Phase composition and microstructure of B₄C particles reinforced aluminum matrix composites fabricated via direct laser deposition

Aluminum matrix composites (AMCs) reinforced by 5 wt% B₄C particles were fabricated by direct laser deposition (DLD) technology. The phase composition, microstructure, and microhardness of the B₄C/aluminum matrix composites (B₄C/AMCs) were analyzed by OM, XRD, SEM, TEM, EBSD, microhardness test and molecular dynamics simulation (MD) in detail. The results show that acicular microstructure of AlB₁₂ and Al₄C₃ are formed in the B₄C/AMCs fabricated by DLD. With the addition of B₄C, the crystallographic orientation of AMCs changes from (001) texture to random orientation distribution, and the microhardness increases by about 65%. During the DLD process, boron atoms and carbon atoms are released by B₄C decomposition instead of diffusing through the solid–liquid interface between Al and B₄C, and they react with the liquid Al to produce AlB₁₂ and Al₄C₃ in the molten pool. Moreover, B and C atoms distribute along a strip orientation in the molten pool, which may be retained after the cooling to form the acicular microstructures. This work demonstrates the possibility and good prospects of obtaining AMCs reinforced with B₄C, AlB₁₂ and Al₄C₃ phases by the DLD technique and provides new insights into the microstructural evolution of the composites.