Tue, 12 Jun 2018 02:10:27 +0000
High temperature alloy vacuum brazing
Characteristics of high temperature alloy brazing
1.1 if titanium compounds are formed in high temperature alloys during vacuum heating, it is not easy to remove them after high temperature heating, so it is not easy to solder. In this case the high temperature alloy brazing before to take special measures, such as nickel plated surface, or in advance to alloy oxidation, make the surface of titanium alloy oxidation into titanium oxide, and then remove the oxide layer, the surface of titanium alloy quantity drops greatly, in the process of vacuum brazing heating oxidation of titanium alloy surface no longer occur.
A small amount of oxide and nitride on the surface of the soldering does not affect the solder on the base of the wetting and spreading, solder can penetrate the surface of oxide and nitride layer crack and spread out on the parent metal, but if the surface oxide reaches a certain thickness, will hinder the solder wetting, especially the brazing gap hours. Therefore, the oxidation of alloy elements during heating should be minimized.
1.2 for high temperature alloys, good high temperature performance can be achieved only when the alloy elements and compounds are sufficiently solid and dissolved in the matrix. Therefore, the brazing temperature of high temperature alloy should be consistent with that of solid solution and diffusion, and the temperature should be strictly controlled. The thermal insulation time of brazing should be longer to ensure the full diffusion and dissolution of filler metal components to matrix materials. If the amount of alloy elements and compounds dissolved in the matrix is high, the strengthening effect will be weakened. Therefore, the cooling rate after brazing is relatively fast. After brazing these alloys, most of them have to be diffused, invalidated or annealed.
Optional solder for high temperature alloy brazing
The brazing materials used in high temperature alloy brazing should meet the requirements of high temperature working. Nickel base, cobalt base, gold base, palladium base and palladium containing filler metal are usually used.
Key points of high temperature alloy brazing process
3.1 surface oxides should be removed carefully before brazing high-temperature alloy.
3.2 the brazing temperature of high temperature alloy should be consistent with its heat treatment system as far as possible. If the material heat treatment system has no special requirements, the brazing temperature can be determined according to the used solder.
3.3 the vacuum degree shall be controlled over 10-2pa to prevent the formation of new oxides on the surface of high-temperature alloys during heating.
3.4 cooling conditions after brazing shall be determined according to its heat treatment system.
Examples of high temperature alloy brazing process
Brazing material for GH903, one for GH22, soldering components working temperature 400-650 ℃.
4.1 to avoid corrosion of GH22 boron filler metals, suggest that choose BNi72CrSi (brazing temperature 1150-1205 ℃)
4.2 carefully remove oil and wash
4.3 cold vacuum for 10-2 pa, brazing temperature 1165 ℃