Hierarchical Microstructure of Laser Powder Bed Fusion Produced Face-Centered-Cubic-Structured Equiatomic CrFeNiMn Multicomponent Alloy

Abstract

A cobalt-free equiatomic CrFeNiMn multicomponent alloy was fabricated from gas-atomized powder using laser powder bed fusion (L-PBF), also known as selective laser melting (SLM). The as-built specimens had a single face-centered cubic (FCC) structure, relative density of 98%, and hardness up to 248 HV0.5 for both the scanning speeds applied. In this work, we report the hierarchical microstructural features observed in the as-built specimens. These are comprised of melt pools, grains, cell structures including dendritic cells, elongated cells, equiaxed cells (~500 nm), and sub-cells (150–300 nm). The cell and sub-cell walls are composed of a notably high density of dislocations. In addition, segregation of Mn and Ni was detected at the cell walls, but only occasionally at the sub-cell walls. SLM exhibits the capability to produce FCC-structured equiatomic CrFeNiMn multicomponent alloy with the refined and hierarchical microstructure.

Hydrogen Effects in Equiatomic CrFeNiMn Alloy Fabricated by Laser Powder Bed Fusion

“…They concluded that the hydrogen would diffuse initially along the cell walls then into the interior of cells, and the abundant cell walls in the SLM 316L SS act as rapid transportation paths for the H atoms; therefore, it suggests that the higher average hydrogen concentrations in SLM specimens are attributed to the high contents of chromium and manganese, and the cellular structure in conjunction with the elemental segregation and the high density of dislocations in the cell walls. Particularly, the larger average hydrogen concentration in SLM-2 compared to that in SLM-1 is ascribed to the broader cell walls associated with more severe segregation into the cell walls, as revealed in our previous study [10].…”

“…A summary of the composition and microstructure of the samples is given in Table 1. The detailed microstructure of the SLM-built samples has been described in [10]. It comprises fine dislocation cells with some segregation of Mn and Ni alloying elements into the cell walls, and boundaries of grains and melt pools.…”

“…This can be achieved conveniently by powder 2 of 14 technologies [8]. Likewise, laser powder bed fusion (LPBF), which is one of the selective laser melting (SLM)-based additive manufacturing (AM) techniques and is suitable to fabricate HEAs with refined microstructure [9][10][11]. Over the past two decades, SLM has been widely employed in various alloying systems to manufacture bulk parts, including nickel-based alloys [12], aluminum-based alloys [13], and Ti-6Al-4V [14].…”

“…Further advantages include its high level of local process control and building complex shapes compared to conventional methods [15,16]. The microstructure produced by SLM of the cobalt-free equiatomic CrFeNiMn alloy has been reported in detail in our previous paper [10]. The microstructure consists of the fine cellular structure at different scales with a great density of dislocations concentrated mainly in the cell walls, resulting in considerable hardness of the alloy.…”

“…In this research, we focus on the effects of hydrogen on the microstructure of the as-built SLM CrFeNiMn alloy described previously [10]. As hydrogen is known to interact with different kinds of lattice defects, such as dislocations [23] and vacancies [24], we used positron annihilation spectroscopy (PAS) to identify the influential lattice defects, such as vacancies in the materials [25,26].…”