High purity alumina/stainless steel joints were produced via activated molybdenummanganese
(Mo-Mn) route using 72Ag-28Cu solder. Microstructures of the metallized ceramic and
joint sections were observed by scanning electron microscopy. Joint strength was tested by
shear-loading method. Some process factors were characterized and analyzed, which include
temperature, holding time and heating and cooling rate in ceramic metallization process. The effects
of Ni plating and succedent annealing were also investigated. Experimental results show that,
migration of glassy phases is the main mechanism of the ceramic metallization. Glass migration
direction is from metallizing layer to ceramic side. In the ranges of temperature and holding time of
metallization, joint strength firstly increases and then falls with temperature raising and time
extending. More fully sintered metallizing layer can be obtained while the temperature increases
from 1200oC to 1500oC, and the time prolongs from 30min to 60min. Over-sintering of the
metallizing layer will take place with metallizing temperature of 1600 oC and overlong holding time
of 70min, which reduces the joint strength. The slower heating and cooling rate, and the annealing
after Ni plating both help enhance the seal strength, due to relieving or eliminating interlayer
residual thermal stress. However, too slow heating and cooling rate, such as 5 oC /min, is equivalent
to overlong holding time and finally also decline the strength. A thin Ni coating helps solder wet
metallizing surface, and stops solder erode metallizing layer.
Cracking of Copper Brazed Steel Joints Due to Precipitation of MnS upon Cooling
