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

Abstract

Blackening of zirconia (ZrO2) ceramics often occurs in active metal brazing, however, its discoloration mechanism and induced variation in mechanical properties remain unclear. Herein, ZrO2 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 TiO2 + Ti3(Cu, Pd)O are formed adjacent to ZrO2, indicating that partial oxygen in ZrO2 is taken by active Ti in the liquid filler that dissolved from the Ti substrate. Furthermore, the height of the blackened ZrO2 ceramic near the brazing seam is in line with the amount of Ti content added to the filler, which infers that bulk‐sized black ZrO2 can be efficiently obtained by the interfacial reaction between Ti and ZrO2. Additionally, the black ZrO2 is having abundant Zr3+ defects and more tetragonal phase content than the original ZrO2. The formation of Zr3+ defects results in the blackening of ZrO2, while the phase transformation leads to reduced hardness, improved impact toughness, and enhanced wear resistance of black ZrO2. Thus, this blackening phenomenon of ZrO2 ceramics provides a new way to tune the mechanical properties of ZrO2.