Coating processing by self-propagating high-temperature synthesis (SHS) using a Fresnel lens

Abstract
The purpose of this work is to explore the use of Fresnel lenses in materials and coating processing via self-propagating high temperature synthesis (SHS). This is achieved by synthesis of intermetallic compounds of the Ni/Al system. Nickel aluminides offer high thermal stability, corrosion and oxidation resistance and superior mechanical properties at elevated temperatures. In order to obtain the coating, different metailic powders were placed onto a carbon-steel and heated in the focus of the lens. The solar energy concentrated provides the heat impulse to initiate the chemical reaction between Ni and Al. Aluminium melts due to the solar heating and reacts by the SHS process with nickel powders forming nickel aluminide (NiAl). The heat generated from the SHS reaction is high enough to melt the intermetallic compound NiAl activating a diffusion process between coating and substrate. The great advantage of this technology is that the process is initiated at low temperatures due to the exothermic nature of the reaction, and that the aluminide is obtained "in situ" and bonded onto the substrate. Hence, long processing times in high temperature furnaces consuming large quantities of energy are not necessary in SHS processes.