Mechanical and thermomechanical properties of metal spray invar for composite forming tooling

The subject of this paper is the assessment of the thermal and mechanical p roperties of Invar steel coatings, deposited using electric are spraying, a nd the correlation of these properties to the spray parameters and processe s used to offer coatings with characteristics appropriate to the requiremen ts of tools used in the fabrication of precision polymer matrix composite w ork pieces. In particular, two processing methods, inert and air atomizatio n, and three are spray gun configurations (air cap design) were evaluated. The low coefficient of thermal expansion (CTE) properties of Invar are main tained in the spray-deposited coatings using both high velocity oxy-fuel (H VOF) and air-atomized are spraying, although HVOF coatings have significant ly lower CTE and greater durability than those deposited by are spraying. T he mechanical properties of the coatings are low compared to bulk Invar, re gardless of the spray parameters and hardware used. Inert are spraying affo rds more consistent coating characteristics but this comes with a compromis ed durability. The spray hardware was found to be more significant in deter mining the coating properties than the parameters employed.