. 

In this chapter we look first at an important class of alloys designed to resist corrosion the stainless steels. We then examine a more complicated problem that of protecting the most advanced gas turbine blades from gas attack. The basic principle applicable to both cases is to coat the steel or the blade with a stable ceramic usually Cr203 or AI2O3. But the ways this is done differ widely. The most successful are those which produce a ceramic film which heals itself if damaged - as we shall now describe. 

Pettifor, D.G. and Cottrell, A.FI. (1992) Electron Theory in Alloy Design (The Institute of Materials, London). 

The evolution of superalloys has been splendidly mapped by an Ameriean metallurgist, Sims (1966, 1984), while the more restrieted tale of the British side of this development has been told by Pfeil (1963). I have analysed (Cahn 1973) some of the lessons to be drawn from the early stages of this story in the eontext of the methods of alloy design it really is an evolutionary tale... the survival of the fittest, over and over again. The present status of superalloy metallurgy is eoneisely presented by MeLean (1996). 

Alloy Designation Tensile Strength 0.2% Yield Working Hardness Coeff. of Thermal Expansion Thermal Conductivity Cost Index... 

Registration Record of Aluminum Association Alloy Designations and... 

Ahmad studied specimens of an Al-Li-Cu-Mg-Zr alloy designated 8090 in the form of specimens between 1 mm and 3 mm in thickness cut from an extruded bar of cross-sectional dimensions 51 mm x 25 mm. An XPS spectrum of the surface of a sample oxidized for 5 min at 530°C in air is shown in Figure 2.6. In addition to the peaks of carbon, oxygen and magnesium, there is a lithium (Li Is) peak at 56eV binding energy. 

FIGURE 4.5 Schematic of alloy design for SOFC applications. 

Traditional alloy design emphasizes surface and structural stability, but not the electrical conductivity of the scale formed during oxidation. In SOFC interconnect applications, the oxidation scale is part of the electrical circuit, so its conductivity is important. Thus, alloying practices used in the past may not be fully compatible with high-scale electrical conductivity. For example, Si, often a residual element in alloy substrates, leads to formation of a silica sublayer between scale and metal substrate. Immiscible with chromia and electrically insulating [112], the silica sublayer would increase electrical resistance, in particular if the subscale is continuous. 

As an example of a specific magnesium alloy code we may mention the alloy designated by AZ91E-T6. It contains A1 and Zn as principal alloying components. The... 

Chapter 10 provides an exhaustive description of how these techniques can be applied to a large number of industrial alloys and other materials. This includes a discussion of solution and substance databases and step-by-step examples of multi-component calculations. Validation of calculated equilibria in multi-component alloys is given by a detailed comparison with experimental results for a variety of steels, titanium- and nickel-base alloys. Further selected examples include the formation of deleterious phases, complex precipitation sequences, sensitivity factor analysis, intermetallic alloys, alloy design, slag, slag-metal and other complex chemical equilibria and nuclear applications. 

An interesting and important corollary of CALPHAD calculations is to predict sensitivity factors for various important material properties, such as liquidus and solidus temperature, solid state transus temperatures, heat-treatment windows, etc. These can then be utilised both in alloy design and in production of alloys or components. 

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