Grain boundary creep

The intergranular small cavities, formed during the plunging of the interfacial particles, weaken interfacial bonding and induce crack formation at the grain boundaries. The important role of the transgranular nanopardcles is to inhibit lattice diffiisional creep. Grain boundary diffusion, however, is the most... 

On top of this alloy development, turbine blades for the past two decades have been routinely made from single crystals of predetermined orientation the absence of grain boundaries greatly enhances creep resistance. Metallic monocrystals have come a long way since the early research-centred uses described in Section 4.2.1. 

The final stage of creep is known as tertiary creep at which time the creep rate increases rapidly culminating in failure. This acceleration in creep is due mainly to the formation of voids and microcracks in the material which form along the grain boundaries causing the fracture path to be predominantly intercrystalline. 

The effect of carbon on the corrosion of stainless steels in liquid sodium depends upon the test conditions and the composition of the steels . Stabilised stainless steels tend to pick up carbon from sodium, leading to a degree of carburisation which corresponds to the carbon activity in the liquid metal. Conversely, unstabilised stainless steels suffer slight decarburisation when exposed to very pure sodium. The decarburisation may promote corrosion in the surface region of the material and, under creep rupture conditions, can lead to cavity formation at the grain boundaries and decreased strength. 

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