Low-Temperature Densification and Mechanical Enhancement of ZTA Ceramics via MgO-Regulated Sintering Kinetics

Abstract The sintering mismatch between zirconia-toughened alumina (ZTA) substrates and zirconia functional layers remains a critical limitation in multilayer co-fired automotive gas sensors, primarily caused by delayed densification kinetics induced by ZrO 2 incorporation. In this work, a trace MgO doping strategy is proposed to regulate the sintering behavior of ZTA ceramics within the practical co-firing temperature window of 1450 °C. ZTA ceramics containing 10 wt%5Y-ZrO 2 were fabricated with MgO additions of 0—1.0 wt%, and their sintering kinetics, microstructure evolution, and mechanical properties were systematically investigated. Trace MgO significantly lowers the sintering onset temperature by promoting Al 3+ grain-boundary diffusion while suppressing abnormal grain growth through grain-boundary segregation. An optimal MgO content of 0.25 wt% enables near-full densification (99.25%) at 1450 °C and achieves a flexural strength of 630.59 MPa, representing a 16.6% improvement over undoped ZTA. The modified ceramics exhibit shrinkage behavior highly compatible with zirconia functional layers, satisfying co-firing requirements. A diffusion – grain-boundary cooperative regulation mechanism is proposed to explain the simultaneous enhancement of densification and mechanical reliability. This work demonstrates an effective trace-dopant strategy for sintering-window regulation in heterogeneous ceramic co-firing systems.