|Budget Amount *help
¥1,900,000 (Direct Cost : ¥1,900,000)
Fiscal Year 1996 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1995 : ¥1,600,000 (Direct Cost : ¥1,600,000)
Recently, exhaust emission purifier is being made mainly from metal instead of ceramics. High Al stainless steel is used for it. Its structure is coilayr type with alternate pile of flat and corrugated sheets.
To join both sheets, brazing using Ni base filler metal is being employed.
Brazing of high Al stainless steel requires extra high vacuum. Therefore, there are some problems with simplification of equipment and productivity. To solve these prolems, effect of Sn coating by plating or sputtering on brazeability was investigated because Sn has lower affinity for oxygen.
However, stainless steel has passive film on the surface, so coating is very difficult.
First of all, appropriate plating condition was examined as a function of concentration of Sn^<2+> ion in solution and current density.
Sputtering on stainless steel is easier than plating. Thickness of coating by sputtering was adiusted through preliminary experiments.
Coating thickness was varied in the range of 0.1 and 1.0mum.
lity was investigated in a vacuum of 10^<-3> torr (only by rotarypump) and in an Ar atmosphere. Brazeability was evaluated by angle between a droplet of a solder and steel sheet.
In case of plating, the angle decreased with increasig coating thickness.
It was almost invariable with thickness above 0.3mum but the valuse were a little higher than those in case of sputtering.
In case of sputtering, wettability saturated above 0.5mum of coating.
Meximum wettability in brazing in a low vacuum is almost same as that in a high vacuum.
It is lower in an Ar atmosphere than in a low vacuum.
Moreover, effect of Cu which is similar element to Sn was investigated in the range of plating thickness below 0.3mum.
Its effect was almost same or less compared with Sn. Wettability was lower in an Ar atmosphere than in a low vacuum too.
According to observation of microstructure and compositional analysis, there was little difference in characteristics of welded joint between brazing with coated sheet and that with uncoated one.
As a result.there seems to be no practical problems in brazing using this method. Less