Effect of deformation on thermal expansion behavior of Sr_0.2Ba_0.8TiO₃/Cu composite

The negative thermal expansion effect of tetragonal-cubic phase transition in Sr_0.2Ba_0.8TiO₃ particles can be utilized to reduce the thermal expansion of metal matrix composite. However, a portion of cubic-phase Sr_0.2Ba_0.8TiO₃ particles exist in the composites due to the residual stress, which exhibit positive thermal expansion because there is no transformation upon heating. Here, we studied the effects of plastic deformation on as-sintered and annealed Sr_0.2Ba_0.8TiO₃/Cu composite. The results show that residual stress in the composite is decreased by the annealing and deformation, correspondingly, the cubic-phase Sr_0.2Ba_0.8TiO₃ particle content in the composite is decreased. The analysis on Debye-Waller effect based on in situ X-ray diffraction indicates that tetragonal-cubic phase transition of Sr_0.2Ba_0.8TiO₃ particles takes place upon heating, which is helpful to reduce the thermal expansion coefficient of Sr_0.2Ba_0.8TiO₃/Cu composite. Annealing and plastic deformation are effective methods to decrease the content of cubic-phase Sr_0.2Ba_0.8TiO₃ particle and adjust the thermal expansion coefficient of the composite.