SBIR-STTR Award

This SBIR Phase I project introduces a new technology for joining components exhibiting large mismatch in coefficients of thermal expansion. The proposed technology is a reactive joining process that uses reactive multilayer foils as local heat sources for melting brazes or solders. The foils are a new class of nano-engineered materials, in which self-propagating exothermic reactions can be ignited at room temperature with a spark. By inserting a multilayer foil between two braze (or solder) layers and two components, heat generated by the reaction in the foil melts the braze and consequently bonds the components. This new method of joining eliminates the need for a furnace and, with very localized heating, avoids thermal damage to the components. The reactive bonding process is more rapid than competing technologies, and results in strong and cost-effective joints. Phase I effort will: (1) establish the feasibility and effectiveness of this joining method to produce large-area, 4 in. x 4 in., joints between plates of Ti-6-4 and SiC, (2) develop and validate a design model for predicting heat transport and braze melting during the reactive joining process, and (3) demonstrate that the strength of the resulting joints are two times higher than best epoxy joints. Successful development of reactive multilayer joining, and its adaptation to the joining of SiC and Ti-6-4 will not only enhance the performance of advanced ceramics in armor applications, but it will also open new opportunities for industrial joining, mounting and assembly applications.

Keywords:
Reactive Multilayers, Cte Mismatch, Silicon Carbide, Titanium, Armor

The drive to develop the Future Combat System requires improved methods for bonding SiC armor to Ti-6-4 structures. Current methods that utilize epoxy adhesives provide limited strength and ballistic performance. Reactive multilayer joining offers the novel ability to form strong metallic joints between SiC tiles and Ti-6-4 plates, at room temperature and in air. We have demonstrated this ability in our Phase I project, and we have also shown that the resulting joints have the desired shear strength of 52 MPa, twice that of epoxy joints. In the proposed Phase II project we will refine the reactive joining process and demonstrate that arrays of SiC tiles can be bonded onto Ti-6-4 plates with the desired ballistic and physical properties. Specifically, we will (1) optimize the reactive joining process by varying the brazes on the Ti plates, the pressure applied during joining and the roughness of the braze surfaces; (2) establish the ballistic superiority of the reactive bonded SiC-Ti joints over current epoxy-based SiC-Ti joints; and (3) demonstrate that the reactively bonded SiC-Ti joints meet all the relevant military specifications for armor joining.The most direct benefit is the enhanced ballistic performance of SiC armor on Ti-6-4 military vehicles. By doubling the bond strength compared to epoxy, dramatic improvements in ballistic performance are expected. More generally, demonstrating and optimizing the ability to reactive join ceramics to metals will aid all armor mounting programs, including the mounting of alumina to aluminum. Lastly, the ability to bond ceramics to metals will also benefit many other defense and civilian applications where the benefits of ceramics are desired but the means for bonding them is limited.

Keywords:
REACTIVE JOINING, REACTIVE FOILS, CERAMIC ARMOR, BALLISTIC PERFORMANCE, STRENGTH