多数工程结构材料的失效都是从表面的薄弱环节开始发生或者传导，从而引起材料的性能下降，使用寿命缩短。受生物材料的梯度结构启发，近年来开发了多种表面纳米化技术，成功在工程材料表面制备了晶粒尺寸从表层纳米尺度连续变化到内部宏观尺度的梯度纳米结构，强化和保护了材料表面，有效地解决了上述问题。结合国内外表面纳米化的研究结果，综述了金属材料梯度纳米材料的研究进展。首先，介绍了梯度塑性变形、物理化学沉积等表面纳米化加工技术的最新进展。其次，对梯度等轴纳米晶、梯度纳米层片和梯度纳米孪晶等多种表面纳米化材料的微观结构进行了归纳，并对最新发展的梯度纳米结构材料表层晶粒的晶体学取向等微观信息表征方法进行了系统地阐述。随后，总结了梯度纳米结构对工程材料的表面强度、塑性、强-塑匹配、加工硬化、疲劳、耐磨、腐蚀和热稳定性等性能的影响。最后展望了表面纳米化技术制备梯度纳米结构金属材料的发展趋势及工程应用所面临的挑战。

The failure of most engineering materials originates from or results from the weakness of surface, which later reduces the resultant mechanical properties and shortens the service life. Inspired by the gradient structures of biological materials, in recent years, a variety of surface nanocrystallization techniques have been developed, and the gradient nanostructures with grain size continuously changing from surface nanoscale to internal microscale have been successfully prepared on the surface of engineering materials, which strengthens and protects the surface of materials and effectively solves the above problems. Based on the research results of surface nanocrystallization at home and abroad, the research progress of gradient nanomaterials of metal materials was summarized. Firstly, the latest development of surface nanocrystallization processing techniques such as gradient plastic deformation and physicochemical deposition was introduced. Secondly, the microstructures of various surface nano-materials such as gradient equiaxed nanocrystals, gradient nano-lamellae and gradient nano-twins were summarized, and the microscopic information characterization methods such as crystallographic orientation of surface grains of gradient nano-structured materials were systematically expounded. Then, the effects of gradient nanostructures on the surface strength, plasticity, strength-ductility synery, work hardening, fatigue, wear resistance, corrosion and thermal stability of engineering materials were summarized. Finally, the development trend of preparing gradient nanostructured metal materials by surface nanocrystallization technique and the challenges in engineering application were prospected.