About the possibility of brazing of niobium to alumina ВК94-1 ceramics by copper and copper-nickel brazing fillers without applying pressure

Abstract

The effect of Ni addition to copper on wetting of niobium-substrate illustrates that additive of even 1% Ni decreases of contact angles from 70—85 to 30— 35 deg. The addition of 7% Ni to copper which was saturated by niobium almost not influence on wetting of ВК94-1 ceramics. The presence of Ni in Cu melt significantly alters the microstructure of brazed seam: on the border with niobium is formed a new layer with microhardness about 7,1—7,3 GPa and disappear globules which were observed in Cu—Nb system. The technique and special device for determining the temperature dependence of the bending strength were elaborated: the sample is loaded in device at the constant bending load, is heated and fixed beams destruction temperature. Studies have shown that the ceramics strength at room temperature is 280—340 MPa, and saved up to 700—760 ºC, then decreases up to 170 MPa. The mechanical strength of brazed joints at environment temperatures is 240—310 MPa, at 780 ºC — reduced up to 120 MPa, and at 900 ºC — respectively up to 50 MPa. The brazing temperature is slightly higher than the copper melting point. The effects of the introduction of nickel to copper in the range of 3—7% on the strength of brazed joints are not installed. The destruction of the brazed samples occurred in ceramics at a distance of 0,1—0,4 mm from the brazed seam. Lowering the soldering conditions led to decrease in the strength of connections. As a result of the researches it was shown that brazing of the niobium and non-metals with use of fillers on base of copper and copper — nickel alloys can be carry out without using of vacuum pressing equipment.