| Spontaneous infiltration and strengthening behaviors were analyzed in terms of microstructures and tensile properties of Al/BN composite fabricated by pressureless infiltration technique, compared with control alloy without BN fabricated by the same method. The Mg₃N₂ formed by the reaction of Mg vapor and nitrogen gas, which coated the particles in the powder bed, is believed to induce spontaneous infiltration through a great enhancement of wetting via the following reaction, Mg₃N₂+ 2Al→2AlN + 3Mg. This was identified by the finding of AlN particle layers on the surfaces of old Al particles in the powder bed, which contacted with the infiltrating melt. In addition, unreacted Mg₃N₂ was observed outside the composite, where the Al melt directly did not come into contact. Fine AlN particles formed in-situ resulted in a significant strengthening even in the control alloy with no addition of BN. In the composite reinforced with BN, additional AlN was formed by the interfacial reaction of the BN and Al melt as well as AlN by the in-situ reaction. Consequently, both the BN particles and the additional AlN particles formed by the interfacial reaction led to a further strengthening in the composite, as compared to control alloy strengthened by the AlN particles formed in-situ. |
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