Mechanical and Thermomechanical Properties of Metal Spray Invar For Composite Forming Tooling

Abstract

The subject of this paper is the assessment of the thermal and mechanical properties of Invar steel coatings, deposited using electric arc spraying, and the correlation of these properties to the spray parameters and processes used to offer coatings with characteristics appropriate to the requirements of tools used in the fabrication of precision polymer matrix composite work pieces. In particular, two processing methods, inert and air atomization, and three arc spray gun configurations (air cap design) were evaluated. The low coefficient of thermal expansion (CTE) properties of Invar are maintained in the spray-deposited coatings using both high velocity oxy-fuel (HVOF) and air-atomized arc spraying, although HVOF coatings have significantly lower CTE and greater durability than those deposited by arc spraying. The mechanical properties of the coatings are low compared to bulk Invar, regardless of the spray parameters and hardware used. Inert arc spraying affords more consistent coating characteristics but this comes with a compromised durability. The spray hardware was found to be more significant in determining the coating properties than the parameters employed.