Electron microscopy of defects in oxide-dispersion strengthened ferritic alloys

In this work, development of porosity in an iron based oxide dispersion strengthened (ODS) alloy, PM2000, has been examined by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Pores about 10mum in size were found in a sample that had undergone recrystallisation annealing at 1380degreesC for 1 hour. However, the size of the pores increased to about 100 mum when the sample was annealed at 1380degreesC for 2200 hours. EPMA results showed that the Al content in the 1 hour annealed sample was 4.50% but this fell to 3.35% after the long anneal. Based on these results, it has been suggested that some of the pores observed in the ODS alloy may be Kirkendall pores due to the loss of Al. In addition, SEM results have identified that two types of pore are present, one of which is part-filled.