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 (similar to 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. AlB2 nanocrystallites (similar to 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 AlB2 phases via SLM 3D printing and sheds a new light on fine morphological and microstructural features of thus obtained new composites. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Metal/ceramic powder utilization offers new possibilities for 3D printing metal matrix composites with high strength, but presents challenges. This study achieved an AlSi10Mg matrix composite embedded with 1 wt% hexagonal BN microflakes and explored microstructure changes at the h-BN/melt interface during SLM. The inclusion of h-BN microflakes led to increased composite hardness and tensile strength, with AlN and AlB2 phases forming during processing.