Spreading of BAg-5 on Pre-flux Coated Stainless Steel Plate (Report 1)

Effect of Fluxes Mixed with NiCl₂ or FeCl₃

Abstract

Authors had reported already that the spreading of BAg alloy on mild and stainless steels could be improved by adding small amounts of NiCl₂ or FeCl₃ to KCl-LiCl cut. salt flux. In this study, then, when a 18Cr-8Ni stainless steel plate was pre-coated with the mixed salt fluxes and was heated, the corrosion products formed on the plate surface were analized by SEM and X-ray diffractometer. On the other hand, a spreading test of BAg-5 on the same treated plate was done, using only KCl-LiCl eut. salt flux.
From these experiments, the effect of used fluxes on the spreading of BAg-5 was concluded as follows;
1) The addition of NiCl₂ to KCI-LiCl eut. salt promotes the dissolution of chromium and iron from the stainless steel and the resultant corroded surface becomes spongy intermetallic compound, FeNi₃, furthermore, the particles layers of nickel were precipitated on the compound owing to electrochemical reaction.
2) The addition of FeCl₃ to the eut. salt also promotes the corrosion of stainless steel and the surface becomes the spongy compound, FeNi₃.
3) The spread area of BAg-5 on the particles layer of nickel was considerably larger than that on the compound, FeNi₃. This result showed that the wettability of intermetallic compound, FeNi₃, is not superior to the each wettability of both constituent elements, Fe and Ni.
4) The spread area of BAg-5 on the particles layer of nickel was larger than that on a nickel plate, because the former was larger than the latter in a real surface area to be wet. Furthermore, since the spread area depended on the total surface area of particles distributed on the most outside layer, the amount of NiCl₂ necessary to form mono-particle layer was considered to be about 10wt%.
5) "De-chromiumnisztion" phenomenon on the surface of stainless steel may be one of the important effect of flux used.