Improving the resistance to intergranular cracking and corrosion at elevated temperatures by grain-boundary-engineering-type processing

Failure of structural components operating under high mechanical loading and/or in aggressive environments can often be attributed to intergranular degradation, e.g. by creep, corrosion, fatigue or brittle cracking. The present article is focussed on oxygen-diffusion-controlled grain-boundary attack, for example, of a nickel-based superalloy leading to intercrystalline oxidation or rapid cracking by dynamic embrittlement. Since grain-boundary diffusion depends on the crystallographic orientation relationship between adjacent grains, the grain-boundary-engineering approach was applied to reduce the susceptibility to grain-boundary attack. The relevant mechanisms are discussed in terms of modifying the network of general high-angle and so-called special grain boundaries taking the results of cracking experiments on bicrystals into account.