Grain boundary strengthening

As we learn from Sims s reviews, many other improvements have been made to superalloys and to their exploitation in recent decades. Solid-solution strengthening, grain-boundary strengthening with carbides and other precipitates, and especially the institution, some twenty years ago, of clean processing which allows the many unwanted impurities to be avoided (Benz 1999) have all improved the alloys to the point where (McLean 1996) the best superalloys now operate successfully at a Kelvin temperature which is as much as 85% of the melting temperature this shows that the prospect of significant further improvement is slight. 

The active strengthening mechanism at room temperature of the studied material was identified as solid solution strengthening, grain boundary strengthening, and Al3Zr precipitate strengthening. 

An important example of an MMC in situ composite is one made by directional solidification of a eutectic alloy. The strength, (, of such an in situ metal-matrix composite is given by a relationship similar to the HaH-Petch relationship used for grain boundary strengthening of metals ... 

Demonstrations (a) Atomix (to show grain boundaries), (b) Model of dispersion strengthening. Take piece of PMMA sheet == 2.5 mm thick and = 7 cm square. Glue four PMMA strips of section =7X7 mm on top of the sheet to form a tray = 7 mm deep. Cut six = 7-mm lengths of an = 6-mm-diameter PMMA rod. Glue the ends of these to... 

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