Superplastic Forming of Composite Materials: Mechanisms, Processing, and Applications

Abstract Superplastic forming (SPF) technology offers substantial advantages for the near-net-shape fabrication of complex components. However, its broad industrial adoption is often constrained by the stringent prerequisite of obtaining an ultrafine-grained and equiaxed microstructure. In advanced composites, the incorporation of high-stiffness, high-volume-fraction reinforcements, while enhancing mechanical properties, frequently leads to a marked deterioration in plastic deformability. This article provides a comprehensive review of recent advances in the superplasticity of composite materials. Key processing routes for attaining superplasticity, including powder metallurgy (PM) and severe plastic deformation (SPD) techniques—notably equal-channel angular pressing (ECAP), high-pressure torsion (HPT), and friction stir processing (FSP)—are critically examined. These techniques effectively refine and stabilize the grain structure, thereby establishing the essential microstructural foundation for superplastic flow. The review elaborates on the intrinsically synergistic and multi-mechanistic nature of superplastic deformation in composites, wherein grain boundary sliding (GBS) plays a dominant role. This process necessitates accommodation through auxiliary mechanisms, including interfacial diffusion, dislocation activity, and dynamic recrystallization, to mitigate stress concentrations around reinforcements and suppress cavity nucleation. The superplastic behavior and underlying deformation mechanisms in representative composite systems—encompassing aluminum-, magnesium-, titanium-, and ceramic-matrix composites—are comprehensively surveyed. Furthermore, the industrial application potential and prevailing challenges associated with combined superplastic forming and diffusion bonding (SPF/DB) processes are analyzed. Finally, prospective research directions are proposed, encompassing the design of novel materials through interface engineering and multiscale modeling, overcoming strain rate limitations via external field-assisted techniques, and extending investigations to emerging systems such as high-entropy alloy composites. These endeavors are ultimately directed toward facilitating the transition of composite superplasticity from laboratory-scale innovation to broad industrial implementation.