R-curves in transformation toughened lead zirconate titanate

► Additions of zirconia reduced PZT grain size and increased intragranular fracture. ► Zirconia increased initial toughness and plateau toughness. ► The initial R-curve became steeper with increasing zirconia content. Composites from lead zirconate titanate (PZT) and yttria stabilized zirconia were manufactured to assess cracking and R-curve behavior in compact tension specimens. Additions of zirconia led to a reduction in PZT grain size and shifted the fracture behavior from intergranular fracture to intragranular fracture. The R-curves exhibited higher starting values, a steeper slope and a higher plateau value with increasing content of zirconia, albeit the effects on the toughness values were not more than 20%. The results are rationalized through increased crack tip toughness, reduced ferroelastic toughening and enhanced transformation toughening.