Heterogeneous microstructure and tensile properties of HA188/SS316L functionally graded materials prepared by laser directed energy deposition

Abstract

Laves/NbC phase formation due to Nb element segregation is detrimental to the mechanical properties of gradient materials fabricated using stainless steel and nickel-based superalloys. Here, a novel gradient design approach was employed by selecting Nb-free HA188 and SS316L as base materials, enabling uniform transition in element distribution and phase composition. The HA188/SS316L functionally graded material exhibited a heterogenous grain structure, which was also confirmed through the grain boundary distribution map and kernel average misorientation map. The deformation twins have been observed to significantly impede dislocation motion in the fracture region. Notably, the developed gradient material exhibited a yield strength of 392 MPa, an ultimate tensile strength of 608 MPa, and an elongation of 45.2 %, surpassing conventional gradient materials derived from nickel-based superalloys and stainless steels. This research provides valuable insights into the design of heterogeneous gradient materials, offering new perspectives for enhanced performance.