Mechanical and fretting wear behavior of novel (W,Ti)C-Co cermets

Abstract

In an effort to refine the composition and properties of existing hard metals, (W,Ti)C-20 wt% Co cermets have been developed. The present research reports the mechanical and tribological properties of these novel materials. Single-step as well as two-stage and three-stage sintering experiments were conducted on the cermets, processed from the (W,Ti)C solid solution powders. For property comparison, premixed WC/TiC powders were used to fabricate a reference (W,Ti)C-20 wt% Co cermet material. Higher sintered density (9.57 g/cm 3) as well as better elastic modulus (467 GPa) and hardness (∼17 GPa) were obtained after three-stage sintering of solid solution powders. In order to evaluate the tribological properties, the fretting wear experiments (mode I, linear relative tangential displacement) were performed against bearing steel for varying normal load in the range of 2-10 N. The experimental results reveal that the steady-state coefficient of friction (COF) varies between 0.50 and 0.65, and a lower COF is recorded at 10 N load for cermets processed from solid solution powders. Under varying tribological conditions, the cermets sintered from solid solution powders exhibit low wear depth (∼ 1-4 μm) and lower wear rate (7 × 10 -7-18 × 10 -7 mm 3 ·(N · m) -1 when compared with cermet prepared from the premixed WC/TiC starting powders (wear rate ∼ 14 × 10 -7-22 × 10 -7 mm 3 · (N · m) -1). The wear rate data are critically evaluated based on the phenomenological models. Broadly, abrasive wear is the dominant wear mechanism, and limited contribution from localized spalling of tribolayer and tribochemical wear was also observed.