Surface coating on metal substrates has remained a difficult challenge for researchers due to the conflicting requirements for different properties. In recent years, due to their mechanical, thermal, electrical, and tribological properties in many advanced engineering applications, functionally graded coatings (FGCs) have become fascinating materials for researchers worldwide to obtain coatings with specific requirements. FGCs are a novel type of traditional composites in which phases are not equally distributed to form a smooth gradient structure; thus, gradient coatings have shown a new research path. Therefore, this paper critically reviews the different FGC processing techniques by describing the fundamental problems and potential of these processes based on existing literature. Additionally, this research presents the most important potential applications and future challenges for gradient coatings. Consequently, the results expected from the paper are considered a guideline that enables the interested in this field to make informed decisions.

由于对不同性能的要求存在冲突，金属基材上的表面涂层对研究人员来说仍然是一项艰巨的挑战。近年来，由于其在许多先进工程应用中的机械、热、电和摩擦学特性，功能梯度涂层 (FGC) 已成为全球研究人员获得具有特定要求的涂层的迷人材料。FGCs是一种新型的传统复合材料，其中相不均匀分布以形成平滑的梯度结构；因此，梯度涂层显示出了一条新的研究路径。因此，本文通过描述基于现有文献的这些工艺的基本问题和潜力，批判性地回顾了不同的 FGC 工艺技术。此外，这项研究提出了梯度涂层最重要的潜在应用和未来挑战。因此，该论文的预期结果被视为指导方针，使对该领域感兴趣的人能够做出明智的决定。