Glossary

What are transonic airfoils, and what is the active clearance control? Check out our technical dictionary and find out more about engine technology terms – from active clearance control to velocity triangle.

HAE "Hell" "Hard" anodizing Hard chrome-plating Hardening and tempering Hardfacing Heat exchanger High-pressure compressor High-pressure turbine High-speed milling High-temperature vacuum brazing Hot isostatic pressing (HIP) Hypersonic aircraft

Hardfacing

The tips of low-pressure turbine blades are fitted with shrouds which serve to locate the blades relative to one another and to provide the necessary pre-stress. As the shrouds of adjacent blades contact each other during engine operation they are particularly susceptible to wear. Therefore, the shroud contact surfaces are provided with a hard coating.

The coating material (mostly Stellite, an extremely hard cobalt alloy) is applied by buildup welding and then ground to size. As contact between shrouds occurs in these "hardfaced" areas only, shroud wear is markedly reduced.