ON THE MICROSTRUCTURE OF RAPIDLY SOLIDIFIED AL-15 WT PCT MN RIBBONS - EFFECT OF ANNEALING IN THE TEMPERATURE-RANGE 300-DEGREES C TO 600-DEGREES-C

A study has been made of the relationship between the microstructures formed in rapidly solidified Al-15 wt pct Mn ribbons and the precipitation processes following annealing in the regime 300 degree to 600 degree C from 15 minutes to 100 hours. X-ray and TEM analyses reveal that decomposition of this phase is detectable after annealing at 400 degree C/1 h, giving rise to Al//6Mn. At 450 degree C, four phases, viz. , the G, Al//6Mn, G prime , and G double prime intermetallic phases, are observed (in addition to Al), which result from the direct decomposition of the icosahedral phase. At higher temperatures, only the Al//6Mn phase plus Al is observed. The effect of increase in annealing time is simply to coarsen the Al//6Mn particles. Our X-ray and electron diffraction data favor the model proposed by Shechtman and Blech for the icosahedral structure. The investigations were carried out using density and electrical resistivity measurements, differential thermal analysis, as well as X-ray diffraction and optical and transmission electron microscopy.