Determination of microstructure and mechanical properties of VC/Cr3C2 reinforced functionally graded WC-TiC-Al2O3 micro-nano composite tool materials via two-step sintering.

The effect of VC, Cr 3 C 2 and combination (Cr 3 C 2 and VC with varied weight ratios of Cr 3 C 2 /(Cr 3 C 2 +VC)) on the microstructure and mechanical properties of functionally graded WC-Al 2 O 3 -TiC composite synthesized employing two-step hot-pressing sintering (heated to 1700 °C and then immediately cooled to 1600 °C with a soaking time of 30min) was comprehensively investigated. Combined addition of VC and Cr 3 C 2 with an appropriate ratio to WC-TiC-Al 2 O 3 composite performed a more pronounced effectiveness on inhibiting grain growth and improving the homogeneous dispersion of Al 2 O 3 nano-particulates in WC matrix than single addition of VC or Cr 3 C 2 did. Furthermore, single Cr 3 C 2 addition outperformed VC in grain refinement and uniform distribution of Al 2 O 3 . The experimental results show that excellent mechanical properties are achieved for Cr 3 C 2 -VC additions with Cr 3 C 2 /(Cr 3 C 2 +VC) weight ratio 0.6 with a hardness of 25.64 GPa, a flexural strength of 1209.6 MPa, a fracture toughness of 11.49 MPa mm 1/2 and a surface residual stress of −591.9 MPa. High surface compressive stress, strong interface bonding, crack branching and bridging, crack deflection, microcracking and Al 2 O 3 pullout are the major mechanisms contributing to the drastically enhanced flexural strength and fracture toughness. The five-symmetric-layer graded ceramics developed in this paper provide an exceptional combination of high toughness and high hardness, which are conducive to the application as metal cutting tools. [ABSTRACT FROM AUTHOR]