Dissolution and evolution of interfacial oxides improving the mechanical properties of solid state bonding joints

The mechanical properties of solid state bonding joints have always been greatly deteriorated due to surface oxide scales. Here, we report a method to completely heal solid state bonding joints with recovered mechanical properties by hot compression bonding and post-holding treatment. Using scanning electron microscopy and transmission electron microscopy, we discovered that the recovery of mechanical properties of the bonding joint is attributed to the dissolution and evolution of the interfacial oxides. While holding the joint at 1200 degrees C, the interfacial oxides (MnCr2O4) gradually decomposed. With the decomposed oxygen ions diffusing toward the matrix, oxide particles precipitated around both sides of the interface, forming the particle precipitation zone (PPZ). As the holding time increased, the width of the PPZ increased and the oxide precipitates in the PPZ transformed from MnCrxAl2-xO4 to MnxAl3-xO4 and finally to gamma-Al2O3, depending on the local oxygen activity. After holding for 24 h, the interfacial oxides completely decomposed and only a few nano-scale gamma-Al2O3 oxide precipitates remained dispersed far away from the bonding interface, leading to the recovery of the mechanical properties of the bonding joints. This recovery mechanism may be of great importance to the design and manufacture of high-quality heavy bonding joints. (C) 2018 Elsevier Ltd. All rights reserved.