Blackening Mechanism and Mechanical Properties Variation of Zirconia Ceramic Induced by Active Metal Brazing

Blackening of zirconia (ZrO 2 ) ceramics often occurs in active metal brazing, however, its discoloration mechanism and induced variation in mechanical properties remain unclear. Herein, ZrO 2 ceramic and Ti are successfully brazed by Ag–Cu–Pd filler in vacuum along with the blackening phenomenon. In the brazed joints, the reaction layers of TiO 2 + Ti 3 (Cu, Pd)O are formed adjacent to ZrO 2 , indicating that partial oxygen in ZrO 2 is taken by active Ti in the liquid filler that dissolved from the Ti substrate. Furthermore, the height of the blackened ZrO 2 ceramic near the brazing seam is in line with the amount of Ti content added to the filler, which infers that bulk‐sized black ZrO 2 can be efficiently obtained by the interfacial reaction between Ti and ZrO 2 . Additionally, the black ZrO 2 is having abundant Zr 3+ defects and more tetragonal phase content than the original ZrO 2 . The formation of Zr 3+ defects results in the blackening of ZrO 2 , while the phase transformation leads to reduced hardness, improved impact toughness, and enhanced wear resistance of black ZrO 2 . Thus, this blackening phenomenon of ZrO 2 ceramics provides a new way to tune the mechanical properties of ZrO 2 .