Effects of Uniaxial Applied Pressures on Spark Plasma Sintering Behaviors for 86FeB-10Ni-4Al Hard Materials

FeB-Ni hard materials were promising alternatives to conventional cemented carbides due to their high hardness, low cost and environmental benefits. In order to optimize the densification and mechanical properties, Al was selected as a functional alloying addition. In this study, 86FeB-10Ni-4Al hard materials were prepared by ball milling and spark plasma sintering under uniaxial applied pressures of 30, 50 and 70 MPa. The effects of uniaxial applied pressures on densification, microstructures and mechanical properties were also investigated. This study demonstrated that at 1373 K for holding 0.9 ks, both apparent relative density and densification rate increased with uniaxial applied pressures. The values of apparent relative density corresponding to the maximum densification rate of the 86FeB-10Ni-4Al hard materials sintered at 30, 50 and 70 MPa were 0.67, 0.74 and 0.78, respectively, falling between those of pure FeB of 0.53 and 71Ni-29Al of 0.88. With increasing uniaxial applied pressures, the equivalent diameter of binder-binder voids decreased from 0.16 to 0.08 μm, and their spheroidization rate increased from 0.44 to 0.64. At the same time, the binder-hard voids exhibited the same trend as the binder-binder voids. The changes in equivalent void diameter and spheroidization rate further promoted densification and fracture toughness. Among them, 86FeB-10Ni-4Al hard materials sintered at 70 MPa demonstrated outstanding mechanical properties, with a hardness of 14.7 GPa and a fracture toughness of 14.5 MPa·m1/2.