Crystal defects responsible for mechanical behaviors of a WC–Co composite at room and high temperatures – a simulation study

Abstract

The microstructure evolution and changes in the structures of crystal defects of the nanocrystalline WC-Co composite in the process of uniaxial compression were studied by simulations at both room and high temperatures. The deformation processes were demonstrated as a function of stress and temperature for the stages prior to and after yielding of the composite. The Peierls stresses were evaluated for Co and WC dislocations with increasing temperature. The deformation mechanisms for each stage of the stress-strain curve were disclosed, in which the effect of temperature was clarified. It was found that with the increase of stress, from elastic deformation to plastic deformation then to yielding of the composite, the dominant mechanisms are grain boundary migration, formation and motion of dislocations in Co, concurrent motion and reaction of dislocations in Co and WC, and then rotation of WC grains in combination with motion of Co and WC dislocations. At the yielding stage, sliding of WC grain boundaries plays an increasingly important role in the contribution to plastic deformation at high temperatures. With strain the proportion of mobile dislocations decreases, and dislocations pile up at triple junctions of WC grains, WC/WC grain boundaries and WC/Co phase boundaries in priority order, leading to the nucleation and propagation of microcracks in these regions.

Toughening Ceramic-Based Composites by Homogenizing the Lattice Strain at Phase Boundaries

“…Due to the very different elastic moduli of the Co and WC phases, deformation incompatibility would occur in a subsequent loading. To accommodate the deformation and stress at the WC/Co phase boundary, the plastic deformation of the Co phase became significant and simultaneously the dislocations could nucleate in neighboring WC grains . The multiplication and interactions of dislocations at the WC/Co phase boundaries were continued with the applied stress.…”

“…However, the lattice strain inside the WC grain decreased rapidly in the direction perpendicular to the phase boundary. To verify that 27 The multiplication and interactions of dislocations at the WC/Co phase boundaries were continued with the applied stress. Hence, large local inelastic strain and stress concentrations would be generated at the phase boundaries.…”

Could an amorphous binder Co phase improve the mechanical properties of WC–Co? A study of molecular dynamics simulation

“…20 MD results also proved that WC-Co phase boundaries were benecial for toughness, further indicating the importance of interfacial Co. [21][22][23][24] Simultaneously, the interactions of dislocations in Co were the dominant deformation mechanisms. 25 The inuences of Co concentration on the dislocation congurations and densities were discussed by studying the strain threshold for the dislocation nucleation. 26 As reviewed above, the binder phase plays a vital role in the mechanical properties of composites.…”