Boundary 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 ... 

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. 

The properties of non-heat-treatable alloys are less sensitive to welding conditions. Alloys welded in the O temper will likely have weld nuggets that are slightly overmatched relative to the base metal. This overmatching of the weld nugget may be attributed to an increment of grain-boundary strengthening over that which is... 

Surveying the strengthening mechanisms discussed in chapter 6, we see that grain boundary strengthening is not suitable in creep applications because we need large grains as explained above. Work hardening can also not... 

Venkatraman, R. and Bravman, J. G. (1992), Separation of film thickness and grain boundary strengthening effects in A1 thin films on Si, Journal of Materials Research 7, 2040-2048. 

Thus, particle shape, size, and distribution affect the strengthening process of the MMCs (Dieter, 1961 Kumar, 2009 Cheng et al., 2001 Yu, 2010 Suresh et al., 2007 Rao et al., 2012 Goh et al., 2008). For example, in the case of pulsed electric current sintered CU-AI2O3 (5 vol%) composite, there is an increase in yield stress by 370 MPa due to grained boundary strengthening compared with the one without any particles, which is the case for pure Cu (ZeinEddine et al., 2013). 

Grain boundary strengthening precipitation in Ni-base superalloys. (Reprinted from Mitchell, R., Department of Materials Science and Metallurgy, Nickel-Base Superalloys Group, University of Cambridge, http //www.msm.cam.ac.uk/UTC/projects, accessed March 2,2009. With permission.)... 

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