ABSTRACT
Gradient structures are characterized with a systematic change in microstructures on a macroscopic scale. This chapter reports that gradient structures in engineering materials such as metals produce an intrinsic synergetic strengthening, which is much higher than the sum of separate gradient layers. A typical gradient structure is characterized with a microstructural gradient at a macroscopic scale. Gradient structures exist ubiquitously in the nature, because they have superior properties over homogenous structures to weather severe natural environments. The chapter reports that gradient structure in metals produces an intrinsic synergetic strengthening effect, with the strength of the gradient-structured sample much higher than the sum of the strength of separate layers, as calculated using the rule of mixtures. The synergetic increase in strength is attributed to the mechanical incompatibility caused by the mismatch between the Poisson’s ratio in the elastic outer layers and apparent Poisson’s ratio in the central plastic layer.
