Service Communautaire d'Information sur la Recherche et le Développement - CORDIS

Dissimilar metal joining by the use of graded joints

Research was carried out with respect to the development of an improved method for joining dissimilar metals subject to thermal cycling through their creep range. This was achieved by the use of transition pieces with a compositional gradient along their length to minimize the stresses generated by differential thermal expansion in these components. This work was targeted on high temperature steels for power generation boilers and high temperature plant.

The vacuum plasma spraying (VPS) fabrication route proved unable to provide the required mechanical properties and it is not planned to produce graded joints by this route. The joints have exceeded the creep strength of the dissimilar weldment they were designed to replace and have creep properties equal or superior to those found in like/like weldments in the weaker of the parent materials. They have good toughness, superior to dissimilar metal welds, and oxidation resistance comparable to that of the lowest alloyed material in the joint. The tensile properties of the joints are also above the minimum value specified in BS5093 prt2 for the weaker material in the joint. The thermal cycle resistance of these joints has also been demonstrated to be very good and they offer a means of dissimilar metal joining giving improved properties when employed in the creep regime.