Solid-state transformation composite filler: A new strategy to strengthen ceramic/metal joint

Residual stress is the main hindrance to achieve a robust ceramic/metal brazed joint. In this study, yttria stabilized zirconia (YSZ) particles was fabricated into solid-state transformation composite filler, which was proposed as a new strategy to strengthen Ti₃SiC₂/Cu brazed joint. After detailed characterization conducted on YSZ particles and brazed joint, the abnormal expansion properties of YSZ and its strengthening brazed joint mechanism were clarified. The content of Y₂O₃ in YSZ had significant effects on the phase transformation of ZrO₂ from tetragonal to monoclinic. When 3 mol.% Y₂O₃ was added, the maximum phase transformation occurred at about 500 ^◦C, half of brazing temperature, during the cooling process. The phase transformation of ZrO₂ effectively released residual stress in the joint, which was induced by both temperature changes and residual stress. The abnormal volume expansion during phase transformation decreased the thermal mismatch of brazed joint further to strengthen brazed joint.