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

• Published in: Journal of alloys and compounds 2017-06, Vol.709, p.197-205
• Main Authors: Sun, Jialin, Zhao, Jun, Chen, Mengjie, Ni, Xiuying, Li, Zuoli, Gong, Feng
• Format: Article
• Language: English
• Subjects: Aluminum oxide; Bonding strength; Ceramics; Compressive properties; Cr3C2-VC additions; Crack initiation; Cutting tool materials; FGM; Flexural strength; Fracture mechanics; Fracture toughness; Functionally gradient materials; Grain refinement; Mechanical properties; Microstructure; Residual stress; Sintering; Titanium carbide; Two-step hot-pressing
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.03.137

The effect of VC, Cr3C2 and combination (Cr3C2 and VC with varied weight ratios of Cr3C2/(Cr3C2+VC)) on the microstructure and mechanical properties of functionally graded WC-Al2O3-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 Cr3C2 with an appropriate ratio to WC-TiC-Al2O3 composite performed a more pronounced effectiveness on inhibiting grain growth and improving the homogeneous dispersion of Al2O3 nano-particulates in WC matrix than single addition of VC or Cr3C2 did. Furthermore, single Cr3C2 addition outperformed VC in grain refinement and uniform distribution of Al2O3. The experimental results show that excellent mechanical properties are achieved for Cr3C2-VC additions with Cr3C2/(Cr3C2+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 mm1/2 and a surface residual stress of −591.9 MPa. High surface compressive stress, strong interface bonding, crack branching and bridging, crack deflection, microcracking and Al2O3 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. •Cr3C2/(Cr3C2+VC) ratios affect microstructure and mechanical properties of WC-based ceramics.•The two-step hot-pressing sintered functionally graded WC-TiC-Al2O3-Cr3C2-VC ceramics exhibit high mechanical properties.•Grains become fine and Al2O3 dispersion tends to be homogeneous with raised Cr3C2.•Functionally graded WC-based ceramics with a Cr3C2/(Cr3C2+VC) ratios of 0.6 can be used as high-speed cutting tools.•Surface residual compressive stress can greatly improve the mechanical properties of FGM.