Читать книгу Engineering Physics of High-Temperature Materials - Nirmal K. Sinha - Страница 71

The world of metals, metallic alloys, and emerging intermetallics is both vast and complex. It touches our daily lives practically in all aspects. Metallurgy has played such an important role in civilization that several historical epochs have been named after the metals/alloys that enabled the next stage of advancement – often with the exploration of higher and higher temperature applications in society – such as in the Copper Age, Bronze Age, and Iron Age (Ferguson 2008). The engineering of metals and alloys to attain specific properties is an ongoing exploration that requires a detailed understanding of the structure of materials.

The search for high strength materials that would satisfy required creep and corrosion resistance under extremely severe conditions of elevated temperatures and pressures led to the development of “heat‐resistant alloys” or “high‐temperature alloys.” These alloys are known as “superalloys” to go along with the popular fictional television hero of late 1940s, Superman (Boesch 1989, p. 1). These alloys are either (i) solid‐solution strengthened or (ii) precipitation strengthened with or without additional strengthening by the incorporation of fine stable dispersoid (dispersion strengthened). The precipitation‐strengthened alloys are based on nickel, iron, or cobalt (Betteridge and Heslop 1974; Ross and Sims 1987; Stoloff 1987; Stephens 1989). Dispersion strengthening has been applied to many alloy systems, such as Al, Cu, Fe, Ni, Pb, Pt, and W alloys (Arzt 1991).

Superalloys are used extensively in aircraft and land‐based gas turbine engines. About 60% by weight of most modern gas turbine engine structural components, such as blades, vanes, and integral wheels, are made of nickel‐base superalloys. Although superalloys are closely linked to the aerospace industry, the history of nickel‐base superalloys, actually, started almost 100 years ago from the development of 20 wt.% Cr in an 80 wt.% Ni solid‐solution alloy for electrical heating elements (Betteridge and Heslop 1974; Ross and Sims 1987; Stephens 1989). Chromium was added to nickel to improve its strength and oxidation resistance.

Here, we present a basic overview of the structure of several important metals and alloys for high‐temperature applications. This is not intended to be comprehensive, but rather to serve as a reference to understand the models presented in subsequent parts of the text.