Lightweight cellular metal composites with zero and tunable thermal expansion enabled by ultrasonic additive manufacturing: Modeling, manufacturing, and testing

Abstract

In aerospace applications, variations of temperature caused by changing environmental conditions or generation of heat is a common problem. The resulting thermal strains cause separation and alignment errors in optical systems, and stresses due to mismatches of thermal expansion at material interfaces cause failure of components and structures. Because minimizing weight, cost, and lead time are also critical requirements, lightweight, easily machined metals are attractive for aerospace applications, but these materials all have substantial coefficients of thermal expansion. Previous work has shown that the superposition of two metals with dissimilar coefficients of thermal expansion in periodic cellular configurations can result in a composite material with zero effective thermal expansion. However, fabrication of these material architectures typically is either impossible or requires manual assembly. Here, we propose methods to design and fabricate cellular metal composites with tunable thermal expansion and optimized specific stiffness that can be manufactured at useful scales entirely with automated methods. Samples were manufactured with ultrasonic additive manufacturing and computer-controlled machining, and thermal expansion was measured optically. The results demonstrate the practical fabrication of cellular metal composites with zero or negative thermal expansion in one direction, tunable thermal expansion in a second direction, and structural performance indices competitive with the indices of conventional aerospace alloys.