High-energy ball-milling combined with annealing of TiC powders and its influence on the microstructure and mechanical properties of the TiC-based cermets

Abstract

High-energy ball-milling and annealing processes greatly affect the grain size, composition and microstrain of the TiC powders, which play a key role in determining the final microstructure and properties of TiC-based cermets. In this work, TiC-25WC-11Mo2C-18(Ni-Co) cermets were fabricated with four types of TiC powders: microsized (raw), nanosized (milled) and submicron (heated in vacuum at 1350 or 1450℃). Effects of crushing and subsequent heat treatments on the composition and structure of TiC powders were investigated. Morphology and mechanical properties of the cermets were also studied. Annealing decreased the microstrain and oxygen content of the milled TiC, forming submicro particles with high crystallinity. Activated particles accelerated the dissolution-precipitation process and interface reaction of the core-rim phases, leading to thick rims on small TiC cores. Chemical bonded oxygen in TiC grains could only be consumed via full interface reaction of the core-rim structure, leaving small pores in ceramic grains. Spherical TiC grains with uniform and integrated inner rims were observed in samples with annealed powders. Ultrafine TiC-based cermets with high strength (1862MPa), hardness (92.1 HRA) and satisfied toughness (11.32MPamm1/2) were achieved using these annealed submicron TiC powders.