Strengthening mechanism of a spray-formed Cu-TiB2 composite

Cu-TiB2 composite has been manufactured by spray forming process. The microstructures of over-sprayed powder, spray-formed billet, and extruded rod have been characterized by optical microscopy and x-ray diffractometry. The tensile strength of extruded rod was measured by tensile testing. TiB2 particles were formed in a Cu melt of 1500°C by chemical reaction between Ti and B. The TiB2 volume fraction within the spray-formed billet varied by the density difference between TiB2 and Cu melt. The strengthening of Cu-TiB2 alloy was well described by dislocation pile-up model. The results indicate that yielding of this composite was subject to reinforced particle fracture by local stress concentrations caused by dislocation pile-up between obstacles. Reinforcement fracture also has an effect to decrease the work hardening rate with the increase of reinforcement volume fraction during plastic deformation. We believed that this is because of the strengthening loss due to the increase of fractured particles with increasing TiB2 volume fraction.