Surface Modifications in Aerospace Applications

Abstract

The long service life, often in harsh environmental conditions, and the stringent requirements of lightweight design make surface modification an essential part of materials technology for aerospace applications. Six contemporary developments are described, which are representative of advances in corrosion protection, fatigue life extension, metal matrix composite (MMC) based new design, and enhanced temperature capabilities by ceramic protective coatings. Coatings and corrosion inhibitors for aluminium skinned aircraft provide survivability, corrosion protection, and cosmetic appearance. Environmental concern on the presently used chromate have led to developments of self-priming topcoats, flexible primers, e.g. based on self-assembling silane molecules, temporary and multifunctional coatings. Fatigue life of titanium parts is shown to be enhanced by laser shock peening introducing compressive surface stresses. Preventing the onset of fatigue cracking from surfaces of titanium alloys and titanium aluminides is also the purpose of recently developed coatings, which hinder oxidation and oxygen penetration into titanium. Oxidation is also a major degradation problem of C/C and C/SiC composites. Classical protective coatings based on SiC are continuously complemented by multilayer coatings including, for example, yttrium silicates. The basis for future enhanced thermal barrier coatings may be provided by alternative ceramics such as lanthanum hexaluminates and an improved understanding of their damage mechanisms.