All kinds of brazing joints of ceramic metal forming, because of the existence of coating or plating, the ceramic component is limited in high temperature, it is difficult to exert the superiority of high-temperature stability, requires people to find direct soldering.
The direct brazing of ceramic can solve the connection problem of incomplete pretreatment of metal parts due to blind hole or geometric factors. It can greatly simplify the brazing process and meet the requirements of high temperature use of ceramic components. This method uses brazing filler metals containing Ti or Zr active elements to braze ceramics and metals, ceramics and ceramics, ceramics and graphite directly. The brazing temperature of the brazing filler metal is higher, which can meet the requirements of the high temperature state of the ceramic component. In order to avoid cracks due to different thermal expansion coefficients, a buffer layer can be sandwiched between the two materials. According to the working conditions, the brazing filler metal should be placed between the two brazed parts as possible as possible, or placed in the gap filled with filler metal, and then brazed as a universal vacuum brazing.
For metal ceramics, such as containing 10% free silicon and less than 500ppm of iron and aluminum silicon carbide ceramics, can be used as brazing filler metal germanium powder directly, germanium powder sandwiched between ceramic pieces, germanium powder thickness is 20 ~ 200 m, the base vacuum pumped 10-2Pa, vacuum degree is 8 * 10-2Pa. The brazing temperature is 1180 degrees centigrade, insulation 10min, obtained joint microstructure of Ge-Si solid solution, the remelting temperature of 1200 DEG C, can be used in high temperature environment. In the production of a heat exchanger and an infrared radiation source, often made of alumina ceramic and alkali resistance corrosion of metals Ta, Nb and alloy brazed together, brazing process using plasma spraying equipment in alumina ceramic surface coated with a layer of tungsten or molybdenum, mixed solder and then prepared (Ni + Fe 17% powder or powder Nb powder + Ni powder 15%, binder mixed into roller grinding for several hours, in order to make solder powder suspending in the binder) combined with coated ceramic and metal surface, the thickness is 0.125 ~ 0.25 mm, dry after a few hours, into a vacuum furnace brazing, cold background vacuum pumping to 8 * 10- 3 Pa, vacuum degree of not less than 3 * 10-2 Pa, brazing temperature 1500 to 1675 DEG C, holding 5 ~ 10 min, thus obtained the brazing seam density, tensile strength is 140MPa, good corrosion resistance of joints, brazing seam can withstand high temperatures above 1000 degrees.
Due to the poor thermal conductivity of ceramic, brazing rate is not too fast, brazing, takes a long time to reach the uniformity of temperature; and poor plasticity, heating or cooling rate is improper, will cause deformation, and lead to cracking of ceramic. Therefore, the correct selection of brazing process parameters is of great significance to ceramic brazing.