Interface investigation of Ti-Cu-Ni threefold coated ZTA particles reinforced high chromium cast iron matrix composites

Ti-Cu-Ni threefold coated zirconia-toughened alumina particles (ZTA_p@Ti-CuNi) are prepared by the combination of mechanical coating and electroless plating assisted with choline chloride-ethylene glycol (ChCl-EG) additive. The thicknesses of Ti coatings on ZTA surfaces can be regulated through the mass ratio of Ti powders during the mechanical coating process of Ti coating on ZTA surface (ZTA_p@Ti). Then uniform CuNi coatings are obtained on ZTA_p@Ti surfaces by electroless plating and the role of polyvinyl alcohol (PVA) films in the activation pretreatment is highlighted. The coating sequences for ZTA_p@Ti-CuNi are analyzed and an empirical model is also proposed to elaborate the formation process of the Ti-Ni-Cu threefold coatings. The wetting behaviors between ZTA_p@Ti-CuNi and high-chromium cast iron (HCCI) matrix show that the wetting angle decreases to 110.5° after surface modification and belongs to chemical interaction. Besides, ZTA_p@Ti-CuNi reinforced high-chromium cast iron (ZTA_p@Ti-CuNi/HCCI) composites are fabricated by nonpressure cast-infiltration and the elemental map at the ceramic-metal interface indicates that there is uniform distribution of Ti, Cu and Ni and a thin TiO layer is also formed. A schematic illustration of the cast-infiltration process is put forward to interpret the interaction mechanism between modified ZTA and HCCI matrix. Moreover, nanoindentation tests show that the microhardness and modulus of the interfacial layer in ZTA_p@Ti-CuNi/HCCI are improved to 11.51 GPa and 225.00 GPa, respectively. The interface plays a good transition role, thus alleviating the great difference in plastic deformation between ZTA and HCCI, and making the composite show excellent comprehensive mechanical properties.