Microstructure evolution during AlSi10Mg molten alloy/BN microflake interactions in metal matrix composites obtained through 3D printing

Utilization of metal/ceramic powders opens new possibilities for 3D printing of metal matrix composites of complex shape with high strength, but it is still a great challenge. In this work, an AlSi10Mg matrix composite embedded with 1 wt% of hexagonal BN phase microflakes ( h -BN) was obtained by means of 3D printing. Then the present study elucidated microstructure evolutions occurring at the h -BN/melt interface during selective laser melting (SLM) of an h -BN-AlSi10Mg powder mixture. During short-term (0.15 ms) high-temperature (∼2900 K) processing the BN inclusions partly dissolved in the Al–Si melt. This process was accompanied by the formation of an AlN phase at the BN surfaces. The AlN crystallites, 100–200 nm in size, had spherical/semispherical shape and formed a continuous layer along the BN/metal grain boundaries. The peculiar growth of AlN grains along the metal/BN interfaces was governed by the specific features of localized N diffusion in the vicinity of interfaces. By contrast, B atoms, released from the dissolved BN phase, were randomly distributed over the melt. AlB 2 nanocrystallites (∼10 nm in size) precipitated from the supersaturated Al–Si melt during cooling stage. With the addition of h -BN microflakes, the composite hardness and tensile strength increased by 32% and 28%, respectivelly. The observed experimental results were supported by ab initio molecular dynamics simulations. Our study demonstrates the possibility and wide prospects of obtaining a dense BN/AlSi10Mg material reinforced with h -BN, AlN, and AlB 2 phases via SLM 3D printing and sheds a new light on fine morphological and microstructural features of thus obtained new composites. • During the BN/Al(Al–Si) melt interactions AlN crystallites are formed along the BN/Al(Al–Si) grain boundaries. • AlB 2 nanocrystallites precipitated from the supersaturated Al–Si melt on cooling. • N atoms are less mobile as compared to B atoms due to the vibration amplitude differences.