Effects of whisker surface modification on microstructures, mechanical and thermal properties of β-Si3N4 whiskers reinforced Al matrix composites

Highlights: • The Ag-coated β-Si₃N₄ whiskers were successfully obtained by electroless plating. • The β-Si₃N₄ whiskers was surrounded by an amorphous Ag enrichment layer and well bonded with Al matrix. • Both the fracture toughness and the thermal conductivities of composites were effectively improved. • The maximum fracture toughness and 25°C thermal conductivity of composites were 23.9 MPa·m^1/2 and 198.6 W/m·K, respectively. In order to modify the interfacial bonding of β-Si₃N₄ whiskers (β-Si₃N₄w) reinforced Al matrix composites, the Ag-coated β-Si₃N₄w with varying Ag contents were incorporated into the Al matrix by a hot pressing method. The interfacial structure showed that the β-Si₃N₄w was surrounded by an amorphous Ag enrichment layer and well bonded with Al matrix with no pores and reaction products near the interface. The relative density, fracture toughness and thermal conductivities of composites were distinctly improved by the modified interface because of improved wettability, reduced thermal mismatch stress and lowered interfacial thermal resistance between Al and β-Si₃N₄w. When the Ag content on whiskers is 1.8 vol%, the composites shows the maximum fracture toughness (23.9 MPa·m^1/2). When the Ag content is 2.7 vol%, both the maximum ductility and the maximum thermal conductivity were obtained, corresponding to an elongation at fracture and a 25 °C thermal conductivity of 15.5% and 198.6 W/m·K, respectively. However, excessive Ag content on whiskers didn't bring about promotion in mechanical properties and thermal conductivities due to the evolution of microstructure and the limitation of the relative density of composites.