The study of alpha-alumina scale failure at welded joints in high temperature ODS alloys

• Published in: The journal of corrosion science and engineering 2003-01, Vol.6
• Main Authors: Muangjunburee, P, Tatlock, G J
• Format: Article
• Language: English
• ISSN: 1466-8858; 1466-8858

The high temperature oxidation behaviour of laser welded PM2000, an Oxide Dispersion Strengthened (ODS) ferritic stainless steel, has been studied during cyclic oxidation exposures in air between room temperature and 1050 deg C, in order to understand the scale failure mechanisms in the vicinity of the joints and further enhance the joint oxidation resistance. The PM2000 laser weld microstructure, oxide morphology, oxide thickness, cracks and spallation were examined using a combination of optical microscopy, scanning electron microscopy and energy dispersive X-ray analysis. The welds and heat-affected zone around the welds were studied in some detail. The results indicated that, although alpha-alumina scales formed at and near the welds, these regions behaved differently from those in the weld free regions. After a certain period of long-term cyclic oxidation, the surface of the samples started to change colour in the vicinity of the weld. This lighter coloured band spread out from the weld and broadened with time. The oxide scale thickness at the weld was greater than in the regions away from the weld. Convoluted scales, cracks, cavities and small spalled areas were initially observed in the region of local convex curvature located round the periphery of each weld pool. Energy dispersive X-ray analysis did not reveal any compositional change across the scales. The number of cracks in the oxide increased with time and spread out to the rest of the weld and the adjacent area. Tensile stresses normal to the interface generated through scale thickness cracks and lead to spallation after prolonged testing. [This is an unrefereed preprint].