Identification of phases and precipitates by AFM in duplex stainless steel unions

ABSTRACT

Atomic Force Microscopy (AFM), a characterization technique that generates topographic images of surfaces at very high resolutions, works by recording the surface relief details of the material with a cantilever which moves over the sample, while a piezoelectric sensor monitors changes in height. This technique is useful for identifying phases, particles and precipitates on a nanoscale and is therefore proposed for identifying them in the fusion zone of welded components and for early identification of faults due to cracking. This is a technique that does not require conductive samples, or special metallographic preparation of specimens as is the case with electron microscopy. The material studied is a duplex 2205 stainless steel, welded by means of gas tungsten arc welding (GTAW). The welded material was subjected to stress tests. The test specimens were characterized using optical microscopy, scanning electron microscopy, atomic force microscopy and nanoindentation tests. The results focus on the identification of the specific magnetic, topographic and hardness characteristics of each of the phases, particles and areas present in the base metal, the fusion zone and the zone deformed by the fracture.

KEYWORDS:

• Atomic force microscopy
• austenite
• duplex stainless steel
• ferrite
• GTAW
• nanoindentation

Acknowledgments

We would like to thank Dr Yuriy Kudriastev and MC. Georgina Ramírez CINVESTAV Mexico from the Department of Electrical Engineering-SEES in AFM as well as the MC. Lourdes Santiago Bautista and Engineer Diana Carolina Romo Mendoza from COMIMSA. We would like to thank all of them for their important work in the stages of preparation and characterization of the material studied.