Processing of Ultrafine/nano-grained microstructures through additive manufacturing techniques: a critical review

Additive manufacturing (AM) has emerged as a transformative technology that produces complex, high-performance components, enabling unprecedented design flexibility and material efficiency. This paper explores the potential of additive manufacturing processes to produce ultrafine/nano-grained microstructures, which are characterized by superior mechanical properties, enhanced corrosion resistance, and improved thermal stability. The study delves into various AM techniques based on the physical phenomenon incorporated to additively bond the material portions. Accordingly, the reported results in the literature were reviewed by categorizing the methods into melting-based and deformation-based approaches and examining the conditions and parameters critical to achieving ultrafine/nano-grained microstructures. Key factors, including the optimization of process parameters as well as the specification of initial feedstock material, are discussed. This comprehensive review shows that in melting-based methods, lower power and higher scan speed result in reduced heat input, leading to smaller melt pools and faster solidification rates, which in turn produce finer grains. On the other hand, in deformation-based methods, smaller initial particle sizes and higher particle velocities generate greater impact energy, which can lead to grain size reduction. This review article also highlights the current potential and achievements in the field of additive manufacturing for producing ultrafine/nano-grained materials, which may contribute to the development of high-performance materials and components for the next generation.