Drastic Improvements in Bonding of Highly Dissimilar Materials

One of the very important issues in many industries is bonding of dissimilar materials, since high bond resistance to high and rapid thermal and mechanical loads is required. The problems associated with the bond durability stem from fundamental differences in the coefficients of thermal expansion and thermal conductivity. For example, ceramic has a relatively low coefficient of thermal expansion (CTE), while metals have a relatively high CTE. In addition, thermal conductivities are very different too, which actually adds to the problem: under conditions of rapid temperature increase it is found the metal airframe may become hotter than the ceramic because of the differing thermal conductivity characteristics. The objective of this project is to achieve a revolutionary improvement of the bonding process between highly dissimilar materials used in various industrial applications. The proposed technology is applicable to both adhesive and brazing types of bonding. Achievement of a dramatic increase in the bond strength in the metal alloy/adhesive (braze) and composite/adhesive (braze) interfaces of existing advanced materials and structures suitable for advanced industrial applications is the main goal of the Phase I project, which will also focus on implementation of the proposed technology for newest materials developed up to date and scaling of the proposed technology to large area and complex shape ceramic- and composite-to-metal structural joints. The proposed technology developed at Integrated Micro Sensors Inc (IMS) is based on laser- assisted fabrication of Micro Column Arrays (MCA) on the surface of the two dissimilar materials prior to adhesive bonding or brazing. There are several advantages of the MCA technology in the drastic improvement of bonds between any similar and dissimilar materials. First, mechanical strength increases due to the interlocking of the adhesive or brazing material between micro columns. Second, the bond strength increases due to the increase of the specific surface area by more than an order of magnitude. Third, stability increases due to the inherent elasticity of the micro cones during a deformation that can occur due to stresses induced by differences in thermal expansion between the material and adhesive or braze or under shear stress . Fourth, increase in the bond durability because of the repeated bend contours of the surface preventing hydrothermal failure. Fifth, wettability of the material surface significantly improves due to (i) a highly developed surface morphology at the micro and submicron level, and (ii) changes in local chemistry due to surface oxidation that could be beneficial to promoting a stronger bond. Sixth, the MCA technology is efficient, highly reproducible, environmentally safe, and can be applied virtually to any solid state material. Seventh, the MCA technology is highly scalable to large areas and minimum processing times, as the MCA fabrication efficiency is proportional only to the average laser power (see Task 1 of the Work Plan section for details). Commercial lasers with powers up to 5 kW are currently used for cutting of large area (several feet) materials. The combination of these unique features will result in a significant improvement of the bonds between materials targeted in this project. Integrated Micro Sensors Inc has already filed a U.S. Patent application on this technology. This project will be conducted by Integrated Micro Sensors Inc in collaboration with a team from the University of Houston, which will provide facilities and expertise in mechanical testing of coupon samples fabricated to demonstrate the advantages of the proposed technology.