Gradient structures are characterized with a systematic change in microstructures on a macroscopic scale. Here

we report 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. This is caused by macroscopic stress gradient and the bi-axial stress generated by mechanical incompatibility between different layers. This represents a new mechanism for strengthening that exploits the principles of both mechanics and materials science. It may provide for a novel strategy for designing material structures with superior properties.