Alloy metal honeycomb vacuum brazing

FeCrAl alloy is an important electric heating material, usually used for electric heating elements. As one of the most widely used metal electric heating materials, FeCrAl electric heating alloy contains a large amount of Cr and Al. Under high temperature conditions, a dense oxide film will form on the surface of the alloy, so it has high temperature oxidation resistance (up to 1300℃). The excellent high temperature oxidation resistance, high resistivity and low price of FeCrAl alloy provide conditions for its large-scale use. Therefore, it is widely used in burners, high temperature gas filtration, gas sealing and sound absorbing materials.
In recent years, some experimental studies have been conducted on the high temperature performance, FeCrAl coating and metal honeycomb carrier of FeCrAl alloy. Among them, automobile exhaust purification carriers and electric heating devices based on FeCrAl alloy foil or wire have received widespread attention from many material workers.
In the welding of actual burner components and honeycomb carriers, due to the thin FeCrAl alloy foil, the device to be prepared has many holes, many brazing seams and uniform and dense distribution, and the high temperature strength is low. Therefore, low melting point brazing filler metal can be used for vacuum brazing to reduce the influence of brazing thermal cycle on the microstructure and properties of the base alloy.
BNi82CrSiB brazing filler metal is a Ni-Cr-Si-B brazing filler metal. It is a nickel-based brazing filler metal with Si and B elements as melting reduction elements, and its melting temperature is 970~1070℃; it has good wettability and fluidity for stainless steel, high temperature alloy and structural steel, and the welded joint has high strength and anti-oxidation corrosion performance. Therefore, this work uses BNi82CrSiB strip brazing filler metal to conduct vacuum brazing experiments on FeCrAl alloy foil strips, and analyzes and studies the preparation process of porous devices, microstructure and phase composition of brazed joints.

Vacuum brazing
The vacuum brazing experiment uses a VBF-80 vacuum brazing furnace, the maximum heating temperature of which is 1320℃, the furnace temperature uniformity is ±5℃, and the vacuum degree during brazing is not less than 2X10-²Pa.
The vacuum brazing temperature of this experiment was 1070℃, and the brazing time was 10min. The specific parameters were as follows: from room temperature to 950℃ for 60min: keep at 950℃ for 5min; from 950℃ to 1070℃ for 8min; keep at 1070℃ for 10min. After welding, the sample was cooled in the furnace to ensure the minimum deformation of the sample.
(1) Under the process conditions of brazing temperature of 1070℃ and brazing time of 10min, the porous device was successfully prepared by vacuum brazing the base material FeCrAl alloy foil with BNi82CrSiB strip brazing filler metal. The surface had no macroscopic defects, the brazing joint was dense and complete, and 99% (about 8000 in total) of the brazing joints in the sample were connected.
(2) The brazing joints are composed of y-Ni based solid solution, intermetallic compound and eutectic structure. It is roughly deduced that the phases in the brazing seam include y-Ni, Fe-Nig, AINig, CrB and Ni/Sis. There are more boride phases in the brazed joints.