Towards a Better Understanding of the Interaction of Fe 66 Cr 10 Nb 5 B 19 Metallic Glass with Aluminum: Growth of Intermetallics and Formation of Kirkendall Porosity during Sintering.

Metallic-glass-reinforced metal matrix composites are a novel class of composite materials, in which particles of alloys with an amorphous structure play the role of reinforcement. During the fabrication of these composites, a crystalline metal is in contact with a multicomponent alloy of an amorphous structure. In the present work, the morphological features of the reaction products formed upon the interaction of Fe₆₆Cr₁₀Nb₅B₁₉ metallic glass particles with aluminum were studied. The composites were processed via spark plasma sintering (SPS), hot pressing or a combination of SPS and furnace annealing. The reaction products in composites with different concentrations of the metallic glass and different transformation degrees were examined. The products of the interaction of the Fe₆₆Cr₁₀Nb₅B₁₉ metallic glass with Al were observed as dense layers covering the residual alloy cores, needles of FeAl₃ protruding from the dense shells as well as needles and platelets of FeAl₃ distributed in the residual Al matrix. The possible role of the liquid phase in the structure formation of the reaction products is discussed. The formation of needle- and platelet-shaped particles presumably occurred via crystallization from the Al-Fe-based melt, which formed locally due to the occurrence of the exothermic reactions between aluminum and iron. At the same time, aluminum atoms diffused into the solid Fe-based alloy particles, forming an intermetallic layer, which could grow until the alloy was fully transformed. When aluminum melted throughout the volume of the composite during heating of the sample above 660 °C, a similar microstructure developed. In both Al–Fe₆₆Cr₁₀Nb₅B₁₉ and Al–Fe systems, upon the reactive transformation, pores persistently formed in locations occupied by aluminum owing to the occurrence of the Kirkendall effect. [ABSTRACT FROM AUTHOR]