Mechanical Properties of Heterostructured Materials Fabricated by Metal Additive Manufacturing Process

Abstract

Metal Additive Manufacturing (MAM) is poised to play a crucial role in the 4th Industrial Revolution due to its numerous advantages. However, there is a prevalent perception that MAM materials possess inferior mechanical properties compared to conventional casting or wrought materials, primarily due to internal defects. However, recent advancements in MAM research have demonstrated that MAM materials can surpass conventional materials in mechanical properties by leveraging their unique microstructural characteristics. Additionally, efforts are being made to harness the MAM process's capabilities to control microstructures precisely by location. This study investigated the ‘Mechanical Properties of Heterostructured Materials Fabricated by Metal Additive Manufacturing Process.’ The study consists of two major parts: (1) The chapter on ‘Mechanical property control through cell structure engineering’ aims to thoroughly understand the Process-Structure-Property linkage between process conditions, microstructure, and mechanical properties. (2) The chapter on ‘Manufacturing of heterostructured materials through local microstructure control’ proposes a new methodology of heterostructure to enhance the mechanical properties of MAM materials. Initially, to comprehend the impact of MAM process conditions on microstructure and mechanical properties, the tensile properties of 316L stainless steel fabricated using the laser powder bed fusion (LPBF) process at both room temperature and cryogenic temperature (77K) were examined. Two samples, 'Fast' and 'Slow,' were prepared with different laser scanning speeds. The 'Fast' specimen exhibited high strength at room temperature but showed reduced strength and ductility at cryogenic temperatures due to excessive martensite transformation. Conversely, the 'Slow' specimen, which had lower strength at room temperature, demonstrated high strength and ductility at cryogenic temperatures due to delayed martensite transformation over a wide strain range. The difference in Deformation-Induced Martensite Transformation (DIMT) at cryogenic temperatures was explained by the cellular structure that promotes or hinders DIMT. These findings indicate cellular engineering can effectively control DIMT and overall mechanical properties. Secondly, it was demonstrated that MAM can be effectively applied to develop heterostructure materials with excellent strength-ductility synergy. Employing various MAM process conditions in distinguished regions enabled the creation of heterostructured materials with varied microstructures in different areas. These heterostructure materials exhibited additional strengthening effects due to the hetero- deformation-induced (HDI) strengthening effect. This methodology can be integrated into additive manufacturing without further processing to produce heterostructures. Also, it is versatile as it can be applied to any printable alloy without special restrictions.